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Old 11th October 2011, 12:19 AM   #31
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Location: Boulder, CO
Originally Posted by kmaier View Post
You're correct on both counts... and yes, the B+ will come up before the input and output tubes heat up. This will give you a surge on the filter caps (no load) so be sure the caps can handle the surge. I prefer to use either a 5V4G or 5AR4/GZ34 as they typically have a good 10 second delay before B+ builds up and it builds slowly. Your current draw is high for a 5V4G so I'd stick with the 5AR4.
Sorry to resurrect this thread, but I had my last 5AR4 do weird things (too much hum), so I'm thinking about using the solid-state rectifiers that I built in...

Won't the solid-state rectifiers also put a lot of B+ out before the tubes warm-up?

Any recommendations? Thanks! Dave
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Old 11th October 2011, 04:57 AM   #32
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Location: Warwickshire UK
Yes, the SS rectifiers will apply B+ instantly, and this may give problems.

The modern-production GZ34/5AR4 seems to be less than perfectly reliable, too - so many of us here use "damper" (efficiency) diodes - either 2 tubes in a full-wave rectifier, or paired with (eg) UF4007 SS rectifiers in a hybrid bridge.

The 6CJ3 and PY500A are examples of good rectifiers in this position. They not only delay the application of B+, but also cause it to appear very slowly across 30 seconds - meaning you don't get unpleasant surge currents, as well as protecting the signal-valves while their heaters/filaments warm up.

There's lots of different dampers to choose from - but please use Duncan's PSUD2 to find out the repetitive peak current in your power supply, to make sure the damper can handle it. But suffice to say, the diodes named above can cope with 500Vdc supplies with 50uF directly after the rectifier, and still be working years later. The reliability of dampers is much better than 5AR4s!
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