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21st Century Maida Regulator

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#261
Ah yes, output to ground diodes in the HP manual, and I agree it's a cheap CYA, and maybe the power amp output transformer and/or speaker load could cause the load voltage to go negative under some fault or shutdown circumstances.

I was thrown by the reference to the input to output diodes in the LM317. None of the app notes I have for that device show output to ground protection diodes.

Sorry for the confusion.
 
#266
The size of the heat sink depends on how much power is dissipated and how hot you want it to be. The key is to keep the junction temperature of the cascode device (Q1) below 150 ºC (preferably well below). I have a spreadsheet on my website for calculating the thermal resistance of the heat sink.

I usually go through Heatsink USA for my heat sinks. When I lived in Europe, I had good luck finding surplus heat links in the aluminum scrap bin at the local recycler.

For a while I used a heat sink for a Pentium PRO with my Maida Regulator. Power dissipation was about 10 W. The heatsink was rather hot (90 ºC) which is too hot for an external heat sink, but fine for an internal one.

As said above, the only requirement as far as the MaidaReg board is concerned is that the heat sink is flat so Q1 can be mounted to it without moving it from the board.

~Tom
 
#274
What about using your reg to feed a SALAS shunt reg?

Could it be the best of both worlds or a mess?

There were some folks speaking of success using a cap multiplier before the SALAS which made me think ...

ALSO, can your reg be used for lower voltages (40 to 50 volts)? This would be with Salas's jfet phono amp.

Thanks,
 
#277
Regulator #1 up and running. At 500VDC out and 540 Volts in, drift over 4 hours is 170mV. My Keithley 2015 measures around 230nV AC with the amp (PP UL KT88) running at higher than normal listening levels (12 inch leads to and from the regulator).

I don't have any high voltage scope probes so I don't have a safe way to measure noise but I am elated!
 
#279
Testing the remaining three regulators went off without a hitch - Residual ripple and noise was pretty much the same for the second 500V regulator - I didn't test the second set of regulators - don't have a suitable real world load at this stage but the output voltage was rock steady at no load in both instances.

Thanks Tom for a really well engineered regulator!

I read in several different posts that if one chooses to use a regulated B+ power supply, then one should do the same for the bias psu as well. The 21st Century Maida seems an overkill for a bias supply - any suggestions for a scaled down Bias regulator?

Jay M
 
#280
Depends on what you mean by "bias supply". For screen grid regulation, a 21st Century Maida Regulator would be well suited as the screens generally draw some current and need a good, stiff supply. However, deriving the screen supply from the regulated B+ should work well as well, albeit, with slightly lower performance.

For a negative bias supply, such as the fixed bias in my Damn Good 300B Amp (see my website), a zener regulator with an emitter/source follower works well. That could work for a screen supply as well. Note, however, that an emitter/source follower can only supply current in one direction (sink or source, not both). A CSS loaded emitter/source follower could work provided that the CSS can absorb any wiggle in the load current.

~Tom
 
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