Trouble Shooting an Amp

[yalesmith]

I'v had a carvin valve master amp for sometime which i modded (hasserl mod) and it worked great until i decided that i knew more than i did and made more changes and what you know it stopped working. The amp was subsequently shelved, since then I have built 6 amps and know a little more. This is what i KNOW:

a. The voltages off the filter caps are okay
b. V1 and V2 plate are not drawing any voltages (v3, v4 and v5 seem ok)
c. Cathodes on v1 & V2 are grounded
d. noticed the tubes are a bit dim. the voltage off the pt for filaments is only 3.1 and 2.2 vac
e. I get a little sound (very weak) , but when i switch channels nothing.

What is DC filament on v1 and v2? never seen this before. I figure that looking at the schematic, v1 and v2 share filament and are not drawing any plate voltage that this seems to be the culprit......dc voltages on v1 and v2 are about 1.5 vdc on pins 4,5, and 9.

Any help or ideas would be appreciated

[Super_Reverb]

Looks like this design uses a bridge rectifier off PT taps to generate DC filament voltage for V1/V2.

I assume, by grounded, you mean that there is zero volts on cathodes of V1/V2. This says that the tube is not conducting.

Check DC voltage from V1/V2 pins 4/5 to 9 verify your DC filament supply is working. Your schem shows there should be 5-6 VDC at pin 9 with respect to 4/5. There is a FW bridge D6-D9 and several filter caps that generate this voltage.

You can check diode with a voltmeter: it should have [low] ohms of resistance in one direction and when you switch leads, it should look open. That's why they call it a SEMI conductor


rob

[yalesmith]

i checked the dc filament voltages and it came in at 3.5 vdc....this is a summing when you say "at pin 9 with respect to 4/5" you mean put leads on pin 4 and pin 9 then on pin 5 and pin 9.

As far as the bridge rectifiers I pulled them out and they checked out okay on the diode test but the resistence was double....hmmmm

i guess I should change those diodes and see what happens?

Thanks

[NickC]

i checked the dc filament voltages and it came in at 3.5 vdc....this is a summing when you say "at pin 9 with respect to 4/5" you mean put leads on pin 4 and pin 9 then on pin 5 and pin 9.

..........

Pins 4 and 5 should be tied together (connected).

DC heater voltage is measured by metering pins 4/5 and pin 9 (one meter lead to pins 4/5, the other to pin 9).

[yalesmith]

yeah now the voltages are 12 vdc......I hate this thing. I feel I may just scrap the PC board and salvage the chassis and pt.

thanks