300B driver
How much current do you run through the 6sL7 per tube, or per side?
When Thorsten reported good results with the C3G tube, he ran them in pentode mode, not triode mode. Has anyone tried both triode and pentode mode for this driver and preferred one over the other?
Retsel
How much current do you run through the 6sL7 per tube, or per side?
When Thorsten reported good results with the C3G tube, he ran them in pentode mode, not triode mode. Has anyone tried both triode and pentode mode for this driver and preferred one over the other?
Retsel
The best word I could find to describe your comment is unfortunately in Russian, it is некультурный.
Yes, of course. The 300b needs more HT voltage as you say. I just got it up and working with my existing PSU. This can be changed. I can swap in a more sophisticated input transformer - I have a Lundahl LL1554. I will also swap in an amorphous core NP Acoustics plate choke, which will mean the EL33 will have 15mA current through it. The LL1682 OPT sounds very nice with a 300b, so that stays. Sounds better than a LL1664 which I also have. Only gapped for 50mA current, though, hence the HT needs to go up.
But at least I have it working now and sounding in the general ballpark, which is promising.
I hadn't thought about using 2a3 outputs because of the 50mA limitation on the OPT, but maybe that could be tried with my LL1664/70mA
Last edited:
I don't even find it technically correct in the case of the TSE amp. I have not tried the C3M, D3A or any of the European high GM tubes, since they were not generally available in the USA 15 years ago when I designed the original TSE, which is a well received HiFi amp....and yes during the torture testing phase of the design, I played my guitar through it.
For many triodes including the 5842/WE417A used in the TSE, the distortion into a high impedance load like a CCS feeding the plate, buffered with a mosfet follower into the output tube grid is extremely low, and mostly 2H. I measured numbers in the 0.15 to 0.5% with WE tubes at the grid of the 300B when driven to 5 watts of power at the output of the amp. Raytheon 5842's are a bit higher in THD.
I have also seen some 12AX7's produce extremely low THD into a similar load but there are many different things called "12AX7" and not all are created equal.
Gordon Rankin's "Baby Ongaku", uses a 12AT7 in SRPP, and a 2A3 that has 300V plate to filament, and 50mA. But the output transformer has a 2.5k primary. The 2A3 used a 1k self bias resistor with bypass cap, that meant the driver had to drive +50V to -50V (100V peak to peak).
A simple but elegant design, that sounded good.
I believe an LL1682 will work with the 2A3 at 300V and 50mA. You will get lower power, but lower distortion and higher damping factor.
And look at the charts of the WE 300B that has many different plate voltages, 5k primaries, and many plate currents, including 50mA.
Example:
350V plate to filament; -76V bias; 50mA; 5000 Ohms RL; 6.2 Watts; -30dBc 2nd Harm. (3.16%); -45dBc 3rd Harm. (0.56%)
A simple but elegant design, that sounded good.
I believe an LL1682 will work with the 2A3 at 300V and 50mA. You will get lower power, but lower distortion and higher damping factor.
And look at the charts of the WE 300B that has many different plate voltages, 5k primaries, and many plate currents, including 50mA.
Example:
350V plate to filament; -76V bias; 50mA; 5000 Ohms RL; 6.2 Watts; -30dBc 2nd Harm. (3.16%); -45dBc 3rd Harm. (0.56%)
Last edited:
Not the best operating point for 300B ... nor EL33.
If you use 300B with this low current (50mA), try to elevate anode-cathode voltage up to 400V, so B++ at about 470V.
The EL33 distortion is lower at about 240-250V, 22-25mA operating point.
Attachments
Thanks for the suggestions. I don't need the a-k voltage to go that high in my system, so I'll run it a bit lower.
The EL33 distortion may well be lower at 22-25mA and I'd prefer that also. Again here, I'm having to compromise because my smaller NP amorphous core plate choke is gapped for 15mA. I have one other really good plate choke, a big NP Acoustics amorphous core, 40mA gap and 180H. I have 5 amplifiers at the moment so will have to decide which one it goes into.