| Author | Message | ||
     steveh |
Hi, I've got a HD 130 combo that's been gathering dust for a year or so, and I've downloaded the schematics for it and got thinking about a potential Power supply mod which would reduce the very high voltages to the power tubes, to provide power amp breakup at lower volumes. The Power-supply uses a voltage doubler to supply about 560/700vDC (lo/hi power), which could be reduced to 280/350 by rewiring the voltage doubler as a bridge rectifier. If my understanding of the voltage doubler circuit is correct, then the PT should cope fine, since it needs to supply twice the required current into the voltage doubler, so effectively it will be running at 50% capacity with a bridge rectifier wired in instead. I guess I could even try some 6v6s in there, but I suppose it might need a different OT to work well. Think 6L6s should work OK. Are there any problems to stop this working? Has anyone tried it? Should be easily reversible if I don't like the results, and apart from some OT mismatch, I *think* it should work OK. Any comments appreciated! Steve | ||
| Steve Kennedy (admin) Username: admin Registered: 03-2002 |
The HV "doubler" circuit does TWO things, it provides the 700Vdc plate voltage and it also provides the 350Vdc control grid bias voltage. If you simply bypassed this circuit you would cut the plate voltage by half but you would lose the proper matching grid bias reduction. The Hi/Lo power selection switch already provides 1/2 the plate voltage but maintains the proper grid voltage without any modifications! Steve | ||
| steveh |
Hi There, Thanks for the reply. I've put this idea on hold for now, and have turned my attention to some other projects! Appreciate what you say about the screen grid regulation, will probably leave it stock for now! Steve |