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In Reply to: RE: Do i need to modify this driver circuit for PSE KT88 posted by DAK on August 26, 2014 at 13:40:47
DAK,
Keep the 6SL7 as input and go with a 5687, ECC99 or 6H30PI (or similar) as a driver for the IT. The 6SN7 is a great tube, but...the above will be easier to implement as a IT driver.
Did you get the SE LL1660 primaries or PP? IF PP, you'll have a better chance with the 6SN7...If SE what's the gap?
Stuben
Follow Ups:
Hi Stu, I seriously want to keep all the tubes octal based. If I were to go with a 5687 type driver I would also change the input to 12ax7, but I would probably forego the IT rather than switch to the mini tubes.
As far as transformer coupled, I am leaning towards saving my ITs for a different tube setup as it seems that they are more suitable for other tubes. regards, Dak
DAK,
The 6BX7-GT is a high transconductance, high plate current twin triode in an octal format....used as an IT driver, would be perfect...I have one but have not yet used it...
FYI
Have fun
Stuben
Hi Stu, I actually have quite a fair number of those tubes. Do you know of a circuit that would be applicable to my needs? regards, Dak
Here's a PP application..
http://www.kandkaudio.com/images/pentodekt88amp.pdf
I so far have only implemented SE on the primaries. I built an EL84 PP amp using the LL1660S (SE/PP) primaries gaped for 18 mA. The driver is a 6H30P dual triode running about 18/20 mA. Being a 2 stage amp, some voltage gain ahead of it is necessary to really let the magic out.
Many options...much fun
Stuben
Hi STu, I also have quite a few 6BL7 as well. The RCA tube manual has the plate resistance for the 6bl7 at 2800 ohms. right where we need it for the driver right?
Could I use the front end from the K&K kt88 schematic working as a single ended driver for the IT? That seems like an interesting idea. cheers, Dak
Yep, it appears you could use the 6BL7 as a driver with a MU of 15, you'll need gain ahead of the driver in another stage or in the form of a line stage preamp. If you want to go SE on the IT primaries, make sure you ask for the primaries to be gapped for SE.
When I ordered my first set of LL1660S, I neglected to specify SE and I received and pair ready for PP primaries...had to send them back. If memory serves, I connected all of the primaries in a series loop to get the most inductance. I'd run at least 20 mA on the primaries. The wonderful thing about an IT phase inverter for PP operation...it never gets old...
Stuben
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