Voltage Doubler Question

dorrisant · Post by **dorrisant** » Sat Jan 21, 2017 8:31 pm

I have a question about the use of the MOSFET B+ Reducer with a voltage doubler...

In using the B+ Dropper, you have to interrupt the rectifier circuit ground path and insert the Dropper. I just want to make sure I'm wrapping my mind around the theory of use.

Question is... If you look at the schematic below, is the red circle next to the rectifier diode the insertion point for the dropper in a voltage doubler? Just want to make sure it is before surgery...

martin manning · Post by **martin manning** » Sat Jan 21, 2017 9:34 pm

Almost... see below.

dorrisant · Post by **dorrisant** » Sat Jan 21, 2017 9:37 pm

Ok... Thanks Martin.

Looks like I need to insulate the MOSFET from the chassis in this case.

I was hung up on thinking this had to go directly to ground. The way I was thinking, would have pulled the reservoir out of balance even if it would have worked... I see your solution would affect both sides of the rectifier equally.

martin manning · Post by **martin manning** » Sat Jan 21, 2017 9:42 pm

martin manning · Post by **martin manning** » Sat Jan 21, 2017 10:38 pm

Tony, my solution still puts it out of balance (reduces voltage on one reservoir only), so your way is better- no drain voltage to isolate. I don't think being out of balance is an issue.

mrn1ngstr · Post by **mrn1ngstr** » Sat Jan 21, 2017 11:01 pm

Martin can you explain whats happening in this circuit?

dorrisant · Post by **dorrisant** » Sat Jan 21, 2017 11:02 pm

martin manning wrote:Tony, my solution still puts it out of balance (reduces voltage on one reservoir only), so your way is better- no drain voltage to isolate. I don't think being out of balance is an issue.

Ok now I'm confused...

Are you saying that my original insertion point should work?

martin manning · Post by **martin manning** » Sat Jan 21, 2017 11:14 pm

dorrisant wrote:Are you saying that my original insertion point should work?

Yes, sorry for the confusion. It will work either way, and I ran a simulation to make sure!

martin manning · Post by **martin manning** » Sat Jan 21, 2017 11:39 pm

mrn1ngstr wrote:Martin can you explain whats happening in this circuit?

Voltage doubler or B+ reducer?

dorrisant · Post by **dorrisant** » Sun Jan 22, 2017 3:44 am

Thanks for the clarification Martin...

mrn1ngstr wrote:Martin can you explain whats happening in this circuit?

Dropper topic is here, if that's what you're asking about...

https://tubeamparchive.com/viewtopic.php?t=27035

dorrisant · Post by **dorrisant** » Mon Jan 23, 2017 9:01 pm

Just to update... I inserted the dropper where the red circle is (see schem in OP) and it works perfectly. This was without isolation between the MOSFET and the chassis too.

Thanks again Martin!

martin manning · Post by **martin manning** » Tue Jan 24, 2017 12:28 am

Sure, this was interesting. Thinking about it some more, probably the best place to put the FET is between C8a and C8b (that is if they are separate), and moving the filament CT ground over to keep it grounded. I say this is best because in this case the voltages on C7 and C8a will be the same.

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