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Historic Harmonica Amplifier
Historic Harmonica Amplifier
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Old 3rd April 2013, 04:42 AM   #11
gingertube is offline gingertube  Australia
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Location: Adelaide South Oz
The local "Hysterical" Radio Society to the rescue with a useful index.

Last edited by gingertube; 3rd April 2013 at 04:45 AM.
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Old 22nd July 2017, 05:40 PM   #12
jfetter is offline jfetter  United States
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Location: North Houston
Historic Harmonica Amplifier
Originally Posted by gingertube View Post
For your possible interest.

I have this amp on my bench for repair. The lady who brought it to me says it was her grandpa's Harmonica Amp and would like restored. Did a circuit trace. Very interesting tone control, treble boost/cut by feedback around the output tube. I looked up the tone control in RDH to find that the entire design is a 1942 W.N. Williamson design, Yep same Williamson who did the famous (well certainly the most copied) HiFi Amp design. Could have saved the circuit trace effort if I had know that up front.
6J7 triode mode to 6J7 pentode mode to 6V6 with an 80 rectifier. Lamp in standby switch line as a HT fuse.


I'm going with the THd Univalve modded similar to your 1942 but adding a pentode(screen/suppressor linked/triode mode) front end.

That is a nice unit schematic, shows someone loved it.

Truth is found in the simple, not complex.
-Sir Issac Newton.
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Old 23rd July 2017, 07:15 AM   #13
PRR is offline PRR  United States
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Location: Maine USA
> scan of all of Radio TV and Hobbies

{much later}

American(!) Radio History has part of 1939 to 1947:
RADIO & HOBBIES; Australian hobbyist magazine

W.N. Williams article:
http://americanradiohistory.com/Arch...es-1942-06.pdf --page 21 of 5MB PDF
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