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I just got a UL, and one of the kt88's is glowing a little blue-haze inside, I'm thinking it's some kind of gas leak or something from shipping, and I'm thinking it's not gonna last too long. Now I have to buy new tubes and I wanna get 6l6's, but I don't see the kt88/6l6 switch inside, it's says in their brief insructions that the switch is discontinued on later models. I'm not fully sure what this means. This amp is from December 2002, but all VHT dealers and the VHT website say the UL has the bias switch. I also don't see an adjustable bias pot inside. I looked very thoroughly, but all I see is tubes, transformer, and the chassis. Is there no switch, or adjustable bias????? Someone please enlighten me as to what is going on??? Also the kt88's are labelled in hand writing 118, is this the number tubes that I need to order, if I have to get kt88's, to be able to put them in without rebiasing???
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Re: VHT Experts, help w/ tubes!!!
Their website is not up to date. They dropped the switch to interchange 6L6 and KT88/6550 tubes. if you don't have that switch (I think it should be somewhere between the powertubes) I don't think you have that option. I think they stopped that in late 2002 or early 2003. You'd be best off asking VHT. Send them your serial number and they'll be able to tell you.
I think you will still be able to run 6L6 but a tech will have to change a little more inside the amp than just the bias (screen grid resistors for example if I'm not mistaken...I'm not a tech, so someone more knowledgeable than me can feel free to correct me).
Even if you stick to KT88 I'd have it rebiased to give you optimal performance and longitivity of your tubes. -
Re: VHT Experts, help w/ tubes!!!
The newer UL's no longer have the 6L6/KT88 switch. The amp was designed around KT88s so those would be the best type of tubes to use. The bias pot is in insied the amp on the PCB.Comment
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Re: VHT Experts, help w/ tubes!!!
If you go to 6L6s from KT88s, you're making a big mistake!!
The KT88s are MUCH better. They are half the reason to go VHT.
Also, bear in mind. The tube may not be ready to go (although I guess it could be, haha) Many tubes will glow a nice dark blue...It's from impurities, like cobalt, flourescing when electrons from the cathode hit parts in the tube. Svetlana tubes usually do it for one. It's just part of the way they operate inside.
However, ionized air that has leaked into the tube is a strong purple, almost pink. That means the tube is on it's way out and it's time to replace it, like now...
If they're factory tubes, they're probably sovteks, I'd replace them with SED Svetlanas. Give the tubestore that number you see and see see what they say. Maybe they'll know what to give you where you won't have to get it biased. Although I would want to get it biased myself.
VHT's are a bit odd to bias, but a good tech won't have a problem.
Be careful, KT88 amps run a TON of voltage in them around 650-700+ compared to around 450 in a Marshall.
[ November 21, 2003, 06:19 AM: Message edited by: Cleveland Metal ]Comment
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Re: VHT Experts, help w/ tubes!!!
Thats good to know. I think the tube will be all right. I was just worried because it was only one of the tubes glowing blue, so i thought that it might be on its way out, but a VHT dealer told me some of his glow blue too. The amp sounds fine, so everything should be working good. I want to get some Svetlana KT88's when I get some cash, but they're like $160 for a quad, compared to like $60 for 6l6's,and I kinda blew all my cash on this head. I just wanted to try 6l6's in it, and was curious why I didn't see the switch. Everything is all right now, I'm once again worry free. Thanks to you all, good to know there's people with knowledge of all things musical.Comment
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Re: VHT Experts, help w/ tubes!!!
Call Stevie, Thats part of what you paid for.Comment
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