Hey guys, long story short I just replaced my tubes in my ampeg svt classic which it VERY much needed. I used 6 6550 electro harmonix mediums. I followed the "standard" for letting it warm up being off stand by but when I went to bias control the red LEDs will not go out. The green will but the red will not.... Any ideas? Ive read the ampeg manual and it's looking like I need a tech or something I'm not looking forward too. Haha. Thoughts?
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Red LEDs on bias won't go out
- Thread starter SavesNewJersey
- Start date
Something obviously isn't right.
First thing to do is to make sure that you new tubes are installed properly. There's an index key on the 6550 tube base that is supposed to ensure that the tube can only go in one way. On some tubes the index is too small and it is possible to install the tubes incorrectly. Verify that the tubes are installed properly.
If that isn't the problem, I would reinstall your old tubes and try to bias the amp. If the bias can be set, this indicates that you amp is ok and the problem is your new tubes. If your old tubes are too run down, you won't be able to bias them either.
If one or more of the tubes has an issue, you may not be able to set the bias. If that's the case, the tubes need to be returned to the seller.
First thing to do is to make sure that you new tubes are installed properly. There's an index key on the 6550 tube base that is supposed to ensure that the tube can only go in one way. On some tubes the index is too small and it is possible to install the tubes incorrectly. Verify that the tubes are installed properly.
If that isn't the problem, I would reinstall your old tubes and try to bias the amp. If the bias can be set, this indicates that you amp is ok and the problem is your new tubes. If your old tubes are too run down, you won't be able to bias them either.
If one or more of the tubes has an issue, you may not be able to set the bias. If that's the case, the tubes need to be returned to the seller.
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Do new SVT's have some computer controlled self-biasing thing? Weird.
I assume you've followed manual instructions precisely?.
Try pulling them all and starting over, making sure all are well seated?
Any tube sockets or indi idual pins feel loose? (Intermittent connection, etc.)
Do the tubes have some numbers written in marker on the top or side? (Doean't matter at this point if you know what the numbers mean. It does tell you a real human took that tube, stuck it in some sort of tester at some point, and took note of what happened).
I assume you've followed manual instructions precisely?.
Try pulling them all and starting over, making sure all are well seated?
Any tube sockets or indi idual pins feel loose? (Intermittent connection, etc.)
Do the tubes have some numbers written in marker on the top or side? (Doean't matter at this point if you know what the numbers mean. It does tell you a real human took that tube, stuck it in some sort of tester at some point, and took note of what happened).
No but they do have an LED system for setting the bias so that you don't have to use a volt meter like you do with the old ones. Turn the bias pot till the LED turns green. The SVT-VR also has a balance LED. The concept is good but the implementation isn't as accurate as it should be.
Hi.
OP, did You buy (/paid for) a matched set?
If You did, return them.
If You did not, try to return them and buy a matched set.
Preferably not CP EH if You ask me, but that's just based on personal experience.
The concept is IMLE/IMO a notch above the trimmers inside the chassis, but also a notch or a two below the old system.
I very much prefer the individual test points (and trimmers) that only handful of manufacturers -Smarvo for one- care to include in their amps.
Regards
Sam
OP, did You buy (/paid for) a matched set?
If You did, return them.
If You did not, try to return them and buy a matched set.
Preferably not CP EH if You ask me, but that's just based on personal experience.
The concept is IMLE/IMO a notch above the trimmers inside the chassis, but also a notch or a two below the old system.
I very much prefer the individual test points (and trimmers) that only handful of manufacturers -Smarvo for one- care to include in their amps.
Regards
Sam
There's more to the story then I had mentioned but it's a lot to write. Haha
But I did put my old tubes back in and the bias works perfectly fine.
In a nutshell, I ordered a matched sextet set of tubes from GC online. When I received the tubes after having spent the money on two day shipping they send me TWO tubes. So that was awesome.... So I get on the phone with GC (guitar center) who I must admit does have a good customer service line. And they overnight the tubes to come the next day, they also threw in all new preamp tubes for the troubles. I get the 6 - 6550s yesterday and open them and 3 of the 6 tubes have broken glass inside them! At this point as most of you all know, I was livid. So after another HOUR on the phone with guitar center and a 50 credit to their store they are giving me a refund and I'm taking my tube business elsewhere. However, they agreed to let me play the tubes until I order new ones from another company. So being that I NEED to have this amp running I put the tubes in, turns out one of the tubes (without the glass inside it) doesn't even work.... At this point my mind is blown at the QC of guitar center and electro-harmonix. So being that I have two other tubes that they first sent me... I use one of those tubes in my head to replace the bad one that didn't work... Still a 6550 and same brand just not from the set of 6 the sent. All the tubes worked... But the bias did not. I'm assuming that has something to do with it?
Also, if you even read all of that my question to you guys is... A.) is that most likely the reason the bias doesn't work and B.) any suggestion of where online to shop for the best tubes/prices? Thank you very much in advance for responding and helping me out. It's greatly appreciated.
Also, I need my amp this Sunday. Is it safe to but the new tubes back in if the bias won't set properly? Thanks!
But I did put my old tubes back in and the bias works perfectly fine.
In a nutshell, I ordered a matched sextet set of tubes from GC online. When I received the tubes after having spent the money on two day shipping they send me TWO tubes. So that was awesome.... So I get on the phone with GC (guitar center) who I must admit does have a good customer service line. And they overnight the tubes to come the next day, they also threw in all new preamp tubes for the troubles. I get the 6 - 6550s yesterday and open them and 3 of the 6 tubes have broken glass inside them! At this point as most of you all know, I was livid. So after another HOUR on the phone with guitar center and a 50 credit to their store they are giving me a refund and I'm taking my tube business elsewhere. However, they agreed to let me play the tubes until I order new ones from another company. So being that I NEED to have this amp running I put the tubes in, turns out one of the tubes (without the glass inside it) doesn't even work.... At this point my mind is blown at the QC of guitar center and electro-harmonix. So being that I have two other tubes that they first sent me... I use one of those tubes in my head to replace the bad one that didn't work... Still a 6550 and same brand just not from the set of 6 the sent. All the tubes worked... But the bias did not. I'm assuming that has something to do with it?
Also, if you even read all of that my question to you guys is... A.) is that most likely the reason the bias doesn't work and B.) any suggestion of where online to shop for the best tubes/prices? Thank you very much in advance for responding and helping me out. It's greatly appreciated.
Also, I need my amp this Sunday. Is it safe to but the new tubes back in if the bias won't set properly? Thanks!
You can run on those tubes, the (idle) bias point will just not be optimal. Most likely the two tubes you received first do no match the sextet you received second and is why you can't get the bias correct.
www.thetubestore.com ,www.tubedepot.com, Invalid Link Removed are all good reliable sources. EH would not be on my personal list of choices or recommendations. I have seen too many EH sets that will not bias properly.
www.thetubestore.com ,www.tubedepot.com, Invalid Link Removed are all good reliable sources. EH would not be on my personal list of choices or recommendations. I have seen too many EH sets that will not bias properly.
Hi.
It has everything to do with it.
The glass/mica bits inside a tube is annoying, but IMLE doesn't do any more harm than good.
That is rather common in USSR/Russian tubes.
Since the SVT works with 2 banks of 3 tubes, and the bias can be adjusted for both banks individually (=3 tubes), those three tubes should be as closely matched for the optimum performance.
The amplifier does work with mismatched tubes as well, but if a certain bias setting puts one tube significantly hotter or colder than the rest, bad things will happen.
You can keep swapping the tubes from bank to bank hoping that one combination will be close enough for the idiot lights to give you a green light, but with just 7 tubes to work with, I wouldn't hold my breath.
Assuming Your handle has something to do with your location, suggestions from across the pond are pretty much useless, but the US TBers will be offering plenty of options in no time
.
For decent 6550's or KT88's, IMO do not cheap out, it'll only bite you sooner or later as you already discovered.
Regards
Sam
It has everything to do with it.
The glass/mica bits inside a tube is annoying, but IMLE doesn't do any more harm than good.
That is rather common in USSR/Russian tubes.
Since the SVT works with 2 banks of 3 tubes, and the bias can be adjusted for both banks individually (=3 tubes), those three tubes should be as closely matched for the optimum performance.
The amplifier does work with mismatched tubes as well, but if a certain bias setting puts one tube significantly hotter or colder than the rest, bad things will happen.
You can keep swapping the tubes from bank to bank hoping that one combination will be close enough for the idiot lights to give you a green light, but with just 7 tubes to work with, I wouldn't hold my breath.
Assuming Your handle has something to do with your location, suggestions from across the pond are pretty much useless, but the US TBers will be offering plenty of options in no time
.For decent 6550's or KT88's, IMO do not cheap out, it'll only bite you sooner or later as you already discovered.
Regards
Sam
As you have indicated the likelihood of faulty tubes due to shipping and QC, I recommend not running the amp until you get a set of good tubes in it. If one tube is bad, trying to set the bias using the LEDs could result in a bunch of fried resistors. Each side of the bias sense circuit looks for the total current through 3 of tubes. If one tube is fried, you will be running way too much current through the two functioning tubes to get the required current flow through the circuit necessary for a proper LED indication. It is possible to run the amp with only two tubes in each bank of three but you need the right tools to set the bias so each individual tubes is in an acceptable operating range. The LEDs will not be useful for this.
If you are handy with a volt ohm meter, you can check for a voltage drop across the screen resistors on each tube to confirm which tubes are actually working. If only two are working in each bank of three, you can set the bias at test points K1 and K2 for 48mV. With all three tubes functioning, these test points should read 72mV when the bias is properly set.
I wouldn't push the amp hard if you are only running 4 tubes as the resultant impedance mismatch will be hard on both the tubes and output transformer.
As the original tubes work fine, I would go with those if you have a gig. IMHO this is your best solution.
Another possibility, both the amp and tubes may be fine. It's possible that the range of the bias circuit is not set up for the grade/brand of tubes you bought. For example tubes graded as 5s tend to require a different level of bias than tubes graded as 1s. If your amp is set up to run 5s it may not be possible to run 1s without changing the value of the dropping resistor that feeds the bias circuit. I haven't personally experience this on an SVT CL but I have on other tube amps with adjustable bias.
Although not cheap, I would recommend TAD tubes if you need a source in Europe. As a another TBer mentioned you don't want to cheap out on tubes in an SVT. In the long run this will cost you more.
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Here is very good place to deal with. They test the tubes well and their matching process is about as good as you will find. They will sell you a set selected for the voltages in the SVT CL. Even if you don't go with them, ask them what they would recommend for your amp. If you want early, average, or late distortion, they can do that for you as well.
As was mentioned, your best bet is to reinstall your old tubes and rebias them till you sort out a new set of tubes. A badly matched set of tubes will cause the problem that you are seeing.
As was mentioned, your best bet is to reinstall your old tubes and rebias them till you sort out a new set of tubes. A badly matched set of tubes will cause the problem that you are seeing.
