Question about Ampeg SVT-3PRO Series Head

sneha1965 · #1 04-23-2010, 07:05 AM

I have an Ampeg SVT-3PRO Series Head which has a crackling noise while I'm playing. I've verified the chord is not bad by running it through a different amp with no problems. I've had the amp apart and have tapped the tubes which are not microphonic, so I am wondering if this could be the epoxy transitor(s)?

Has anyone else run into this problem?

sneha1965 · #2 04-23-2010, 10:13 AM

Anybody?

stiles72 · #3 04-23-2010, 10:24 AM

Could you describe the "crackling noise" a bit more? It could be a couple of things. How old are the tubes? Generally preamp tubes last a long time. I had a set last about 6 years with heavy use before they began making sounds like you describe. I replaced the tubes and all was good. Another possibility is the MOSFET bias. When the bias goes out of wack, the power amp section will begin to make a low distortion or crackling sound. The way to check for this is to run your preamp out to a seperate power amp. If the signal is clean with no noise or distortion - you may need the bias adjusted. This is something better left to a tech - but its a simple adjustment and should only run you a bench fee.

sneha1965 · #4 04-23-2010, 11:17 AM

The crackling sounds like a chord is shorting. If it were the tubes, wouldn't I be able to tell from tapping them with a pencil? They're not microphonic when tapping..

joeyjoejoe · #5 04-23-2010, 11:25 AM

i had all kinds of weird noises after playing mine for about 5-6 years that all went away with changing the tubes. i believe some of those noises were crackling. especially when really pushing things.
the stock tubes aren't anything special so it wouldn't hurt to change them out either way.

joeyjoejoe · #6 04-23-2010, 11:26 AM

also, the microphonic noises i've heard are more of a ringing.

NKBassman · #7 04-23-2010, 11:34 AM

Quote:

Originally Posted by joeyjoejoe

i had all kinds of weird noises after playing mine for about 5-6 years that all went away with changing the tubes. i believe some of those noises were crackling. especially when really pushing things.
the stock tubes aren't anything special so it wouldn't hurt to change them out either way.

Same here.

sneha1965 · #8 04-23-2010, 11:42 AM

I purchased new Groove Tubes when I purchased the amp 7 years ago. I'll give it a try.

stiles72 · #9 04-23-2010, 11:45 AM

Quote:

Originally Posted by sneha1965

The crackling sounds like a chord is shorting. If it were the tubes, wouldn't I be able to tell from tapping them with a pencil? They're not microphonic when tapping..

Not necessarily. Tubes don't have to be microphonic to be bad. They could just be worn out.

I'd start with checking that preamp out signal. If it's perfectly clean - then have the MOSFET adjusted. If the preamp out signal crackles - change the tubes. I've tried JJ's and Tung Sols in mine and really can't tell a difference. In fact the next time I retube I plan to go back to the stock Sovteks. If changing the tubes doesnt fix it - take it to a tech.

joeyjoejoe · #10 04-23-2010, 11:47 AM

groove tubes are stock. at least they were in mine.
i put some electro harmonix tubes in there. i know they're not top of the line, but to me, i think things sound better.

sneha1965 · #11 04-23-2010, 12:03 PM

Groove tubes are not stock. Don't remember what is but because I'm at work but they are different tubes.

joeyjoejoe · #12 04-23-2010, 12:03 PM

they were stock in mine. i bought it new.

sneha1965 · #13 04-23-2010, 12:08 PM

Interesting. I'll have to check to see what's in mine. I'm positive they are not GT's. Wonder now if GC sold me a used amp or re-tubed as new?

joeyjoejoe · #14 04-23-2010, 12:09 PM

its also possible ampeg has just gone through different sets of stock tubes.

sneha1965 · #15 04-23-2010, 12:12 PM

Keep telling me that. I rather hear that then the other thought dancing in my head.

stiles72 · #16 04-23-2010, 04:01 PM

My 3-Pros came with Groove Tubes in V1, and plain Sovteks for the rest of the 12AX7's. I beleive the 12AU7 was a no name tube. However, the Groove Tubes that my amps had were just rebranded Sovteks (you could see the faint "SOVTEK" marking on the tube). Nowadays I think Groove Tubes are rebranded Chinese tubes.

vin*tone · #17 04-23-2010, 04:24 PM

Quote:

Originally Posted by stiles72

My 3-Pros came with Groove Tubes in V1, and plain Sovteks for the rest of the 12AX7's. I beleive the 12AU7 was a no name tube. However, the Groove Tubes that my amps had were just rebranded Sovteks (you could see the faint "SOVTEK" marking on the tube). Nowadays I think Groove Tubes are rebranded Chinese tubes.

Yeah this is the most common tube arrangement. For a while there SVT3's were shipped with a GT swing-tag. Some SVT3's have all GT's, older ones are all Sovtek.

Groove Tubes have always been manufactured by different companies/factories - Sovtek, Svetlana, Shuguang etc...- and rebranded after a quality control process. They have one factory in California where they manufacture a more boutique line I believe.

joeyjoejoe · #18 04-23-2010, 04:30 PM

my amp is over 10 years old at this point i think.

rdwoody1 · #19 04-23-2010, 06:37 PM

Crackling sounds like a tube to me, but, if that isn't the problem, the MOSFET bias may be off. I've heard that is somewhat common in the 3-Pro.
SVT3Pro Bias Setting
This thread has some good information on the MOSFET problem if you want to give it a read. I believe that thread has more people saying they had a mild fuzz/overdrive even at low volumes. But, that's not saying there can't be various symptoms for a bias problem.

Jerrold Tiers · #20 04-23-2010, 08:44 PM

For quite a while, whether or not the brand was marked, the 'sensitive" tubes were graded/selected by Groove Tubes. Some were marked "Ampeg", later I think we just had straight up Groove Tubes parts in them.

Tubes need NOT be microphonic to be bad. That's just one way they can be bad. crackles, noise, etc, that's quite typical.

As for the "epoxy transistors"....... don't fall into the typical trap of identifying an expensive-seeming part and assuming that has to be the bad item...... Actually, it is one of the least likely for the 3PRO.

Tubes first..... bad solder next, a noisy component after that, possibly bias setting, sure.

Swap in a good new quiet tube for each of the 12AX7, one by one (same tube, swap in and if no difference replace original and move to next) and see if one of them isn't noisy. That's the first thing to do, because it only costs you for one tube, and you can, if you unplug and let the voltages bleed off before you stick fingers in, do it yourself cheaply.