Doesn't the plate-to-plate feedback from the LTP to the driver separate it from a Mullard 5-20?
I'm talking about the Maplin amp. It was designed around that output transformer so it would be the ideal build to avoid any issues with stability.
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Here is that one. Hard to say what make an amplifier special sometimes! One extra resistor can make all the difference.
Following article has description of two circuits for 807 PP amps, first with triode connected 807 tubes.
Both circuits use 6J7 / EF37A as input voltage gain stage, 6SN7 as LTP splitter & driver and 807 as outputs.
Basic PSU's for both with different OPT's for each.
Any thoughts on these ?
Asking because i'm considering these for the beginning, first trials, with 807 PP output tubes.
Both circuits use 6J7 / EF37A as input voltage gain stage, 6SN7 as LTP splitter & driver and 807 as outputs.
Basic PSU's for both with different OPT's for each.
Any thoughts on these ?
Asking because i'm considering these for the beginning, first trials, with 807 PP output tubes.
Those are decent circuits, but with 16dB feedback, your choice of output transformer will be critical, and you will need a scope to tune it properly. Also, as is typical with these early feedback designs, there is no compensation circuitry to account for the high-frequency boost created by the feedback. The amp is sure to have a lot of ringing in the square waves, and would probably oscillate if you breath on it.
Here is a modern Williamson design that is fully tested and stabilized. It uses low-cost edcor transformers. The author used 1625 tubes, which is the 12V version of the 807. You could simply substitute 807s and 6SN7s. You could build this and be assured that you will have a professional-quality amplifier.
https://audiokarma.org/forums/index.php?threads/williamson-ultralinear-amp-w-edcor-opt.1011032/
For a higher-end project, you could build my version of the American-style Williamson, and use 807s in place of the KT66s. With a 5V4 rectifier you will not exceed the capacity of the 807s.
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=7557
Here is a modern Williamson design that is fully tested and stabilized. It uses low-cost edcor transformers. The author used 1625 tubes, which is the 12V version of the 807. You could simply substitute 807s and 6SN7s. You could build this and be assured that you will have a professional-quality amplifier.
https://audiokarma.org/forums/index.php?threads/williamson-ultralinear-amp-w-edcor-opt.1011032/
For a higher-end project, you could build my version of the American-style Williamson, and use 807s in place of the KT66s. With a 5V4 rectifier you will not exceed the capacity of the 807s.
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=7557
Here's another, again with 1625s and using Hammond iron.
https://audiokarma.org/forums/index.php?threads/the-1625-amp-mk-ii.778418/
https://audiokarma.org/forums/index.php?threads/the-1625-amp-mk-ii.778418/
Thanks for the comments. Aware that the feeback will probably have to be used and tuned on the scope. As for the transformers currently i'm saving for some higher quality units to be made locally by the ex-manufacturer in pension, these should be made to work with feedback without trouble.
Can You please post schematics - can't open the page for some reason.
Thanks, Krca
By the way, you can build that circuit as triode as well, I have the feedback changes somewhere here.