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Old 23rd Sep 2020, 7:24 pm   #96
AdrianH
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Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,567
Default Re: Hope to start an audio amp with CV415/CV4046/TT15

I have read several comments on the EF91 like that in this thread and to be honest the only time I had the issue was down to the amp self oscillating at 1.25MHz, once that was cured they are fine, I am not finding them microphonic, I can tap them and they do not ring in the speakers when I last did a measurement of peak signal to noise I obtained a reading of 74.6dB. The measured distortion on my last test with the amp was 0.2% at something like 5 Watts output.

Is it Hi-Fi, no I guess not, but this project has already achieved something for me, building something with odd-ball valves that seems to work. I put it down to the Millar/Radford design and good transformers. By the way the EF91's in use are in fact CV4014/M8083's which are a military version and from the National Valve Museum's page is this comment:-

"The M8083 is a special quality version of the EF91. The M8083 has a more rugged build than the EF91 and was designed for applications where vibration during operation was unavoidable and where the performance could be predicted when subjected to such vibration. The obvious application is mobile communications especially military."

Still awaiting some steel to make my final PSU chassis which should give me the required HT to have over 10 Watts audio, I hope?

Adrian
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