Dick's Page

Bill ...A brand new KT88 push pull am plifier...

N ice to m eet you: Bill is the nam e...

The old KT88 goes back six years. A lthough the listening results are still very good, I see to m any points that are qualified for im provem ent. S hortly put: It is possible to build an even considerable better am plifier, technical and sounding, w ith the sam e m eans, but w ith six m ore years of experience put into it. If I look at the costs, then and now , it looks like if the new am plifier can be build less expensive. Y ou can say w hatever you w ant, but that’s quite unique now adays …

They have to be tw o firm little am ps, good for about, say 50 and 100 W atts. “W hat do you say? Tw o?” Y es, there’s also a brother of Bill, nam ed: ‘Bob’. Could it be a little bit m ore? That’s the general idea behind these tube am plifiers. Bill has tw o KT88 pow er tubes a channel, all build on one chassis. Bob is getting double that num ber of tubes and is configured as a m ono block.

The evolution:

• M ore pow er. E ven sw itched in triode m ode, there’s still 25 w atts left. U ltra-linear sw itching w ill double that figure.

• The pow er supply is m ore firm and m ore stable. Both channels w ill have their ow n rectifying, capacitors and chokes. • The output transform ers are specially m ade for this project and clearly im proved: a w ide bandw idth and over-dim ensioned for a very deep low reproduction.

• Easier and foolproof to build.

• Parts are easy to get, even the cabinet!

• There is enough room (in the am ount of voltage am plification) to apply feedback, if that’s w hat your speakers w ant.

• The am plifier stays stable as a rock at capacitive loads, w hat electrostats w ill do jubilate…..

W hy Bill and Bob?...

I get on a regular basis questions of m en ( unfortunately, is w hat I call for years, but you have to find fem ale DIY ’s w ith a m agnifying glass), w ho sim ply w on’t have enough to a single ended 300B am plifier, but nevertheless still w ant to drive their “m ore juice appreciating favorite speaker system ” w ith a tube am plifier. A noble thought, w hen you ask m e…. A lthough I w ill not claim to be entirely im partial…..

There are tw o w ays to go in tube-audio land: A n am plifier w ith a sm all but o so fine pow er output, driving speakers w ith a higher than average output in dB, w hich you have to like how ever. These kind of speakers have often their singularities and typical characteristics. If that is w hat you w ant, the choice for an appropriate am plifier is clear. A big horn speaker has enough to be supplied w ith a couple of m illi-w atts, to reach an ‘ear-blow ing’ sound pressure.

The second w ay to go, is using a m ore general applied loudspeaker system , w hich indeed has often a som ew hat less sensitivity, but also adds m ore often a not easy to handle im pedance. (just look at the num ber of speaker system s using a double w oofer, w hich, in 9 tim es to 10, produces a loudspeaker im pedance of som ew here around the 4 Ohm , w ith exceptions m uch low er than that). A specified sensitivity of f.i. 90 dB/w /m looks very sym pathetic, but if assum ed that there w ill be a load of 8 Ohm , there w ill be effectively 87 tiny little decibels left, if it’s about a 4 Ohm system . The am plifier m ust deliver at halve im pedance tw ice as m uch current. That m eans tow ards a tube am plifier that if you connect your speakers at a 4 Ohm tap of your output transform ers, it w ill cost you half your output voltage. It is the one or the other.… To give your m usic m ore ‘S lam m ’ you need a tube am p w ith m ore m uscle. That’s w here Bill and Bob com e in focus. I invented Bill for the less w ealthy m an, w ho needs m ore pow er, but don’t w ant to use a solid state am plifier. Y ou cannot buy a fabric am plifier w ith a little bit of quality for a few bucks, but that’s no new s. But if you can build a m ore than w orthy KT88 push pull am plifier for 7 a 800 euros w hich can w ithstand the challenge against the tw o, four or m ore tim es expensive fabric am plifiers, it w ill be very interesting.. That’s a reachable goal w ith som e savings.

But isn’t it difficult to build a tube am plifier? Do I have to search the w hole w orld for parts? A ll that fuzz w ith the custom s, im port fees, high delivery costs etc? The answ er is a big: ‘N o’…

A nother designing goal of Bill is, that this am plifier could be build in a easy w ay, w ith contem porary com ponents, w hich are for sale everyw here in our country. A nd it succeeded very w ell. Designing an am plifier you have to start at the transform er set. Y ou look at the tubes you w ill use and begin to philosophize, calculate and w eigh.. In this case, w here w e are talking about push pull am plifiers, there w ill be looked at the type of phase splitter that w ill be used, how the end stage w ill be configured; class A , class A B, if I use an extra tube in the pre-stage, how I w ill build the pow er supply etc. etc…

The setup of the end stage w ill be a single pair of KT88’s or a quartet. I w ill go for a setup in class A B, w here the biggest part is functioning in class A . That m eans that the am plifier w ill operate on a higher voltage level as the previous KT88PP am plifier. The pow er supply m ust also be better as the last m entioned. W e’ve gathered som e know ledge the last couple of years … W hen I designed the old KT88 am p, there w as no Duncan, w ith his beautiful PS U designer softw are, from w hich you can sim ulate an alm ost perfect pow er supply, if you bother to take som e tim e and use it w ell. W hat’s im portant is: you can study the behavior at changing loads. For exam ple how fast the voltage is recovering w ithout strange variations, after a high current dem and for a short period. Because of this, w e can assem ble a cooperative team of capacitors and chokes. In the early days, it w as m ore or less a guess. N ot that it produced bad am plifiers, but a clearly better setup is now in reach. That’s w hy you see different com binations of Caps and Chokes in m y later am ps. In the pow er supplies of the older designs, I first looked at the shelf w hat parts I had.

A subtle m usical pow erhouse...

For Bill and Bob I w ant lots of pow er, but m ore than that, I w ant m usical quality w ith a low frequency reproduction that stands. A tube is not per definition the m inor of a S olid S tate am p in the low er regions. The tube can produce a striking, beautiful precise, low frequency reproduction. Y ou do need som e OT’s w ith enough iron and a m assive pow er supply w hich can deliver the pow er dem ands A nd som etim es a feedback, if a speaker is dem anding that. Don’t be to difficult about that. If you need to de-couple som e dB’s for a better sound reproduction and w ith that a better total reproduction, there is nothing against that.

W here som ething is against is: putting m any dB’s feedback in the circuit, for no reason, w ith the phrase: ‘W hen it’s not a bad thing, it w on’t harm anything also’. But that it does and so w e w on’t. Y ou can m ake your choice here if you do or don’t need a feedback. Key is, that the base, w ithout negative feedback, m ust produce a fantastic am plifier. N egative feedback is no bandage or drug, but, to say it in a trendy w ay: a usable tool..

‘Bob’ w ill be a different chapter. It consist of tw o large m ono blocks, for w hich a pair of fat (and so expensive) C-core OT’s are specially w ounded. Bob m ust be som ething special, w ith som e new ideas put into it. But also w ith the sam e focus as Billy.

The decision to use KT88 tubes w as m ade fast. It is the m ost pow erful pentode (beam to be precise), w hich is happily easy to obtain now adays. There are several m anufacturers w ho produce this classical G EC design once m ore. G ood for us, because alm ost nobody can afford the original G EC KT88’s.

The voltages w e need on the pow er transform er w ill be investigated as one of the first things w e do. The Pre-am p tubes can be glow ed at 6,3 as w ell as on 12,6 volt, w hat w idens the choice. The pow er supply w as exam ined using the Duncan PS U program , to determ ine the high voltage of the PS transform er.

I w anted to use a supply voltage 470, 480 volts to achieve the desired pow er and to use contem porary 500 V olt capacitors. The OT’s are huge things, w ounded on a fat EI 120 core. Everything w as calculated and determ ined. But yes, the stuff had to be realized in a practical sense. W il Blaauw of A E-Europe becam e a very reliable partner in the past years and w ho realized all m y transform er escapades. A nd that definitely w ere no standard transform ers. I’m alw ays short on voltage taps w ith standard confection transform ers and the voltages and/or current are alw ays just to low or just to high. The silly thing is, that you need in addition to the high voltage, also m any filam ent taps on the transform er. That requires a tailor-m ade job. A t a confection plant is ‘custom m ade’ not done, because of the high costs. In that respect is a flexible m anufacturer, w ho is not easy surprised, ideal.

E ven now it w as no problem . W ithin a short period of tim e, I found a few boxes w ith ‘heavy m etal’ behind m y front door. If you don’t have a Hernia, this is a good w ay to obtain one… @ $ % & & # , m aybe that’s just reason enough to think about building transisssssstor am plifying, of course w ith super light sw itching pow er supplies. Happily is everything as it w as the night before, as I w ake up in the m orning from such a bad dream … J

Phase splitting considerations...

Bill is a classical design pur sang. I let pass all the different types of phase splitters.. The cathodyne, w ith it’s very sim ple setup. I’ve used this one several tim es already and alw ays w ith success. If you take a few things into account, it rem ains a stable and w ell sounding stage. But because w e have to apply a three stage setup to get enough am plification in the circuit, this circuit is dropped. I w ant to drive the end tubes w ith a firm tube to overcom e the dreadful M iller capacity. The M iller capacity is the capacity betw een the control grid and the anode, m ultiplied w ith the am plification factor. That produces a total capacity, that, in com bination w ith the output resistance of the line stage, quickly can lead to a low pass filter, w hat lim its the am plifier in bandw idth.

A variation on the cathodyne is the phase splitter w hich D.T.N . W illiam son used in his classic. This double stage is still often used now adays, also in com m ercial designs. W illiam son placed an extra tube buffer betw een the phase splitter and end tubes, w hich is a m uch m ore easy load for the phase split outputs. Plus the fact that it didn’t have to stress itself com pletely, because of the low er output voltage that have to be delivered for m axim um driving the tube, w hat w ill low er the stress. The ‘in betw een’ tubes are taking care of that now . Y ou often see a tube w ith a low Ri and not to m uch am plification on that spot, w hat on its turn is taking care of a nice low output im pedance, w hich is/w as very w elcom e. There w as a tim e m assive feedback w as applied in a indecent w ay, and that did cost a lot of am plifying pow er. W ideband OT’s w ere scares and that had to be leveled out w ith m any dB’s feedback. A nd that produced a less stable circuit w hat had to be fixed w ith a tactical placed capacitor. Hm m m m …. That’s som ew hat like putting the horse behind the carriage…. But if you think about the fact that it w as 50 years ago. J ust before the ‘golden age’ of tubes. The audio hobby w as just developing. They didn’t even had a descent m usic source. But that changed dram atically in the years that follow ed.

Bill’s first setup in the initial phase contained this buffered cathodyne stage. I perform ed the necessary m easurem ents and it all looked w ell. A n am plifier can sound w ell w ith this kind of stage.

That’s w here Bill got it’s nam e from . 'W illiam ' becam e a sim ple 'Bill'. The circuit changed, but the nam es stayed because it sounded nice. 'Bob' is a transcription of 'Brother Of Bill'. Bill has nothing, nada to do w ith the richest m an on earth: 'Bill G .' as a ‘ clever’ reader suggested.... A s if this is a site for PC’s and related stuff and not about glow ing glass tubes... The electronics shouldn’t be the lim iting factor for an am p, although OT’s have an enorm ous bandw idth in respect to the earlier designs. If you m ake the electronics the lim iting factor from the start, w hy should a transform er m anufacturers bother to m ake a OT as beautiful as possible? A nno 2004, w here the CD is an out-of-date m usic reproduction m edium , and the old analog m edium , the vinyl, is better than ever, it is not be done to build an am plifier w hich is lim ited just above the 20Kc. Or you opened your hart to the pathetic ‘quantity’ above ‘ quality’ of that m p3 stuff… …N o, the am plifier and quite not a tube am plifier has to be the bottleneck.

A nother candidate...

The second candidate an old acquaintance too: the ‘Floating Paraphase’ trap. The first tube is used as an am plifying stage, w here after a second tube is used to shift the signal 180 degrees. U sing a handy floating driver and a an even handy used feedback on the splitter tube, you get a fine w orking am plifying phase splitter. W ith only one ‘but’. To let this stage operate in a optim al w ay, the am plification of the last m entioned m ust be infinite. A nd that can’t be done.

M uch often you see ECC83 tubes used in the classical circuitry. A w orkable alternative, w ith again a ‘but’ (M urphy stays w atching…). This stage w ith its relative high output im pedance is a lovely prey for M urphy’s brother in law : M iller. A buffer should be used betw een pre and end stage to overcom e that problem . I have to tell you that this is often seen in a floating paraphase stage in com bination w ith an EL84 end tubes, w hich are less critical tow ards M iller because of their low er grid/anode capacity in respect to an EL34 or a KT88. There are m ethods to suppress this higher output resistance. Y ou can use an extra ECC83 and sw itching both tubes in S RPP, or even better a so called m u- follow er, a S RPP com bined w ith an extra bootstrap resistor, w hich produces a higher am plification and a low er output resistance. Or you can go your ow n w ay w ith a less am plifying/low er Ri tube in the circuitry and regulate the differences aw ay using a pot m eter or better a voltage divider. Y ou can use an ECC88 or an other steep tube. A tube w ith a high steepness has from itself a low er inner resistance. A n ECC88 produces an am plification factor of 33, so it is just w orkable. E ven an E CC81 could be a good choice. A fairly low R i coupled to a high am plification factor 60. There are m any w ays tow ards the holy Rom e, as you can see, Happily for us… A nd of course you find enthusiastic proponents for the one solution and fundam entalist opponents for the other solution. I can only share m y ow n practical experiences w ith you and tell you that I’ve tried all variations resulting in fantastic am plifiers w hich I’ve build and listened at hom e. It is not just in the used principle, but m ore in the technical developm ent, also on com ponent base... I ask m yself often how anyone can be so absolute pro or against a solution. Has such a m an tried these solutions him self? Or is he one of m any prejudice m en w ith a lot of preconceptions? If you know the answ er you m ay tell it.… I do know that the audio w orld is ‘enriched’ w ith a lot of so called: ‘arm chair audiophiles…’ and that’s how it alw ays w as. Do you w ant to find out w ith you ow n ears? Heathen up your solder iron and find out for yourself. Let your ears be judging …

The one w ith the long tail...

The third possibility I also used in m y previous KT88 am plifier: The ‘longtail’ Phase splitter, also called the ‘S chm itt’ phase splitter. The first voltage am plifying stage w ill be dc coupled (w ithout a coupling capacitor) to the second stage w here the phase splitting is taking place. The first stage is very im portant for the right setup of the second. This second stage is som ew hat special in that sense that the second tube half is getting the signal via the cathode and the control grid is strapped to m ass for the m usic signal. Ideally, there w e go again, there should be an infinite high shared cathode resistor, to m ake the anodes output voltages identical. But w e have to find a w orkable alternative here also, using a resistance of 10 to 12K. Otherw ise the voltage drop w ould be so high, that an im practical high supply voltage should be applied.

Here also has to be com pensated. The anode resistors w e used have a slightly different value to level out the driver voltages for the end tubes. The advantage of this setup is the use of a tube w ith a very nice low Ri for the phase splitter. M uch am plification isn’t necessary because of the presence of the first am plifying tube in the circuit. A n ECC99 or 5687 are perfect candidates. Tubes w ith m uscle. M iller goes KO before he can enter the ring. Because of the voltage drop over the shared cathode resistor, it is necessary to apply a sufficient high supply voltage. N othing to w orry about for Billy w ith its end stage running on 470 volts. W ith a little drop resistor it becam e about 445 volts.

The first am plifying stage...

….has got a 6 of 12S N 7 tube (The m iddle tube in the picture). Both variations are possible, the tube w ith 6,3 volt filam ent voltage, the 6S N 7, or the 12,6 volt version, the 12S N 7. These tubes are identical w ith exception of the filam ent voltages. Do you have som e nice 12S X 7 tubes lying around? Y ou can use them w ithout any problem , a very nice tube.

In principle there are m ore possibilities, like the old as the alw ays beautiful ‘76’. W here you really have to be strict is the anode voltage because it’s crucial for the dc setup of the direct coupled phase splitter stage. U se the right anode and cathode resistors for a precise voltage on the anode, or other w ays put: that the control grid of the E CC99 phase splitter gets the right voltage.

M aybe you find it visual m ore attractive to use a noval tube like the ECC82 (even an ECC88 can be used w ithin its lim itations). N o problem . Both last m entioned tubes are not m y favorites, but that isn’t the point. I’m not pur sang against the use of the ECC82, but I do find that there’s a lot of rubbish w ith this kind of tubes, w hat m akes it not easy to find som e tubes as nice and quality like as a U S A 6S N 7. Furtherm ore the 12S N 7’s are still easy to find now adays for a reasonable am ount of m oney. Contem porary Chinese and Russian equivalents of the 6S N 7 I find personally not m uch good. A thin copy of the ‘real stuff’. To react directly on people w ho think right now that I hate A LL Chinese and Russian tubes… Rubbish! I find that there are som e nice tubes com ing from that regions today. Especially in China the quality is now adays not com parable anym ore w ith the stuff they m ade in the beginning of the 90’s, w hen the glass becam e brow n after a couple of hours. That’s not the case anym ore for m odern tubes like V alve A rt and Full M usic. Those m anufacturers becam e m ore and m ore trendsetter for trustw orthy quality (end) tubes. But those relabeled 6S N 7’s I still don’t w ant to use on m y am plifiers…

The cabinet...

The cabinet is m ade again com pletely in m y hom e style. A nice w ooden fram e w ith a firm copper plate on the top and a perforated plate at the bottom . I like to give these retro am ps a retro look. But don’t let m e stop you if you w ant to build it in another shape, a closed cabinet for instance, to protect it against the hands of little children. But alw ays take care of a good airflow . M ake a lot of holes in the bottom plate and a perforated top plate protect the tube against over heating. In the early days, I had a stereo am plifier w ith 8 EL34 end tubes in a 19” cabinet. W ith 2 slow turning vents the stuff stayed on a reasonable tem perature. It conducted a lot of dust into the cabinet, w hat m ade the use of a vacuum cleaner m andatory..

Bill’s top plate is a 2m m thick copper plate, 420m m w ide and 350m m deep. The three transform ers are 90 degrees turned in respect to each other on the back of the deck. The tw o chokes are build into the cabinet, below the OT’s. The fat 500 µF caps are m ounted through the chassis using a fitting brace. I posted them as close to the OT’s as possible, to reduce the w iring lengths. The sam e is done for the other supply decoupling. A s you can see, both double caps for decoupling of the pre stage and phase splitter, are m ounted very close to the phase splitter tubes.

M ore building...

A s you can see the am p is build as a pow er am plifier, thus w ithout an input selection sw itch and volum e regulator. Y ou can install them in w ithout a problem . If you w ant to build an integrated am plifier w ith these regulators, look at the article about building the A nnastasia am p how it is done. The input sensitivity of Bill is m ore than enough to connect a CD player or tuner. Even if a feedback is applied. Building it for use w ith m y ow n system , the Cleo V pre am plifier, I have to reduce the input sensitivity w ith a voltage divider. Otherw ise w e get a very nervous behavior of the volum e regulator, because if w e don’t w e reach after a few clicks of the stepped attenuator an ear blow ing sound pressure. A nother negative result is the am plification of all the hum m and w hite noise rests of the pre-circuit, and w e w on’t have that. I m ade the voltage divider in a w ay, that it becam e the sam e input sensitivity as the rest of m y am plifiers. The am plifier needs 250 m V input for m axim um output if no feedback is applied. The feedback I tried, resulted in an input sensitivity of 0,8 volt. In practice a w orkable situation, even if you build it as a integrated am plifier, w ith volum e en input selection sw itch.

Other circuitry …

The J J ECC99 w ill be driven by the 6S N 7. This ECC99 has a silk like sound, w ith a nice open detail reproduction character, w hich m ake m e think about another favorite tube: the ‘76’. Only w earing Hum pty Dum pty seven-league boots. W hat m akes the E CC99 m ore suitable than de ‘76’ here, is its m uch low er resistance (R i), and higher am plification factor. The Ri m akes a tight driving of the KT88 end stage possible w ithout additional buffering. Y ou can see in the circuitry that the resistors have relative low values. There is also no trace of lim itation in the higher frequencies. The driver stage over classes the already very high bandw idth of the OT’s w ith its ow n high bandw idth.

In the first circuitry test, I putted a higher current through the ECC99 and 6S N 7, w hat produces a lot of heat, but no better behavior. The m easuring results w ere not w hat I had expected and listening w ise the sound w asn’t loose and free of stress. By accident I found an appendix of the English m agazine Hi-fi W orld and I m y eyes focused on an article of an am plifier w hich w as also using a S chm itt phase splitter. W ithin that, the KT88 end stage w as driven by a 5687, w hich on his turn w as provided w ith a voltage and receives its settings from a pentode tube in the first stage. A t large that’s not m uch different as a 6S N 7/ECC99 com bination. I w ent to w ork w ith those settings. S w itching back is also a part of developing equipm ent.

In the picture above you can see 4 different S N 7 tubes. From left to right: R CA 5692, G eneral Electric 6S N 7G TB, RCA 6S N 7 and 12S N 7. The only difference betw een the last and the rest is the filam ent voltage, 12,6V instead of 6,3V . The 12S N 7 is a lot cheaper to purchase.

That w ent a lot m ore relaxed...

I set the 6S N 7 a lot m ore sym pathetic, w hat is good for its live span, and suddenly everything fell on its place. A nice generous output voltage, an evidently better sound and nice distortion num bers. The nice thing is that the pre stage and the end stage com plete each other and show a nice harm onic spectrum . N o spiky uneven harm onics and absent even harm onics.

That’s an item w hat’s often overlooked as unim portant. N othing less is true. A nice distortion spectrum is determ ining the total character of the sound. J ust like a single ended am plifier don’t need an excessive preference for even harm onics, a push pull am plifier m ust not persist in sm othering the even harm onics and peaking at the uneven d3 rests. A n am plifier w ith a clear preference for the last m entioned, w ill cover the total sound picture w ith an icy breeze. I put it here som ew hat in black and w hite to m ake m y point, but the people w ho experienced it, w ill recognize it im m ediately.

The end stage is set for about 20 w atts in class A . A bove that it w ill sw itch to ‘A B’ m ode. The transfer can be seen on a spectrum analyzer by a steady increase of the uneven harm onics. N ice and inoffensive. Y ou are listening for 99% of the tim e to the w idely present pure class A pow er, w here the am plifier is on its best. Betw een 20 and 50 W atts its still a beautiful am plifier w here nothing is going out of hand. S hould you continuously need an average pow er of 30, 40 W atts to reach a listening level, there is som ething w rong w ith your ears or they are in danger in the near future. A re your speakers the problem ? W ait than for the big brother: Bob…

I notice that an am plifier as Bill let m e turn the volum e knob open m ore easily. Everything goes at ease. Big peaks in sound levels are childs play. M etallica, Black S abbath, this m orning even the first album of Boston, nothing can m ake the am plifier blush. But neither huge em its in classical m usic, as I found out yesterday evening, w ith a S A CD sam pler of Channel Records in the player. It contains som e heavy stuff, I norm ally let go less volum e out of m y speakers. I w as sitting to far from the volum e knob to react quickly. M y ears w ere protesting clearly earlier than Billie. A nd that gives m e rather a kick…haha…

But M ost of all...

The very first W att, that ultra im portant 'sm allest' W att, the undoubtedly the m ost significant W att. How is Billy boy doing his job there? W hy that first W att is so im portant? Because that’s the place w here all the spatial inform ation in m usic is, all the acoustical sighs and reflections in the room w here the m usicians play. If the resolution is short there, you have a am plifier that sucks. In that case you can forget hearing the differences betw een f.i. a CD and S A -CD. A ll adventure is disappearing form m usic if the reproduction is not suitable. I heard this m uch to often on m oderate am plifiers. A nd do I have to tell you they w ere m ostly solid state am plifiers? Of course, I’m preaching for m y ow n com m unity, but I had only a few solid state boxes at hom e, w hich could convince m e of the advantages of S A CD and V inyl (and I m ean convincing w ith a letter C). One of them (a very expensive one) m ade of everything a unity sound. I couldn’t hear the difference betw een a CD and a sim ultaneous turning DV D-A version of an album . A nd I can assure you, w hen that happens there’s som ething w rong.

Bill let m e experience all the advantages of the ‘hi-res’ m edia and V inyl. If, just before the m usic begins, the room begins to breathe and the tension is build before the first tone, I know everything is w ell. This is som ething w hat’s alm ost unachievable w ith the old CD.. Com pare it w ith a picture w ith a lot of sun and shade and w here the shade is flow ing over, because the photo paper can’t bridge the contrast, the negative has w ithin, w hat’s m aking uncle J ohan disappearing in the darkness. A picture taken on a Kodachrom e slide w hich w ill be projected on a screen, show s all the detail, even uncle J ohan, w ho w as photographed evidently. … I hear people already ask: ‘But if Bill is that good, are the A ttilla, G oliath and also the Little Ceasar serving no useful purpose?’ N o, certainly not. These single ended giants en little giant are even better equipped to catch the am biance, w ith a m uch m ore richness in detail and sm oothness in character. S om ething that’s so typical for a nice single ended am plifier and I have never experienced w ith a push pull design in that sense.

I receive on regular base the question: ‘On w hat position in your favorites list is this or that am plifier?’ Okay, I w ill try … I think Bill is w ith no doubt better than all the transistor am ps I listened to. I find Bill clearly better than m y last push pull am ps. I could be old w ith this am plifier quite-w ell. Billy is not just an am plifier for the m an w ho’s in need off al lot of w atts, he is also for the m an w ho’s listening w illingly to subtle m usic. It’s an am plifier w hich doesn’t focuses to itself, but is just giving m usic. Hum m and noise are strangers for him .

Passive com ponents…

M ost of the tim es you see a shared pow er supply in stereo am plifiers. Both channels w ill be paralleled connected to the central supply line. I w on’t say it isn’t a good w ay to build, but I can find m yself better in a double setup to be freed of any kind of influencing from the one channel to the other.. Could that be done w ith just one transform er? S ure, both sides becom e their ow n rectifying and further treatm ent. M easurem ents on channel separation w on’t produce anything w ith m y equipm ent. The separation betw een the channels is better than -80 dB w hich is m y m easurem ent lim it. The other (m aybe m ore im portant) advantage, is that a hit on a bass in the right channel, has no effect on the left. That’s w hy I w ant (even w ith a single transform er) a com plete separation. W ith tw o additional diodes you can m ake a perfect separation. I use the fast BY W 96 Philips diodes for that, w ith a nice soft recovery, w hich leaves less spikes on the supply line. S om ething that couldn’t be said of norm al diodes.

Fat cool....

W hen I saw that J J w ould sell 500uF electrolytic caps, I knew directly that this firm am plifier w ould be the place to put them in. J J is m aking caps w hich are clearly focused to the audiophile, w ith their clean silk like character, I like to use them and I use them on a regular base. W ho still think that all electrolytic caps sounds bad, dirty and brutal, m ust once try these J J ’s. N ext to the super expensive Black G ate, the J J is m y favorite electrolytic capacitor (elco), and beside that, they are priced very sym pathetic.

Duncan’s sim ulation show ed, that a very stabile pow er supply, w hich shines in pulse behavior, w as possible w ith the used series capacitors. V ery im portant w ith a class A B am plifier. The supply w ill be loaded dynam ically by spikes in m usic. Y ou don’t w ant a horrible ‘ringing’ on your supply line, because it needs to m uch tim e to recover. This stable supply can be recognized im m ediately in the clean sound reproduction.. The supply line begins w ith tw o capacitors in series. W atch out, m onolithic types are used here, in opposite to the ones som ew hat further in the supply line w here double capacitors are used. The big 500uF J J elco is a m onolithic type also. The in series placed caps are m andatory to prevent a short in one of the 500 volt type capacitors, especially w hile heating up. The first relatively sm all capacity is taking care of a heavy pow er on current. The standby sw itch is also helping out there, but in m y opinion the am plifier m ust be fool-proof, even w hen you had forgotten to sw itch off the stand-by sw itch. It m ay not derail because of an deviation in a sw itch-on ritual. That w ould be som ething …

Than a very fat choke com es in sight. It is w ounded specially w ith a low resistance. 5 Henry provides the possibility to use a thicker than norm al w ire and it is an ideal value in this pow er supply setup. A fter the choke, the earlier m entioned big 500uF capacity is placed. Together w ith the choke it provides a very clean supply line, w hich has a lot of m uscle w hen needed. A fter that the phase splitter voltage is provided by a RC decoupling, w here the double caps of 50/50 uF/500 volt are used. It is a firm pow er supply w hich is very com pact after all. That w ill only w ork out w ith elco's. Fortunately they are of outstanding quality now adays. It is not that long ago, I looked the other w ay w hen I saw electrolytes, w hen I had to m ake a pow er supply... R esistors...

There are a few resistors placed in the circuitry, that m ay not be underestim ated. Before you know it, the lot is overcooking. The anode and cathode resistors in the phase splitter stage are cooking the m ost. I used 3 w att types there and on som e places even parallel or in series. That’s keeping the heat in control. A s rule of thum b: If 1 w att pow er is continue consum ed, use a 3 w att resistor at least. M ore is okay too.

In the picture you see the 1 w att resistors next to the 3 w att types.

These are the carbon resistors you find m ore often in m y projects. They are sound w ise very beautiful, but because they are bought in a non audiophile shop, they are very cheap.. Try them , I should say. Y ou’re ready for a few euro per am plifiers... I know , that leads to suspicion by people w ho are conditioned because they are used to pay insane 'audiophile' prices. Its m uch to cheap.. so it can’t be good...

Because the tubes are set w ith a fixed bias (and thus a negative grid voltage) the fat cathode resistor is m issing, w hat’s also good for heat spreading in the cabinet.

Capacitors...

W hatever you use as a couple capacitor, bew are not to focus on audiophile types only, but also on the ones w ith outstanding electrical qualities. N ot all the old (oil) caps are 100% electrical free of leaks. The setting of the end tubes can be drifting or w orse, going on the run totally. In an end stage that can be deadly for your am plifier. A nice foil capacitor is here on his place at best. I like to use A uricaps m yself. A capacitor w hich very less adds or leaves by itself and in m y ears one of the best. But be free to use your ow n favorite Cap. Hovland, W ondercap, REL, M undorf... you nam e it. I like to try everything I can put m y hands on in this area. V ery enlightening, but a heavy burden for your hobby w allet...

Tube sockets...

The tube sockets in this am plifier are all contem porary types. Five tim es octal 8-pin and tw o tim es noval 9-pins. There w as a tim e it w as not easy to obtain new tube sockets, but thanks to the quick com e back of the tube the last ten years, these essential parts are plentiful produced again.

V olum e attenuator and related things....

Bill is w ell suited to build as a integrated am plifier, thus w ith volum e attenuator, input selection sw itch and a couple of input term inals (cinch). There are several possibilities to regulate the volum e. First you have the ‘Fifteen in a dozen’ logarithm ic stereo pot from the radio shack at the corner. Leave them there, they are nothing and never w ill be. Those things only irritate you.

S im ple and already m uch better is the w ell know n blue A lps regulator. It is a sham e they don’t produce the 'Black Beauty' A lps anym ore, those w ere even nicer. But it w ill really go super deluxe a stepped attenuator. Y ou can choose the num ber of steps yourself. 12, 24 or even m ore. In m y pre am plifier I use a 41- stepper, but via EBay I obtained a few nice 24-steps ladder sw itches. Build w ith a large num ber of Dale resistors. A nice sw itch for 50 Dollar.

The 41-steps series regulator w hich is displayed here, is next to audio optim al also very com fortable. U sing a little notch on the back, you can alter the w eight of the click. Because of the large num ber of steps, the volum e can be set in a very precise w ay in every volum e you w ant. The only negative thing I can say about this beautiful m ade thing is? W hat do you think? The price…. Bought by w w w .acoustic- dim ension.com

I have one in m y pre am p and don’t w ant to m iss it ever. the question is: 'is Billy boy w orth such a costly volum e regulator?', w ith other w ords: 'Is this am plifier good enough to hear som e results from an extra investm ent as this?'. The answ er to this question is a very definite: 'Y es'. W hen it’s w orth to you and you can spend the m oney, don’t leave it out.

Y ou can read in the A nnastasia and S tan & Oliver projects, how volum e regulator and selection sw itch are placed in the am plifier. The best is to place the input selector as close as possible to the cinch busses, using a long axes to the back side. Y ou can connect the 6 m m axes w ith an axel connection bus. I alw ays buy them from Conrad, but the regular radio shack should have them too. It is the bronze colored bus w ith the little bolts. In front the pass trough busses. Y ou can easily m ount them in a m etal cabinet, but in a w ooden cabinet I glue them . Don’t try to stick an axel thru a hole in the w ood. The axel w ill m ove to all sides and is giving an extra m echanical load to the regulators. That’s not good for its live span.

Cinch, loudspeaker term inals and w ire...

It’s becom ing a little boring, but also easy. A gain I buy these thing from Conrad. A fter a long period of tim e they sell descent cinch term inals again.

Here you can see duo loudspeaker term inals as w ell as the w ell know n instrum ent clam ps. Both good stuff.

For the internal w iring you have to use high quality stuff. For m e that is w ire and PTFE, also called Teflon isolation. That stuff is absolute aging free and it w on’t m elt if you hold your solder iron against it. In the signal path I use pure silver w ith a PTFE tube around it. This cabling is to obtain from the transform er m an. Even so for the pass trough rubbers that are displayed on the building pages. U se them absolutely.

Further m ore you need som e sw itches, a pow er connector, nice and easy is the one w ith a built-in fuse. A ll bought from ....? Indeed. for a sim ple pow er supply of a 12S N 7 I often use a nice PCB. I have them m ade by Doede Doum a m y ‘ tubes buddy’ w ho lives en w orks in G erm any. If you can’t or w on’t w ork w ith experim ental boards, this is a nice option. The com ponents are com ing from ...? Tadaaa!

A nd first the rough w ork again …

W e begin w ith a large picture of the top plate. A ll holes w ill be m arked and hit w ith a center point. But an aw l w ill also w ork fine. A w alking drill is the last thing w e need...

Then it’s over w ith the clean and tidy w orkbench... First w e w ill give the transform ers a facelift. There w ill be a part rem oved from the m ounting brackets to give the w iring the room it needs.

M ake it sm ooth w ith a file.....

N ow w e can m ark the locations of the pass trough rubbers used for w iring.... The holes should have a 8m m diam eter. The transform ers w ill also be standing on (thicker) rubbers, in spite of the very low resonance of the transform er... The holes should have a 11 m m diam eter.

Here the pass through rubbers are still loose...

Then, the thunder begins...brrrrrrrrraw w w ... Put som ething in your ears!

The big holes for the tube sockets are m ade w ith a steel m etal punch...

22,5 m m for the noval tubes, 27 m m for the octal and 37 m m for the pow er supply capacitors.

The sides of the holes w ill be sm oothened...

W hen everything is drilled and punched, the copperplate is m ade to a chassis… naked copper so far, but even so...

The copper plate for the connectors at the back plane also need to be handled. Copper is a relative easy m aterial to w ork w ith...

A paint job…. A nd the result is there....

W atch out: first use a fine sanding paper on the plate. A pply tw o layers (thin layers) prim er. I use the light grey colored M otip prim er, from an aerosol. A fter that w e spray the definite color to it, also in nice thin layers. Than w e spray tw o layers of blank lacquer to finish it.

The M otip aerosols I use, have the num bers: ..... for the prim er, num ber.... for the color lacquer and ..... for the blank lacquer. I buy the stuff in the car accessory shop at m y hom e tow n.

The m ore noble job …

The m echanical w ork is done. Every step w e m ake, is bringing us closer to the 'looks' of a real tube am plifier....

W e begin w ith rubber pass trough rings. The big ones are used for m echanical decoupling of the pow er supply transform er at the chassis. N ot as if the transform er is resonating or som ething, but it’s better to expel all doubts....

Pow er transform ers alw ays have to be decoupled, in m y opinion...

The tube sockets, capacitor clam ps and w ire stands w ill be screw ed...

One m ore close-up....

Here you can see w ell how the transform er is standing on thick rubbers. Don’t screw them to tight, that bolts and nuts.... I use a drop of to fixate the nuts on the bolt.

N ow it’s beginning to look like an am plifier...

The big 500 uF caps are placed. Y ou can see this is a very practical w ay to m ount them ....

I m ake the central ground point of loose solder stands. This is the only point w here the circuitry m akes a hard contact w ith the m etal chassis plate. Try to prevent at all costs to m ake an m ass loop... To insure that there is a good contact, a notch ring is applied betw een m ass-star and chassis. By turning the bold en nuts tight, you push the ring deep in the copper plate (or any other m aterial you use).

It’s tim e for an overview ...

These are the decoupling capacitors used for the pre stage and phase splitter. Physically they are tw o caps in one shell. V ery practical in use. W atch how close the capacitor is next to the stages that have to be decoupled. That m akes the w ires very short... The first w ires are laid-out for glow ing the first am plifier stage...

These are the tight tw isted w ires for supplying the glow voltages. Tw isting the w ires I alw ays do using a drilling m achine. Tw isting effectively prevents the em ission of hum m , w hat can be picked up by other w ires and so on…..

The high voltage rectifiers are m ounted …… g n

de hoogspanning ...

A nother detail picture....

The pow er transform er is quite full now ... the blue w iring is connected to the center taps of the several voltage connectors, w hich are all connected to the central ground connector.

Y ou need a incom ing as w ell as an outgoing w ire on the first Electrolytic Cap. Tw ist the blanked outer end w ell and pre-solder it. U se after soldering an isolation shrink tube. A nd then blow ing som e heat to it....

I alw ays cut a large am ount of shrinking tube....

The outgoing w ire of the buffer cap (in this case the in series paced 47uF caps) goes to the choke...

On the other side of the choke it is becom ing m uch m ore chaotic. W e have to supply three separate paths of current.. The junction is m ade on top of the firm ly m ounted fat 500uF supply cap. One outgoing w ire goes to the B+ (CT) connector on the OPT, the other one to the decoupling of the pre-stage, in front of the cabinet. Don’t m ake that w ire to short...

The CT connections on the transform er w ill be joined.... to supply both coils w ith current.

A nother detail of the buffer cap w iring...

A lot of detail pictures...

(above) The left side is identical to the right side...

H ere above you can see the stand-by sw itch....

The rectifying diodes...

G rid resistors are soldered as close to the tube sockets as possible...

The decoupling caps of the pre-stages are very close to the m entioned stages...

The speaker connectors… w atch the blue w ire w hich connect the black connector to ground....

A s you can see here, the decoupling caps are connected to a satellite ground term inal, to w hich the pre-stages are connected as w ell. From there goes a single w ire to the central ground....

The thick purple w ires are connecting the caps to ground. The vanishing w ires (left and right) are going to the 500uF caps

The thick 3-w att resistors are placed parallel by tw isting the w ires. That m akes m ounting easy..

N ext they w ill be tightly connected betw een and soldering strips...

The M KP cap here is no coupling cap. It connects the second grid virtual to ground (for m usic signals). This tube half becom es its (m usic) signal from the cathode.

A nd again there’s som ething to fix …

The w orld turned around? Y es, a little bit. I m ake it unnecessarily difficult for m yself to apply a pot m eter and input selection sw itch to Bill at this building m om ent. It not that hard to handle this last m inute change. But I encourage everybody to do this job at the beginning of the m echanical building stage. Bill is m uch m ore in his elem ent this w ay. It is a circuit w ith a lot of gain to begin w ith and is so to speak m ade to function as an integrated am plifier. For the m ono block enthusiasts: There is a ‘M ono Bill’ in the pipe line. It has an slightly different lay-out, w hereby a tube stage is cancelled and the am plifier is really m eant to be connected to a pre-am plifier. The intention is to put on the pow er in about 2 w eeks. N o, this ‘M ono-Bill’ is not the earlier m entioned Bob. I get a lot of questions about the possibility to m ake Bill in tw o separate cabinets, w hat fastened up the priority of the M ono-Bill. Bob is dropped dow n on m y to do list. M ono-Bill is for a m uch larger audience.

W om an’s Lib…

Bill, w ho ended the integration course successfully, is playing now daily by an audio girlfriend.. Y e, I’ve m anaged it for the second tim e, after the ‘A nnastasia’, to furnish a w om an a tube am plifier. Isn’t it a crazy thing, that only m an can listen to their m usic on a tube am plifier? A nd I can tell you right now , that both w om en can set m ost of the m an aside w hen it’s about know ledge of m usic. … S irs, there is still a lot to do about W om an’s Lib. in this area. Y ou also w ant to have m ore w om en w ith som ething better as a little ssssolid ssstate am plifier?

There w e go...

I’ve chosen for a beautiful A lps pot m eter, The w ell know n bleu one. D on’t forget to set the num ber of steps before you put it in. In case of Bill, it becam e three sw itch able input paths. The sw itch and pot m eter are m ounted w ith sturdy L-shaped m ounting strips to the chassis. I m ade som e oval shaped holes in them , to get a stress free m ounting. Take care that there is never m echanical stress on a volum e regulator or sw itch.

.

The input selector is of a w ell know n type, easy to obtain in a electronic parts shop.

A fter careful determ ining the places of the knobs, tw o big holes are drilled, big enough to m ount an axel throughput. The hole m ust be large enough to fit the throughput tightly.

Y ou can’t stick an axel through a w ooden w all w ithout som e form of support. D on’t give in on quality at this point. The operation of the knob has to feel sturdy, also after being several years in use.

W hen everything is at it’s right place, the selector sw itch and A lps pot w ill be m ounted to the L-shaped m ounting clam ps. A little bit of grease to the axel, there w here it’s sticking through the support, is a very good idea. Feel if the knobs are turning stress free. If not, loosen up the stuff and realign again. Take your tim e for this.

M y big audio friend M arco m ade m e again a pair of heavy brass knobs. N ice and chique…

U pgrades?…

A re there possible upgrades possible on this am plifier? There sure are! W hen the m oney is burning in your pocket, you could think about replacing the pre- stage decoupling caps to tw o Black G ate W KZ 47/47/500 volt types. That’s a pricy but easy to perform m odification. The BG ’s fit in the sam e clam ps as the J J ’s. The sound w ill get m ore ‘grunge’ and a larger feeling of low base, the typical Black G ate characteristics. Y ou better stay aw ay from the 500uF J J , w hich is essential for a sufficient current supply to the pow er tubes. The pow er supply is calculated at this capacity value. A low er capacity gives you a w orse recovery after a spike. Don’t underestim ate the quality of the J J cap… The Black G ate W KZ is absolute the better one, even a huge favorite, but look at the difference in price. …

Furtherm ore there is not m uch to w in. I have used beautiful and superior quality com ponents everyw here.. It is possible to m ake the Bias regulating pots settable from the outside of the cabinet. Place them on a spot w here it’s hard to give them a turn accidentally. M ake a m easuring point to each tube, using 2m m connectors, fitting your m easuring probes. By that, you never have to be inside of your am plifier again. N either if you w ant to change your pow er tubes.