Filament voltage

m17xr2b · 1237

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Offline m17xr2b

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on: July 18, 2017, 04:03:37 AM
Hello,
After much tinkering with the BeePre to install the balanced transformers I now want to fix the filament voltage. The 300B spec is 5V and I would like to get exactly that.
I previously had 5.13 and 5.12 which I believe is what causes my slight hum. I have replaced all the transistors and now I have 5.07 and 5.11 so getting closer.
All my resistances and voltages are within spec using 230V exactly from the P5. Any suggestions?


Offline Paul Birkeland

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Reply #1 on: July 18, 2017, 05:21:09 AM
A slight hum can happen if there isn't enough voltage going into POS IN to allow the regulator to operate properly.  There isn't anything wrong with having 5.12V, that's less than 3% off from spec, and anything within 5% is well on target.  You can drive yourself a little crazy trying to get exactly 5V, and there isn't a performance reason to do so.

If you are able, bumping up your line voltage to 240V may provide some extra regulator compliance.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

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