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Question on Tube Swapping and Biasing

First time tube swapper. I’ve had my Luxman MQ-88use and CL-38use preamp for about 5 years. They sound fine, but it’s good to have a backup set of tubes. So I bought a matched set of 4 Gold Lion KT88 tubes and replaced the stock JJ tubes.

So far so good, everything sounds good, and hopefully even better after breaking in.

Should I be concerned about not setting the bias for these new tubes? And how would I go about doing that? The Luxman manual says nothing about this.

Some online sources recommend having an audio professional bias the tubes, but to my limited understanding the bias is affected by the actual current going into the amp, so having a servicer bias it at a shop might not be the optimal way to go.

Could I hurt the amp or the tubes my not properly biasing them? Or am I overthinking all of this?

jaylat
westcoastaudiophile
819 posts
 

I use plug-in bias tester, similar w/ case to https://www.amazon.com/Nobsound-Current-Probes-Amplifier-Cathode/dp/B0777F8DBK

the problem of measuring resistor voltage drop to setup bias is relatively inaccurate resistance, 5%..10%, which degrades with time. 

in order not to leave any fat / or other stuff on glass, tubes need to handle in clean cloth gloves.

more aggressive tubes like gold lion degrade performance significantly after 50..500hrs, while JJs are softer initially, but still strong after 3000hrs, and that’s why Luxman choses them. there is also improved KT88 variant for valuable amps to consider: https://www.telefunken-elektroakustik.com/product/kt88-tk-vacuum-tube/

jaylat OP
15 posts
 

Thanks for all the info! @westcoastaudiophile what is "improved" about the Telefunken KT88? Have you tried them? 

dogearedaudio's avatar
dogearedaudio
295 posts
 

ghdprentice is correct.  It's not that complicated.  You can get a digital mulitmeter at any hardware store, then just follow the directions Luxman provided.  Don't get thrown off by the chatter anf noise.  Sorry, folks, but he has new tubes and just wants to bias them correctly.  The instructions are simple and quite clear.

westcoastaudiophile
819 posts
 

higher max plate voltage, and pre-burn-in.. haven’t tried them yet, will do it in next tube swap..

faustuss's avatar
faustuss
850 posts
 

"Thanks for all the info! @westcoastaudiophile what is "improved" about the Telefunken KT88? Have you tried them?" 

@jaylat If you click on the link that @westcoastaudiophile provided for you and hover your pointer over the image you can read on the side of the box that it is a JJ tube that's been screened, tested and cryo'd.

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