Terman prototype

[jfetter]

I looked at Terman's circuit and put it in a feedback loop, very interesting FFT but H2 is maybe too low, only 10db higher than 3rd.
Thd is very low on the Terman so I sent out the board with capability of operating in all three modes described in Glen Richardson's 1952 inverted triode thesis. All of the circuits have data from very low voltages (zero) .

 

[disco]

I looked at Terman's circuit and put it in a feedback loop, very interesting FFT but H2 is maybe too low, only 10db higher than 3rd.
Thd is very low on the Terman so I sent out the board with capability of operating in all three modes described in Glen Richardson's 1952 inverted triode thesis. All of the circuits have data from very low voltages (zero) .

If THD is low enough there is nothing to fear Which tube did you research?

 

[jfetter]

Testing variations on it for a year or so.
The 6sn7 has similar fft to 12bh7.
12au7 is good only in one circuit topology.
12ax7 and pentodes awaiting full test.
12av7 is ugly with higher h3.
The variations using grounded grid are highest H2 and have to be throttled.

The thesis attached here.
"Inverted triode amplifiers " by Glen Arthur Richardson


I do not use the voltage reducing anode input.

 

[disco]

Interesting topology for a pre amplifier because of the low THD or for a compressor because of the possibly to reduce dynamics, making use of the non-linear area. From the text I took this setup. Do you have any recommendations for building an experimental unit?

 

[jfetter]

Use a sa/ne5532 opamp to drive the cathode, 1k buildout .
I used 700uA CCS on grid pull-up, 22k on anode to minus supply. (+-15v).
But the open loop thd is very low.

The output buffer is opa1622 headphone/line out.
Gain is optional on buffer.

I'm going to sea for two weeks so will have no internet.

-

 

[jfetter]

Look in this thread, has both GG and fft from your ckt.
Super Triode Connected (STC) chip amp

 

[disco]

Well, it's interesting but not very practical I guess. For my circuit in #4 it takes a lot of drive to swing that HV PS. Replacing Ci capacitors with a transformer would throw away the advantages of the circuit. Perhaps someday one would com back to build a compressor / limiter.