SRPP circuit question

[pwgtang]

Question: for a srpp circuit if the the top triode cathode use LEDs
for bias instead of resistor,can we still call it srpp?Thanks.
Paul

[kevinkr]

Originally posted by pwgtang
Question: for a srpp circuit if the the top triode cathode use LEDs
for bias instead of resistor,can we still call it srpp?Thanks.
Paul

While it will work from a dc perspective from the ac perspective the grid and cathode of the upper tube are virtually shorted together by the led's low dynamic impedance. I suspect it would not work too well.

[oldeurope]

Originally posted by pwgtang
Question: for a srpp circuit if the the top triode cathode use LEDs
for bias instead of resistor,can we still call it srpp?Thanks.
Paul

In this case the bottom triode has ri of the top triode as a load.
In the srpp it has Rk x µ + ri. This should be much higher.

ri = internal dynamic resistance of the (top) triode
Rk = cathode resistor
µ value of the top triode

Kind regards,
Darius

[kevinkr]

Originally posted by oldeurope


In this case the bottom triode has ri of the top triode as a load.
In the srpp it has Rk x µ + ri. This should be much higher.

ri = internal dynamic resistance of the (top) triode
Rk = cathode resistor
µ value of the top triode

Kind regards,
Darius

I.E. The plate of the lower triode is looking directly into the cathode of the upper tube in series with the small dynamic resistance of the led, not a good load.. Pretty close to a short. (low impedance)

[pwgtang]

I am asked because I had build a preamp used 6AQ5 tubes looks
like Moebins 6AQ5 line preamp, I am not to happy with the distortion,about 0.25 at 3vrms output 1khz,I try to replaced the top resistor with LEDs and the distortion drop to 0.05 and the output V drop 1.5db.Frequency response and inpedence about
the same.This preamp only had 3.2 times gain.

[kevinkr]

Originally posted by pwgtang
I am asked because I had build a preamp used 6AQ5 tubes looks
like Moebins 6AQ5 line preamp, I am not to happy with the distortion,about 0.25 at 3vrms output 1khz,I try to replaced the top resistor with LEDs and the distortion drop to 0.05 and the output V drop 1.5db.Frequency response and inpedence about
the same.This preamp only had 3.2 times gain.

Schematics would help as well as other details, perhaps you need a lot more B+ and/or different operating point.

[Eli Duttman]

Mœbius is a Poindexter design. The schematic is here.

Poindexter's home page is here.

[pwgtang]

That is it. The 82R replaced by LEDs.

[Jonathan Bright]

Look, this is a technical question about accessing the circuits posted on this thread. I have the parts and intend building an SSRP circuit. I am interested in any modifications people come up with but when I download the circuit Eli put up in Post#7 I find I can't read it properly, some of the lines are missing. This happens often. So how can I download it and then expand it to make it readable? I'm sure my 2Oyr old daughter can fix it but she's in Paris this week.............and I'm not!

Jonathan

[ray_moth]

What I do is hover the mouse pointer over the diagram and eventually an 'expand' box appears in the bottom right-hand corner. I click on that and the diagram expands to its full size.