6v6pp design

[kopite]

I have a number of nos 6v6's and I would like to build a pp amp with them. I also have a few ECC81's, ECC83's and GZ34.
I had thought of using Sy's driver circuit from his RLD amp.
The mains transformer I have on hand is a Hammond 370HX 550v ct.
Using solid state rectifiers I think I may fall short of the 350v needed for this driver circuit. I think max ht would be around 320 -330v.
For the output transformers I have a pair of Z565's.
I would appreciate a little help to choose the driver circuit and or any other comments for the design. I don't have enough room on the chassis for extra transformers.
Thanks.

[Colt45]

SS / CLC with a 275-0-275 should do about 350v bang on.

[radiotron]

Hi, nice to see another Kiwi flag there sir!
Driver stages for PP have always been a bit a trouble, prefer a transformer phase splitter here, or split load if no suitable transformer about, pretty simple to set up a 6J5, 6C4 or simliar with equal plate and cathode resistors, and bias from voltage divder across HT and GND. Does not like being overdriven though, due to different impedances in plate and cathode ccts.
SS rectification, yes, more volts HT, but mechanical sound to me, GZ34 is OK, though my current SE amp really likes 5R4WGYB "potato masher", and they're still pretty cheap and available NOS, even with freight to NZ.
Tube choice for driver, low mu is good, 6SN7 still rocks, very linear as a simple RC stage.

Cheers

[gingertube]

Kopite,
G'day from across the ditch.
I had a vague recollection that you tried a "Baby Huey" design at one time. If so - and if you liked it - here is the latest 6V6 version.
6V6 Ultralinear
Cheers,
Ian

[Eli Duttman]

Kopite,

As a "proud papa", I'll immodestly suggest "El Cheapo". The 'AQ5s called for are essentially 6V6s in 7 pin mini bottles. Use your NOS with zero signal path parts value changes.

The trafo set you already have is FINE. SS rectify the B+. Voltage multiply the 5 VAC winding to obtain the B- rail. The only additional "iron" required is a choke or 2.

[kopite]

Thank you all for the replies.
Eli would it be possible for you to put voltages on your El Cheapo circuit? I do like the idea of using an ECC81. I have a choke for the psu.
Ian, I have a good supply of 6SL7's so I will consider your circuit, thank you. I really like your designs and your technical know how.
I also remember a design by Joel Tunah using a 6SN7 followed by a pair of 6v6's the phase splitter is the same as Sy's RLD and my available HT may be more suited to this and I can use a valve recitifier.
Has anyone any comments about the sound of the 6V6 compared to the EL84.
I read somewher that the max HT for ultra linear 6v6's should not exceed 275v, this does not seem to be a problem with the EL84.
Thanks again for your helpful comments and ideas.

[gingertube]

Kopite,
I'm running NOS 6V6GTs in Ultralinear at +310 Volts.
I have a CLC power supply where its easy to adjust the voltage by adjusting that first C. (2uF for 310V). I was originally running at +350V. The tubes did'nt object but I thought the sound was a little more relaxed with I pulled it back to +310V.

My view is that (in an identical circuit) EL84 gives a technically superior sound to the 6V6 (higher gm tube) and that additional gm is certainly usefull in shunt feedback circuits BUT I really do like the 6V6 - it is "easy, restfull, relaxed" compared to the EL84 but without the bottom end punch or the top end extension of the EL84.

So you have a some good reference circuits to work from.
SY's "RLD" Pentode Mode Output at 15 to 18 Watts
Eli's "El Cheapo" Triode Mode Output at around 4 to 5W
are both good designs.

The "Baby Huey" is slightly more complex and is right down the middle in terms of power at around 8 to 10 Watts.

Cheers,
Ian

[Miles Prower]

Here is a design for an 807 amp that I did. The front end could very easily be adapted to the 6V6, in that the 807 requires a Vi= 22.5Vp, and a 6V6'll take a Vi= 19Vp. The front end'll do 180Vp-p easily, and so has lots of headroom.

If you decide to go Ultralinear (more easily do-able with the 6V6 since it likes a higher Vg2) you can eliminate the parallel feedback, as well as the need for active screen regulation.

It already works great with 807's, so 6V6's shouldn't be any big problem.

[Eli Duttman]

Eli would it be possible for you to put voltages on your El Cheapo circuit?

The requirements of the 12AT7/ECC81 splitter/driver control. The 'T7 sounds good with 200-220 V. on the plate and I_B = 3 mA. 150 V. get dropped in the 50 KOhm load resistors. So, a B+ rail voltage of 355-370 V. will do very nicely. Less than 2 V. are dropped in the decoupling filters. Everything else falls into place once the B+ rail voltage is right.

If the B+ rail voltage comes in on the high side, increasing the shared cathode resistors 1 standard value is probably a good idea.

Z565 O/P trafos allow for an amp that can switch between triode and UL modes. G2 in 6V6s is tougher than g2 in 'AQ5s. So, the screen grid resistors can safely come down to 470 Ohms. The higher quality of Z565s also allows the high pass capacitance at the I/Ps to be increased, up to 90 nF. total.

If you look carefully, you will notice that 90 V. are "dumped" by resistors in the B- circuitry. The circuitry chosen is the most economical "hash" free design we could concoct for North American builders. 40 V. should be quite adequate as the B- voltage. A 100 Ohm Carbon film part is certainly adequate in the thermal isolation role, between the 'T7 cathodes and the CCS.

The 6V6 family is incredibly linear, when triode wired. Speaker efficiency permitting, go triode.