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SVT-CL issue

#21
Take a video when the problem is happening along with making sure to catch the sound it is making during the video clip. You can use this to show the tech in case he cannot reproduce the problem. Not doubting your tech but I would ask other musicians around town who they swear by. I took mine to one guy and he said everything was fine and randomly replaced the fan because he said it was making a lot of noise which the new fan was worse. I went to him because he was an authorized Ampeg tech. I took it to the place everyone recommended and they put in new power tubes and the whole problem was fixed. They also enforced some electrical connections on the inside free of charge so I would not run into any issues. That was after 4 years of owning it and post tech visit I am going on 5 years. About to pop in some new JJ power tubes to replace my Winged C's which are starting to go. Sound volume fluctuates at times and one of them is about to go. Winged C's are unfortunately way to expensive now but I am really pumped to try out some JJ's after hearing all the good things.
 
#22
Thank you to everyone for chiming in here. A couple of you recommended I recorded on video, I did that when it acted up Saturday night and e-mailed it to my amp tech. I've known him for years so he knows I'm not crazy but he does think now that it's probably a bias issue of some sort. As for the tubes, he actually did recommend that I go ahead and replace them all. Basically he said, yeah they're good, but they're on the verge of going so he recommends a full set which I'm planning on doing. I just want to make sure that we get this other issue, if there is another issue besides tubes........(and I believe there is now), sorted out before I jeopardize new tubes or any other part of the amp. Thanks again to everyone. I'll update the thread as I learn more.
 
#23
Slpbass81 said:
Take a video when the problem is happening along with making sure to catch the sound it is making during the video clip. You can use this to show the tech in case he cannot reproduce the problem. Not doubting your tech but I would ask other musicians around town who they swear by. I took mine to one guy and he said everything was fine and randomly replaced the fan because he said it was making a lot of noise which the new fan was worse. I went to him because he was an authorized Ampeg tech. I took it to the place everyone recommended and they put in new power tubes and the whole problem was fixed. They also enforced some electrical connections on the inside free of charge so I would not run into any issues. That was after 4 years of owning it and post tech visit I am going on 5 years. About to pop in some new JJ power tubes to replace my Winged C's which are starting to go. Sound volume fluctuates at times and one of them is about to go. Winged C's are unfortunately way to expensive now but I am really pumped to try out some JJ's after hearing all the good things.
Click to expand...

I've been around our music community her for decades. Pretty much every musician around here uses the same guy. He is "the man" when it comes to anything amp related. To clarify, upon his first examination while he couldn't replicate the issue, he let me know that there's obviously something going on and needed more information. I decided to take the amp back to rehearsal and was able to duplicate it again. When this happened the first time I didn't notice the bias lights being on so I took the time and recorded a video for him. Like somebody else mentioned here, he believes there is some sort of a bias issue likely with circuitry.
 
#24
deichman said:
Thank you to everyone for chiming in here. A couple of you recommended I recorded on video, I did that when it acted up Saturday night and e-mailed it to my amp tech. I've known him for years so he knows I'm not crazy but he does think now that it's probably a bias issue of some sort. As for the tubes, he actually did recommend that I go ahead and replace them all. Basically he said, yeah they're good, but they're on the verge of going so he recommends a full set which I'm planning on doing. I just want to make sure that we get this other issue, if there is another issue besides tubes........(and I believe there is now), sorted out before I jeopardize new tubes or any other part of the amp. Thanks again to everyone. I'll update the thread as I learn more.
Click to expand...

Yes, please update! I just swapped all the tubes, which cost me between 250 and 300.. If there's something with the bias circuit that could harm the amp or the new tubes, I'll want to know what it is and how to fix it.

Btw, I haven't replaced any of the preamp tubes, could that be a culprit in the bias? My understanding was that the bias was just for the power tubes
 
#26
B-string said:
Only output tubes (the 6 large ones) need manual bias. The small ones are self-bias (they self-adjust), but the smaller tubes down on the power amp should be changed with the output tubes if you do a retube.
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That's the first I've heard. Why is that? I thought preamp tubes are set to last much longer and seldomly, if ever, need changed.

Regardless.. What are the cheaper driver tubes you'd recommend for the CL?
 
#27
I had to jump in here. I'm a long-time friend of deichman, and play in his band. Just wanted to boast a little on the tech that is looking at the amp. He has been in business for almost 40 years. He's not only "the man" locally, he's written for national publications such as Electronic Musician, Keyboard Magazine, he's built pedals for Eric Johnson "yeah, that Eric Johnson" Most recently just did a complete restore on a vintage Oberheim synth for Patrick Moraz. He's built tube amps from scratch, does amp mods, builds custom switching systems, etc. He specializes in tube amps. He's truly a wizard in every sense of the word. Highly respected with good reason. If he can't fix it, it can't be fixed. Mike Metz at thesisaudio.com

I know everyone here that mentioned "your tech" had good intentions, and we've all experienced the bad techs. I just wanted to jump in before someone else suggested looking for a new tech. You can rest assured the tech is in control.

Those power tubes were glowing like burners on a stove. I've never seen anything like it. Not sure I've smelled anything quite like it.

Oh, one last thing. JJ tubes are the absolute bottom of the barrel. Mr. Metz literally has a cardboard box FULL of JJ's that have failed. Guitar amps, bass amps, it happens so frequently that he started saving them to show clients who want JJ's why, no, you don't want JJ's. I'm surprised to read that someone has heard good things about them. I've seen the box. I wouldn't spend a dime on them, and to replace Winged C's with them is like replacing your Ferrari with a skateboard.

Sorry to interrupt. Carry on.
 
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#28
LowEndWooly said:
That's the first I've heard. Why is that? I thought preamp tubes are set to last much longer and seldomly, if ever, need changed.

Regardless.. What are the cheaper driver tubes you'd recommend for the CL?
Click to expand...

The driver tubes are under much higher loading driving the output tubes. Different application (not being used as a preamp tube) than just a low current voltage amp. With NOS 12AU7's still affordable I don't recommend cheap tubes at all.
 
#29
12ax7's are crazy expensive these days, though, so I do recommend cheap tubes for them ;) Honestly, mine has JJ's everywhere and I'm quite happy with them. JJ's aren't the greatest tubes ever, but they seem to work well in my SVT.
 
#31
.endofstory said:
I had to jump in here. I'm a long-time friend of deichman, and play in his band. Just wanted to boast a little on the tech that is looking at the amp. He has been in business for almost 40 years. He's not only "the man" locally, he's written for national publications such as Electronic Musician, Keyboard Magazine, he's built pedals for Eric Johnson "yeah, that Eric Johnson" Most recently just did a complete restore on a vintage Oberheim synth for Patrick Moraz. He's built tube amps from scratch, does amp mods, builds custom switching systems, etc. He specializes in tube amps. He's truly a wizard in every sense of the word. Highly respected with good reason. If he can't fix it, it can't be fixed. Mike Metz at thesisaudio.com

I know everyone here that mentioned "your tech" had good intentions, and we've all experienced the bad techs. I just wanted to jump in before someone else suggested looking for a new tech. You can rest assured the tech is in control.

Those power tubes were glowing like burners on a stove. I've never seen anything like it. Not sure I've smelled anything quite like it.

Oh, one last thing. JJ tubes are the absolute bottom of the barrel. Mr. Metz literally has a cardboard box FULL of JJ's that have failed. Guitar amps, bass amps, it happens so frequently that he started saving them to show clients who want JJ's why, no, you don't want JJ's. I'm surprised to read that someone has heard good things about them. I've seen the box. I wouldn't spend a dime on them, and to replace Winged C's with them is like replacing your Ferrari with a skateboard.

Sorry to interrupt. Carry on.
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Lighten up, Francis ;) Nobody said the tech was bad. We just thought he may have missed something because he didn't give the amp time enough to misbehave. Winged C's are no longer being made and cost as much as freaking NOS power tubes, so I would never put them in my amp in a million years. Also, I was not a big fan of JJ's before either, but they've already lasted two years in my Heritage SVT, so I will keep them till they break, and likely use them again unless something else better comes along, which doesn't seem to be happening.
 
#32
I don't believe I have made any comments about his amp tech? If the tubes were glowing like in the circled pic below:

tubered.jpg


The amp has a concern that needs to be addressed. The one thing I did mention is the driver tubes as the bias adjustment is done between the two sections of the driver tubes on the CL.
 
#34
JimmyM said:
Lighten up, Francis ;) Nobody said the tech was bad. We just thought he may have missed something because he didn't give the amp time enough to misbehave. Winged C's are no longer being made and cost as much as freaking NOS power tubes, so I would never put them in my amp in a million years. Also, I was not a big fan of JJ's before either, but they've already lasted two years in my Heritage SVT, so I will keep them till they break, and likely use them again unless something else better comes along, which doesn't seem to be happening.
Click to expand...

No chance Winged C's are worth the price they are at now. Nothing else sticks out being much better and kinda weird a tech would keep a box full of used tubes just to show clients. I guess he finds most people don't take what he says too seriously ;)
 
#35
The winged =C= 6550C's were darn close to the old US 6550A's for sound, output and longevity. Today's prices are driven by the fact there is no new production and their high quality. Wish I would have bought a lot more back when Svetlana was the distributor, I was paying about $16 USD each matched.

I have a "troubled" box of tubes, not unusual.
 
#36
JJs are more than ok when they are working.
But then I also had a brand new JJ 6550 drawing air after 3h of usage and blowing an onboard fuse on my amp.
Tiny little round hole in the glass body, definitely a defect in material.
Amp wouldn't go out of standby anymore then, so I had to ship it to have it repaired under warranty.
Glad that is was just the fuse that saved my amp from more damage.
As all of the tubes were new I replaced the dead one with another JJ later, but next time will probably try another brand.
 
#37
deichman said:
My SVT head power tubes (all 6) are getting very hot ... all 4 bias lights are on, both red and green ... starts squealing quite loudly.
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This is making me wonder whether the amp could be oscillating, starting at a very high (and thus inaudible) frequency. I think with no signal only the red or green bias light should be on, not both at once. Any signal (whether playing, or oscillation) will make both lights appear to be on.
 
#40
jmpiwonka said:
whjat exactly causes an amp to oscillate?
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Microphonic tubes oscillate although normally at an audible frequency like squeeeek squeeeel.
They are easy to find by tapping the glass lightly with somthing like a chop stick while the amp is on and listen for any ringing and singing.
RF suppression capacitors can fail or become disconnected and leave the amp open to Radio Frequency amplification,
which can be inaudible.
It sounds like there is a microphonic pre amp tube in it and the bias system for the output tubes has gone wrong or the output tubes are compleatly out of bias range.
Has this amp allways been operated into the correct loudspeaker load impedance for the selector.
In the case of eight by ten cabs the more voice coils you fry, the higher the cabinet impedance goes and the higher the voltages in the output tubes and transformer primaries go.
Get a 9V battery and check all cones move and hopefully all in the same direction?.
 
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