How to fix hum noise Ampeg SVT AV Tube Bass Guitar amplifier 

Keep it up bubby. Remember, If you do what you love doing for a living, you never work a day in your life!

Update: Owner reports Hum is gone, never worked better. If you have this issue, take a good look at those PCB mount Cliff input jacks!

All the best to you Terry! Thanks for taking the time to do videos AND take care of your lucky customers as well! Laurent

Heck Terry, I've been watching your videos for a while now and you always do your best, Much appreciated.

Always a good idea to mark or color code plug-in connectors with a sharpie before you unplug them, so that you know where they plug back in. The white and blue connectors on the rear left hand corner of the preamp board look the same and I didn't see anything put there by the factory to differentiate which one goes where. By the way, those types of plug-in connectors are prone to oxidizing and they don't clip on all that tightly either, so you can expect problems in a high power bass amp that gets heavily vibrated, not to mention physically shot when somebody carries it around and sets it down hard because their arm is about to pull out of its shoulder socket! At the 3-day Voice of the Wetlands Festival in Houma Louisiana last October, hosted by Tab Benoit, an SVT with an 8 speaker cabinet was the on stage "house" amp for every band and performance, for the first two days or so, until finally it failed after much heavy usage, and was replaced by a Gallien Krueger amp which they must have had as a spare or back up. I don't know if it was a newer or older SVT, probably a newer one; didn't the original SVT have a 9 speaker cabinet?

Good quick fix ( at least quick in the video) From a musician thanks for taking care of those guys. Good stuff Terry as usual

Still worthy of a thumbs-UP, Terry. Thanks for sharing it with us. 73 DE K7RMJ Frank

Thanks Terry. My back couldn't handle that heavy amp!

always appreciate your videos, Terry; but take it easy. What you do always works for us (your customers and viewers, who appreciate your talents and good will to share). But it has to be fun for you, or it isn't really working for anyone in the long run. Be good to yourself, too; not just us folks in RU-vid-land. You need to have a life, not just a digital life.

I love old SVTs. New ones are a nightmare.

There's such a stigma with these things when it comes to techs, I've met a lot that were uncomfortable being in the same zip code as one. The one I found that was experienced with them had a $90 minimum charge to even look at it.

More vids for us, and more wine for you!

I don't know if the AV has the same power board as in the VR, anyway, according to the VR schematic diagram, the polarity switch simply connect a 0,0033uF bypass capacitor from GND to main L or N or none.

So you fixed it 9 months ago, and now the same problem again. Forgive me if I don't feel complete confidence in you lol

Hi Terry, it's interesting that you got an SVT in for repair. I just repaired an SVT classic a few days ago, which was a nightmare. The newer SVT's have the output tube sockets mounted on a PCB...6550's no less. one of the output tubes shorted and turned more than 1/2 the board into a hunk of charcoal. I am not fond of output tube sockets mounted on a circus board. What were the design engineers thinking? The older one's made in the 70's were made so much better. in 1980, Magnavox bought out Ampeg and it was down hill ever since. it was later owned by Loud Technologies and now recently acquired by Yamaha..Ampeg used to be made here in my home state...New Jersey. I could tell you war stories that would go on for a week LOL :) I tell my customers to try and find an early 1970's vintage SVT. the early one's not only sounded great, but they were more reliable. Great videos as always. Keep 'em coming :) Watch your lower back with lifting those suckers onto the bench.

The ONE thing I needed..how to get to the other pre amp tubes...cant pull that front panel off. You forwarded over

I think this the first guitar amp I've seen where the tubes are mounted upright instead of upside down. Most consumer electronics is either upright or sideways.

All that money to buy one, and it’s not even a double-sided, plated through board. Wow! Since yo mentioned old TV’s, do you remember when we had to get up and adjust the rabbit ears, or rotate the antenna?

When do you have time to do all these repairs and videos? I thought you had a day job. Good work!

have B-25 on bench new output tubes cleaned pots / reseated all jacks worked fine. 1st culprit was bad contact on spkr jack switch. did 3 wire ac cord mod, pulled polarity switch, moved stdby up front where polarity switch went..now i have a that increases with vol on both chan . the guit comes through to.../? have no clue . filter cap hum is usually constant.. this increases with vol control..bad coupling cap in preamp? does same using ext amp output to another amp. its only 50 yrs old..LOL...ps: love your vids..and choice of wines

Where are you located? It would be great to have a music repair shop locally like yours who knows well about this stuff.

Never been a fan of surface mount input jacks. Try to change them out at the first opportunity I get.

Mine is lowering the sound while i m playing . Whats the issue ?

Terry. All your good content is so entertaining and informative that you are starting to make me mad! Just kidding, of course, but your granddaughter's occasional appearance on the channel is just unfair! Thanks, and thumbs up.

What was the actual problem and repair here? You seem to say "... input jacks COULD have been the problem all along". Was that the problem this time round? Just curious.

Mr d-lab I have 2 peavy 4 10 classic 50s I do play loud my oldest one had caps change no problem pretty quiet second one 1997 had caps done and has loud hum like the amp peg and could I email the issue to you your far from me but it shows the problem no one seems to can cure

Nice!!

There's a machine designed to unleash thunder!

Mine developed a bad hum, was the 12AX7 inverter tube

Old svts are the only way to go.

Is it me or is the actual component repair missing ??

wow I never knew those svts were built so cheaply

So Terry....when are you going to retire and become full time D-Lab!!

Interesting there's no handle on the top. maybe it's just TOO heavy for one handle!

2:50 lol

tell owner to save his back with a quilter bass block-only weighs 4 pounds and won't let ya down. 800 watts