GEC KT66 vs Genelex reissue bias question..

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Melodyman
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GEC KT66 vs Genelex reissue bias question..

Post by Melodyman » Sat Sep 16, 2017 3:18 pm

Hi folks..

I have a nice set of old GEC KT66's in my JTM 45 and I want to take them out and save them for recording dates and instead use a new set of KT66 Genelex Gold Lions reissues for gigs etc. Can I just do a swap or do I need to re-bias. I have the GEC's set on the cool side for longevity but i'm unsure if the new ones can handle the voltages etc of the old in a straight swap. What say ye?

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Re: GEC KT66 vs Genelex reissue bias question..

Post by harleytech » Sat Sep 16, 2017 8:23 pm

I would check the bias on any power tube swap. Then you know where you stand. IMHO...

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neikeel
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Re: GEC KT66 vs Genelex reissue bias question..

Post by neikeel » Sun Sep 17, 2017 7:42 pm

harleytech wrote:
Sat Sep 16, 2017 8:23 pm
I would check the bias on any power tube swap. Then you know where you stand. IMHO...
Always.
Neil

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Re: GEC KT66 vs Genelex reissue bias question..

Post by Melodyman » Mon Sep 18, 2017 2:18 pm

Yes, It looks like I will have to take it in for this. I was just curious as to whether the new Gold Lion reissue KT66's have the same specs as the originals do regarding their ability to handle similar voltages etc or if (due to newer tech restraints on construction and materials) they have to be set much lower to avoid red plating than the NOS GEC ones. Thanks for the feedback <S>

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Re: GEC KT66 vs Genelex reissue bias question..

Post by neikeel » Mon Sep 18, 2017 4:53 pm

Melodyman wrote:
Mon Sep 18, 2017 2:18 pm
Yes, It looks like I will have to take it in for this. I was just curious as to whether the new Gold Lion reissue KT66's have the same specs as the originals do regarding their ability to handle similar voltages etc or if (due to newer tech restraints on construction and materials) they have to be set much lower to avoid red plating than the NOS GEC ones. Thanks for the feedback <S>
I have installed the Gold Lions in a couple of 60's amps with pleasing results. I have not had any feedback to say that they died prematurely.
Neil

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Re: GEC KT66 vs Genelex reissue bias question..

Post by VelvetGeorge » Thu Sep 21, 2017 11:27 am

Very early in Super-Plex production I changed to Gold Lion KT66's from Valve Art. All seems good so far, knock on wood.

The specs have varied quite a bit, but I have plenty of sweep in the bias adjustment.

In general, all modern output tubes benefit from higher value screen grid resistors. Often when there is a failure it's the screen. Whether a purist can accept changing the value is another discussion...


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Re: GEC KT66 vs Genelex reissue bias question..

Post by Roe » Fri Sep 22, 2017 3:20 am

I suspect that one reason for failure with the RI is bias drift. More specifically, the bias takes a long time before it settles completely after you fire up the amp, particularly with kt66s that are not burned in (something that may take 40-70 hours)
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Re: GEC KT66 vs Genelex reissue bias question..

Post by Melodyman » Mon Nov 13, 2017 9:22 pm

Thanks for the replies. I know biasing is important but it isnt always easy or cost effective to take it in and have it done, especially if I want to swap out the GEC's for recording and swap back to the GLRI's for gigs. So was looking for a definitive answer as to if this is safe to do from a blueprint standpoint.. Didnt want to try it and then have a meltdown or blow something up.. I guess what im asking simply is if there is any reason I Should not do this..

Thanks again for the help..

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Re: GEC KT66 vs Genelex reissue bias question..

Post by neikeel » Tue Nov 14, 2017 4:42 pm

Correct biasing is essential if you want to get the best out of your tubes.

Ideally do it yourself. Either add some 1ohm 1% resistors instead of the ground wires on the output sockets or get a couple of biasing sockets.
You may find that your GECs and the other tubes are in the same range of current draw at the same setting and your worries are over!

Your GECs will not sound at their best or at worst die prematurely and your modern ones will certainly die early if they are too hot.
Neil

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