Rule #1 in guitar amp repair - Check the obvious!

[Enzo]

I have been training technicians for many years, and it is amazing how many obvious things are not obvious to everyone. I have yet to find a solution for that.

[drewl]

Always start with the power supply
The first rule of electronics.

[Enzo]

I certainly agree^^^^^

[SoulFetish]

I have been training technicians for many years, and it is amazing how many obvious things are not obvious to everyone. I have yet to find a solution for that.

That's why we can't get rid of you old timers just yet. I wouldn't have thought to check the speaker if I had the symptoms Tone Meister was describing.
My boss would though. He's a venerable old bastard as well. Having his 35+ plus years experience in the business has been invaluable to me and I wouldn't even be close to the technician I am without it.
I still forget to reinstall the tube "shields" every f*cking time I reassemble an amp though. Every time.
(But it's probably because I think they are near useless and unless painted flat black, then they mostly just radiate heat back to the tubes. Ugh, the sound they make when fitting them on makes me cringe)

[bsco]

I need all you old timers as well......so you can't die off just yet...I have to completely pick your brains...you guys have forgotten more than I will ever know in my life time...and the knowledge that I saw here was the reason I joined this forum.......and I looked at a few of them.......and this one as far as I am concerned was and still is the best.......keep up the great work......people like me need it......

[R.G.]

Given that this thread is current and people are thinking about the issues:

Back in 1997, I wrote up a debugging procedure for tube amps. the Tube Amp Debugging Page is here:
http://www.geofex.com/ampdbug/ampdebug.htm
I tried to cover all the bases for debugging in a disciplined way to lead the uninitiated through the process. I would love for the collective you to read over the Tube Amp Debugging Page and critique it. I've had quite a number of comments over the intervening 21 years that it works, but I would very much appreciate the interested audience looking it over and commenting.

[bsco]

Given that this thread is current and people are thinking about the issues:

Back in 1997, I wrote up a debugging procedure for tube amps. the Tube Amp Debugging Page is here:
http://www.geofex.com/ampdbug/ampdebug.htm
I tried to cover all the bases for debugging in a disciplined way to lead the uninitiated through the process. I would love for the collective you to read over the Tube Amp Debugging Page and critique it. I've had quite a number of comments over the intervening 21 years that it works, but I would very much appreciate the interested audience looking it over and commenting.

Will do...Cheers

[bsco]

Hey R.G. Had a look at that.....actually it is very good...I like the nail polish one.......that must have been a bit of a teaser for sure......
Cheers

[Reader]

Very nice article. I will follow the path thru it the next time I work on a broken amp and let you know if I end up with any suggestions.

It would be good if more people read things like your article before they post their question. I think this because there is a huge amount of repetition in the forum repair discussions. Especially when they start with an initial posting like "My amp stopped working. Do you think I should replace the output transformer?"

[bsco]

I just fixed a Yorkville powered speaker amp.

Nothing major.
An aweful lot of cheezy solder joints.

Ha Ha!

Both speakers are blown.

Just had a Traynor DB200 with weird intermittment noises...turns out that the fuse holder clips were not gripping the fuse ends tight enough...if you pushed gently on the fuse with a wooden stick, you could force it to happen at will........but at first it would appear to be something more serious.....

[bsco]

I just fixed a Yorkville powered speaker amp.

Nothing major.
An aweful lot of cheezy solder joints.

Ha Ha!

Both speakers are blown.

which one was that??

[SoulFetish]

Given that this thread is current and people are thinking about the issues:

Back in 1997, I wrote up a debugging procedure for tube amps. the Tube Amp Debugging Page is here:
http://www.geofex.com/ampdbug/ampdebug.htm
I tried to cover all the bases for debugging in a disciplined way to lead the uninitiated through the process. I would love for the collective you to read over the Tube Amp Debugging Page and critique it. I've had quite a number of comments over the intervening 21 years that it works, but I would very much appreciate the interested audience looking it over and commenting.

R.G., firstly, if it wasn’t for people like you, Randall Aiken, and later on Blencowe (and others) contributing to sites like geofex.com, I would not be doing what I do today. Do you know how many times I read “The Technology of the Fuzz Face” early on until I began to start making sense of it? geofex was one of the places I knew I could go to to tumble into this rabbit hole that changed the course of my life.
Enough of the sentimental retrospective, lets get back to the debug artical...
Its been a while since I’ve read it, so I’ll give it another read. But from what I remember, there was a section On troubleshooting noise issues based on the type of noise snd most common causes for each type. I found this section to be really helpful on a couple of occasions. Plus i used this as a reference wich helped me identify a faulty coupling cap between the Pi and output tube grids on my very first build.

[R.G.]

It was intended specifically for that, to help out with the morass of how to find out what's wrong. I'm glad it helped.

I got the sense that it might have missed a few issues, and I'd really like it if I could find the holes and plug them. We're into a time where people who are debugging tube amps now may not have been out of grade school when I wrote that, and maybe we can help them out.

[SoulFetish]

I would maybe offer 2 amendments.
First, would be signal cutting out/very low: Does the amp have an effects loop? Does the signal level return if you put a jumper between the send and return? if yes, then oxide has built up on the switching jack and spraying contact cleaner and cleaning the jacks usually helps.
The second issue which is fairly common is mentioned under the heading "low power or volume drops off", but in my experience is almost always accompanied by unpleasant distortion as well. This happens when one side of a push pull amp is not amplifying any signal. Most often, this is due to one of the plate resistors in the phase inverter failing or open screen resistor on one of the output tubes. I usually check the voltage across the screen resistor first, and if necessary, check the voltage on the plates of the PI tube. If the voltage is too high, at the HT rail potential, then the resistor has gone short. If I'm getting voltage readings fluctuating in the mV range, then the resistor has gone open.
Those would be some initial thoughts, and I would ask the other techs for a consensus my second suggestion.

[Justin Thomas]

Given that this thread is current and people are thinking about the issues:

Back in 1997, I wrote up a debugging procedure for tube amps.

Every time I "meet" a noob who seems open to learning how to do this I point them to your page. Usually it's on Facebook. I know there are still some incomplete sections, but that page has saved my butt multiple times.

Justin