Repairing Radio Sets

repairing radio sets

PART 5 GORDONJ. KING

After H. W. Hellyer's discourse on dial drives last month, it is now my turn to take up pen and discuss audio section faults in valved equipment. So far we have passed through the average radio set from the aerial to the detector, taking in the r.f. dial bulb, the remaining intact heaters will fail to light. rather like the effect when one bulb in a series amplifier, frequency changer, i.f. stages and of Christmas tree fairy lights fails. A.C.-only sets o.g.G., and experience has taught that in using a main,s transformer usually have parallel- these stages of the receiver the more oonneo:edhea,ters, which means tha,t one (or more) difficult-to-find fault is harboured. cou'ld go open-circuit without affecting the lighting of ,theremaining intact ones. Fault-finding in the audio stagesis ,relativelyeasy Check (ii) is oflten the first (after checking valve once it has been proved that this is where the fault heaters for glo,w) made by technicians coming up lies. This is always ,the most difficult part of servic- against an apparenrtly dead set. Normal level of ing r'adio receivers-locating the fault area. residua,l hum from the loudspeaker indicates (a) tha.t Let us start by supposing that the set is com- the loudspeaker is working (b) that ,the loudspeaker pletely dead. The first m,ove is ,to find out as quickly transformer is working (c) almo,st certa.inly that the as possible just where ,the fault ,lies (not necessarily output valve is passing current (i.e., reasonable emis- the actual guilty component). Although a set may sion) and (d) that h.t. supply is reaching the ,output fail to respond to a transmission,this should not be valve. It will be agreed that this is quite a lot of taken to mean.that the set is completoly dead for the information from one s.implelistening,test! aud,io stages may be working! We can at least find Check (iii) in'dicates that the rectifier is, at least, out with the least delay whether the power supply receiving h.t. input from the main,sand that the ou't- is active by (i) seeing whether ,the valve heaters are pu't valve is drawing h.t: currenrt from the rectifier, alight (ii) listoning closely at ,the loudspeaker for assuming that 'the envelope temperatures are not signs of residual mains hum and (iii) feelin:g 'the abnormally l.ow or excessive. Abn,ormally lo,w tem- tenlperature of the h.t. rectiflor (if this is a valve) perature could mean that the heater dissipation and the output valve. alone is warming the glass, indicating lack of anode current and anode dissipation. HEATERCHAIN An excessive 'ternperature in the reotifier could mean excessive current demands due to a leak or Check (i) is obvious, of course, and ,this proves short on the h.t. line or feed circuits or even a short ,that mains curren't is gefting ,to the set, that the on/oft in the rectifier ittself. In the ou,tput valve excessive switch and fuse (if fibted) are in order and that all anode curren't could be due to faulty grid biasing or 'the valve heaters are intact. It should be noted. a leak in ,the grid cou,pling capacitor which would, though, that non-lit heaters in an a.c./d.c. type of of course,destroy the biasing,anyway. set may not be definite proof that the mains input is defective because the heaters of all ,the valves (and NO RESIDUALHUM dial light) are connected in series acro,ssthe main;s supply with the heater current being limited by the Let us suppose that our "dead" set exhibits n,o mains dropper resistor, as shown in Fig. 5-1. resi.dual mains hum and 'the rectifler and output Thus, if one series element goes open-circuit, such valve are running very cool. We can conclude lack as one hoater, mains dropper, on/off switch, fuse or of output valve anode current due rto lack of h.'t. curren,t (cool rectifier). The first test should be to establish ,that 'the rectifier an'ode is receiving mains To anode Limiter of HT. section supply, via the limiter resistor (see Fig. 5-l). A multi- rectif ier meter switched to 250V a.c. will soon prove this. Voltage ,at the mai,ns side of the limiter but not at on/off Ac/Qc, ,the Swltcn marns the rectifier ano'de si.de means that resistor is O.O5tF open-circuit. il o At this stage it would be as well to switch ,the set off (disconnect fr'om the supply) and check for a sho,rt with the rectifier valve removed from the an.odetag on its holder to chassis.If ,thereis a short, connected fro'm anode to Valve heaters the filter capacltor, often chassis (the 0'05rlF in Fig. 5-1, for instance) will Fig. 5-l: The heater supply circuit in an a.c.ld.c. set.Also probably be responsible. This must be replaced with showing the h.t. rectifter anode feed. via surge limiter. the component of like value with a 250V. a.c. rating.

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The set would work without this filter capacitor, circui't. In ,the lattor case, the resisto.rwordd tend to but it may give {he symptom of hum when accur- overheat since its relatively low value would pass ately tuned in to a station or carrier. This is called substanttialshort-circuit current. modulation-hum, and its presence should first lead to a check o,f the filter capacitoi for ,opon-circult in DON'TFORGET THE LOUDSPEAKER a.c./d.c.sets. A short in the capacitor will immediately blow the Finally, for the same symptom, attention should surge limiter resistor, often a section of the mains be directed rt,o the loudspoaker itself and i'trs con- dropper. If there is no short on the anode tag, re- neotion to the secondary of the 'loudspeaker trans- i.nsert the ,rectifier valve and itry again. A short'this fo.rmer. Sometimes the transformer is fixed (bolted time means that the h.t. rectifier is faulty and needs or riveted) to the loudspeaker chassis; if not, it is replacin,g. The rectifier, however, would be more I'ocated somewhere on the chassis near the output likely to be running very hot ,than cool with this valve. {rouble. I,t is by no means rare for the speechcoil winding If the rectifier is run,ning hot an'd rthere is still no of the loudspeaker to go open-circuit, but this can residual mains hurn, there could be a partial short easily ,be checked by co'nnecting ,an oihmmeter across on the h.t. supply from the cathode of the rectifier. the speechcoil tags, making sure ,that the speaker is disconnectedon one side fro,m the secondary of its transformer. Otherwise, even {hough the speech coil rnay be open-circuit the ohmmeter will register a low resistancethrough the secondary winding itself. If an ohmmeter is not to hand, a small l'5-volt battery connected across ,the tags should rgsult in a click or crackle when,the conneotion is scrapod. Fig. 5-2. Typical "smoothing' crrcuit of modern receiver. Some sets have ,an extension loudspeaker socket A dead short here would blow ,the valve and/or su'rge (or pair of ,sockets)at the rear o'f rthechassis, with a limi,ter resistor. Mos,t sets nowadays have a filter pressure screw, switch or some other device for resistor fro,m rectifier ca'thode to ,the h.'t. s'upply cutting out'the i,nternalloudspeaker if required when i (Fig. 5-2) with electro,lyticeitther side, s,oa short the running the ex,te.nsion.This switching arrangement is vulnerable, and it should certainly be looke.d at if i set side o,f this resisto,r would run the reotifier hot, ; possibly without blowing it, whi,le overheating the the foregoing hints have done nothing about bring- resistor its€{f. D.C. voltage tests along the line would ing back residualhum in the set'sIoudspeaker. soon prove'this trouble. Of course, an exten.sion loudspeaker could be tried if one happens to be handy. Most 'technicians, OPENTRANSFORMER PRIMARY in fact, have such a loudspeaker permanently in posi,tion o.n a shelf at the rear of the bench con- If both 'the rectifier and the output valve are run- nected to a pair of flying 'lead,sfor immedi,ate 'test ning hot, still wi,thout residual mains hum, and the con,necltion. above-mentioned ltests have failed to reveal any We rnust now assurne that the dead set exhibits major fault, 'the screen-grid inside the output valve residual hum. This ,may n,ot be vory loud, but it i,s should be closely .observed. If this appea'rs 'to be overheating or running red-hot, o,ne need look no further than the anode circuit o,f the valve for an open-circuit to the h.t. supply. In the vast majority of sotsdhe anode is loaded to the loudspeaker transformer, and an open-circuit primary winding is a typical cause of the symptom. A rattrer loudish hum (not ordinary mains hum) 4t I accornpa'n,ying the syrnptom of a red-hot screen- {, grid means thait 'the valve anode is sta.rve'dof h.t. !. supply due to a short-circuit on the ,anode. Some 4; 5 inexpensive sets h,ave a capaoitor froqn anode to oarth to minimise the effects of third-har'monic distortion (a single pentode stage being very prone to this kind o,f distontion).The capacitor applies plenty of treble-cu,t and gets rid ,of the higher-order har- mon{icsat the sa,metimel Better circuits may have a tone-control or flxed resisto,r in series with ,this capaci'bor, so if 'a short develops the effects are less dram,atic. With a ,tone control. the track will burn o'ut when ,the knob is i fu'lly advanced and with a fixed resistor the sho,nt- -reading $ ci,rcuit current through it is barely en,o,ughto cause 7 even sl,iglr,ttemperature increase. Another cause of lack of residual ,mains hum is Fig. 5-3: Audio section of recent mains powered a.c.ld.c, ( an open-circuit screen-grid feed on the output pen- set. This circuit is sometimes extended to push-pull by the tode. Sets which use a scree,n-grid feed resistor and use of two triode-pentodes, the pentodes being the out- { bypass caglacilto,r to chassis should have the resistor put pair and the triodes as phase splittet and voltage checked for open-ci,rouit and the capacitor for short- amplifier. VLL*)--'o^ ^ u,/c,lr- all 2g7 ooLS\u ,.,. fr.,'ll i,V 'A U < + t:r t cv.Ll ..r,.,)^.., generally heard reasonably well with an ear close the loudspeaker when the tip of a screwdriver, uporr to 'the loudspeaker, depending on the efficiency of the metal side of which is resting a finger, is touched ,the set's smoothing and the nalture of ,the set. Hi-fi on the va,lveholder tag or rthe centre tag of the sets have very little ,residual hum output, so this volume oontrod (witth the control tur'ned fully clock- test may not assist much with sets (and amplifiers) wise) correspondi,ng to the grid of 'the triode section. of ,this kind. The resulting loud hum is caused by ,trtre body We should ,no\tr move lto the iinput of the au'dio passing ripple voltage (at very high impedance) to stages in an endeavour to get a signa,l in here to see the grid circuit. Atrternatively, pure ripple signal can whether it arrives at the loudspeaker. An audio be obtained from the heatter line, via a 0'0lg.F capa- gener.ator or osci,llator is an ideal instrument for citor and l0k0 resistor to the control grid. If there this purpose, as a,lso is the "audio" (tone) output is no response, then the audio section is dead. from an r.f. signal generator. Most signal generators The next best rnove is to go tthrough exactly the have an aud,io ou,tput socket at the fixed tone of rthe $arne process again, but this time injecting trtresig- r.f. modulation, which can be used on its own, nal into the control grid of the pentode seotion. The sornetimes regulated by an ,audi'o level control, sensi,tivity here may be insufficient for tthe "finger/ depending upon the sophistication of the instrument. screwdriver hurn test", but a loud hum should be The signal should be fed in at the control grid of obtained by injecting ripple from ,the heater line the first audio stage (direotly following the detector) as before. via a length of screened lead, inner conductor lto If tthere i,sno response at the triode, but adequate signal "live" an.d the ;braid to "earth". Again, i't response ,at the pentode, ,the ,triode stage is faulty. must be stressed that a.c./d.c. sets have their chas- These checks can be undertaken very quickly in sis co,n,necteddireot to one si'de of ,fihe mains supply practice although they take time to explain. (see Fig. 5-1), so if transformer mains isolation is Triode stage trouble could lie in the valve itself not used, it is impera,tive that the mains be connec- or in ,the a,nrode supply circuit. The valve oan be ted so thatt the neutral side is to set chassis. A.C./d.c. checked by metering the voltage across the cathode sets muot never be earthed direot, n'ot even when resi'stor. In Fig. 5-3, however, this resistor is not the chassisis at mains neutral. used for biasing, but purely for 'the injection of negative feedback from the output transformer. BACKTOTHE EARLIER STAGES! Never,theless,a correotly emitting triode should give a sm,all voltage acro,ssthis low value (22O) resistor, With a.n audio input of between 50 and 100mV, but a lo,w-reading voltmeter would be needed to almost full ,audio output should be developed in the record it, as in Test 1. loudspeaker. trf rthere is no output or if a signal of Test 2 would tell how the anode supply is work- substanttially greater level is required ,to obtain a ing, but again the voltage here may not be as high mere trace orf output, the au'dio section is cer,tainly as expected owing to the voltmeter loading on the at fault. If, on the other hand, a solid output is 270kO anode feed (,load) resistor. However, if the obtained, the fault lies somewhere before the audio h.t. side of the resistor reads about 200 volts. the sedtion (up to the detector), so back to the earlier anode side should read about 80 volts on a meter of stages we must go and make 'tests ,trhere as ex- not less than 10,000 ohms/volt sensitivity on the plained in the iprevi'ous articles (Parts I aind 3). 200V r'ange. If ,the pointer only just albout rnoves The circuit of a typical recenrt (valve) audio sec- from rthe zero mark on the scale, the anode resistor tion is given in Fig. 5-3. This comprisss a triode has probably gone very high in value or even open- voltage amplifier and a pentode audio output stage. cirrcuit, and it should not take very long ,to prove In later sets it is conventional to use a single triode- this. pentode valve of the ECL82 class, as in the circuit. On the other hand, trouble in the triode section Right through the ages the average radio audio sec- of the valve could be encouraging ,the va,lve to pass tion has consisted of two such stages but in some excsssive anode current, in which oase the volts-drop older sets a double-diode-triode valve was used in acr,oss 'the 270k0 anode load resistor would be front of an ordinary pentode, the two diodes being abnormally high. used for demodulation and a.g.c. The biasing of ,the tniode section is interesting. In There ftrave been variation,s o'f this theme, wirth all diodes and valve grids loa'ded i,nto a very high diode i.f. pentodes and double-diode-pentode output resistance (10MO in this case), 'the residual diode valves. Now, though, audio circui,ts have stabilisod (grid) current, created by eleotro-chemical effects almost exclusively to the set-up in Fig. 5-3-with within the valve, produces a voltage of sufficient minor differences in detai'I. rnagnitude across the high value load to bias trhe Modern triode-pen;tode valves can deliver up to valve withourt the usual catlhode resistor. The 22A 3 watts or more (at about 10"/" total distortion at cathode resistor on ,the triode in Fig. 5-3 is solely full power) with an input of 50-100mV, adequate for negative feedback, as already mentioned. for working from the signal output of a diode detec- trf the triode seotio,nappears normal d.c.-wise, yet tor. A pair of valves can also produce a reasonable signral still fails to pass ,through it to the output push-pull stage with much lower total distortion and pentode, the only vulnerable co,mponent lerft in cir- higher power, and this ,technique is usod in some of 'the cuit is the coupling capaoitor Cl. This rarely causes better class radios and radiosrams. complote failure of the set, although it can be responsible for other syrnptoms, as we shall see. DYNAMICTESTS Lst us now suppose that our earlier dynamic tests (with audio signal and hum) failed ,to prduce If an audio generattoris not available, the sensi- respo'nse at either the triode or penrtode grid, yet tivity of the audio seotion,is generally sufficient when residual hurn is present. This wo'uld imply trouble in working correctly to produce a violent ourtput from the pentode stage, and the pentode sootion could be

288 faulty, as also could the h.t. feed elements. However, vol,tage amplifier anode load resistor for value this trouble would be likely to prevent residual lncrease. hum, .but one cannot be absolutely sure (ha,t ,the Motor-Boating: Check the catho'de hypass electro- pentode stage is in'tact when residual hum i's prosent. lytic of the output 'valve, the screen-grid capacitor *1 and other associated electrolytics for decrease , in value or for open-circuit conditi.on.(Record TESTSIN THEOUTPUT STAGE Symptom 7.) Low-frequency Instability: Check any smal'l value Thus, ,m'uch of what is now abou,t to be said (pF values) capacitor on the co.nlrol-grid, screen- cou,ld also apply to a set devoid of residual hum grid and anode electrodes of the audio valves for (i.e., completely dead in all respects).The flrst check open-circuit. Forr inStance, open-circuit of ,the l00pF should be for cathode voltage, as in Zest 3 in Fig. capacitor on the controlgrid of the pentode stage in if 5-3. A normal reading here is about 12 to 14 volts .t( Fig. 5-3 could cause the symptom. Check nega- with a 170-volt h.t. lirne and a cathode rosistor of \,' tive-feed;back loops and componentrs for value abou't 390f1. Assuming that the cathode bypass increase. Check smoothi,ng and bypass electrolytics. electrolytic is no,t shonting, lack of cathode voltage (Record Sympt'om 6.) signifios tha.t the output pentode is failing to pass Very Severe Distortion and Lack of Bass: Check I current. This could be due to a bad va,lve, of the speech-coil of the loudspeaker for movemen't. course, or a break in the h.t. feed ,to the screen-grid. *Q If necessaryre-centre ,the loudspeaker speech- We ,have seen ,thattan open anode circu'it produces L' coil in its magnetic gap. (Record Symptom 8.) l- 1 other symptorn,s,&Dd in this even,tthere would still Lack of Treble and Low Yolume: Check loud- A be cathode voltage due to the heavy screen-grid speaker itran'sfor.mer for shorting turns, preferably J current, but it would be below normal ln Fig. 5-3 by substitutio'n.Check cathode eleotrolytic on output the 32p"F electrolytic on rthe screen-grid serves a:s a val've. Check all audi,o coupling capacitors fo,r value smoother in conjunctio,n with 'the lkO resistor the increase. I in t h.'t. feed. A short in trhis capacitor, therefore, would 3. have t,he results i,ndicated in Fig. 5-2. lt would also i put the set out of commission. RADIOGRAMFAULTS I We have now covered most a,speotsof complete failure in the audio circui,ts, but there are many Any of the faults and effectsdescribed in ,thisand f other symptom,s (hat result fro'm troubles in this the previous articles co,uld, of course, 6"ygl6,p in a area of the set. These will now be detailed. radiogram as well as any ordinary radio. However, Excessive Mains Hum; If present with the volume there are so,me fau'lts which occur only in radio- control tu,rned right down, a smoothing electoly'tic grarn's, and these are main,ly concerned with the (Cl and/or C2 ,in Fig. 5-2 and C2 in Fig. 5-3) will record ropnoduction. almost certainly be responsible. If possible, check by If gram reproduction is impaired whi,le radio is paralleling a known-good capacirtor of correot volt- normdl, one can be almost certain that the trouble age rating and capacitance across the suspect. If Iies in ,the record, pick-up or associated fiIter/feed the hum develops progressively in i.ntensity as ,the nqtworks. If both radio and gram reproduotion is volume control is turned up, su,spect a condition impairod, however, the audio stages are to blame, causing hum to be injected in from the earlier and ,testing along the lines suggested in this article stages. Also check ,the au.dio valve(s) for heater/ sho,uld restore both to normal. It i,s unusual fo,r cathode leakage. audio trouble to affect radio reproduction and not Low Audio Sensitivity: Check audio va'lves for gram, though 'this can happen if the radiogram emission and replace if low. Check the cathode carries a separa'teaudio channel for record repro- bypass el€ctrolytic for low value of open circuit. duction only. The economics today prohibit this tech- Open-cirouit here produces current nega,tivefeed- nique, but it was enrployed in some of the earlier, back, having a degenerative effect on sensitivity. rather expensiveradiograms. Intermittent Volume changes: Check the audio Weak volume and distortion are the most common coupling capacito.r (Cl in Frig. 5-3) for intermit- record reproduction complaints, excluding those, of *{ ,ten'cy.It is best ,to change this component if course, concerned wi,th deck mechanics. The finst J there is any doubt as to its goodness.(Record thing to do is to make sure ,that the record itself is Synrptom 5, on P.W. Fault Finding Record.) free from fault, and it is a good idea to keep one Small Distortion: Check negative feedback circuit or two test records available of known qualitty. and cornponen,ts. Check output valve for emission The next thing is to suspect the pick-up cartridge. and voltage amplifier anode load resistor for value Most radlograms use crystal or ceramic cartridges, increase. Check voltage amplifier valve for g,rid- and these, especially the former, deliver substantial current, especi,ally in circuits usi'ng the grid-cur,rent sign,a,lvo,lttage allowing connectio,n straight into the method of biasing, shown in Fig. 5-3 and explained grid circuit of ,the volt,age amplifier, via the radio/ earlier. gr,am switching. Provided this ,type of cartridge is Large Distortion: Check audio valves for emis- loaded in,to a circuilt of n'o,t less than I MO (prefer- sio,n and replace if low. Check the ooupler Cl for ably 2MO) equalisation is not necessary. leakage. This is best done by monitoring the cathode If the input load is less ,than this, however, there voltage as in Test 3 while connecting and discon- is a bad drop in bass response, bu,t morst well- *O necting Cl. If the carthode voltage rises when designed radiogr:ams incorporate a simple matching /' Cl is conneoted, ,then it is most certai,nrlyleaky pad (RC network) betwoen the oartr,idge and ,the electrically and must be replaced. (Record Syrnptom arnplifier inpu,t to socure the best outpurt responge 9.) from the cartridge used. For this reason, therefore, Large Dirtortion and Low Volume: Check the the correct replacernedt canlridge should be used. It is often difficult ,to decide whether he cart.ridge the voltage amplifier is fed through the coupler to or stylus i's responsirblefor 'the poor grarn roproduc- the grid of the output pentode. tion. Weak output accompanied with distortion The voltage amplifier pentode is biased partly by (radio all right) almost always indicates a faulty grid-current (10Mf) grid resi'st.orand par'tly by fihe cartridge, and this can sometimes be proved by Lt. voltage. That is, the potential differencebetween applying a very small side-pressure to the pick-up- the contr,olgrid and the heater,or part of the treater. head while it is playing a disc, first one side and ou,tput pento'de is main,ly biased by the volts- then ,the other. If ,this restores volume and decreases drop across the 5600 resistor connectedin series 'the distortion, the cartridge is faulty. with the h.t. negative supply). H.T. current for the Hi,gh distortion but not neces'sarily low volume, rVhole set flows through this resistor, so the voltage with a 'tendency for the pick-up ,to skate across ,the across it is dependenton the cuffent taken by other * 1 n disc, indicates a worn stylus. It is important sectionsof the set. r v that the correct replacoment Stylus be used. The voltage is negative with respect to chassis The effeots resulting from a cartridge and/or stylus a,ndthe filamen,tof the output pentode,a,nd the valve defeot are given in Record Symptorn 10. is biased by its control-grid being returnod to the It shou,ld be n.oted that rnono-onlv recolds wi,ll negative side through the 2.2Mo- resistor. This evenltually cease 1to be made and thai all issues will technique is common in this type of set. Comrnon then be stereo ones. As there is no such thi,ng as a faults include: "compatible record" (rnono/stereo), radiograrns will Distortion: Caused by low batteries, low emission have ,to be equipped with cartridges of sufficient or over-run valves, increase in value of anode and vertical oorqplia,nce to track the cornplex stereo screen feed resistors, very slight electrical leak in groo\r'e withoult damage and with the min,imurn dis- coupling capacitors, alteration in the value of the tortion. Compliance, incidentally, is ,the reciprocal 560O biasing,resistor and changein bias voltagedue of stiffness-thus, trigh compliance means .low stiff- to other parts of the set taking abnormal h.t. current. ness. Low Sensitivify: Caused by low emission valves, Already such mono oantridges are being developed increase in value of the screen-grid voltage arnpli- for ordinary radiograms ready for when the tirne fier feed resistor or leak in associatedbypass capaci- oomes. Indeod, radiogram owners even today may tor. Increase in value of anode load resistor. Low want to convert to allow tthe rnono reproduotion of batteries. steroo discs. This can be achieved by using a stereo Motor-Boating: Caused by open-circuit h.t. line cartri'dge (of sirnilar char,acteristics 'to the existing bypasscapacitor. mono one) and connecting the left and right chan- Whistling as H.T. Battery Runs Down: Open- nels jn parallel. circuitt of the rnain h.t. line electrolytic capacitor These rernarks, of course, do nst apply to stereo (,the8pF in Fig. 5-4) is a frequent causeof this symp- radiograms, which already have suitable cantridges. tom. H.T. battery may also have to be replaced if its "on-load" voltage is lessthan 60V. CONTINUEDNEXT MONTH BATTERYAND MAINS/BATTERYAUDIO Finally, a few words about audio troubles in PRACTICAL ELECTRONIGS barttery and rnains/battery valved portables. The audio seotion of such receiver is given in Fig. 5-4. The convention is again followod, but the voltage arnplifier is a pentode instead of a ffiode. Also, a TRANSISTORISED diode is fltted in the pentode for detoctor and a.g.c. The audio signal dweloped across the anode load of BTTEINDICATOR A compact self-contained unit for attachmentto a fishingrod. Particularlyvaluable for night fishing. THE CHEMOSTAT An electronic thermostat with remote temperature feeler for accuratethermostatic control of chemical liquids.Temperature rcnge (17'C-4r0'C) suitablefor colour and monochrome photo-processing.

special feature MICROELECTRONICS Beginning a specialsurvey of a rapidly developing field of electronic technology. Describes various integrated circuit devices and how these may be applied to amateuruse.

AUGUSTISSUE ON SAIE JULY14 - 216 Fig. 5-4: The audio section of a battery portable.

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