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previous: Charles >>The mods aren't used because the ... -- 9/8/1997 5:37 PM

Re: rectifier diodes

9/9/1997 10:25 AM
Bruce	Re: rectifier diodes Charles... Bruce here again, Yes it does effect the power supply voltage.... but in a positive way! Yikes... no pun intented. The diodes drop the AC voltage ahead of the rectifier tube by an insignifcant amount..... The amount of the voltage drop across the SS diode junction. .6v .7v or so. Big deal. But it does give the whole power supply and filter section a leg up on the ripple effect and now the rectifier tube's anodes sees only positive going voltage too. I can see on my scope a difference in the ripple with the diodes ahead of the rectifier tube. Maybe it has something to do with the additioanl voltage drop the tube has and it acts like a nother filter section or something. I bet that makes life easier for the tube too. This little mod the RG is talking about is a must (IMO) for anyone using 6V6 tubes in a DIY amp. Those new 6V6's seem to blow up real easy with anything over 375V to 425V. I put the diodes in EVERY amp I fool around with because it is transparent in sound and assures that no AC can get to the filter caps and power tubes, .etc .etc. I also put a diode after the smoothing choke or first dropping resistor to keep the power amp from pulling current (under a big load) from the rest of the power supply caps. Sounds silly, but try it. That mod does make a little difference in sound, but I like what it does. ************************************** By the way RG, Have you read all the stories about bypassing the Hi voltage diodes with a hi ohm resistor and .01 cap...etc? 220K-470K .01 ?? I read a great article in one of my older ham radio rags about the futility of that and how it makes absolutley no differnce with modern SS diodes, execept to make sure the diodes see the same voltage divide across the resistors. But totaly unecessary and a waste of good parts. Hence the reason some prefer to use 3 diodes in series I think. I use 2 in each leg myself. But on BIG homebrew RF amps at 4000 V @ 1 amp I've used 6-8 diodes (each leg) in a voltage doubler to be safe. I used one 1n4007 diode in test jig of mine and tried like crazy blow the diode up at 800 VDC through a big huge 650ohm ceramic tube type resistor to ground and could not do it. Yes the tranny dropped a ton of voltage, but I still could measure close to 600 VDC on the resistor. That was close to 500 watts DC!! In one teeny SS diode! Remarkable! Why three? Probably the peak reverse voltage scare thing? another novel... Bruce

9/9/1997 10:25 AM

Bruce

Re: rectifier diodes

Charles... Bruce here again,
Yes it does effect the power supply voltage....
but in a positive way! Yikes... no pun intented.
The diodes drop the AC voltage ahead of the
rectifier tube by an insignifcant amount.....
The amount of the voltage drop across the SS
diode junction. .6v .7v or so. Big deal.
But it does give the whole power supply and
filter section a leg up on the ripple effect and
now the rectifier tube's anodes sees only
positive going voltage too.
I can see on my scope a difference in the ripple
with the diodes ahead of the rectifier tube.
Maybe it has something to do with the additioanl
voltage drop the tube has and it acts like a nother
filter section or something.
I bet that makes life easier for the tube too.
This little mod the RG is talking about is a must
(IMO) for anyone using 6V6 tubes in a DIY amp.
Those new 6V6's seem to blow up real easy with
anything over 375V to 425V.
I put the diodes in EVERY amp I fool around with
because it is transparent in sound and assures
that no AC can get to the filter caps and power
tubes, .etc .etc.
I also put a diode after the smoothing choke or
first dropping resistor to keep the power amp from
pulling current (under a big load) from the rest
of the power supply caps. Sounds silly, but try it.

That mod does make a little difference in sound,
but I like what it does.
**************************************
By the way RG, Have you read all the stories about
bypassing the Hi voltage diodes with a hi ohm
resistor and .01 cap...etc? 220K-470K .01 ??
I read a great article in one of my older ham radio
rags about the futility of that and how it makes
absolutley no differnce with modern SS diodes,
execept to make sure the diodes see the same
voltage divide across the resistors. But totaly
unecessary and a waste of good parts.
Hence the reason some prefer to use 3 diodes in
series I think. I use 2 in each leg myself.
But on BIG homebrew RF amps at 4000 V @ 1 amp I've
used 6-8 diodes (each leg) in a voltage doubler
to be safe.
I used one 1n4007 diode in test jig of mine
and tried like crazy blow the diode up at 800 VDC
through a big huge 650ohm ceramic tube type resistor
to ground and could not do it. Yes the tranny
dropped a ton of voltage, but I still could measure
close to 600 VDC on the resistor. That was close
to 500 watts DC!! In one teeny SS diode! Remarkable!
Why three?
Probably the peak reverse voltage scare thing?

another novel...

Bruce

Replies:

R.G. Actually, there are two ways to do ... -- 9/12/1997 4:54 PM