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In Reply to: RE: Dual 5AR4 input capacitance posted by gkargreen on September 16, 2016 at 17:07:39
That 20 μF. cap. will be perfectly safe. Look at the 5AR4 data sheet. The type can take up to (sic) 60 μF. Your amp has 2 5AR4s too boot. :>)
What could be a problem is today's higher average AC mains voltage. Close on the WVDC is OK, but don't exceed the rating under "routine" operating conditions. Remember, some surge headroom is available. BTW, AA sponsor Jim McShane shows a 100 μF. X 100 μF./500 WVDC clamp mount part. If that part fits your chassis opening, you are good to go.
Eli D.
Follow Ups:
Thanks, Eli, that is most appreciated! The plan is to use those clamp in caps for the power supply as the two poles in each channel and then wire in the remaining two poles which are fairly small capacitors, just as you suggested!
Randy
I have five of these amps and they are fantastic.I use a 30uf at 600v poly but you can go 700v but it's not necessary.It doesn't reach anywhere near the 600v but you can use a 30uf at 630v solen or a 30uf at 700v wima.
This amp has over 500v even after the choke so the 500v caps are being over voltaged a bit..The AC voltage when the amp was made is lower than it is today.You can also use the Authenticaps which are 550v and 600 surge and I'm going to be using them in mine.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Thanks, Michael! Yes, it looked to me that the voltage is high for those cans, so Authenticap make ones at higher voltage? BTW, this particular amp is a bit of a wreck, it is all there, but dirty and half in pieces as the owner tried to do a half-ass resto and gave up, that is where I am taking over. Do you know where or do you have any pcb-mount 9 pin sockets that have the ground pin on the side for the tube shield? The ones on the boards are pretty corroded. Also, I was talking to a friend at the meet and he really thinks the amp is shit because of the implementation of the paraphase inverter, what do you think? Thanks, Randy
Paraphase splitters do have issues. BFD. If the "iron" is decent, tweaking the signal path topology is easy enough.
Look at the schematic. Way more open loop gain is present than that required by modern digital sources. You degrade S/N performance by attenuating the driving signal at the I/Ps.
I suggest you switch to Mullard style circuitry, with an EF86/6267 voltage amplifier and a 12AY7 as the LTP. Please notice that no additional burden is being placed on the power trafo filament winding. Definitely use a 10M45S CCS in the LTP's tail.
Eli D.
Eli
Draw something up if you get time and maybe address that over voltage in the power supply you can.The power trafo does make a nice omelette cooker after it's on for 3 or 4 hours ..LOL
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Bringing the B+ rail voltage down is easy. Use 5R4s, instead of 5AR4s. Slightly "soften" B+ rise with a CL-90 between the rectifiers and the PSU filter.
Like the KB85, the original Mullard 5-20 employs self biased "finals". Replace R8 with a 10M45S CCS. McShane has New Sensor made 12AY7s.
BTW, Mullard's schematic does not show "death caps." and the KB85 does. The "death caps." must go and a proper, 3 wire, safety grounded, power cord installed.
Eli D.
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