JTM45 Clone-Switching out Groove Tubes KT66 for NOS Sylvania 6L6's

[sweetpea]

I think the amp sounds great, but was wondering if it could sound even better with a higher quality power tube(s). Do I need to adjust the bias if I swapped them out. I suppose it would be the optimum thing to do...

Thanks.

[Riscchip]

Yes, the bias will need to be checked and possibly adjusted by someone qualified to do so safely (please don't kill yourself poking around in the amp). That would be true for any tube swap, even other KT66s, assuming it's close to a real JTM45. They're fixed bias amps, so the bias has to be "fixed" at the right spot for those particular tubes.

What kind of JTM45 clone is it? Do you know if it has a bias adjustment pot and / or bias test resistors or test points?

[John Phillips]

I think the amp sounds great, but was wondering if it could sound even better with a higher quality power tube(s). Do I need to adjust the bias if I swapped them out. I suppose it would be the optimum thing to do...
Yes, you do - or at least check it... it may not need adjusting, but you have no way of telling without measuring it.

BTW, don't bias up to 70% of 30W just because 6L6GCs are rated at that. It's a KT66/5881 amp and should be biased for those, even though the 6L6s have a higher rating.

Just FWIW, while I always prefer old-production tubes over new ones when comparing the same type of tubes, I would not recommend Sylvania 6L6s in a JTM45. I think they sound much better with KT66 types. Higher quality does not necessarily mean better tone when you're changing the tube type as well.

...and in fact, I prefered the 'cheap' Shuguang KT66s to the 'more expensive' Groove Tubes ones in a JTM45 I tested recently.

[Scott_F]

Eurotubes now has some of the new JJ KT66's in stock. I'm waiting for my next build to complete so I can try them out.

[sweetpea]

As always, thanks for the informative information guys. I am learning bit by bit here on TGP.:p