I need to information for a few tubes, specifically what operation they control on my Gavotte. So here goes.
I have crisp FM reception but zero AM and SW.
ECC85
ECH81
EF89
EABC80
EL84
EM80
Thanks!
Mark
But if you're wanting to identify tubes that serve AM only, pull them out, one at a time while listening to FM. The ones that don't affect the FM reception must be for AM only.
(It's best to pull tubes with the power to the set off.)
Doug
:Hi gang!
:I need to information for a few tubes, specifically what operation they control on my Gavotte. So here goes.
:
:I have crisp FM reception but zero AM and SW.
:
:ECC85
:ECH81
:EF89
:EABC80
:EL84
:EM80
:
:Thanks!
:Mark
Your set’s toobie lineup functions are :
ECC85 FM RF amp and Mixer
ECH81 FM if Amp or AM mixer / AM local oscillator
EBF89 AM-FM IF amp
EABC80 AF Preamp AM detector
EL84 Audio Output tube
EM80 Tuning eye tube
Also, seems like there might be a schematic of the set pasted somewhere inside of the cabinet ?
This Telefunken might not be the EXACT vintage of yours, which is probably circa “58,
but should certainly be close enough to work with, with your set having a minor variance in the audio output EL84 and prior AF preamp stage (which uses a EL86 which has both functions in one tube---whereas yours uses a separate EABC80 and EL84).
So, this sets schematic is probably a bit newer.
With your mentioning all of your set working, we can suspicion the ECH81 tubes area circuitry, as its pentode section is functioning as an FM IF amplifier in the FM mode and as the AM mixer when the set is in its AM mode, with its triode section function being the AM local oscillator.
I have provided technical referencing, where you can see that all signal flow is fine except, we have to evaluate the AM portion [Blue line markup]:
I initially suspect a bandswitching contact problem wherein it might not be getting contact of a coil assembly or as you can see, the local oscillators Plate supply voltage distribution is even dependent upon a mode switch contact, you can ALSO see that the FM / AM IF transformers are being switched between with contact members.
An initial test might be to take the set and switch between all modes one ‘hunna ‘lebenteen times too initially give the switch contacts a mechanical frictional polishing / cleaning.
Then you put the set in the AM broadcast band mode and track down pin 2 of the ECH81 and connect one end of a a loose insulated “aerial” wire of ~ 10 foot length to that pin. Then tune thru the BC band and see if anything comes in, that would be bypassing that loop antenna that you swapped out, in case there is any issue with that.
Standing by for Ree-sults:
Rerferencing:
73's de Edd
Thanks a million Edd!
I'll print out the info you provided.
I'll get back with you after I trace down the problem.
Thanks!
Mark
:
:
:
:Your set’s toobie lineup functions are :
:
:
:ECC85 FM RF amp and Mixer
:
:ECH81 FM if Amp or AM mixer / AM local oscillator
:
:EBF89 AM-FM IF amp
:
:EABC80 AF Preamp AM detector
:
:EL84 Audio Output tube
:
:EM80 Tuning eye tube
:
:
:
:Also, seems like there might be a schematic of the set pasted somewhere inside of the cabinet ?
:
:
:
:This Telefunken might not be the EXACT vintage of yours, which is probably circa “58,
:
:but should certainly be close enough to work with, with your set having a minor variance in the audio output EL84 and prior AF preamp stage (which uses a EL86 which has both functions in one tube---whereas yours uses a separate EABC80 and EL84).
:
:So, this sets schematic is probably a bit newer.
:
:With your mentioning all of your set working, we can suspicion the ECH81 tubes area circuitry, as its pentode section is functioning as an FM IF amplifier in the FM mode and as the AM mixer when the set is in its AM mode, with its triode section function being the AM local oscillator.
:
:I have provided technical referencing, where you can see that all signal flow is fine except, we have to evaluate the AM portion [Blue line markup]:
:
:I initially suspect a bandswitching contact problem wherein it might not be getting contact of a coil assembly or as you can see, the local oscillators Plate supply voltage distribution is even dependent upon a mode switch contact, you can ALSO see that the FM / AM IF transformers are being switched between with contact members.
:
:
:An initial test might be to take the set and switch between all modes one ‘hunna ‘lebenteen times too initially give the switch contacts a mechanical frictional polishing / cleaning.
:
:Then you put the set in the AM broadcast band mode and track down pin 2 of the ECH81 and connect one end of a a loose insulated “aerial” wire of ~ 10 foot length to that pin. Then tune thru the BC band and see if anything comes in, that would be bypassing that loop antenna that you swapped out, in case there is any issue with that.
:
:
:Standing by for Ree-sults:
:
:
:Rerferencing:
:
:
:
:
:
:
:73's de Edd
:
:
:
: