Ampeg SVT 200T head problem

[alembic1989]

I've owned this amp from new and love the tone.

However some years ago it developed  a fault...the volume slowly " fizzled out" after playing for 20 mins or so...and the faded in and out of it's own accord.

I took it to Surrey Amps, and they did a very thorough job servicing/ repairing it.

The fault came back..they very graciously had another look, and could find nothing wrong with it.

I hadn't  used it for a while..plugged in again..and now...nothing.

Curiously..in the past, the amo would sometimes leap into action, if I hit the strings hard with the palm of my hand.

Does anyone know an Ampeg expert..?

I'm out of touch with " new" mini amps..I tried a mini mark bass amp..and didn't like the tone.

Is it time for a new amp?

Are these old transistor amps inherently unreliable?

Any suggestions welcome.

If any of you are amp repair experts..fancy buying a wounded Ampeg?

HELP!

[Bigguy2017]

Sounds heat related? Dry joint developing when amp warms up...

 

The 'chopstick method' when the fault occurs could help to localise the fault. (tap/poke the PCB and components, connectors etc. with an insulated chopstick to find dry joints).

 

Could be a transistor - they have been known to go weirdly faulty after many years.

 

 

[BassmanPaul]

Try the old trick of linking the Send and Return of the Effects loop with a signal cable. Do the same if the amp has a Pre-amp Out and a Power Amp  In.

[paul_5]

Or try plugging your bass lead in and out f the socket repeatedly. Could also be a dry joint on the board.

[BassmanPaul]

22 hours ago, paul_5 said:

Or try plugging your bass lead in and out f the socket repeatedly. Could also be a dry joint on the board.

If it is a failed solder joint this will not solve the problem.

[paul_5]

Agreed, sometimes the jack socket itself can fail, or the conductive surface of the pins can tarnish over time, leading to poor signal conductance.

[agedhorse]

Have them look at it again, if the actual cause is not correctly identified, no repair or miraculous guessing is going to fix the problem. 

 

No, transistorized (and solid state amps in general) are no less reliable (and IMO much more reliable) than most tube amps.

Edited February 11, 2022 by agedhorse

[beans-on-toast]

There are some basic things that you can try. Put a patch cable or short instrument cable between the effect send and return. See what happens. Test the power amp by plugging a preamp into the line in jack. If you don’t have a pre-amp, try plugging your bass directly into the line-in jack. It may or may not work depending on the signal strength from the bass.

 

This is for your tech in case they don’t have a schematic. As a start…. There are some minor resistor changes in the later revisions listed in a table. There are also test point voltage references to read when examining the amp. The amp has a few interconnect cables. These should all be inspected and reseated. Clean if oxidized. The jack shunts should all be cleaned with Deoxit.

 

https://ampeg.com/support/files/Schematics/S Series/SVT-200T, 350T/SVT200T_350T Schematics_PL.pdf