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]

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]

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]

Re: Re: SRPP circuit question

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]

srpp circuit question

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]

Re: srpp circuit question

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]

srpp circuit question

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.

 

[Jonathan Bright]

Thanks. I'll try that.

 

[Poindexter]

Okay, I'm sorry that I missed the crucial beginning of this discussion.  I don't know why bruddah is getting 3% distortion out of this circuit, I never did in the worst case.

If he's putting an LED in the upper cathode circuit, maybe.  Why you guys do this stuff, when you have absolutely no idea what you are doing electronically, and then come and ask these poor dudes to diagnose your screwup?  In the SRPP, the DC resistance of that upper resistor being the same as the AC impedance, and the resultant phase shift being zero, is elemental to the circuit operation.  You voyage off into the swamp of ignorant experimentation, you are on your own, brah.

A possible explanation for the high distortion is the 6AQ5 tube type, examples of which in my experience have varied from moderately to hideously microphonic. I now use the 6T4, here's the current schem, in compact form:

The sound is the best I have made or heard; I will make one for you in a musical instrument grade build if you like.  If you want to build your own, I am at your service for advice, which is worth exactly what it costs.

Hurt me, hurt me!

Poinz

 

[oldeurope]

well known factor ...

Hello,
just for fun, calculate the "well known factor" for this stage.

Kind regards,
Darius

 

[regal]

Its very easy to convert an SRPP linestage to Sy's CCS loaded grounded cathode-cathode follower circuit. I saw THD drop from .22% to .03% by doing this conversion.

 

[oldeurope]

Re: well known factor ...

Hello,
just for fun, calculate the "well known factor" for this stage.

Kind regards,
Darius

Hey hey,
where are the "experts" here?

Darius

 

[Gordy]

Its very easy to convert an SRPP linestage to Sy's CCS loaded grounded cathode-cathode follower circuit. I saw THD drop from .22% to .03% by doing this conversion.

Do you mean SY's Heretic cathode follower, or a grounded cathode followed by a cathode follower? If the latter, which thread please, as I would like to learn?

 

[SY]

Gordy, if you need a little gain out of the Heretical, you can use a 1:2 stepup as the input transformer. If memory serves, Cinemag makes one.

 

[Gordy]

I'll take a look. Many thanks.

 

[pwgtang]

Is this still SRPP?

 

[kevinkr]

Is this still SRPP?

I believe it would be classified as an improved mu follower.. Similar circuits I have built gave gain equal to mu, and not PP operation characteristic of an SRPP.