Hot Rod Deville with No Output

[wattsup]

I have a Fender Hot Rod Deville that was given to me by a buddy. I don’t think it’s more than a few years old. It had stopped working and he didn’t want to fix it. He said it had sound when you turned it on but it would get faint and just stop after a couple of minutes. I couldn’t get it to make any sound. I put in new tubes first. No sound. I checked the output transformer and from what I can tell everything seems to check out ok. No internal grounds at least. I’ve never checked an output transformer before so I’m going on what I can find on the web and YouTube videos. The speaker is ok. I started tracing the signal and it loses output on the second half of the phase inverter tube on pin 7. When I check voltage on the phase inverter plates, I have 435V going in and on the other side of the plate resistors I have -.068mv after the 82K and -.59V after the 100K. Anybody know what could drag the voltages down like that?

[FUCHSAUDIO]

bad PI tube bad plate load resistors. They fail all the time (crap part). Replace both with one watt. Usually one dies, rare for both, but it's a start.

[wattsup]

bad PI tube bad plate load resistors. They fail all the time (crap part). Replace both with one watt. Usually one dies, rare for both, but it's a start.

Thanks fuchsaudio. Replaced both of them and at least have sound now. Output is very low though and it distorts around 3 or so on the clean like it normally would on the drive channel. I can hear the relay click when I switch channels so I don’t think it’s sticking. I also pulled working tubes from my good amp and tried those with the same result so I know it’s not tubes. Voltages all look pretty good now and are stable so that’s looking up.

[FUCHSAUDIO]

Are you plugged into the correct speaker jack ? It happens, not being snarky,.. if your in the second jack, you’ll get shit for output..

[wattsup]

Are you plugged into the correct speaker jack ? It happens, not being snarky,.. if your in the second jack, you’ll get shit for output..

No offense taken. I used to do computer maintenance. I don’t know how many service calls I went on only to find it wasn’t plugged in! Its the simple things...

Had already checked the speaker jack. Plugged it in to my 1x12 and it’s the same.

[pompeiisneaks]

I've also heard a common problem with weak output is that the second output jack is switched and if it's not connected it disconnects the first one, so sometimes weak output is because that jack has corrosion or a mediocre connection between the switched blade and the tip itself, I think a simple test is to get a chopstick and push in really hard on the switch to force a pretty good connection and see if it comes in stronger. If so either clean the jack/tip area and retension that switch OR replace it with a newer switching jack.

~Phil

[Reeltarded]

Also switched jacks for effects loop. To test those, just use a patch cable looped back in.

After these things, a Google search (of this site even) will find the specific 3 other very annoying things these amps do. The most miserable is the ribbon cables. I worked on 4 of these in a month like 5 years ago. I stopped accepting outside jobs the next month.

[Stevem]

Besides those resistors I have had a good number of bad OTs in these amps and power supply filters.

One easy way to check this is to play thru the amp cranked while looking at the output tubes in a dark room.
You will see the inside of the output tubes ( inside the tubes plate openings) glow more if the PI section is working good and driving the output tubes as it should.
If this takes place then you can concider the OT to be shorted if the output jacks are good.

[dorrisant]

I have made the error Phil suggested. You will get a constipated sound until you plug into the main jack. It wasn't a corroded jack though... just the wrong jack.

[wattsup]

Ok it’s all good now. After the new resistors and reflowing solder on the phase inverter socket and ribbon cable, fire it up and it works great!

Thanks for the help everyone!