Volume 27, Issue 5 Sept/October 2016 Alignment of AM superheterodyne radios By CRC Member—Gregory Malanowski When you acquire a vintage superheterodyne radio, its type, there is a possibility that the chassis could be dan- resonant circuits are almost always out of alignment and gerously at or close to the power line potential. There- they badly need your intervention. This could be caused fore, install small capacitors, 1000pF/630V in series by several factors, usually a combination of a few of with the signal and the ground wires from the generator. them. The most common is a result of past attempts to restore the sensitivity of the radio, which had usually The first necessary step is tuning the intermediate fre- been a crime committed by quency (If) filters to the the former owner or by factory-recommended fre- some unprofessional repair quency of your receiver. man, who had mindlessly Use a non-ferrite tuning turned back and forth all tool, whether it is a screw- accessible trimming con- driver or a hex socket densers and ferrite cores wrench. inside the coils. This is the most challenging situation, Some manufacturers sug- for the delicate ferrite gest connecting the signal cores had been often se- generator wire to the anode cured using a hard lacquer, of the mixer tube. That is and could have cracked as usually neither safe nor a result of careless em- easy. You can achieve the ploying a metal screwdriv- same results by applying er. Also, the antique trim- the If signal to the antenna ming condensers, with a input while the radio is mica dielectric or a layer of silver evaporated over deli- tuned to the lowest end of the broadcast frequency cate ceramic plates, sometimes break easily. range. But that will require a much stronger signal from the generator! Then, align the If filters for a maximum The less dangerous "natural" cause of misalignment output level while going backward, i.e. beginning with could be a gradual change in the dielectric constant of the last (detector) filter, and ending with the mixer tube capacitors or decrease in the inductivity of the ferrite- filter. core resonant coils. The former cause is more common, though. Be careful: sometimes you may find that alignment of an old If filter beyond the extreme position of the filter So, if you decide to align your receiver, attach an AC ferrite core, or its trimming cap, could result in a higher meter in parallel to the speaker. You may need to sepa- output level of the signal. However, never attempt to rate it from the DC potential using a 0.1uF capacitor. Do change the factory-recommended intermediate frequen- not use your ear to assess the signal level; the human ear cy to achieve a better output signal. We will discuss the cannot reliably detect variations in the sound level be- implication later. Instead, disassemble and repair the low 3dB. Then, connect the RF output of your 400Hz troublesome If filter (cracked ferrite, defective capaci- amplitude modulated signal generator with the antenna tor?). jack of the receiver via a 300-ohm resistor. Warning: if your superheterodyne radio is a "universal" AC/DC (Continued on page 3) COLORADO RADIO COLLECTORS ANTIQUE RADIO CLUB Founded October 1988 The Flash! © 2016, all rights reserved Message from the President Here we are in the heat of August, BBQ/Auction at the upcoming meet- when a lot of us go on vacation or ing. It will be at the same place as al- travel around a bit more and maybe ways. Thanks to Rich. We now have a find a radio for sale out there at a gar- new Auctioneer-in –training, Cliff age or estate sale. If you haven’t found Shelby, to help out Tom this year. Al- any “new” things for your collection, so at the last meeting Merril said he CRC CONTACTS you will soon have the opportunity to would be able to help Tom and Cliff President Tom Zaczek find them at the upcoming Barbeque/ with this. Thanks guys! Wayne will 303-665-3743 Auction in September. So August is help out to get all the supplies as Dave zacfam at comcast.net Vice President Wayne Russert always a good time of the year to go won’t be at the auction this year. Don 303-660-3799 through that collection of Andrus will get the Deartrail at wans.net radios and see what you drinks as usual. Remem- Treasurer Merrill Campbell 719-596-3482 want to bring to the auc- ber that YOU need to Campbell321 at juno.com tion. bring a dessert or side Egroup Manager Mike McCutcheon (303) 343-2956 dish item. And Alexis ugea07 at denvercommons.net We had a great turnout for and Larry will be sup- Egroup message posting address: colradcol at yahoogroups.com the last meeting in July, porting the auction data Flash! Publisher Steve Touzalin with lots of good show base and software as (303) 988-5394 and tells and preliminary usual. So to help out Stevetou at comcast.net Flash Graphic Editor Rich Kuberski discussion about our up- please email your lot ROKuberski at msn.com coming Barbeque/Auction items info to Alexis Webmaster Bill Grimm th Website www.radioace.com on September 18 . We ahead of time. There is NOTE: at = @ in email addresses ————————————————————————————————————————————————————————— also had a new member more info in this issue Upcoming Events Mike Knospe show up in with all the details. 8/15 1969—Woodstock Opens his Model T (did not have a radio in Thanks to all that help make this a 8/24 79AD—Mt. Vesuvius erupts it) and join the club. special event! 8/28 CRC Meeting in Castle Rock 9/1 1939—Hitler invades Poland The raffle was fairly decent with lots And last but not least, we have a new 9//5 Labor Day of unique items there and as a result Flash Editor! At the meeting Alan 9/11 2001—Attack on America we filled the treasury a bit. Even Burch stepped up and said he will take 9/22 Fall Begins 9/25 1789—Bill of rights Passes though we have an auction coming up, over from Rich. Special thanks to him 9/28 CRC Annual Auction —————————————————————————————————————————————————————— you can still bring that weird stuff to for volunteering. This is great! And the next meeting’s raffle that is not so thanks to Rich for the many years of Meeting Locations “auction worthy”. Keep it coming. It excellent work in putting together the (Unless noted otherwise) Littleton Castle Rock helps the coffers! Flash. March January July May The show and tells were very impres- And as far as Flash articles, we have a November September ————————————————————————————————————————————————————————— sive as you can see from the photo few but will need some more. So think CRC MEETINGS spread in this issue. Thanks to all who about an article or even just a small Meetings are held on the 2nd Sunday of participated. Merril showed some of “restorer’s tip” with a photo! every other month starting in January his typically amazing restorations that (except May is 3rd Sunday) at 1:00 pm. included a Bakelite radio that looked Please note that our next meeting The meetings consist of business, “show & like new and a plastic one whose hing- that we normally have the week af- tell”, raffles, auctions, swap meets, tech- es he had cleverly repaired. Tom ter Labor Day weekend is now on nical discussions and other subjects of in- th terest Pouliot shared with us some more of August 28 . We are doing this to ————————————————————————————————————————————————————————— CRC MEMBERSHIP his museum-quality constructions of avoid the art show conflict at the early spark-gap transmitters. Not one Castle Rock Library. I look forward Annual membership in the CRC runs from but two complete functioning units in to seeing you all at the August 28th, July to June. Dues entitle members to at- different bands that he has used to 2016 meeting in Castle Rock! tend meetings, "The Flash!" our newsletter, discount book prices, participation in our make actual amateur contacts with. spring show and Fall auction. Current an- Quite impressive! nual dues are $20. New memberships will Tom Zaczek be prorated to the following June. We will finalize the planning for the 2 (Continued from page 1) pacitor changes its capacitance over An often-overlooked problem is a minute time, or when the If filters have been change in the capacitance of the so-called tuned to an incorrect intermediate fre- padding capacitor. When two identical, quency. single-shaft tuning condensers are in- stalled in the superheterodyne radio, one To align a superheterodyne radio in for the antenna circuits and the other for which a constant value padding capaci- the local oscillator, it is theoretically and tor is used, align the If filters first and practically impossible to maintain a con- then tune the dial to the recommended stant difference in their resonant frequen- higher crossover frequency B (usually cies (equal the intermediate frequency If) around 1400kHz). Apply the signal over the entire AM broadcast or shortwave from your generator. Adjust the oscil- band. That results in a drastic reduction in lator shunt trimmer for a maximum sensitivity at a certain position of the tun- reading on your AC voltmeter. Repeat ing dial, and you are certainly familiar that at the low crossover frequency A with this effect. The manufacturers allevi- (usually around 600kHz) by adjusting ate that inconvenience by using the tuning the ferrite core of the oscillator coil. condensers of a different profile, or by a Then, return to the higher crossover less-expensive, common method of in- frequency.