Amplifier service

RVA

RVA

Ambassador
My Marshall JVM is getting sluggish to start (light takes a moment to go on), and has not had any maintenance but a tube change and bias in the approx 7 years I have owned it. Otherwise it works fine, but I am led to believe that service is crucial before something goes wrong with a tube amp. Is this something I should undertake myself, or should I bring it to a local, highly qualified amp tech. The tech is expensive ($90 hour) and inconvenient (hours 11am-5pm, mon-fri), and I wouldn't learn anything, but it would be solid. I would like to learn though , so when my less expensive amps need service and don't warrant the $90 hour price tag, I can be self sufficient.

Thoughts?
 
Well Ray, as one who has fixed a few amps with the help of some smarter fellas here, I will say it is likely someone here can help you.
DonP and Ivan for sure will understand almost anything amp related. You will need a schematic for the amp and at least a multimeter and a chopstick and good magnifying eyes with light. Also, obviously soldering tools and wiring tools etc.
 
chilipeppermaniac said:
Well Ray, as one who has fixed a few amps with the help of some smarter fellas here, I will say it is likely someone here can help you.
DonP and Ivan for sure will understand almost anything amp related. You will need a schematic for the amp and at least a multimeter and a chopstick and good magnifying eyes with light. Also, obviously soldering tools and wiring tools etc.
Click to expand...

I recommend a good orange chicken. That will yield a chopstick....
 
Personally I would take it to a Qualified Tech. He might just see something you don't pick up on, that would possibly cost you more in the long run. What I always go by for myself, ( if in DOUBT don't do it!)
 
Working on amps is a good way to get yourself killed if you are not seriously careful!

I've been in the electronics field since 1979 and let me tell you I've seen qualified people get zapped hard. I've even been
zapped a couple times myself. Make absolute sure you know what you are doing before you start working on an amp!
 
Sp8ctre said:
Working on amps is a good way to get yourself killed if you are not seriously careful!

I've been in the electronics field since 1979 and let me tell you I've seen qualified people get zapped hard. I've even been
zapped a couple times myself. Make absolute sure you know what you are doing before you start working on an amp!
Click to expand...

I've been zonked pretty good while modding amps, even after discharging the caps (at least I thought I did it right!).

I think it's cool to want to learn, but I personally wouldn't do it with a JVM. I'd do my learning on something that wouldn't break my heart if I f'd it up.
 
So let me ask these questions:

What would make the LED light slow?

The feedback seems to have increased to intolerable levels. Tube swaps did not help. I currently have new power tubes and 5157 pre-amp tube in V2

Generally speaking, what needs servicing after 7 years other than tubes?
 
Microphonics type of feedback is mostly related to a goofy preamp tube. Did the amp get worse after the new power tubes were installed?

Unusual smells coming from the amp after it's up to temperature?

Swapped all the tubes?

What brand(s) of tubes?

Double checked that 5751? Replace with known good 12AX7?

LED light: Not a clue! House voltages OK?
 
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