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Parmak 1929 Help
05-20-2015, 03:24 PM
A- Black (goes to chassis) B+ power Blue (goes to speaker) B+90 Brown B+ Det Yellow C- Grey C+ Green ( goes to Chassis) And one red lead which goes to one side of the heaters the heaters would this be A+? Also don't see a B- ? It looks as thought I will need 3 voltages? A, B, and C How would they be connected? and at what voltages? The tubes are 5v heaters 5-01A and 1-171 Any help would be greatly appreciated! Eric
05-20-2015, 05:00 PM
Hey Eric
How's things down in Cumming,Ga? Well looks like you got a good handle on the wiring. Yes the red wire is A+. Would bet that A-,B-, and C+ are all tied back to the chassis. I would check the resistance across the audio transformers to be sure that both pri and sec are good not open. The wire coming from the plate pin of the 71A will need to go though a high impedance spkr or a tube type output transformer to a pm spkr. Blue wire from the transformer ( you don't have yet) goes to the 71A plate lead and the red wire goes to HV. The 71A can take up to 180vdc on the plate. Will work fine of 135 or 90v. Hope I've answer all your question for now. GL Terry
05-20-2015, 05:20 PM
Sorry I forgot about the bottom part of your post
A- Black (goes to chassis) - 4 to -6 vdc @ 1.5A (each tube uses 250ma ) B+ power Blue (goes to speaker) +90 to 180vdc B+90 Brown +90vdc (HV for the RF stages) B+ Det Yellow +22vdc the minis side connects to chassis C- Grey depends on how much hv you are using on the 71A -18vdc C+ Green ( goes to Chassis) goes to the +side of the C- battery And one red lead which goes to one side of the heaters the heaters would this be A+? yes +4 to 6vdc @1.5amps Also don't see a B- ? Connect B- to A- (the chassis) It looks as thought I will need 3 voltages? Nah it's looking like 5. Now if you are cheap and clever you can run the spkr and RF stages off of the same 90v buss. Then use a resistor to drop the 90v down to 22v the det voltage A, B, and C How would they be connected? and at what voltages? See above. Terry
05-20-2015, 08:16 PM
Terry
Things here in Georgia are warming up.... You have given me a lot to chew on. I did check both transformers they both read the same 1k on one winding and 5k on the other. There is a horn speaker that I did not take a picture of it plugs in on top between the tube sockets. The three RF coils under the chassis all have continuity and have the same ohm value. Tomorrow I will see about putting some voltage on it I may be asking some more questions...... Thanks Eric
05-20-2015, 09:30 PM
Ask away!
You may want the check the resistance of the spkr driver( wires coming out of the horn) Should be a few thousand ohms. Terry
05-21-2015, 08:31 AM
05-21-2015, 11:04 AM
Terry,
So I have this power supply that a (SARS) club member had and he lent it to me. It has all the taps but I want to run it buy you. A- to chassis A+ 4.6vdc B + power to 135vdc tap B+90 To 90vdc tap B+ Det to 20vdc tap B- add wire from power supply tap to chassis C- connected to adj supply -4 to -18vdc C+ to Chassis Does this sound right? I have a variac with an amp meter in series so I can bring it up slowly Eric 
05-21-2015, 02:34 PM
Before you do much else, perhaps you should sit down and trace the wiring of this receiver and make yourself a schematic. These old TRF sets are usually pretty simple to trace, and it will give you a better idea of the battery connections. The old standard C battery was 4 1/2 volts, usually provided by 3 D cells in series. Standard B batteries came in 22 1/2 volt increments, 22 1/2, 45, 67 1/2, 90, and sometimes 135 volts. the guts of the 22 1/2 volt battery was made from 15 cells, each 1 1/2 volts, in series. Usually all the B batteries use a common ground, and one can series them, tapping off the voltages as needed. Hope this helps. I am attaching a schematic for a typical TRF set from your period. Using your set, you should be able to find the similarities and differences quickly. The battery hook up will probably be very similar to this, although the color code of the wires will probably be different.
[Image: https://40.media.tumblr.com/9a5a7c0c2b6e...1_1280.jpg]
05-21-2015, 06:09 PM
Voltages /wiring look good. Give her a try! As Mike posted most of the battery (TRF) sets are very similar. The diagram he posted has resistors in series with the grids of the RF tubes. This is done to stop any oscillation. Atwater Kent used this system. Others like Silvertone (King) used a neutralization condenser (small condenser between grid and plate pins of each RF tube). Other that and the number of tubes there all pretty close.
Terry
05-21-2015, 06:26 PM
This is the typical hookup for B batteries in those sets.[Image: https://36.media.tumblr.com/2c0715029a3e...1_1280.jpg]
05-21-2015, 07:30 PM
Lot's of good info to check. I applied some voltage as I outlined above but did not go full voltage. I had about 3v on the filaments they all read the same and had about 100v on the speaker also I got a hum out of the speaker. But a thought came to me I have 5 01A's and one 171. The 171 is supposed to be in the last stage audio how can I determine that? Would the 171 be hooked up to the speaker? If you look at the under side of the chassis you will notice that one socket on the end is different from the others it is spring loaded why?
05-21-2015, 09:40 PM
The plate of the '71A will be hooked to the speaker. You will need an old fashioned high impedence magnetic speaker, the horn kind, or a modern speaker with an output transformer, anywhere from 2000 - 5000 ohm primary (tube side), and the output matched to the speaker. This will have to be one of the tube type output transformers, of course, with a high enough voltage rating, and at least 5 watt power rating. If you are only running the tubes at 3 volts you may not get much. 01As and 71As are designed to run with 5 volts on the filaments. Try the set with full voltages on the various connections. These very early sets are pretty rugged that way. If still no luck, next check the audio interstage transformer. Try ringing it out for resistance. or try injecting a signal at the secondary, and primary of the transformer. with the set on you should hear it .. just trace it back as you would with a modern set. Here are the ratings for the '01A and '71A tubes :
http://www.nostalgiaair.org/tubes/01a.htm http://www.tubezone.net/pdf/71a.pdf Looking at the bias needed for the 71A with 135 V on the plate, you will need about -17 volts to get efficiency out if it, so you may need that for your C voltage.
05-22-2015, 05:16 AM
You are going to need to get your filament voltage up to 4-4.5 volts. Don't think 3 going to work. Got an old car battery??? Could use that with a 5v 5amp regulator (like a LM7805 in a TO3 package) or a LM317K it's adjustable. Back in the late '20's that's what was use to power the filament was a 6v car/ tractor battery. Got an old Farmall or Massey-Ferguson??? DO NOT CONNECT THE 12v CAR BATTERY DIRECTLY TO THE FILAMENT BUSS OR YOU WILL BE LOOKING FOR A NEW SET OF TUBES!!!! As for the tube mounting the one tube that is spring mounted is the detector tube. It's mounted like that to minimize microphics ( a ringing sound when tube is vibrated). The 71A should be inserted into the socket that is connected to the spkr terminal. It's not a deal breaker as the set will work it where ever you put the 71 but will work better if it is in the proper place.
Terry
05-22-2015, 07:06 AM
As I said, I have a test rig I borrowed from a club member and am feeding it through a varic which I have it running through a meter so I can watch the current. I only put in 3 volts as I got a 60cy hum so I stopped there not wanting to damage anything. I will post a picture of the speaker and test rig today. I will verify where the 71 is located. Thanks all this site is the best!
Eric
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