[MRCA] Configuring solid-state subs for HV Rectifiers

[Ray Fantini]

Don’t think it makes any difference, I use to replace tube rectifiers with solid state all the time but lately tend to want to use the original tubes. On transmitters you often get additional HV with solid state replacements and on things like receivers you can have a good amount of additional B+.
Have seen where on things like the T-368 you can cook R4 and the clamp tube real good with increased HV, but then again know too many who had that transmitter and wanted to squeeze out every watt and solid stating the power supply will give you more power. If you were thinking of the amount of ripple that the filament transformer interduces look at it this way, on a T-368 they chug along at around 3,000 volts across the filter capacitor. HV supply ripple would be about 5% or 150 volts the 2.5 volts the filament transformers interduce would be about 0.01% so don’t see any advantage there along with on the T-368 the filament transformer makes a nice tie point for the HV line to the filter.
Between the original plate transformer being designed for 117 VAC and now at 125 VAC developing additional voltage and another fifty or hundred volts from Solid State replacements just makes things worse.
On receivers and low power devices where there were 5Y3, 5U4 and 6X4 you also have an additional advantage of a time delay when the tube comes up to temperature where when you solid state that stuff you will find that often you get almost twice the regular amount of B+ until the rest of the tubes come up so that’s an additional stress on everything.
Sometimes think that B+ can be like blood pressure to the extent that it may not be the direct result of component failure but a huge contributing factor and often you will find that things work just as well at a ten to twenty percent reduced voltage. Don’t get me wrong, remember a bunch of years ago a thing about running command set receivers at nine volts and the like but I always thought that was a bit extreme but have no issues running a +250 volt bus at +200
And as a final thought I think twenty years ago I had some weird idea that maybe we would run out of things like 5Y3 and 6X4 tubes but if anything its almost like the opposite, got more NOS 6X4 tubes then I know what to do with.

Ray F/KA3EKH



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Sent: Monday, September 11, 2023 7:22 AM
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Subject: [MRCA] Configuring solid-state subs for HV Rectifiers

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This question may be rhetorical in nature and I should have put it to rest a long time ago. Nonetheless,
when directly substituting mercury vapor rectifiers with plug-in SS substitutes like the STBR3B28, et al, is it necessary or desirable to ensure that the HV take off is not wired to the original filament pin that would require the HV to pass back through the HV transformer filament winding?  I know the winding has insulation for the HV and not the issue.
Fact is, I've always simply plugged them in and they work.  Much about nothing?  TNX
Jeep K3HVG
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