CJ 1.4: Power tubes are working but drivers not ! Help please.

choukard · 22nd March 2008, 11:47 PM

Hello,

I am the owner of a Conrad Johnson Premier Four amplifier. Power tubes (EL34) are working (light, hot) but drivers tubes (5751, 6CG7) are not working (no light, cold). No sound in speakers ( no little noise like it works). Schematics I have on 1.4: only 3. Someone have an idea ?
Thank you very much !

Craig405 · 23rd March 2008, 01:56 PM

Hi,

Well firstly check the heaters are working on the driver tubes. get the pinout from the net (TDSL duncan amps is a good place) and set your DMM to AC and measure accross the heater pins.
If you read 6.3Vish (im guessing these tubes are 6.3v?) then it may be that the filament has expired.
Pull them out of the amp when its off and measure resistance accross the same heater terminals of the tube, it should be near short circuit, if its open circuit then theyre fried and youll need a new set of driver tubes.

Thats a starting point, there may be a reason the heaters are gone so see what happens here before you replace the tubes.

--One more thing be very careful when going inside the amplifier! make sure you use one hand when possible and dont brush any parts when probing.

Cobra2 · 23rd March 2008, 02:34 PM

I just had a VT100 for repair...and this had (among other) the same problem.
Fix: new bridge for heaters. (was 8A/50-100V).

Arne K

choukard · 23rd March 2008, 03:04 PM

Thank you very much for these informations. I have another set of drivers tubes. I try with them but with no result. The thing I don't completely understand is why the four tubes are not working. Power problem ? Schematics diagrams I have download are not complete. Perhaps a bad solder...

Cobra2 · 23rd March 2008, 09:27 PM

On the VT100, the input & driver tubes had separate filament supply.
Check if you have filament(heater)-voltage on the drivers...probably (6,3V) DC
http://tdsl.duncanamps.com/show.php?des=5751
http://tdsl.duncanamps.com/show.php?des=6CG7

Arne K

22nd March 2008, 11:47 PM	#1
choukard diyAudio Member Join Date: Mar 2008	CJ 1.4: Power tubes are working but drivers not ! Help please. Hello, I am the owner of a Conrad Johnson Premier Four amplifier. Power tubes (EL34) are working (light, hot) but drivers tubes (5751, 6CG7) are not working (no light, cold). No sound in speakers ( no little noise like it works). Schematics I have on 1.4: only 3. Someone have an idea ? Thank you very much !

23rd March 2008, 02:34 PM	#3
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	I just had a VT100 for repair...and this had (among other) the same problem. Fix: new bridge for heaters. (was 8A/50-100V). Arne K __________________ Ars longa, vita brevis

23rd March 2008, 09:27 PM	#5
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	On the VT100, the input & driver tubes had separate filament supply. Check if you have filament(heater)-voltage on the drivers...probably (6,3V) DC http://tdsl.duncanamps.com/show.php?des=5751 http://tdsl.duncanamps.com/show.php?des=6CG7 Arne K __________________ Ars longa, vita brevis

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23rd March 2008, 01:56 PM	#2
Craig405 diyAudio Member Join Date: Jul 2005 Location: Sussex	Hi, Well firstly check the heaters are working on the driver tubes. get the pinout from the net (TDSL duncan amps is a good place) and set your DMM to AC and measure accross the heater pins. If you read 6.3Vish (im guessing these tubes are 6.3v?) then it may be that the filament has expired. Pull them out of the amp when its off and measure resistance accross the same heater terminals of the tube, it should be near short circuit, if its open circuit then theyre fried and youll need a new set of driver tubes. Thats a starting point, there may be a reason the heaters are gone so see what happens here before you replace the tubes. --One more thing be very careful when going inside the amplifier! make sure you use one hand when possible and dont brush any parts when probing.

23rd March 2008, 03:04 PM	#4
choukard diyAudio Member Join Date: Mar 2008	Thank you very much for these informations. I have another set of drivers tubes. I try with them but with no result. The thing I don't completely understand is why the four tubes are not working. Power problem ? Schematics diagrams I have download are not complete. Perhaps a bad solder...

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