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Old 11th November 2008, 03:34 PM   #21
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Rockgarden: No pics posted above. A 275-0-275 V xfrmr should be fine, as I started out with too high B+ for EL84's (I was using ss rectification). What rectifier are you planning on using?
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Old 12th November 2008, 02:54 AM   #22
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I'm not really sure yet...what's a good choice? I was thinking 5U4 GB.

Would SS rectification yield a punchier amp?

Cheers!
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Old 12th November 2008, 04:51 PM   #23
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There are folks here that swear by SS rectification, and others that swear at it.

There are lots of opinions here as to which sounds better, but I don't have one because all of my amps use SS rectification.

Do a search, you'll find lots of opinions. If you choose SS rectification, you'll drop less volts, and you can use very inexpensive diodes or splurge and use FREDs for like $1-2/ea. SS rectification yields an "instant on" B+ which may lead to cathode stripping of your tubes but many folks here don't consider that an issue for B+'s less than say 1KV. This can be another heated discussion on the forum. Tube rectification gives a soft start B+ which is a little easier on the tubes.

FRED's are soft recovery diodes, producing less switching spike noise than conventional SS diodes so in my opinion are worth it, but I'm still a newbie.

The best approach IMHO is to get yourself familiar with PSUDII and develop/model either a SS or tube rectified PS that has low ripple, no ringing, and the desired B+. If you want to use tube rectification, PSDUII will steer you clear of using too much capacitance for your chosen rectifier tube.
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Old 13th November 2008, 03:09 AM   #24
chrish is offline chrish  Australia
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5U4 GB gives a very large voltage drop (around 50 volts from memory). It is also a directly heated rectifier, so it has a fast warm up time.

If you need more B+, maybe try a GZ34 (5AR4). Less voltage drop and slower warm up time.

Cheers,

Chris
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Old 13th November 2008, 03:39 AM   #25
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I'll second what Chris said about the 5U4. In my limited experience I prefer the 5AR4 for its slow start and lower voltage drop. I guess I might consider using a 5U4 if I needed a lot of current, say more than 200 mA or so.

Solid state rectifiers are cheap and easy to implement. Maybe consider throwing in a couple CL90 or CL80 inrush limiter devices to help soften the startup a bit.
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