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If I ever run out of projects

75.138.100.58

In Reply to: RE: "it is not a Dynaco any more" posted by xaudiomanx on March 05, 2018 at 16:59:39

...I'll give running one channel of the two stock ST-70s amps a try. Given that the quad-caps in both are original, and both have selenium rectifiers in the bias circuit, it wouldn't be as easy as just hooking them up for an interesting afternoon experiment though.

I've got two MK-III amps which have been waiting for my attention for far too long. And another project which really interests me, which is building a 6BQ5 amp using a pair of Z-565 transformers I have, but on a custom ST-70 sized chassis, as shown below. (not my amp)

Given the excellent results I had with Dave Gillespie's EFB in my SCA-35, I'd use the same bias scheme for this amp, only I'd change it to individual EFB for each output tube. The added chassis space would allow me to use a choke, and maybe some room for those Wima DC Link caps in the power supply.

The real question is, what input circuit to use? Given the scarcity and price of NOS 7247, I wouldn't go with a ST-35 circuit. I bought a pair of current production JJ 12DW7/7247 and sent them to a guy who has a Fisher SA-100 which uses that driver tube. His take on them was that they were "just OK" (shrunken soundstage and "thin" if I remember correctly) compared to his NOS tubes, so that ended the idea of using the ST-35 input circuit.

"Suddenly, I'm not half the man I used to be. 'Cause now I'm an amputee" J. Lennon

Follow Ups:

RE: If I ever run out of projects - xaudiomanx 07:28:50 03/06/18 (1)
That chassis is the same as the one that was sold by Jon Yaeger or it appears to be the same.
- If I recall correctly - 1973shovel 12:33:00 03/06/18 (0)
  I bought mine from ebay, way back when, but I don't remember who the seller was.
  
  The chassis looks nice, so one drawback will be using the SCA-35 power transformer, which all seem to look like they were pulled out of the La Brea tar pits.
  
  "Suddenly, I'm not half the man I used to be. 'Cause now I'm an amputee" J. Lennon
RE: If I ever run out of projects - xaudiomanx 07:24:29 03/06/18 (1)
I have an EL-84 Lafayette tube amp here that I haven't tried in years. Maybe I should! I redid the front end to it suggested by an old audio friend. It used to use the 6AN8 driver/phase splitter. I now uses the 6N1P and sounds great. The gain is lower but who cares.
- Someone gave me a Lafayette - 1973shovel 13:15:04 03/06/18 (0)
  A "Stereo 250A" integrated, years ago, but I never brought it to life. It uses EL-86s as the power tubes, driven by 7199s, (with 12AX7s in the preamp section).
  
  I have a fair number of 6AN8, most GE branded, which I used to pick up at hamfests for my pair of MK-III for $1 each.
  
  The 6N1P looks interesting. Perhaps I should consider that tube for my 6BQ5 amp build. Thanks.
  
  I cycle several of my amps into the system occasionally, just to charge up the caps, and reacquaint myself with the sound. You should try your Lafayette again, just for fun (and to reform the electrolytics)!
  
  "Suddenly, I'm not half the man I used to be. 'Cause now I'm an amputee" J. Lennon

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