300B filament voltage

rkoonce · 5259

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Offline rkoonce

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on: September 14, 2024, 10:40:06 AM
Greets!  Thanks for adding me to the forum.

I have a Bee Pre 300B in my shop for repair.  It was non--functional when I got it.  Not knowing its history, I elected to replace all of the electrolytic caps before I started.  (Owner had a vague story about a 300B getting plugged in wrong and I had some burned resistors on the volume control, the updated attenuator version).  On first test with no tubes inserted, one 300B had 10VDC across the filament pins and the other one was 16VDC.  After some voltage testing with the 6BQ5s in their sockets, I deduced that the regulators on one channel are dead, shorted transistors.  I elected to replace all of the transistors and regulators.  Now, both 300B sockets have 16VDC across them. The schematic shows 10V.   I hesitate to plug in a 300B with this situation to add a load.  What should the unloaded voltage be on those two sockets?

TIA

Ray



Offline Paul Birkeland

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Reply #1 on: September 15, 2024, 08:17:14 AM
Do you have 300Bs in when you are doing this testing?  The BeePre 1 is filament biased and the ~10V or so that is produced on the low voltage filament boards is divided in half by the two 10W resistors up front on each side and the 300B filament itself. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man