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In Reply to: RE: WESTERN ELECTRIC 91A CLONE DISCUSSION posted by Jim Dowdy on November 22, 2014 at 06:00:39
The only one I haven't seen a schematic for yet is Thorsten Loesch's , but by reading his descritption it looks excellent. I think I will be looking at combining elements of all three designs in what I decide to build.
I also read that the earliest WE91A used the 6C6, however there's no reference to the 91A ever using a different power transformer to accomodate the different heater voltage of the 6C6 on the various schematics I have found, so I am hesitant to believe it until I see some more concrete proof.
Follow Ups:
I have his Thorsten's and also a couple (I think) of 310A driving a 300B variants posted to AA. Let me know if you would like me to send you a pdf version.
I like the pentode-drives-DHT sonics and will continue to explore them for the next year or so. I am currently putting some thoughts together for a 6C6 directly-coupled to a 2A3; should produce 45-like power, enough for my GPA duplexes. Now, if only I could get a transformer winder to provide a quote/ commit to winding a mildly custom output trans (ie. adjusting OPT gap)!
Enjoy.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
At least all of them that apply to the DIY HIFI Supply Lady Day 'Billies' 300B SET which I built WAY back when Brian Cherry first sold them as a kit.
By the way, has anyone heard from Brian Cherry lately? He is no longer available at DIY HIFI for at least the last year. Visited him in Hong Kong a couple times over the years but not since 2006 or so.
You probably already have it, but here goes. Edit: you have already linked it below. I was sure there was another, but maybe I am mistaken.
If you would also like some of Thorsten's others posts on the subjects - mostly related to his Legacy - and how these types of amps compare to other faves of his, shoot me a PM so I can send on some stuff by reply email.Cheers.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
Edits: 11/23/14
I have no experience with this circuit - provided for informational purposes.
"I have no experience with this circuit - provided for informational purposes."Yes that's it. I didn't remember it with an SV83/6P15P.
Does anybody have any experience with this type of tube regulated power supply? If somebody wanted to explain how this differs from using a gas voltage regulator tube, then I would greatly appreciate it. Are both useful in lowering hum?
Thanks in advance for any replys,
Jamie
Big speakers and little amps blew my mind!
Edits: 11/23/14
But I seem to recall he made some additional changes in order to flatten the frequency response in the version that DIY HIFI Supply eventually sold as a kit. I think he discusses it in the post below which no longer contains links to the schematics.
"A last trick is implemented in a pair of 1nF capacitors between the 300B Anode and 310A screengrid. This is actually positive feedback at high frequencies. This helps to overcome the HF rolloff inherent to the classic 91 Circuit, where usually 20KHz is around 3db down. In my Amp's I measure -3db somewhere at around 75KHz with this positive feedback in place, without -3db is around 20KHz as expected."
Also the 'optimized WE Cathode Bypass' which he discusses and which I suspect was likely the precursor to Jack Eliano's 'Ultrapath' circuit and which I have already implemented in my 300B amps.
I think, all and all, with his circuit description below and the circuit diagrams in page you linked to, one could pretty much duplicate the final product I heard at RMAF so many years ago.
Link below:
Hey Ivan, I did not notice that the schema had been removed from that post.Here it is:
Note, this design uses the partial WE connection: 50uF cathode bypass capacitor with 15uF B+ to cathode capacitor. Thorsten's later (DRD) amps used the full B+ to cathode connection (50uF+ using multiple capacitors in parallel) with no cathode bypass capacitor.
Cheers.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
Edits: 11/23/14
That's just about the same circuit that ended up in the DYI HIFI Supply WE91 SET amp.
Sure would like to take a whack at upgrading my current 300B amps but would be a LOT of work. Might try it with an octal driver with a 6V heater of some sort, like the 6J7.
Should never post before the second cup of coffee!
RCD,
I would like to second the motion for a Thorsten 91, except with a 6P15P as the driver tube, and with the JCV 6AS7 VR circuit.
Have you ever built the JCV VR circuit? Any comments about it? Does it reduce hum?
Thanks,
Jamie
Big speakers and little amps blew my mind!
Hey Steady,
No, have never built the JCV VR circuit; I am not exactly sure what it is and don't have the time to look right now.
If it is used to stabilise he driver tube screen, my guess is it would have more of an affect with the high GM pentode drivers, but I can't remember why.
Cheers.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
is no longer owned by Brian. I also recall there being some differences of opinion between Thorsten and the new owners regarding some of their boards... the power supply IIRC.
I will see what I can do about Thorsten's posts. I remember it taking a bit of searching to find them on AA, but I now have them saved... somewhere!
Cheers.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
It was for the original DIY Hi-Fi supply version called the Lady Day WE 91 SET, I think.
This is the amp that I heard at RMAF years ago driving as set of 'Bastani' open baffle speakers.
I am not an expert in WE gear, but the attached file is an original WE 91A schematic that clearly labels V1 as a 6C6. I cannot make out the T3 power transformer model number, but it is clearly connected to the 6C6 filament.
This is really interesting!
I think you explained why R41 exists. Also, note that the plate load resistor for v2 in your early version schemaric is 100k versus 90 in the one I posted. Thank you for posting this schematic, it is really cool!
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