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Old 1st May 2004, 09:34 AM   #1
hacknet is offline hacknet  Singapore
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Default Push Pull Power supply. to Tube or not to?

i am in the process of planning a 6L6 acrosound power amp.

in the original schematics, it using a 5u4 to rectify with a CLC of 20uf and 8H.

i was looking forward to an opinion if tube rectifiers were the way to go. i was wondering if a solid state alternative was better? i was thinking along the lines of selenium stacking soft recovery diodes or something fancy like that.

the other thing being that the original schematics implements a CLC. i was wondering if a LCRC was better since LCs tend to have better line regulation.

i`m putting punchy bass as top piority and sweet vocals in second. what would you do?

Thanks a million!
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Old 1st May 2004, 12:07 PM   #2
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I'm sure there will be opinions for both SS and tube rectification. I will venture with a personal opinion and that would be to stay with the original setup with the 5u4 tube. I feel the sound of the tube is warmer than the SS rectifiers are. I have tried both in several amps and still manage to go back to the tube. If you need a 5U4 I can send you one.


Joe
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Old 1st May 2004, 01:15 PM   #3
SY is offline SY  United States
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Selenium is the worst possible choice. If you go solid state, modern silicon rectifiers are the only viable option.

Tube rectification puts out a lot of heat, has lower reliability and worse regulation than solid state, and has a high voltage drop. But it has a built-in slow start and looks cooler. Take your choice.

For punchy bass, it strikes me that you want the lowest PS source impedance and that means silicon. A plain vanilla CLC filter will work fine- the push-pull amp gives you plenty of ripple rejection.
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Old 1st May 2004, 01:30 PM   #4
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Default DELETE SELENIUM FORM MEMORY...

Hi,

Quote:
Tube rectification puts out a lot of heat, has lower reliability and worse regulation than solid state, and has a high voltage drop.
Than there's the hybrid rectifier giving you lower voltage drop than a tube rectifier alone (it's a bridge after all) with the slowstart of the tube still there and no nasty turn off peaks.

Add a CLC filter with a big L, biggish C for the last cap, yet well decoupled with plenty of MKPs and you'd have all the slam you'd ever need provided the OPTs are up to par.

Voila, slam dunk accomplished.

Cheers,
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Old 1st May 2004, 03:31 PM   #5
hacknet is offline hacknet  Singapore
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sounds cool...
i couldn`t find much literature thou.

whats the factor that i have to use to calculate the output voltage from the trans.

eg, solidstate bridge is 1.414, a full wave is 0.6. whats this number for a hybrid?

Burntfingers: Thanks for the offer, it might be cheaper to buy a current production 5u4s than shipping. Thank You for asking!

Thanks! you help is much apreciated
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Old 1st May 2004, 04:12 PM   #6
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Hi,

Quote:
eg, solidstate bridge is 1.414, a full wave is 0.6. whats this number for a hybrid?
Yes, for a capacitor input filter this is roughly what you get.

With the hybrid you can use the formula as per the Graetz FWB minus the voltage drop across the diodes of the tube.

Depending on voltage, current draw and the tubes used this can vary from say 30 to 60 Volts loss so pick a transformer accordingly.

Cheers,
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Old 1st May 2004, 04:18 PM   #7
hacknet is offline hacknet  Singapore
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okay.
thanks!

would paper in oil motor run caps do a better job than polyprop?

since the circuit demands only 20uf as the first cap, i was thinking of a motor run 1st cap with a 10H choke with a 330uf 2nd cap parrelled with a mkp.
is this good?
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Old 1st May 2004, 04:30 PM   #8
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Hi,

Quote:
is this good?
I think so, yes...The choke will swamp the difference IMO.

Cheers,
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Old 1st May 2004, 09:03 PM   #9
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Current production Russian and Chinese 5U4Gs are VERY BAD. All sorts of problems have been reported, including arc over at start up when used in circuits well within specs. The "new" Russian 5U4GB MAY be OK; otherwise stick to NOS 5U4s.

Directly heated vacuum rectifiers, like the 5U4, turn on almost as quickly as SS diodes do. Therefore, they WILL cathode strip IDH power tubes like the 6L6.

Cree high PIV Silicon Carbide (SiC) Schottky diodes have ZERO switching noise. A bridge rectifier constructed from SiC Schottkys feeding a TV damper diode will be: quiet, soft starting, and exhibit relatively low forward voltage drop. A hybrid bridge made from 2 SiC Schottkys and 2 damper diodes would also work FINE.

Aside from damper diodes, 2X 7Z4 IDH Locktals with their plates in parallel are good in a hybrid bridge. At approx. $2/tube 7Z4s cost less than their sockets do.
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Old 1st May 2004, 09:19 PM   #10
SHiFTY is offline SHiFTY  New Zealand
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I used SS rectifiers (fullwave) in my 807 PP amp, and the sound is great. If I had gone for a tube rectifier, I would have definitely chosen a GZ34 as it has a nice soft start, plus it is the only rectifier I have capable of the 240mA current draw without sagging too much. PSUD 2 (the power supply designer software) gave a pretty good prediction.

Unfortunately this is an issue with tube rectifiers, they have poor regulation compared to diodes, and when used at high currents the voltages tend to sag, creating distortion.

You can use a higher first capacitor as well, meaning better filtering. Only drawback is that you need a standby switch.
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