A good amp repair knowledge forum?

[Dingus]

Anyone know of a good amp forum that I could submit some symptoms to?

Here's what's up:

Amp: Fender Hot Rod Deluxe (V2)

Problem: Unwanted Distortion on the clean channel, especially when playing heavy on the low E and A strings combined (like the first 2 notes of a G chord)

Important facts:

- I modded this amp with the Fromel mods about 6 months ago, it was fine after that, and there were no issues.

- After that, I tried installing a set of these 6BG6GA to 6L6GC Adapters (that I had to assemble) and 6BG6GA tubes from this link: http://www.vacuumtubes.com/6BG6.html and I must have wired the adapters wrong and the amp blew a fuse. I replaced the fuse and all seemed well, but I am worried that some damage was done to the amp

- After that, I bought really nice old stock 7581a's and 12AX7WAs and still can't get that distortion to go away no matter how I bias the power tubes (I was using a bias calculator at the Unofficial Hot Rod Deluxe websites though and as far as I know, didn't harm the tubes).

- I've tried other preamp and power tubes and the distortion persists.


Thoughts? Think I could have harmed the transformer?

[Dave]

It might be more guitar centred but guitarnuts2 was the best place for electrics knowledge...I'm sure they have amp threads there too. Also the Electrical audio forum is rammed with amp and gear techs/nerds. I once asked about cheap vintage amps on there and wow, they know their stuff.

[Sloan]

my first thought is coupling caps, it never hurts to change them anyway. caps generally have a useable rated life of 10 years, obviously they can work great longer than that, but sometimes they just go bad. for example, the original filter caps in Marshal JTM60's (1995) are almost always bad. if the caps are bad and you change them, there is usually a very noticeable improvement in sound/tone.

i did this Super Twin Reverb a few years ago for a guy and it absolutely floored him, he said it had never sounded that good.

(don't mind the distortion channel, it's designed to sound like that, alters the tube bias and shit, which is a really really weird/dumb design).




START HERE
http://www.geofex.com/ampdbug/ampdebug.htm
specifically - ( http://www.geofex.com/ampdbug/distort.htm )




If your ok with working on your amp, ask here. Post as much info as possible. Also post a schematic with your mods noted in your first post to be helpful...
http://music-electronics-forum.com/
http://www.diyaudio.com/

[Sloan]

Also, if your afraid the output transformer is busted (if this was the case I would expect you would get getting no signal, or very low volume distortion.), you can check it for shorts with a multimeter. Make sure you plug it back in right after testing...




Don't confuse your transformers.
POWER transformer is a 'step down' transformer, that takes the high voltage of your outlet power and 'steps down' to a lower voltage that your amp uses. it will be connected to your power outlet and power switch. If your amp turns on and doesn't immediately blow up, consider power trans OK.

OUTPUT transformer takes the output from your power tubes and pushes it to your speakers. In my experience, these are more likely to fail than power transformers.

Good info here:
http://lenardaudio.com/education/14_valve_amps_5.html

[Sloan]

Also, I very much encourage people to learn how to fix their own gear, but you have to be very careful. You can definitely DIE. I have had the living fuck shocked out of me, but luckily I didn't get my heart or brain fried. There is always a chance it will happen. ALWAYS.