Hot Rod Deville.. please help!

[todddeville]

I bought the amp used and never had one problem until recently. While I was playing a gig the amp suddenly cut out. It didn't make a loud pop or noise before it did. Just no sound. I changed guitars and checked the fuse and still nothing. I sent it over to a friend of a friend to be checked out and after feeling like I was getting a bit of a run around form the guy he says he has checked everything and can't figure it out. He says that this type of amp some times just does this and it is very expensive. He has had it for about two weeks and now I have to go on the road in one week with still no amp to use.

Is there some sort of mystery problem with Devilles like the guy said or is this not true what so ever? Any help would be great. Thank you!

[Enzo]

He knows they sometimes do this and it is expensive? He knows about this but can;t tell you what is wrong?

"No sound" is one of the easiest things to diagnoze in a tube amp. He may not have what he needs to fix it, but determining what it is should be simple.

The speaker is good or not.
The speaker cord up to the chassis is good or not.
THE SPEAKER CORD IS PLUGGED INTO THE MAIN SPEAKER JACK INSTEAD OF THE EXTENSION JACK. Make sure.

You have all the operating voltages or not.
The tube heaters all light or not.
VOltages at the tube elements all are reasonable or not.
You get something close at the bias test point on the tube socket board or not.
And look closely at the solder on the socket pins of the power tubes, any cracked joints?

[Prairie Dawg]

He knows they sometimes do this and it is expensive? He knows about this but can;t tell you what is wrong?

"No sound" is one of the easiest things to diagnoze in a tube amp. He may not have what he needs to fix it, but determining what it is should be simple.

The speaker is good or not.
The speaker cord up to the chassis is good or not.
THE SPEAKER CORD IS PLUGGED INTO THE MAIN SPEAKER JACK INSTEAD OF THE EXTENSION JACK. Make sure.

You have all the operating voltages or not.
The tube heaters all light or not.
VOltages at the tube elements all are reasonable or not.
You get something close at the bias test point on the tube socket board or not.
And look closely at the solder on the socket pins of the power tubes, any cracked joints?

I tend to agree. Much easier than troubleshooting intermittents.

I froze my ass off out on the flight line doing that kinda stuff for a few winters in Michigan. Makes Iowa seem like a beach resort.

[R.G.]

He knows they sometimes do this and it is expensive? He knows about this but can;t tell you what is wrong?

ROFLMAO!

This is like a doctor specializing in diseases of the very rich.

Is there some sort of mystery problem with Devilles like the guy said or is this not true what so ever?

Well, I have to be honest and understanding about this. Back in the 1300s and 1400s when Europeans were starting to venture around the world in ships, the mariners naturally prized maps. There are a large number of maps from this era with notations in some places on the edges that say "Here be dragons". It's very human to have gaps in knowledge, and also human to not want to expose them.

Here's something I wrote up to help people with exactly this kind of issue. You might want to give it a read, perhaps with your friend as you both puzzle through this. The Tube Amp Debugging Page

I would translate his statement to say this

" I don't know what's wrong with this amp. They sometimes do this - because this one has done it! - and not knowing what it is, I want you to be prepared for the worst, in case it's very expensive."

He's probably trying his best to help you.

On the matter of timing and going on the road: Presumably you're depending on this amp while you're on the road, and therefore a good part of your personal well-being is depending on it as well. You need to make a value judgement about whether you can afford to take off with an amp you've cobbled back into working or if you want to walk out onto the stage and take the chance that the next chord might be your last for the performance. Playing air guitar on stage is one of my personal deep fears; I did that once, as a teenager, and swore I'd never do it again. It was a... um, deeply moving experience...

I strongly urge you to read "Debugging Step #0" and make good judgements about the amp. I also urge you to think about whether it might not be better to take the amp to an experienced tech, explaining about needing an amp in one week for a tour. Techs are usually very interested in getting people back out and playing. If they're not, find another tech. It may cost you some money, even a painful amount, but I can promise that the air-guitar incident will leave some painful education too.

[Gtr_tech]

Plug a cable from the fx send straight into the return. Sound come back? If so in a pinch you can use a short right angle pedal interconnect cable and just leave it in there until you can have it repaired properly.

[R.G.]

Plug a cable from the fx send straight into the return. Sound come back? If so in a pinch you can use a short right angle pedal interconnect cable and just leave it in there until you can have it repaired properly.

Good point - bad jacks on a FX loop can do that to you.

If the sound doesn't come back proceed with subbing tubes.

I started to go update the Debugging page, but I followed the tests, picking between "no sound at all" and "faint hiss and or hum comes out of speakers", which would be the case if a FX loop was open, and found

* Preamp tubes bad
* Preamp power bad
* Input cord or connector is open or has dirty contacts; this can include the effects loop jacks, if present.
* Input jack dirty or corroded
* Open volume or tone control
* Open, shorted, or failing resistor or coupling capacitor
* Faulty signal wiring
* Dirty tricks - I actually saw this once. The clever-but-misguided spouse of a guitar buddy painted the tip of a friend's guitar cords with clear nail polish. All of them. That took a while to find...

I'd forgotten that I had included the FX loop jacks in the testing. That page went up in 1997 and I don't think it's been modified since 2000.

[Phostenix]

* Dirty tricks - I actually saw this once. The clever-but-misguided spouse of a guitar buddy painted the tip of a friend's guitar cords with clear nail polish. All of them. That took a while to find...

[todddeville]

Thank you everybody! I'm finally getting the amp back. This time around when I talked to my friend he says that the guy that tried to repair it said it was a factory defect, kept under wraps by fender... I'm really having a hard time believing this. I can't wait to do tests of my own! Thanks again.

[Enzo]

factory defect, kept under wraps by fender

AH yes, the old industrial secret that somehow some guy out in nowhere knows all about.

[RWood]

Channel (not) Switching?

Does the amp work for a while and then cut out after it warms up?

It appears to have the same channel switching scheme as a Blues Deluxe, which has a fairly well-documented problem with this.

Take a look at the schematic and find R78 and R79, a pair of 330 ohm, 5 watt resistors in the lower right region (the power supply). These heat up, cause intermittant connections on the circuit board, and the result can be no sound. It's worth a check, and it's a pretty simple repair to a bad design (which of course may recur years later when you are sharing the stage with your guitar hero.)

RWood

ps: R.G. your debugging page is great!