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In Reply to: RE: I like these Welborne300b amps with Elektraprint transformers. posted by Chip647 on April 10, 2014 at 04:36:47
I think one is the "DRD" choke that loads the driver plate from the output's cathode, and the other is a filament choke for the 300B.
Follow Ups:
Exactly.Those are two chokes on the top side..I'm taking out the series connected 560uf JJs and I put in a 100uf@600v EC concepts poly.I'm going from 280uf in electrolytic to 100uf in a poly,but at 550v, I would think that 100uf would more than enough filtering there..I did parallel in a 2nd 100uf poly and couldn't hear any difference in hum as it was dead quiet.
Honest amplification is better than excessive 2nd order distortion anytime.
Mike, if that's a DRD circuit which it looks like, remember that one of those caps, likely the big motor run is the "ultrapath" cap (which has to be rated at the B+ rail PLUS the AC signal). It needs low ripple at the PS node, otherwise it'll get into the cathode circuit. By lowering the final C's value in the PS, you might affect this issue.
Edits: 04/10/14
That's good to know..The series connected 560s feed the plate of the 300b thru the output transformer but what if I add pair of 30uf polys in parallel,giving me 160uf total? These caps are ultra low esr and they really store and deliver nice bursts of energy.
Honest amplification is better than excessive 2nd order distortion anytime.
Is one of those chokes connected between the driver plate and a voltage divider in the 300B cathode circuit?
If, yes then this what you have. I don't know how low of ripple is "low enough", but figure that probably the designer already made that call.
I not advising, just saying pay attention to what is important when tweeking this circuit, you know what you're doing. Since you claim to have good recipes for signal cap combinations, the cap marked "oil" above, is one.
It is DRD..The 100uf poly is dead quiet tho but I can parallel in another 100uf poly or a pair of 30uf giving me 160uf total.
Honest amplification is better than excessive 2nd order distortion anytime.
I don't know how the DC filament supply is done there, but if it's CLCRC then that could be improved by going LCRC or LCLCL or LCRCL. If a C is last then a pair of resistors to the cathode node instead of off one side might help get the final PS C out of the equation. I think it's Thomas Mayer who
suggests an L for the last component having good AC rejection.
Hi Michael,
Add a 0.1uF Teflon cap after the last power supply cap. It made a big difference on my Starchiefs.
You could also parallel a 0.1uF Cu cap (Audyn true copper or Vcap CuTf) across the Ultrapath cap.
You get lower noise and greater transparency with the Teflon and body and soundstage with the Cu.
Other than that not worth spending any more on the DRD as I have found out.
Cheers
Smart845
Thanks Smart
I have both Teflon and paper in oil caps..I have Audyn caps and SonicCap plats.I love the Russian FT-2 and FT-3..Both are excellent as are the KBG pio and the K40Y caps but they all need break in.
Honest amplification is better than excessive 2nd order distortion anytime.
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