Hi everyone. I have a Temple trf set with 4 rf coils. I have recapped rewired and resoldered everything. Replaced both audio interstage transformers.Plate voltages etc all seem within specs.Tested all tubes and replaced them even though tested like new. Volume controls test fine not finicky. I get intermittent volume from first rf tube all
the way through the chain. Could it be faulty rf coil?
Some green spots but coils test reasonable resistance.
Touching grid of second tube seems to snap everything back into shape as long as its not insulated. Thanks Gordon

Gordon,
You didn't say what you considered "reasonable resistance" of the coils. Is this referenced to documented mfr data or just guessing. The scattered green spots you noted would indicate copper corrosion, with a good chance of a high impedance connection or a complete break or plainly and simply not to be trusted over the long term. I found the same green spots on a field coil a while back, which ultimately involved 15,000 ft of 32 AWG, and four days winding time with an ice cream freezer motor/transmission, and my home built mechanism.

marv

:Hi everyone. I have a Temple trf set with 4 rf coils. I have recapped rewired and resoldered everything. Replaced both audio interstage transformers.Plate voltages etc all seem within specs.Tested all tubes and replaced them even though tested like new. Volume controls test fine not finicky. I get intermittent volume from first rf tube all
:the way through the chain. Could it be faulty rf coil?
:Some green spots but coils test reasonable resistance.
:Touching grid of second tube seems to snap everything back into shape as long as its not insulated. Thanks Gordon

...Faulty resistors, too, as well as rusty grid cap connections (if a grid cap is used). I've had trouble with the latter with my 4 tube TRF (RF, DET, AF, and RECT.).

T.

:Gordon,
:You didn't say what you considered "reasonable resistance" of the coils. Is this referenced to documented mfr data or just guessing. The scattered green spots you noted would indicate copper corrosion, with a good chance of a high impedance connection or a complete break or plainly and simply not to be trusted over the long term. I found the same green spots on a field coil a while back, which ultimately involved 15,000 ft of 32 AWG, and four days winding time with an ice cream freezer motor/transmission, and my home built mechanism.
:
:marv
:
::Hi everyone. I have a Temple trf set with 4 rf coils. I have recapped rewired and resoldered everything. Replaced both audio interstage transformers.Plate voltages etc all seem within specs.Tested all tubes and replaced them even though tested like new. Volume controls test fine not finicky. I get intermittent volume from first rf tube all
::the way through the chain. Could it be faulty rf coil?
::Some green spots but coils test reasonable resistance.
::Touching grid of second tube seems to snap everything back into shape as long as its not insulated. Thanks Gordon Primarys are 1.9-2.1 ohms secondarys are 3.4-4.1 ohms measured out of set and in set. the green spots are not on the coil but on the copper leads back to terminals but not on terminals.I pulled on wire to see if it would seperate but it held.However the first coil secondary does bounce on digital multimeter from 3.4 -3.9 the rest of them seem to remain more stable. I also cleaned the 2 grid caps. Also checked all resistors in set.Maybe I should just bite the bullet and rewind coils.I hate trying to keep track of windings count.

How thin is the wire and how badly is it corroded? If it isn't too thin, and it's corroded at a rivet or terminal, you can clean the copper and then solder it for a better connection. The actual windings should be coated with enamel, and shouldn't be turning green. If they're really thin, and are cloth covered (probably bare underneath), then you might want to rewind them (with enamel covered wire). That is a common problem with 1930s Philcos (so I've heard). I had the problem with my Philco 60. The oscillator secondary corroded through. Of course the radio also came out of a flood, but who knows when the actual corrosion started. I got the radio the day of the flood, so the corrosion might have been older (I don't remember when I examined the oscillator coil....it was weeks before I even replaced the power transformer).

T.

:How thin is the wire and how badly is it corroded? If it isn't too thin, and it's corroded at a rivet or terminal, you can clean the copper and then solder it for a better connection. The actual windings should be coated with enamel, and shouldn't be turning green. If they're really thin, and are cloth covered (probably bare underneath), then you might want to rewind them (with enamel covered wire). That is a common problem with 1930s Philcos (so I've heard). I had the problem with my Philco 60. The oscillator secondary corroded through. Of course the radio also came out of a flood, but who knows when the actual corrosion started. I got the radio the day of the flood, so the corrosion might have been older (I don't remember when I examined the oscillator coil....it was weeks before I even replaced the power transformer).
:
:T.IT looks like 34 gauge primary 30 or 28 gauge secondary both enameled copper but no appearance of corrosion on any terminals. I just hate to wind new coils if not necessary.I guess I was hoping someone would have an experience that would be of help pinpointing this problem. Its tough when its not continuous especially in the rf since any testing changes the capacitance in the circuit. Thanks Gordon

Perhaps you could monitor plate or cathode voltage at each tube (one at a time) while the phenomenon you tell of occurs. If a tube is shorting internally or soemthing, it'd show up with voltage fluctuations (perhaps). It's too bad you can't monitor coil resistance or grid voltage. That'd tell a lot. Placing things on the grid circuit while it's operational will throw off tuning, though.

T.

:Perhaps you could monitor plate or cathode voltage at each tube (one at a time) while the phenomenon you tell of occurs. If a tube is shorting internally or soemthing, it'd show up with voltage fluctuations (perhaps). It's too bad you can't monitor coil resistance or grid voltage. That'd tell a lot. Placing things on the grid circuit while it's operational will throw off tuning, though.
:
:T.
Been there done that, nothing showing on cathodes or plates, all remains fairly constant. A signal tracer with proper probe does not seem to bother grid circuit but does fluctuate in signal strength from plate and grid of first rf tube. Changed tube same symptom so i`m thinking it must be antenna coil or first rf coil. Possibly a high impedance for rf but not dc?I guess rewind and of course resolder new coils. Thanks Gordon

If you say that the trouble exists in all of the RF stages, I am assuming that you tried to feed a signal into each successive stage (it'd be done easily through a .01 MFD cap at the plate terminal of the preceding stage, with the tube removed). That would leave the trouble in the last stage, or in the AF stages. Definitely check out the detector. If it has a grid leak, check it for accurate resistance. If the resistance is off, the circuit can perform in random ways, or perhaps the resistor is changing in resistance if it has become damaged somehow (cracks, bad connections, etc.). Check the audio circuits, too. Feed some audio in at the plate of the detector through a .05 MFD cap. A CD player works well. Listen to the audio section.

Leave no cap or resistor or wire overlooked. Go over all solder connections in the radio with fresh solder.

In my Crosley 148, sometimes the audio would pop in and out, especially when the set was turned upside down. Touching things would kick it back into action. I finally found that bumping the output tube made the most difference. Sadly the spot weld to the cathode lead had been burned thin right from the factory. The tube was probably always either faulty, or on the verge of being faulty, with only a slight vibration to crack the connection all the way through. Such a problem would of course show up at the cathode resistor of the output tube. I also had a type 27 tube with a faulty cathode connection in my Majestic 180. I had a very hard time finding the actual break, but it finally wouldn't work no matter how hard I bumped it, and sure enough, when tested, it tested at 0. Resoldering the pins did nothing to help.

T.

:If you say that the trouble exists in all of the RF stages, I am assuming that you tried to feed a signal into each successive stage (it'd be done easily through a .01 MFD cap at the plate terminal of the preceding stage, with the tube removed). That would leave the trouble in the last stage, or in the AF stages. Definitely check out the detector. If it has a grid leak, check it for accurate resistance. If the resistance is off, the circuit can perform in random ways, or perhaps the resistor is changing in resistance if it has become damaged somehow (cracks, bad connections, etc.). Check the audio circuits, too. Feed some audio in at the plate of the detector through a .05 MFD cap. A CD player works well. Listen to the audio section.
:
:Leave no cap or resistor or wire overlooked. Go over all solder connections in the radio with fresh solder.
:
:In my Crosley 148, sometimes the audio would pop in and out, especially when the set was turned upside down. Touching things would kick it back into action. I finally found that bumping the output tube made the most difference. Sadly the spot weld to the cathode lead had been burned thin right from the factory. The tube was probably always either faulty, or on the verge of being faulty, with only a slight vibration to crack the connection all the way through. Such a problem would of course show up at the cathode resistor of the output tube. I also had a type 27 tube with a faulty cathode connection in my Majestic 180. I had a very hard time finding the actual break, but it finally wouldn't work no matter how hard I bumped it, and sure enough, when tested, it tested at 0. Resoldering the pins did nothing to help.
:
:T.
Thanks so much Tom. I will follow all steps you suggest as I was not aware of these procedures. I will let you know how I make out. Thanks again Gordon

As you move closer to the detector, selectivity and sensitivity will diminish. Use strong signals. Use a pin from a dud tube if you wish. That'll allow for easy connecting of an antenna or signal generator. Insert the pin into the plate hole of the socket you wish to inject into. If you're using an antenna, connect it through a .01 MFD cap. That'll keep B+ out of the antenna. If you're using a signal generator, connect its shielded lead to the .01 MFD cap, and then connect the outer shield to the radio's chassis. The cap will isolate the generator from B+.

T.

http://www.nostalgiaair.org/PagesByModel/003/M0044003.pdf

.....You know........I've been thinking about this for a while. At first I was thinking that the set was breaking into oscillation, which still may be a possibility, though usually you'll get a squeel and a snap, and then there won't be much reception at all, if any.

The schematic above is for the 880. I can't find your schematic. I'll just have to assume that the 881 is similar, though it may not be. If you look at the schematic you'll notice 1000 ohm resistors in series with the grid part of each RF coil. If one of these was to open up or severely drift in value, the signal might make it to the grid via capacitance of the resistor, though the grid wouldn't be attached to bias in a solid manner, so bias might fluctuate at the grid, causing a change in volume. Touching the grid would discharge the stray bias, causing the tube to snap back into action.

If this is the case, measure resistance between the 2nd RF tube grid cap and the chassis. If not around 1000 ohms (assuming that your radio is like the 880....if not, let me know), then you have a fault either in the resistor or in some other connection. Check all other RF grids as well. If your set is like the 880, most of the RF grids should have 1000 ohms between them and the chassis (plus any resistance of the RF coil).

If your radio is like the 880, the volume control, unlike a lot of other TRFs, doesn't control cathode bias of the RF tubes. The RF tubes are simply set for maximum allowable gain, and that is that. The volume control only adjusts the amount of signal from the antenna. Since RF circuits are always operating at maximum gain, be sure that all shields are in place. All RF tubes should be shielded, and it might be a good idea to shield the coils, too. That is the best option, though they aren't always shielded. With the RF circuits not properly shielded, they can feed signals back at eachother, and can break into random oscillation.

Hopefully you have a schematic for your radio. Check all resistances against originals. If resistances are altered, biasing might be unstable (if, say, a resistor in a grid circuit was significantly increased in value), or the set could break into random oscillation (say, if cathode resistances are decreased, causing more gain).

.....Also, I notice a 10 ohm variable resistor (rheostat) in parallel with the plate coil of the 2nd RF tube (again, assuming that the 880 is like the 881). If that is faulty (dirty), it could cause volume fluctuations. Touching the 2nd RF grid might send enough of a surge through the rheostat to temporarily clear up the problem.

T.

:http://www.nostalgiaair.org/PagesByModel/003/M0044003.pdf
:
:.....You know........I've been thinking about this for a while. At first I was thinking that the set was breaking into oscillation, which still may be a possibility, though usually you'll get a squeel and a snap, and then there won't be much reception at all, if any.
:
:The schematic above is for the 880. I can't find your schematic. I'll just have to assume that the 881 is similar, though it may not be. If you look at the schematic you'll notice 1000 ohm resistors in series with the grid part of each RF coil. If one of these was to open up or severely drift in value, the signal might make it to the grid via capacitance of the resistor, though the grid wouldn't be attached to bias in a solid manner, so bias might fluctuate at the grid, causing a change in volume. Touching the grid would discharge the stray bias, causing the tube to snap back into action.
:
:If this is the case, measure resistance between the 2nd RF tube grid cap and the chassis. If not around 1000 ohms (assuming that your radio is like the 880....if not, let me know), then you have a fault either in the resistor or in some other connection. Check all other RF grids as well. If your set is like the 880, most of the RF grids should have 1000 ohms between them and the chassis (plus any resistance of the RF coil).
:
:If your radio is like the 880, the volume control, unlike a lot of other TRFs, doesn't control cathode bias of the RF tubes. The RF tubes are simply set for maximum allowable gain, and that is that. The volume control only adjusts the amount of signal from the antenna. Since RF circuits are always operating at maximum gain, be sure that all shields are in place. All RF tubes should be shielded, and it might be a good idea to shield the coils, too. That is the best option, though they aren't always shielded. With the RF circuits not properly shielded, they can feed signals back at eachother, and can break into random oscillation.
:
:Hopefully you have a schematic for your radio. Check all resistances against originals. If resistances are altered, biasing might be unstable (if, say, a resistor in a grid circuit was significantly increased in value), or the set could break into random oscillation (say, if cathode resistances are decreased, causing more gain).
:
:.....Also, I notice a 10 ohm variable resistor (rheostat) in parallel with the plate coil of the 2nd RF tube (again, assuming that the 880 is like the 881). If that is faulty (dirty), it could cause volume fluctuations. Touching the 2nd RF grid might send enough of a surge through the rheostat to temporarily clear up the problem.
:
:T.
Sorry to take so long to get back to you, I didn`t know you had written back. The schematic of 8-81 is on this web site under Temple corporation. If you look you will see it is not the same.There is bias control as well as signal control as well as control on the first audio tube. There is one 1k resistor in circuit leading to the fourth rf grid it does measure 1.1k. I think that is not to far out but I can change it. The cathode bias resistors all measure good according to schematic. Also they are wire wound. They do not appear to change when monitoring voltage drop when this symptom appears. I have replaced volume controls with two separate controls, a 250k volume control for audio and a separate 10k wire wound control that I had in stock. I took apart the wirewound control and cleaned very well with solvent. I also checked on ohm meter and it appears not to be intermittent.While I was off line I changed first rf coil with pc-70-rf from antique electronic supply and rewound the antenna coil, however its still doing it. All small capacitors have been replaced with orange drop 600 volt. 2 uf and up replaced with 600 volt metalized polyester. All tested before and after installation. I just wish the radio would quit! I can`t stay on it as I take care of 90 year old grandmother with dementure and work full time.I am going to start methodically as you suggest and I will get it if I live long enough. Thanks again for everything, Gordon

The 1K resistor that you say is at 1.1K is probably just fine.

Perhaps check the resistors and transformers in the detector and audio circuits. An open resistor at the detector would allow the detector grid to saturate with electrons. Touching one of the RF grids might shock the detector back into operation....perhaps from static. You might also try turning the volume all the way up to see if you get the same result as touching the 2nd RF grid with your finger.

Open transformer secondaries in the audio circuit would allow grids to wander around as far as bias is concerned. At one point or another the grid connected to the problematic transformer would saturate with electrons, and amplification would decrease or cease all together. Distortion might accompany the other symptoms.

If your original volume control tested fine, then you can probably put it back into operation......if not now, then certainly after you have found your source of trouble.

T.

Thomas,

Also we shouldn't rule out the bronze spring contacts that make between the stator and rotor of the tuning capacitor(s). Dirty contact(s) generally show up when tuning the capacitor. It is possible to cause trouble at other times.

Radiodoc
**********

:The 1K resistor that you say is at 1.1K is probably just fine.
:
:Perhaps check the resistors and transformers in the detector and audio circuits. An open resistor at the detector would allow the detector grid to saturate with electrons. Touching one of the RF grids might shock the detector back into operation....perhaps from static. You might also try turning the volume all the way up to see if you get the same result as touching the 2nd RF grid with your finger.
:
:Open transformer secondaries in the audio circuit would allow grids to wander around as far as bias is concerned. At one point or another the grid connected to the problematic transformer would saturate with electrons, and amplification would decrease or cease all together. Distortion might accompany the other symptoms.
:
:If your original volume control tested fine, then you can probably put it back into operation......if not now, then certainly after you have found your source of trouble.
:
:T.