fender hot rod deluxe low volume & distorted output

[52 Bill]

Exactly, just like checking the tube sockets for cold solder joints and the 5 watt power resistors for coming loose.

[Enzo]

And... and... spinach between your teeth.



Hey, you gotta look good for the customers.

[Djeans]

Old thread, and I'm new, but just wanted to say thanks. I had a deville that I couldn't figure out what was wrong with and this thread solved it for me. That same 82k resistor on the phase inverter tube. Thanks again.

[Djeans]

Spoke too soon

Old thread, and I'm new, but just wanted to say thanks. I had a deville that I couldn't figure out what was wrong with and this thread solved it for me. That same 82k resistor on the phase inverter tube. Thanks again.

Today amp is back to same old problem of low distorted output. Haven't had a chance to pull it apart yet, but almost positive it's the same 82k resistor. The one I put in was a half watt, should it have been larger? Would a higher wattage resistor have any negative effect on the amp?


Thanks in advance for any replies.

[Jazz P Bass]

I have seen bad output tubes that eat the 82K resistor.
If one comes in like that, I will change out the PI tube along with the output tubes.

[Djeans]

Thanks for he reply. I had just swapped out the power tubes (was first step in the trouble shooting process - matched pair of T.A.D) as well as resoldered all the power tube socket joints. I did not change out the phase inverter tube tho. Will do that this time. Should I stick with the half watt resistor, o go to 1 watt?

[Jazz P Bass]

A 1/2 watt 82K resistor is fine.

[Djeans]

Ok, now I'm lost. The resistor seems fine, but it sounds exactly like it did when the resistor was dead.

Here are the most recent readings i have taken

Left most power tube, when looking from the back - Pin 3: 477v Pin 4: 366v
Right power tube Pin 3: 475v Pin 4: 475v
Phase inverter tube - Pin 1: 284.7v Pin 6: 274.6v
The 82k resistor - 81.9kΩ

I have replaced the power tubes, biased to 60mv, re-soldered all of the power tube joints, and replaced the phase inverter tube.

Any suggestions?
Thanks

[JoeM]

Check the screen resistor on the left power tube.

[Djeans]

If that's the one that connects to pin 4, then

.471 MΩ

The same resistor on the right tube reads 471Ω

Is this the likely culprit?

[J M Fahey]

They should both measure 470 ohm, within 10% as usual.

[Djeans]

They should both measure 470 ohm, within 10% as usual.

OK,

Replaced that resistor, have to go to work now, but will post new values. Amp has a little more output, but not much, so there has to be something else that I'm missing.

[Djeans]

Ok,

Left tube pin3: 483v pin4: 483v
Right tube pin3: 483v pin4: 483v
Phase inverter pin 1: 288.5 pin6: 281.5

After checking the screen resistor on the left tube, I could tell it ha been replaced before, instead of a 470, they put in a 470,000 ohm resistor. 470 back in place now.

Low volume on the clean channel, no output what so ever on the drive channel. What would you check next?

[52 Bill]

Low volume on the clean channel, no output what so ever on the drive channel. What would you check next?

Sounds like you have the power amp fixed now, and now need to check the preamp. For a first test, plug your guitar into the power amp in jack. Do you get a good clean strong signal from the speaker?

Check the low voltage supplies for both + and - 16 volts. Also check the preamp tube sockets for cold solder joints. I don't remember did you change the preamp tubes?

[J M Fahey]

*If* a former owner got (soldering) gun happy in the power amp, might have also messed with the preamp.
That amp is a minefield.
Just sayin'
I'd start by checking *all* voltages indicated on the (excellent) schematic.
Beware that within 10% (and *up* to 20%) difference is normal, don't worry because some plate shows , say, 260V and you actually measure 240V.