Great point. I need to fuse before the switch. Thanks.trobbins wrote:My concern was that the FET drain is connected to chassis through the FET package rear metal (as I can't see an insulator pad). If that is the situation, then the FET source-drain is in parallel with the fuse - so the fuse won't function as intended for protection.
MOSFET B+ reducer
Moderators: pompeiisneaks, Colossal
Re: MOSFET B+ reducer
I build and repair tube amps. http://amps.monkeymatic.com
Re: MOSFET B+ reducer
Dorrisant - Did you ever try this? Can anyone verify that this does indeed work with a non-center tapped full wave bridge setup?dorrisant wrote:Could this be used with a TX that has no center tap?
Full wave rectifier produces too low of a voltage... appox 244vdc.
Full wave bridge rectifier produces too high of a voltage... approx 485vdc.
Looking for about 340vdc but it could be higher. I could drop it after the reservoir cap. Just wandering if this method would be appropriate here, or am i pissing up a rope. I really don't want to change out the PT... and learn a vital lesson at the same time.
Tony
I don't see why it shouldn't, but....
Working on a salvage build right now and pretty sure I'm going to end up ~50vdc on the high side.
Deric®
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martin manning
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Re: MOSFET B+ reducer
Yes this technique will work for reducing the B+ from a FWB rectifier.
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dorrisant
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Re: MOSFET B+ reducer
Yes I did try it and yes it works as Martin said.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: MOSFET B+ reducer
A big thank you to dorrisant for the nice PDF and DIYLC documents for the MOSFET B+ reducer, posted at top of thread.
I build and repair tube amps. http://amps.monkeymatic.com
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dorrisant
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Re: MOSFET B+ reducer
Thank you Xtian for stirring up this topic... much needed.
Also, just glad to contribute!
Also, just glad to contribute!
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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dorrisant
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Re: MOSFET B+ reducer
I had some boards made... PM me if you are interested.
If anyone is offended, I will delete this post and move it to the FS section.
If anyone is offended, I will delete this post and move it to the FS section.
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"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: MOSFET B+ reducer
Awesome! Not offended!
Can we tackle the VVR for fixed bias next?
Can we tackle the VVR for fixed bias next?
I build and repair tube amps. http://amps.monkeymatic.com
Re: MOSFET B+ reducer
I considered doing this but again held off as a courtesy to Dana who piped up when this discussion was started.xtian wrote:Awesome! Not offended!
Can we tackle the VVR for fixed bias next?
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dorrisant
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Re: MOSFET B+ reducer
Someone is already doing it...Colossal wrote:I considered doing this but again held off as a courtesy to Dana who piped up when this discussion was started.
http://grangeramp.com/shop/index.php?ma ... cts_id=567
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: MOSFET B+ reducer
Thanks for the Granger tip! Pretty good kit price.
I build and repair tube amps. http://amps.monkeymatic.com
Re: MOSFET B+ reducer
Yeah, he's been doing it for a while. There are a few other guys out there as well.
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dorrisant
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Re: MOSFET B+ reducer
Further question for the brains...
How would you apply this circuit to a voltage doubler? Or did I just spin for a whammy?
The CT is the usual insertion point. Without a CT, the rectifier ground is the insertion point.
With a voltage doubler as in the Fender Twin 135w UL...
The rectifier is grounded. The high voltage CT is fed to the voltage divider/balancer floating at half of HT to ground. Would you insert it at the rectifier ground or just don't use it?
I'm a bit confused here.
Tony
How would you apply this circuit to a voltage doubler? Or did I just spin for a whammy?
The CT is the usual insertion point. Without a CT, the rectifier ground is the insertion point.
With a voltage doubler as in the Fender Twin 135w UL...
The rectifier is grounded. The high voltage CT is fed to the voltage divider/balancer floating at half of HT to ground. Would you insert it at the rectifier ground or just don't use it?
I'm a bit confused here.
Tony
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martin manning
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Re: MOSFET B+ reducer
You would insert the reducer between the negative side of the bridge and ground. The CT will be at the half-way point between the B+ and the negative voltage at the FET source (not at half of B+), so you can't connect it to the center of the cap stack. I would use balancing resistors (which are already there in the schematic shown), and leave the CT unconnected.