I have a 300B and it is very dynamic and so on. But amplification is a bit high.
The trannie is LL2752.
So up came the idea of a internal feedback (anode-anode, not across the output transformer.
This is the basic idea:
The lower freq limit is lower than the -3db of the input (should be 25) but is modelled as 43 Hz. is fine with me. Lowering will give a little rise in the Va curve at the bottom end.
The high freq is quite high, at 80 kHz simulated.
Without feedback I get 8 Hz. And some 30 KHz. measured.
With different drivers I sometimes got 60 KHz measured,
any comments?
The trannie is LL2752.
So up came the idea of a internal feedback (anode-anode, not across the output transformer.
This is the basic idea:
The lower freq limit is lower than the -3db of the input (should be 25) but is modelled as 43 Hz. is fine with me. Lowering will give a little rise in the Va curve at the bottom end.
The high freq is quite high, at 80 kHz simulated.
Without feedback I get 8 Hz. And some 30 KHz. measured.
With different drivers I sometimes got 60 KHz measured,
any comments?
Move - Over to the WE91A
The previous design was t osee how far I could get.
What I have done in the mean time is re-make the WE91 design, one I have had for many years. Previously I had the 10Y - long plate as outut tube. It has almost the same output power as the 300B.
So now 300B and a 6SN7 input. Same tube as 6C6.
I increased the screen voltage to 117 volts (initially with a zener, now stabilized)
I have two coupling modes, direct connected Va-Vg witha 100n mica; the second option is usung a source follower via a 100n VitQ PIO. I have a spdt switch to go from one to two.
The first starts to drop with 18kHz -1 dB; -3 dB at a low 25 kHz.
The buffered option has -3dB at 55 KHz.
The first option is gorgeous. Natural.
The previous design was t osee how far I could get.
What I have done in the mean time is re-make the WE91 design, one I have had for many years. Previously I had the 10Y - long plate as outut tube. It has almost the same output power as the 300B.
So now 300B and a 6SN7 input. Same tube as 6C6.
I increased the screen voltage to 117 volts (initially with a zener, now stabilized)
I have two coupling modes, direct connected Va-Vg witha 100n mica; the second option is usung a source follower via a 100n VitQ PIO. I have a spdt switch to go from one to two.
The first starts to drop with 18kHz -1 dB; -3 dB at a low 25 kHz.
The buffered option has -3dB at 55 KHz.
The first option is gorgeous. Natural.