OK so it's new amp time and I'm leaning heavy toward a svt3-pro. Are there any known issues or years to stay away from? Any years more desirable? Searching just brings up about a million posts.
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Ampeg svt3 pro advise
- Thread starter grendle
- Start date
I have one from 2002 or 2003 and have had no issues from it. Its common to bias the mosfets on these amps, I did that on mine.
I would try to find an SVT3pro used, there should be alot out there....
I would try to find an SVT3pro used, there should be alot out there....
With respect, no one should try to re-bias a MOSFET amp who doesn't have a lot of experience with SS power amps!
How do you bias a mosfet power amp? Mosfets are basically switches with built in switch points / voltages inherent in the design of the component. Are you referring to adjusting the voltage potential sitting on the gate? Usually that set in the circuit by design. Sounds like I need to check the schematic of one of these puppy's.
I bought one way back in the 90's, I believe they had just came out around then, and it sounded great, and had some pretty nice features, but it had a few issues, I believe the transformer kept blowing, it was under warranty and Ampeg replaced the entire head with a new one, 3 times before I gave up on it and bought the classic all tube SVT-AV (basically the CL, but with silver grille cloth, instead of black)with matching 8x10 cab and never looked back since. so for me personally,hearing the name SVT3pro kinda leaves a bad taste in my mouth, but that's not to say they haven't improved it since then, hopefully so, since its still on the market?
Yep looks like that's what they are doing. That could get dicey depending on the tol. of the components used. I can see where that design might give some troubles. I would almost consider replacing those 1/2 watt resistors sitting on the gates with some 1% mil spec ones. That would keep things happy n stable, just not too cost efficient. I do like the tube layout though. Put a good clean hi fi tube up front and get some dirty ones for the back. Interesting.....
I just bought one of these off Ebay and I had to set the bias. This is what it looks like inside. Mine is from 2006.
The red number is the mV measured across the big resistors. The blue/white thing at the bottom left corner of the row of mosfets is where you adjust the bias. It is very very very sensitive.
Sounds great through my 610hlf now that it is adjusted correctly.
The red number is the mV measured across the big resistors. The blue/white thing at the bottom left corner of the row of mosfets is where you adjust the bias. It is very very very sensitive.
Sounds great through my 610hlf now that it is adjusted correctly.
What do you adjust the pot for and where / how do you measure it? Are you looking for even voltage #'s across the resistors? or for a min / max type of adjustment? Yeah IMO those sand box resistors need to go , they work OK , but as you can see from your #'s the tol. is garbage. I would replace the 14,29, and 32 v reading components personally , but thats just me. I might replace that trim pot with a good 8-10 turn pot also. It will make it less touchy and let ya get the adjustment more precise. Other wise it looks pretty good. Silicone / glue is a PITA but it keeps stuff from bouncing around.
From reading posts from Jerrold Tiers who used to work for Ampeg. You measure the voltage across those resistors with a meter and it is expected that the individual resistors would have varying measurements, you want the average of each group to be around 25mV.
http://www.talkbass.com/forum/f15/svt3pro-bias-setting-437406/
http://www.talkbass.com/forum/f15/ampeg-svt-3-pro-tube-gain-question-425889/index2.html
http://www.talkbass.com/forum/f15/svt3pro-bias-setting-437406/
http://www.talkbass.com/forum/f15/ampeg-svt-3-pro-tube-gain-question-425889/index2.html
Great point. Jerrold Tiers walked me through it on mine. The readings I got on mine showed that the resistors were not very well matched.
Wish you were closer, as I've got an unreliable SVT-3Pro that I'd swap for almost anything interesting!
I bought mine used in the mid 90's and I have yet to have a single problem with it.
I've used it with countless different cabs over the years and it's consistent, reliable and it sounds great. It should be noted that these heads are really better suited to a 4 Ohm load for the best tone, but they do okay with 8 as well. It also should be noted that the gain should be set so that the red light is being lit most of the time that you are playing to really get the full flavor of this amp.
I just re-biased mine about two months ago according to the JT thread that was listed earlier, which improved punch and output without really changing the character of the amp - a win-win. It turns out it had been underbiased, probably for years, but it still sounded pretty darn good. It sounds even better now.
I've heard people say that these heads are unreliable, and I can't dispute other people's experience, but it's been rock-solid for me. Mine was built, I think, in 1993 or 4.
I've used it with countless different cabs over the years and it's consistent, reliable and it sounds great. It should be noted that these heads are really better suited to a 4 Ohm load for the best tone, but they do okay with 8 as well. It also should be noted that the gain should be set so that the red light is being lit most of the time that you are playing to really get the full flavor of this amp.
I just re-biased mine about two months ago according to the JT thread that was listed earlier, which improved punch and output without really changing the character of the amp - a win-win. It turns out it had been underbiased, probably for years, but it still sounded pretty darn good. It sounds even better now.
I've heard people say that these heads are unreliable, and I can't dispute other people's experience, but it's been rock-solid for me. Mine was built, I think, in 1993 or 4.
I've had mine now for 10+ years with no issues. A problem I see is that this amp has almost too many tone controls and people just turn the up without knowing what they are doing. Just remember less is more and if you used the graphic EQ, the slider on the right is output and not a tone control.
Biasing should only be done by a tech or someone with a meter who knows what they're doing. The pot is very touchy and can cause the amp to burn up if it's not adjusted within spec. So if you're unsure, take it to a tech. Won't be any more than a bench charge usually.
