Minefield - Tube Rolling Input or Power Tubes?

[DaveF]

Just wondering what people's experience here has been with tube rolling, specifically input or power tubes. Which of two have you found made the biggest difference (if any at all) when you changed tubes?
I'm waiting on word back from Jadis to see if my DA88s can safely run kt120's. I believe that Jadis actually recommend using kt120 over kt88's in the JA80 monoblock amps.
Ive also wondered about the smaller signal valves. The DA88s uses the fairly common 12AU7 and 12AX7 valves. They seem cheap enough so no harm in buying a few pairs to try out.

[Ken Moreland]

Here's an interesting site http://www.audiotubes.com/ . He has a lot of background info on NOS tubes and has stock for sale too.

[Steve]

I think there's definitely a few on the forum who have dabbled with this...

My own experience has been that most significant improvement was with rolling the power tubes, swapping out KT88's in favour of the KT120's. Probably not surprising really as it's not a case of "apples for apples" since the KT120's are a different spec than what they replaced. Differences between various brands of KT88 that I tried previously were far less noticeable.

Can still get good results when rolling the small signal valves. On my pre I rolled the stock 12AX7's for NOS Sylvania GB5751's and the stock 6922's for NOS Telefunken E88CC's. Happy with outcome. Found the GB5751's suited my setup well as have slightly less gain. Gave a more textured top end. Tele's seemed to up the resolution a little. To be fair, I might just be trying to justify the purchase!

On the JA80's, I have also rolled the 12AU7's in favour of Mullard CV4003's. The 12AX's are JJ-Tesla's that I picked up years ago. And might also roll for a set of the GB5751's that worked out well on the pre. The Mullard's seemed to bring a little of the sweetness back that moving to KT120's had diminished. So nice balance.

Overall though, as said the KT120's certainly gave the most bang for the buck..

[tony]

I just went for Genelex KT88's reissued. On the signal valves I think I have all RCA5814's got from a good source.
Expensive signal valves could be great but are you going to take the risk on that expenditure? Jim Mcshane is a good one to try but expensive.

Did you sort the regenerator issue?

[DaveF]

I just went for Genelex KT88's reissued. On the signal valves I think I have all RCA5814's got from a good source.
Expensive signal valves could be great but are you going to take the risk on that expenditure? Jim Mcshane is a good one to try but expensive.

ah I wont be spending silly money on signal valves. The whole tube rolling thing seems to be very circuit dependent from what I've read. No harm in having one or two sets anyway.
As for the power tubes well I'd need 8 of those which probably wont come cheap. On the KT120 front I was looking at the Tung Sol Kt120 as they seem highly regarded. It would set me back a bit.
Where have people bought them anyway? ......caught with import duty etc?

Did you sort the regenerator issue?

The manufacturer was unable to solve the fizzing noise issue. I've been offered a refund if I want to take it. For now I just have the unit connected to the CDP, TT and phonostage and it's very quite. Not convinced that its making a difference to be honest. The input voltage never varies outside of 138 to 142 volts which is more than acceptable.

[fergus]

I cannot really help you here Dave as I do not tube roll but what I will say is that my amp uses KT90s which I find are a big improvement over KT88s. They do not offer "better" bass but they offer a sound that is more "rounded" overall; very smooth. If you are told that you cannot use the KT120s then it would be worth asking the same question about the KT90s as they might suit your circuitry more easily.

[Diapason]

I got into a whole tizzy about valves about a year ago, spent lots of money, the usual stuff. Ultimately I can report that in my case there are definitely differences between input valves (the power valves are all made in the one place so I can't hear any difference) but whether the difference is worth the price is another story. I thought it was at the time, but now...? There's just so much bull out there that it's hard to cut through it all.

Tung Sol are the only firm making KT120s (or they were until recently anyway) so it shouldn't matter where you get them.

[DaveF]

I cannot really help you here Dave as I do not tube roll but what I will say is that my amp uses KT90s which I find are a big improvement over KT88s. They do not offer "better" bass but they offer a sound that is more "rounded" overall; very smooth. If you are told that you cannot use the KT120s then it would be worth asking the same question about the KT90s as they might suit your circuitry more easily.

Thanks Fergus, KT90's are ok to use according to the specs on the Jadis website. As for the kt120's, its a question if the transformers can handle the extra increase in current draw. They run hot enough as it is.

[Adrian]

I tube roll every second month.... going to remove my EL34's next week and fit 6CA7's next, then it will be KT66's, KT77's, KT88's, then finally back to 6L6GC's.

However I do believe the manufacturer when he designs an amplifier, has a particular valve in mind.... so sometimes just running with the stock valve is best.

I would like to try KT90's but I don't think my amplifier can handle those. Good strong valve the KT90 is.

[Fran]

Yeah, its a minefield. In some circuits the small signal valves make a difference, in others its the power valves. Sometimes different brands of the same one make no difference, in others its huge. I have a phono stage and the valves make a significant difference. In another power amp swapping EL34 for KT66 made a big difference, but swapping brands of 12AU7 made none.


Fran