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Ampeg SVT-CL standby light flashing red/green

micahturner

micahturner

Feb 20, 2010
374
2
Fort Lewis, WA
#1
I fired up my SVT this morning and my amp made a fart sound and soon after I noticed what smelled like electronics burning. The Standby/power light was flashing red to green and the red bias light was lit as well. Any ideas before I dish out the cash for a tech?

Thanks
 
#9
Heard back from the tech yesterday. Three of the plate resistors had blown and he suggested that I replace all the power tubes. The amp still had the original Sovtek 6550's so I'm upgrading to a sextet of Tung-Sols. My question to you guys is this; would it be a good time to change out the preamp tubes? I am leaving for a long string of shows next week and I do not want to run into any more bumps in the road since this is my only amp.

Your input is always appreciated.
 
#13
micahturner said:
I'm upgrading to a sextet of Tung-Sols. My question to you guys is this; would it be a good time to change out the preamp tubes? I am leaving for a long string of shows next week and I do not want to run into any more bumps in the road since this is my only amp.
Click to expand...

A new set of tubes can also be a bit risky. New tubes can blow if they have a fault in them. Fortunately, if a tube is going to blow, it will do it soon after installation. Some places sell tubes that have not only been tested but are also burnt in for some period of time, typically 24 or 48 hours. You pay more but if reliability is important, it is worth the investment.

I would change whatever tubes you are going to change. Then make sure they are burnt in by using them as much as you can before hitting the road.
 
#14
I think that amp uses half of a 12BH7 to bias one bank of three tubes, and half of another 12BH7 to bias the second bank of three. Maybe half of one 12BH7 crapped its pants and allowed one bank to run away, until the plate resistors saved the day by opening up? Maybe an SVT/tube heavy will pop in and say whether that's even a possible failure scenario. (Hell, I might even have the topology wrong...)

Might have to withdraw my recommendation about not replacing any preamp tubes. But let's see what the folks who really know SVTs have to say.
 
#15
I'm not sure if they have been burnt in. I'm buying them from the tube store and the tech is doing the install and biasing. No strange power issues at my last gig that I know of. I'm not knowledgeable about the technical side of tube amps. I just know that they sound great and they have the capacity to kill you.
 
#16
Got my SVT back from the tech. He replaced the 2k plate resistors with 5k plate resistors and retubed the power section with Tung Sol 6550's. The head sounds amazing, and he told me that I should have nothing to worry about when I take it out on the road for my upcoming tour.
 
#18
I asked the tech if I should replace the preamp tubes and he said that they had tested strong. The preamp tubes are 12AU7's(I think) or maybe the 12AX7. He told me that there was no reason to replace them. He also said that the 2k resistor was of poor quality and should be replaced anyway.

I don't know. My amp works and sounds great, so I'll take his word for it. It's all greek to me.
 
#19
I went to GC yesterday and seen an ampeg svt classic and got excited to try it out "with an 810 stack" because all I've heard was good things. The dude plugged it up and turned it on and this same red/green thing was going on. Needless to say I was disappointed. Man I wanted to hear this baby sing! ***! So I tryed an ampeg amp with preamp tubes. I still like my tnt for the tuff as nails quality but man I wanted to try the svt!
 

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