VVR to 100 W Marshall 1959HW tubeamp ?

[harryk]

My customer is interested in to have a VVR to his Marshall which is a 100W tube amp. I have installed Danas fixed bias VVR-kits to many amps with success but they all have been maximum 50 W amps. A friend of mine installed VVR kit to his 100W Marshall but took one pair of power tubes away and put two mosfets in parallel to it. Has anybody tried two mosfet cofiguration with 100W amp and if so what happened? Harry

[UR12]

I know that some have used KOC's kit in a 100 watt amp by paralleling mosfets. My only concern is that without the mosfets being balanced, one may draw more current than the other and as they heat up the condition becomes worse to the point where one mosfet gives it up leaving the total load for the other. You would also need some serious heat sink and probably a fan if you can get it to work reliably

I am working on a design for a 100 watt amp with VVR but it won't be a kit that can be installed in any amp. The power supply will be completely different and the OT is a custom design also. I have the chassis and trannys already and hopefully this will be a winter project.

[harryk]

Hi Dana! I think that I have to test that 100W version in some test rig before I install it to any customer amp. My customer lives some hundred kilometers away from my home and it is not nice to repair a broken VVR-circuit in that case. Harry

[UR12]

Hi Dana! I think that I have to test that 100W version in some test rig before I install it to any customer amp. My customer lives some hundred kilometers away from my home and it is not nice to repair a broken VVR-circuit in that case. Harry

The VVR (single Mosfet) was tried in a 60 watt Komet with the mosfet just bolted to the chassis and was deemed unreliable when the amp was left on for 24 hrs at a time. I would test the crap out of it before I sent the amp off to someone far away.

[jaysg]

There's an expensive package in the ISOTOP vein, which is meant to dissipate gobs of heat...forget what it's called.

[edit]k...check this out:

[stoo]

KoC also uses "cascoded" mosfets in Series, I think he puts 2 high value 2 watters across them to balance the voltage. "course each mosfet needs it's own reference zener and gate stop.