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In Reply to: RE: MP Engineering OTL posted by Kasanay on June 06, 2016 at 08:11:38
Hi KasanayNice vintage OTL amps ! , I like it ,
-referenced to yours schematics I would say that yours amps are conceptually very close to Futterman H1 amp , basically they are very simple.. ,
same 6AU6 tube on input voltage gain stage further DC coupled to grid of 6S4 phase inverter /driver stage tube ,and the same but many more numbers than in H1 12B4A triode power tubes in SEPP OPS ,
- one of differences is that 6S4 cathode resistor (R7-33K) is by your amps connected directly to ground line, but by Futterman OTL amp that resistor is connected on positive or `hot` speaker line , which is one characteristic original solution for Futterman OTL amps ,
- as Lew says there is no coupling cap to LS ,
- SEPP OPS have bipolar PSU same as is by H1 , but
negative bias network is designed in different way than from H1 , and so on..,
- any way , I think that your vintage OTL amps need and deserves very very careful cross check examination of every active and passive element before further and normal every day use ,after all they are made in 1962 !
-it is great that you have original schematics and specification list ,that will help you a lot for your future repairing & servicing job.
Best Regards !
__
"Art which does not have the appearance of art is true art."
- Old Roman saying -
Edits: 06/06/16Follow Ups:
Banat,
Thanks, for the reply and info. As I stated in another post, I am no expert so i hope you don't mind me asking for information:
"SEPP OPS" = Single Ended Push Pull ?opposing sides?
When you say "which is one characteristic original solution for Futterman OTL amps" are you saying the Futterman design is superior in area?
Thanks,
- SEPP OPS mean Single Ended Push Pull-Output Power Stage ,- No I did not say that Futterman OTL amps are superior,
I just say something like this , `by connecting phase inverter tube cathode resistor to loudspeaker `hot` line and not directly on the ground line is one characteristic solution or invention detail of J.Futterman`, that characteristic solution was implemented in many different models of J.F. OTL amps ,
and that specific solution allows to both side of SEPP OPS to dynamically behave in the same manner,
- but the question is , why MP Engineering did not implemented that solution in your OTL amps ? ,
maybe J.Futterman patent pending rights was the reason which did not allows that implementation .
__
"Art which does not have the appearance of art is true art."
- Old Roman saying -
Edits: 06/06/16
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