Can you help me describe the problem I'm having so I can research it?

[J M Fahey]

he's holding a 2W flamepruf resistor that fell out of it saying "this transistor went bad." And wondering / demanding to know why we can't just replace that transistor while he waits.

Well, it may get worse.
While you repair it, he Googles that particular resistor, finds it costs 10 cents, so if you charge more than two bucks you are ripping him off.

Or the other version: he tries to stay right by you all the time, so you can't pull his expensive parts and replace them with inferior ones.

[Chuck H]

OK... Quick story... I'll try to keep it short.

Before I was modding. building and eventually designing and selling custom amps, I had to take my amps to the shop when they broke. My memory is not so selective that I can't remember all the bad advice and poor service I recieved from most repair shops. The worst was a well reputed shop in the bay area CA. I had an intermittent fault and they couldn't recreate the problem and fix it. They DID charge me for bench time and suggested that I not place the amp head on the cabinet anymore!?! So I went back to my bands practice room and opened up my amp. I fired it up and started poking components with a wooden stick until one showed sensitivity to movement, popping and what not... I lifted the board and though I didn't have a soldering iron I did have a wire clothes hanger, a torch and my drummer (his house) had a roll of solder. I repaired the amp myself using stone knives and bones and never had another problem with it. So...

My confidence in MOST shops offering fair and diligent service is pretty damn low. My best advice is that the OP either commit to learning about electronic circuits and accept that it may be some time before he knows enough to fix his own amp, or... Early on I had my best repair experiences with one man guitar amp specific repair shops. Even Dan Torres (who was my amp guy for a short while) was working out of his home garage when I met him. No offense to the guys here but in the real world most shops that do general electronic repair, even for the music industry, aren't very good and I would avoid them if I were a novice.

[Steve Conner]

Well, I did say any good amp tech. If you can find a good one.

I've never taken anything electronic for repair in my life. When I was in high school, I used to pull TVs out of dumpsters, drag them home and try to fix them, for the challenge. I fixed about two thirds of them.

But I feel what it must be like when dealing with plumbers, car mechanics and so on. You say "It's making a knocking sound when I drive round corners, I think it is the CV joint" and they nod and smile as if you were a 4 year old who just brought them a pretty drawing. Most of the time when it comes to cars, I get it wrong, so maybe the mechanics are justified in ignoring me. (The last time my car did that, it was the wheel bearing.)

[Chuck H]

(The last time my car did that, it was the wheel bearing.)

That's very nice, Steve. I'm sure it was the "wheel bearing". You know what? I'm gonna put this post right up on the refrigerator. Who's my special guy?

"It's making a knocking sound when I drive round corners, I think it is the CV joint" and they nod and smile as if you were a 4 year old who just brought them a pretty drawing.

Great analogy. Almost woke the wife laughing.

[J M Fahey]

and they nod and smile as if you were a 4 year old who just brought them a pretty drawing.

It applies even more when you visit your Doctor or Lawyer with some problem, and you tell them what *you* think is happening.
Oh well.
By he way, I'm visiting my Divorce Lawyer in 1 hour and my Diabetes Doctor tomorrow morning, so I'm getting ready to receive "that" condescending look and the accompanying pat in the head.
Oh well 2.
I'd better stick my "expertise" to Electronics.

[Jamez0r]

Thanks guys for all of your responses. Ron, sorry I didn't mean to come off as rude - Not only do I want to fix this amp, but I want to learn about amplifiers as well. I'd rather not take it to a technician until I've tested everything I can. I have a BSEE, but no hands-on exp with tube amps, so I'm starting from the ground up (hence my original intent to figure out how to 'describe' the problem so I can find information).

UPDATE:

1) In researching the problem I came upon this information:

A tube amp must have a load connected to the speaker output whenever there is a signal applied to the power stage. The load can be a loud-speaker, a resistive / inductive power attenuator, or a combination of both. It is only possible to operate a guitar amp without a load when you are using the preamp stage alone and no signal is being fed to the power amp.

Using a tube amp without a load is SUICIDAL to the amp. You can arc the output tube sockets, short the power tubes, burn the screen supply, damage the filament supply of the power transformer, and fry the output transformer in minutes. I've seen printed circuit boards burst into flames!

Before ever using your amp without a load, connect a loud-speaker to it first. If you hear any sound through the speaker then you must leave the speaker connected (or use a power attenuator). If you are sure that there is no sound then you can remove the loud-speaker.

It is much safer to leave the speaker cabinet connected at all times just in case someone turns up the master volume or FX return to the power amp.

After reading that, I remembered that the date of the incident (burning smell, etc) I had put the amp on top of my friends cab that was in the closet. I couldn't see the back of the amp that well, and accidentally plugged the speaker cab into the Line Out. Stupidly enough, I didn't realize how much of a problem that is until I read the above quote (I had honestly forgotten that I did that). I tried playing for a good 30sec (testing various other things like volume, volume on guitar, pedal mute, etc) before I realized I had the cab plugged into the line out. *Then* a minute later we noticed the burn smell. Ouch

2) I've taken the chassis out of the enclosure and tested the following:
-Tap test on all tubes sounds fine
-No tubes look bad (discolored, burnt, filament not glowing, etc)
-All caps/resistors that are visible look fine (which is 98% of them, the only ones I can't see are on boards attached to knobs/inputs etc. I plan on looking at them when I have time)
-Swapped preamp tubes with new ones (I had 2 to test it with, so did 2 at a time in combinations). The sound was a little bit brighter with the new preamp tubes but didn't effect the crumby bass response when palm muting.


I'll continue researching what having no load could destroy, and see if I can narrow it down to the problem. Thanks for everyone's help so far!