[538] Stabilized Thermionic Amplifier

Date: October 16th, 2009 | Comments : [2] | Categories: DIY.

Tube Mu-follower

This is one of the designs in a vacuum tube amplifier patent filed in 1949. The first gain stage (V1 & V2) forms a type of mu-follower.

You can download and read the entire patent to find out more about this circuit.

The circuit can be converted to work with jfets, as shown here. Use 1M for R1 and R3, 1k for R2 and a 5k trimpot for R4.

The trimmer should be adjusted until the dc voltage at the source connection of Q2 is 5.0v (+/-0.5v). Start with it set for about 1k between the wiper and Q2’s source.

The circuit has a lot of gain, so it may not be a totally clean boost, as it can run out of headroom rapidly when powered by a 9v battery. If you try this design, let me know your results.


2 Responses to “Stabilized Thermionic Amplifier”

[870] RnFR Says: 11:39 am, November 28th, 2009

hey jack!

have you tried modding the whole series mu amp circuit above for FETs? i know that there are similar circuits out there, but just wondering if you had tried this one in particular.it looks to be DC coupled, which i find interesting. also, i have been having some fun lately with cascode circuits. very flat freq response, great for boosts. have you ever experimented with cascodes?

[871] admin Says: 5:45 pm, November 29th, 2009

I did breadboard the version shown above but nothing else yet from the patent.

regards, Jack


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