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87.53.108.41
Were you pleased?
Can you share your schematic(s)?
PM me if you like.
Thanks very much.
"What did the Romans ever do for us?"
Follow Ups:
Before committing to to any of these schematics I would take a very long
look at the power supplies used.
J Epstein's PS rings. The Welborn amp PS does not ring but takes forever
to settle.
Has anyone ever really considered the PS for these? I am in the process of
designing one with a very well designed PS. Will let you know.
Cal
I may be wrong, but I think that at this level of DIY most builders will take responsibility for their own power supplies. The topology of direct coupled driver using the cathode resistor of the OP tube to derive the plate voltage of the driver is the salient technical focus. How one gets to a complete amplifier design is up to the individual.
You are correct. DC or DRD amps will only work properly if the tube voltages are perfectly balanced.
The original poster asked about existing schematics and how they sound.
Probably not so good with the PS used.
I'm just saying if you want get to "this level of DIY" don't blindly
follow schematics found online, design your own.
Cal
Hi Cal,
For JUST such amps, what the heck have I been posting up here for five years, (and Tube Wrangler, the 1989 originator), and for fast settling, JLH and John Swenson ????
Its on this Forum, can be dug out, right before everyone's noses. Performs like a champ, which of course, it is.
Jeff Medwin
Hi Jeff
Exactly what I was trying to say. The last 6 months or so I have spent
a lot of time with psud2 working with various ideas. Some of your ideas,
some of John's ideas and some from Henry.
I have come up with some nice PS's. Very quick settling times.
My beef is with some of the schematics posted online, some people
may take these as absolute Gospel but are often very poorly designed.
I am going to be seriously looking into DC and DRD amps this coming year,
using this type of PS, should be fun.
Cal
Henry's 35 or 40 mHY L1 is great as far as being used in L1 position, and its 2 A. current rating goes a long way to avoiding overload from spikes. Its a shame he never built and actually heard an amp using this Cal. Thats OK, others have, I have !!
Try 2.2 HY 7 Ohm as L2.
Jeff
Hi Jeff
I am looking at 2.5H, 5 Ohm, chokes for L2, or lower DCR, depending on
what Heyboer can build for me. Works very well with a 100mH, 6 Ohm L1.
Cal
Here's a variant , for some reason I labelled the plate choke as 320mH but it's actually 320H . Power supply uses paralleled CV31 rectifiers 500-0-500V TX 10H choke with 0.22uF input cap/snubberAl
Edits: 11/26/10
I assume you have the schematic from Jeremy's website? If not, the link is below. It is similar to other choke loaded driver direct coupled amplifiers such as the DRD and "Full Monkey", except that it does not complete the AC current loop to B+, but conventionally to ground.
how others have modified it.
"What did the Romans ever do for us?"
Yes, I have built it, and various similar designs like the DRD using the exact parts specified by Jack E. How did it sound? Pretty good, but not the best I've heard. I like direct coupled amps, and have now gone more to the 12AX7 direct couple to a 2A3 route. Sound, to me, is faster, better tone and dynamics are amazing. while the DRD and Monkey designs are attractive because of their efficent use of parts, and clever topology, the sound didn't do it for me. Of course, this is only my opinion and your experience may be very different. I think Welborn had good success with his version of Jack's amp. My advice is to build it and have a listen. The only big parts difference between this and a more conventional direct coupled design is the pate choke and you can easily resale those if you don't like the finished amps.
The issue with direct coupling is the big bypass cap on the output stage, how are you dealing with that?
Welbourne uses an ASC poly in oil 50uF. I use a Solen poly for now.
The bypass on the cathode resistor? Black Gate cap bypassed by Russian teflon cap. Nothing is perfect but over the years I have tried A LOT of designs. And I know that my current amp can be optimized even further, but of the stuff I've built, it is my favorite so far.
I read that Epstein wasn't that happy with it either. I haven't been able to find a schematic for the Welborn, but surely they are around. I just need to look harder. Morrison's design is somewhat different. They are all somewhat different. I have also read discussions about the 12AX7, good and bad, as a driver. Thanks very much.
"What did the Romans ever do for us?"
On Jack's site...
I didn't realize that the Weborn amp was the same as Jack's. Thanks.
A little ignorance can go a long way, eh?
"What did the Romans ever do for us?"
Here's the schematic for the Welbourne amp from the manual that came with the kit. All the 'monkeys' are variations on a theme. This one uses a 6DJ8 variant as the driver. I think that you need to build one and experiment to see what you like. Also check out the Komuro 300B as I believe it is the inspiration for all these, the archetype perhaps, although it differs in that it is a stacked supply with three stages. It seems like the 'monkey' was an effort to simplify the Komuro.
And of course, this is for a 300b, not a 2A3, though the 300b isn't run very hot. Jack's schematic puts 700v on the top of the 300b. Personally, I don't like messing with supplies much above 480v. The Welborn schematic looks like it is running the 300b around 16w - for maybe 4 or 5 watts out?
That's exactly correct about 4W. As long as you are satisfied with 4W there is no need to go to a 700V supply.
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