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Old 4th June 2009, 12:59 AM   #1
alexg is offline alexg  Philippines
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Default 5u4g input capacitor

I have checked the datasheet for 5u4g and I find two values for input capacitor, one says maximum of 4uf , and one says 32uf

I needed the higher value so I can get around 420VDC on my B+.

Is it safe to use 30uf?
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Old 4th June 2009, 02:07 AM   #2
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Depends on the transformer winding resistance. Use PSUD from duncanamps.com to see if the repetitive peak current is within the tube's rating. With a wimpy transformer, 100 uF would be fine. With a low DCR 9considerably oversize...), 4 uF may be it.
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Old 4th June 2009, 04:37 AM   #3
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Note that the 4 uf is a "typical operation" value not a maximum. In the RCA
receiving tube manual (1950) they have typical capacitance at 10 uF, but then
show a circuit for a 25W 6L6 AB1 amp which has a 5U4-G followed by 40 uF.

As was noted, the real maximum limit is the instantaneous current, which
for this tube is around 2.3 amps, so the real limit depends on the plate-to-plate
impedance through the transformer.
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Old 4th June 2009, 05:25 AM   #4
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Default Re: 5u4g input capacitor

Quote:
Originally posted by alexg
I have checked the datasheet for 5u4g and I find two values for input capacitor, one says maximum of 4uf , and one says 32uf

I needed the higher value so I can get around 420VDC on my B+.

Is it safe to use 30uf?
Depends on how much current you're pulling, and how much ripple you can stand. Why use a 5U4G anyway? The 5U4GB has a much higher Isurge rating.
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Old 4th June 2009, 05:33 AM   #5
alexg is offline alexg  Philippines
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Default Re: Re: 5u4g input capacitor

Thanks for the enlightening replies.


Quote:
Originally posted by Miles Prower


Depends on how much current you're pulling, and how much ripple you can stand. Why use a 5U4G anyway? The 5U4GB has a much higher Isurge rating.
I will be using it on a direct coupled 5842-2a3 SE amp. I was thinking that the ST bottle of the 5u4g will look good with the 2a3.

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