In which ways does my amp need servicing?

[beans-on-toast]

Is your bass active pickup or passive.

If it is active change the battery in the bass.

 

[110s lover]

Is your bass active pickup or passive. Have you tried a different bass through your amp? Serious loss of tone and volume could be a preamp or driver/PI tube but make sure the amp is the trouble, it is only the middle of the signal chain.
Bass guitar is first with pedals if you use them and the speaker cabs are last that could also be at fault.

The bass is passive and my ibanez, which is active, sounds okay as it was my 1st bass (beginner bass), i ever bought sounds okay considering. Yeh, i think having a look inside it is a must.

 

[110s lover]

I have a VBA400 and can say from experience that getting that amp to a tech WHO KNOWS THAT AMP is the first thing I would do. It's a different critter from other tube amps.
As these amp are now approaching 20 -25 years of age, it definitely would be wise to have it checked over by a QUALIFIED tech.
Upon buying mine, I had it looked over and cleaned. New pre-tube installed and it's back to sounding great!
If you liked the amp before the problems, well the answer seems pretty simple...
Fishheadjoe

Hey man, how is it different to other tube amps? I hear its alot like an svt inside? But yeh...i know someone who is supposed to great with any music (biasing and retuning amps, building amps and pedals etc) so yeh, no way im even gonna consider opening this thing haha.

What tubes do you use and are the powers stock?

 

[Bim1959]

We all know tubes can last forever IF WELL TAKEN CARE OF. He got the amp USED, not new. Do we know how much use the amp had before the current owner got it?

I really doubt if it would be caps and resistors already, but things do happen.

If it were mine, I'd take it to my shop and test the tubes, run a 1kHz signal thru it and check it with an o'scope, check the bias and clean the pots and jacks. But as I said, that's me. It would give you a good idea of how it's holding out and what kind of overall shape she's in. And to me it would be money well spent. After all, isn't that why automotive dealerships call for preventative maintenance to PREVENT problems from happening and seeing what shape your vehicle is in? Same with amps.

Knowing Marshalls like I do, I'd put my money on tubes being out of whack.

Heck, I remember a few years back when Crate was still being made by SLM that they recommended you replace output tubes every 3-6 months and preamp tubes every year.

 

[Fishheadjoe]

Hey man, how is it different to other tube amps? I hear its alot like an svt inside? But yeh...i know someone who is supposed to great with any music (biasing and retuning amps, building amps and pedals etc) so yeh, no way im even gonna consider opening this thing haha.

What tubes do you use and are the powers stock?

I would really like to answer your question, but I honestly don't know. My tech, who has been repairing amps since the 60's had never seen a VBA 400 before. Yes, he was quite intrigued getting his hands on it and told me that it's design was similar but different to many of the tube amps he is familiar with (read Ampeg, Traynor etc...) The amp has 8 6550 power tubes and 4 "pre" tubes and that is the extent of my understanding. He gave it a complete once over, changed out some caps that were not up to spec and installed a new pre-tube. Amp has run fine since than (except at a gig with crap power!)
I bought it used just about a year ago. I don't believe that the power tubes are original, but the seller also wasn't the original owner, so he didn't know either.
(humorous side note... my tech giggled a bit when he told me about powering up the amp in his shop.... the darn thing dimmed the lights when taking it out of standby! LOL)
Fishheadjoe

 

[Coolhandjjl]

In terms of cleaning, I was talking about oxidation that built up on ¼" jacks and other connectors. Again this occurs with all amps. But it is also a good idea to blow the dust out of the inside of an amp if there is a buildup. It helps it to run cooler.

+1
Pots can get dirty and need a shot of de-oxit, even solder joints can decay. A good tech will know where to look.