Ampeg SVT4 Issues

[nikrox2]

First, thanks for taking the time to read this..we're all busy!

I'm more of a player than a techy..so excuse me ahead of time here..

Basically I'm running an SVT-4 Pro thru an 8x10 Cab...I've had this rig for about 2-3 years now...no issues (well my first SVT4 burnt up..litterally)..so now I keep a spare in the rack (just in case)...but lately (past three shows)...after about an hour..I start loosing volume..first I thought batteries in my wirelss unit, then batteries in my guitars (2 9v each)..so I switched all, switched guitars..everything...the last show, it again lowered in volume, then it would bump back up during a song..no ryhme or reason..later I noticed a "crackly" sound also...especially when I cranked it up during the lower volume times...

Are the tubes going out? Is there more to the picture than I see (or hear?)

This SVT4 is a USA model..my back-up is a Vietnam unit...as I hadn't had to use it (at all), when I quickly changed over I set it up to match my upper unit...(fan in between & removable rack covers on front & back - should be no heat issues) ...I did get the "occasional" gun blasts from my cab..but dialing the lower eq down ended that...but there is a difference between the units..no doubt. ;-(

[Mark Black]

This might sound a little strange, but I guarantee it's a valid troubleshooting technique: ball up your fist and whack the amp on the top and/or sides while listening for crackles, noises, or volume changes. Doesn't have to be a pile-driver hit, just enough to vibrate the amp innards.

If you hear any noises or volume changes at all you probably have some connection problems inside the amp, most likely (in my experience with those) due to thermal and/or vibration cracking of solder joints. If that is the case (and maybe even if you can't make it mess up that way) I would say based on the age of the unit it's time to have a tech who is familiar with those go through and do a comprehensive solder retouch.

The factory soldering quality is a known issue with those (actually just about everything that comes out of the Ampeg or Crate factories, among others).

Best of luck!

[52 Bill]

And also the break jacks in those amps have been known to cause similar symptoms. The next time it happens, try patching a spare cord from pre-amp out to power amp in or FX send to FX return.

[nikrox2]

thank you both...I'll try all suggestions and see where it may lead ..ya never know??

[zero cool]

the other issue can be heat. after time, dust and gunk can up build inside and act like a blanket causing the amp to run hotter. Pull it out, crack it open, give it a good cleaning and see how it does. these amps have tiny heatsinks and rely on a fan for cooling. make sure the fan spins freely, give it a shot of lube.

[chipprogr]

Ive had about 5 of these in my shop with bad MUTE jack on the back of the amp. It would cause anything from volume drops to all out silence. Cheap jack that costs a couple bucks can cause so much more in stress.