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Old 13th November 2012, 04:09 PM   #21
TheGimp is offline TheGimp  United States
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Get rid of the RC and just run a CLC. This will minimize your DC losses.

Use a large C2 value (330uF) and adjust the first cap value to set your B+.
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Old 13th November 2012, 08:23 PM   #22
tomchr is offline tomchr  United States
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If PSUD won't dance for you, PSpice, LTspice or regular spice will.

Just place two inductors, L1 and L2 along with a 'K' spice directive: K1 L1 L2 0.999
This makes a transformer with a coupling coefficient between primary and secondary of 0.999 (99.9 %).

Include the DCR of all the components - including both the primary DCR and secondary DCR of the transformer.

~Tom
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Old 14th November 2012, 07:46 AM   #23
vingenz is offline vingenz  Italy
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It's better PSU then LTspice for transformers....i think
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Old 14th November 2012, 02:45 PM   #24
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Quote:
Originally Posted by vingenz View Post
Hello folks!
I've built an amp with 2x6l6gc P-P AB1 in the power section. There is problem that I can't solve: after full wave rectifier, B+ is 460VDC (372VAC on secondary) at idle, and 395VDC (350VAC on sec.) at full power.
Power transformer specs are: 250mA; 372-0-372VAC.
6l6 are biased (fixed bias) at 35mA each. Diodes are 1n5408 (1000v, 3A)
Well, i need more clean headroom and I can't understand why it's sagging too much . Suggestion? Tricks?
Thanks!

well the best thing is to increase regulation. about another 100Uf or so in the power supply would work nicely. but regardless of how stiff you make the power supply, it supposed to sag slightly without inducing power supply noise.

like this power supply : this is for 4 6l6's and 4 12ax7's the 2H choke was deleted in final design that mesa boogie uses.

Copyrighted schematic deleted by Moderation

Last edited by DavesNotHere; 14th November 2012 at 02:53 PM.
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Old 14th November 2012, 02:58 PM   #25
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If you really want to increase headroom in the amp. Make the B+ hotter like 480-500V to the plate. But this path should be left for the ones who are not afraid of pushing the envelope. And making sure they adjust the bias when upping the plate voltage.
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Old 14th November 2012, 03:14 PM   #26
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and I encourage use of the series caps with bleed resistors as this safely discharges the circuit when the unit is turned off.
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Old 14th November 2012, 05:04 PM   #27
vingenz is offline vingenz  Italy
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Quote:
Originally Posted by DavesNotHere View Post
If you really want to increase headroom in the amp. Make the B+ hotter like 480-500V to the plate. But this path should be left for the ones who are not afraid of pushing the envelope. And making sure they adjust the bias when upping the plate voltage.
How?
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Old 15th November 2012, 01:10 AM   #28
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Sorry, moderator deleted my schematic. I'll have to make one instead of posting my originals ( even though they settled on a different design).

O.k. with using public domain knowledge, we'll walk you through the designing phase. So give me a few minutes as I will have to setup some sort of flicker accoun
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Old 15th November 2012, 01:21 AM   #29
Enzo is offline Enzo  United States
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Several people suggested it, did you provide us the DC resistance of the power transformer windings? From your report, your AC voltage at the transformer was dropping considerably. If that voltage drops, then so will the resultinbg rectified and filtered DC. You can consider the resistance of the winding to be in series with it and causing voltage drop with current flow.
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Old 15th November 2012, 01:26 AM   #30
tomchr is offline tomchr  United States
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You also need to consider the resistance of the primary. The total resistance that should be considered to be in series with the secondary winding is:

Rtotal = Rprimary*(Vsecondary/Vprimary)^2 + Rsecondary

~Tom
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