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I'm finally getting around to completing a project I got some advice for here quite some time ago. I am improving the PS for some Bogen MO-30A's and want to make sure I'm not creating a problem such as ringing. The Bogens use PP 7868's with a 7247 for input/driver.
The original PS used two 40uF caps for the voltage doubler feeding B+ and another 40uF for the Screens. I am now planning on using two 50uF for the V Doubler, then a 1H 50 ohm choke, then 100uF for the B+ reservoir, and 50uF for the screens. The 50 ohms of the choke will help reduce voltages which are a little high, presumably from higher line voltage.
Without making anyone go to the trouble of modeling can anyone tell off the top of their head if it looks reasonable? Since this is a mono-block would 50uF after the choke be adequate? Would two 100uF for the doubler then 50uF after the choke cause ringing or require inrush limiters?
Thanks in advance,
Gary
Follow Ups:
Talk to AA sponsor Jim McShane. He's expert at improving voltage doubler PSUs. Back when your Bogens were new, really large caps. for doubler stack service were very costly and physically large. Modern etching techniques have IMPROVED the volumetric efficiency of 'lytics and at much more favorable prices.
You should be able to safely increase the doubler stack capacitance, considerably. Part of the total package is the installation negative temperature coefficient (NTC) inrush current limiting thermistors. Among other things, the thermistors prevent power transformer clanging, at unit power on.
Eli D.
Eli,
would you post a link or description of what thermistor you would use? I have been wondering for some time specifically what to buy. Thanks. JH
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Here you go.
The first column is the model #
The second column is the resistance at turn on
The third is max current
Then go to the right and pick the % of max current
that your amp pulls and that will be the resistance
after warm-up of the thermistor.
DanL
PS if you want a bigger version post me
and I will send it to you. It shrank 8^D
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you should use those in both legs of the AC primary to the transformer. Or is one ok? I have done both.
Pete
You can, but it is no different than putting 2 in series. The bottom leg of the primary is really going to ground, there is no balancing of the load.
Pete
I use the CL-90 which has 120 ohms at start-up
then goes down to about 2 ohms afterwards.
With the CL-90, one is all that is needed.
DanL
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This should be fine for the MO-30, as I wold expect to draw less than 1A (CL-90 is rated 2A max). I often can use a smaller fuse after installing an inrush limiter, as original was oversize to handle inrush current.
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