Fender Hot Rod Deville Amp

[bob p]

is anybody really that retarded?

[Tone Meister]

is anybody really that retarded?

I've seen it happen with JJ power tubes more than once. The pins and indexing pin are a smaller diameter and it isn't that difficult to install them incorrectly. Since the keyways were broken off the original power tubes in this amp it would be even simpler for the inexperienced to get it wrong, wouldn't you think?

[Justin Thomas]

I should look into that...I have a JJ 6V6 that is "easy" to insert into the socket wrong, and "easier" to insert right...

Justin

[TwinBeech]

I put a 4mv 1KHz sine wave into J1 and here are the voltages I am getting: schematic volts in (). V1 pin 1 237V (196mv); pin 3 2V (1.93V); pin 7 0V (15.5mv); pin 6 243V (324mv). I really don't understand these high voltages. I may be chasing ghosts here. Any thoughts?

Cheers

[bob p]

I hate to beat a dead horse, but I like to start off by looking at a complete voltage table because it makes it easier to see the big picture.

[g1]

I really don't understand these high voltages. I may be chasing ghosts here. Any thoughts?

I think you are comparing DC operating voltages to AC signal voltages shown on the schematic.
Voltages shown in ovals are AC, voltages shown in boxes are DC.

[TwinBeech]

That makes sense. Now back to the circuit using this knowledge. Thanks for the input.

[mac dillard]

The times that I have broken an index pin it has been a result of rocking the tube when pulling it..Hope I have learned not to do that by now.

[Chuck H]

To go along with what g1 said, those AC voltages indicated occur only when the amp is under test conditions indicated on the schematic. That is, they are not static AC voltages that exist when the amp is idling and will differ under any test conditions other than those indicated on the schematic. Anything different can alter the voltages indicated. Since you don't have a dummy load there is already a small difference in the test parameters. Just a small one though. Knob settings, etc. are given on the schem and should be used as such. And I see you've already noted and used the input signal correctly.

But just for giggles... As I mentioned, if you indicate the DC voltages on all the tube pins with the amp at idle we, here, can interpret them in the context of the circuit.

[TwinBeech]

While tracking down the noise ( popping, crackling) I hooked up another amp at the pre amp out and NO noise at the new amp spkr. At V3 I grounded through a cap pins 2 and 7, NO change. Still noisy. Then I grounded pin 5 on V4 and still noisy. Then I grounded pin 5 on V5 and almost all the noise is gone. All the popping and crackling just some low freq occasional static. I changed C26, C27, and C30. Still noisy.Can the resistors cause this kind of noise? I spray them and move them but no reaction. Any thoughts?

Cheers

[Tone Meister]

If you have the old black phenolic tube sockets, they would be high on my list of suspects for that noise you're describing. The amp being right at 20 years old, I doubt you could retension them and expect them to be reliable, especially the preamp sockets.

[TwinBeech]

Yes that is what it has. So are you saying these sockets can cause noise like that? If so, I guess changing them is in order.

[Tom Phillips]

Tony,
Have you tried connecting the pre-amp out jack to the power amp in jack with a known good guitar cord. If your crackling occurs when the amp is vibrated by a sound signal it could be bouncing or dirty contacts inside the power amp in jack. This test helps diagnose that problem.
Tom

[TwinBeech]

I just tried that hookup and nothing changed. Still lots of static. I can still ground pin 5 of V5 and cancel most of the static. Just some low freq noise occasionally.

[52 Bill]

I just tried that hookup and nothing changed. Still lots of static. I can still ground pin 5 of V5 and cancel most of the static. Just some low freq noise occasionally.

Did you check the two plate resistors on the phase inverter tube as G1 suggested? The 82K is a common failure point in these amps.