New amp
Modded McGary SA-1 brought to the "E" level.
New caps, better biasing on power tubes, and upgraded power trans
Attachment:
mcgary2.jpg [ 318.61 KiB | Viewed 3713 times ]
Attachment:
mcgary1.jpg [ 188.09 KiB | Viewed 3713 times ]
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| Author: | Pelliott321 [ September 19th, 2021, 11:00 am ] |
| Post subject: | Not DIY |
New amp Modded McGary SA-1 brought to the "E" level. New caps, better biasing on power tubes, and upgraded power trans Attachment: mcgary2.jpg [ 318.61 KiB | Viewed 3713 times ] Attachment: mcgary1.jpg [ 188.09 KiB | Viewed 3713 times ] |
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| Author: | SoundMods [ September 19th, 2021, 11:19 am ] |
| Post subject: | Re: Not DIY |
Pelliott321 wrote: New amp Modded McGary SA-1 brought to the "E" level. New caps, better biasing on power tubes, and upgraded power trans Attachment: mcgary2.jpg Attachment: mcgary1.jpg So -- you went Ultralinear in lieu of SET. Does the McGary enable triode operation as well? I ask this because I found that KT-88s (I expect the beefier KT-90 as well) and EL-34s don't seem to do well running Faux triode where the KT-66s seem to prefer that operation. BTW -- despite what some designers are doing with EL-34s, Mullard originally advised against that operation of EL-34s being that they are pentodes and not beam tetrodes. Their comments included the fact that the suppressor grids would overheat. And how does the "self-bias" work when they advertise compatibility with a long list of tubes (6L6GC, KT66, KT77, EL34, E34L, 6CA7, 6550, KT88 and KT90)? Is there a means to adjust the bias? Some early designs had adjustable cathode bias. Is that what McGary did? |
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| Author: | Pelliott321 [ September 19th, 2021, 11:30 am ] |
| Post subject: | Re: Not DIY |
The SET is still there. Evaluation of the McGary will take awhile. Just because I own it doesn’t mean it’s the best. It sound good, very musical. It cam with 6550 I will be trying KT66 Plenty of power for either the 97db Razz or the 85db Quads. The biasing in the McGary is cathode bias with a twist that is proprietary and I can’t talk about. All I can say it’s not microprocessor controlled like PrimaLuna or VAC. |
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| Author: | SoundMods [ September 19th, 2021, 12:07 pm ] |
| Post subject: | Re: Not DIY |
Pelliott321 wrote: The biasing in the McGary is cathode bias with a twist that is proprietary and I can’t talk about. I am almost certain that what they have done with "a twist" is a matter of public record established almost 60 years ago -- so why the mystery? The versions I have seen include adjustable cathode bias on each tube together with balance between pairs as the most complex -- to just simple tandem-connected cathode pairs with a common bias resistor with bypass. Then there is the Zener diode "school" that try to regulate cathode bias although that kind of defeats the purpose of cathode bias. Or 3-pin regulators with adjustment -- I've seen that scheme as well. Then there is the ancient G.E. scheme copied by Jadis where you have a certain amount of fixed bias by setting a negative voltage on the control grid as a fixed bias starting point with cathode-bias taking care of "the heavy lifting." |
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