Ampeg SVT-CL - tube issue or bias issue???

[bhoff5150]

Hello,

Purchased a used USA made SVT classic locally a while back. Great amp as we all know. The amp sounded as it should and both green LED lights lit up on the back of it when I first got it. Now one of the green LEDs does not light up. I allowed it to warm up for 30 min of playing time as noted in the manual, but I am unable to get that second green light to light up no matter how I adjust either bias knob. Does that mean I need a new matched triad of power tubes on that side or both sides? As far as tone goes the amp might be a little less "tight" in the low end than it previous was, but it does not sound bad. My other tube amps, when it was time to replace the power tubes, you could hear it. I'm not necessarily experiencing that here.

Should I re-tube the power section, or am I not missing something on the biasing.

For other SVT owners, have you found them easy to bias? Has the bias needed to be changed as your tubes got older?? Did you experience an extremely noticeable change in the tone of the amp when they needed biasing or replacing?

Looking for advice and experience from my fellow SVT owners.

Thanks guys !!!!

 

[basscapes]

@JimmyM

Wanna chime in on this?

I've been hearing way too many posts like this- kinda makes one shy away from buying one, doesn't it (see previous rant about the 10% of peeps who praise a product while 90% rant about issues)?

To the OP- Sorry to derail this, if even slightly. The topic of later issue SVTs with problems is plentiful around here. JimmyM knows his SVTs!

 

[coreyfyfe]

I posted the same thing in another thread the other day but if the bias lights don't come on at all check the 12AU7 driver tubes. Easiest thing to do is swap the two, if the bias light issue moves sides you've found your problem.

As far as easy to bias, yes, the user bias system gets the job done well enough.

I've been hearing way too many posts like this- kinda makes one shy away from buying one, doesn't it

They're a very popular amp and lots of them out in the wild, I'd be willing to be the rate of issues is on par with any other tube amp in terms of percentage of those in use.

 

[JimmyM]

@JimmyM

Wanna chime in on this?

I've been hearing way too many posts like this- kinda makes one shy away from buying one, doesn't it (see previous rant about the 10% of peeps who praise a product while 90% rant about issues)?

To the OP- Sorry to derail this, if even slightly. The topic of later issue SVTs with problems is plentiful around here. JimmyM knows his SVTs!

It only makes wussies shy away from them The topic of later issue SVT's with problems is almost always related to tubes, which Ampeg doesn't make and doesn't have control over. And any USA SVT is going to be at least 11 years old, so no wonder they might need a new tube or three from time to time.

Bhoff, I believe you're right that you have a bad tube in the second triad, but just to make sure, swap each triad around and see if it follows to the other side. The triads are grouped in triangles, not straight lines. If it follows, it's definitely a tube issue. If not, then further diagnosis will be needed. But most of the time, it's a bum tube.

 

[basscapes]

It only makes wussies shy away from them The topic of later issue SVT's with problems is almost always related to tubes, which Ampeg doesn't make and doesn't have control over. And any USA SVT is going to be at least 11 years old, so no wonder they might need a new tube or three from time to time.

Bhoff, I believe you're right that you have a bad tube in the second triad, but just to make sure, swap each triad around and see if it follows to the other side. The triads are grouped in triangles, not straight lines. If it follows, it's definitely a tube issue. If not, then further diagnosis will be needed. But most of the time, it's a bum tube.

@JimmyM . Thanks for the "anti-wussy" boost of confidence! LOL!

I've been down the road of tube Fi-Fi gear many times (even had a grunter, 6550 driven power amp, and still use a tube preamp in the Analog Rig at home!), so I understand the deal with flakey tubes, both pre and power. Must be a lot of people out there than don't realize that the care and feeding of a tube am is a little more hands on than solid state!

My "little" restored hi-fi power amp (sold a few years ago)- a SERIOUS 100 Watts per side there...

@bhoff5150 JimmyM is right.

 

[bhoff5150]

It only makes wussies shy away from them The topic of later issue SVT's with problems is almost always related to tubes, which Ampeg doesn't make and doesn't have control over. And any USA SVT is going to be at least 11 years old, so no wonder they might need a new tube or three from time to time.

Bhoff, I believe you're right that you have a bad tube in the second triad, but just to make sure, swap each triad around and see if it follows to the other side. The triads are grouped in triangles, not straight lines. If it follows, it's definitely a tube issue. If not, then further diagnosis will be needed. But most of the time, it's a bum tube.

Thanks for the input Jimmy. Will do.

And for the record, I absolutely love my tube Ampeg gear. I also have a 1993 V4B, and two SVT-IIP (non pro) preamps. I bought two because the first one was so amazing I didn't want to be without one if it ever went down. The IIP preamp is my gigging rig for the last several years. I only bought the SVT-CL because a local guy was hard up and sold it to me for $600. Was trying not to buy another amp I don't use often, but for six hundo I ran out of excuses and caved in.......