OPT with cathode feedback

[tinitus]

hey, I remember a thread with members debating this
but can't find it

and that noone produce those trafos anymore

well, Amplimo makes them now
and holds the patent too

if some could link to that thread, I will remove this one

 

[Wavebourn]

You jay use an ordinary transformer with 4 and 16 Ohm secondaries for push-pull cathode feedback.
For SE cathode feedback any secondary may be used.

 

[Eli Duttman]

Cathode feedback windings are NOT new. Whatever patent Amplimo holds is not on that concept.

Amplimo and Plitron (Canada) are "joined at the hip". Plitron builds Vanderveen designed toroidal trafos. Descriptions of Plitron's tube O/P trafos, including those with CFB windings, can be found here

 

[LinuksGuru]

Its really not new, I have seen cathode feedback design in Russian magazine published back in 1958.

Vintage amps like Sansui AU-111 and Quad II are examples of cathode feedback. McIntosh unity coupled is actually a 50% cathode feedback (invented in 1936).

Below you can see draft assembly of PP amp with CFB trafos of my own design

 

[tinitus]

great, thanks

magic word, cathode feedback

hope you don't I 'corrected' the thread title

 

[tinitus]

how about this one ?

 

[tinitus]

oh, and with the 'desired' UL tap for driver tube
suddenly figured that out, after long osmosis
maybe

not sure about specs on trafos

well, lots of

 

[tinitus]

hmm, maybe anode phase splitter choke for driver tube

and 'added' trafo for cathode and garter bias
due to current, sutrely not an interstage
but how about a toroid power trafo
not a CT, but double symmetric windings
though all primary, wouldnt they also work ok as 2x primary and 2x secondary

 

[tinitus]

interesting Crowhurst amp

original DIY 'kit' from 1957-1960
curcuit and setup explained in detail

http://www.audioxpress.com/magsdirx/ax/addenda/media/1960crowhurst.pdf

 

[smoking-amp]

Or just use a circlotron output stage. Two OTs for the Twin versus two power supplies for the Circlo.

 

[tinitus]

btw, AquaBlue describes a monster 807 amp, coupling a multitapped Lundahl with cathode feedback

 

[smoking-amp]

The schematic in post #7, looks like the feedback to the V1 screen is positive feedback (from the V2,V3 output tube plates, but maybe neg. fdbk from V1 plate to V1 screen). The feedback to the V1 plate from V2,V3 plates is negative though.

 

[tinitus]

The schematic in post #7....

hey, I think I made some mistakes from looking at pushpull CFB designs,
and this is SE
just for the record, the corrected version
like you, I also have my doubts, ofcourse

well, for one, it needs to be a high current trafo
maybe a 'cheap' custom trafo could do it

 

[ilimzn]

If cathode feedback is implemented, and the screen is referenced to ground, then this also implies a measure of ultralinear (screen feedback). To prevent that, the screen should be referenced to the cathode by using a floating power supply, or, there should be an UL tap with teh same percentage feedback as the CFB, but 'crossed' between the screens so that it cancels out CFB. Looking tat that arrangement ot first glance it may appear as positive feedback to the screen grids.

 

[smoking-amp]

"the screen should be referenced to the cathode by using a floating power supply, or, there should be an UL tap with teh same percentage feedback as the CFB, but 'crossed' between the screens so that it cancels out CFB"

I think thats what Tinitus is doing with the lower windings shown now. (needs some phase dots on the windings) (and the two winding sets shown at bottom are in parallel so they could be combined into one)

My earlier comment about pos. fdbk on the screen was referring to the V1 input tube screen connection in post #7. The latest version now looks like the so called "E-linear" connection for V1, which is fine. "Schade" style neg. feedback. Maybe a bit of overkill on the Neg. fdbk unless the CFB% is low (like use the secondary winding for CFB).

 

[tinitus]

I dont know, but looks like I was focused on the pushpull CFB
but cross referenced feedback wouldn't be possible with SE design, would it ?

maybe I should have cross referenced grids to cathodes, Garter style
to balance the bias between the tubes

is there any kind of feedback from the added trafo ?

 

[tinitus]

wait a minute
in a PP design the garter bias is cross referenced with opposite phase to grid, yes ?
but in a SE it cannot be
well, does it work at all then

 

[tinitus]

if you are still around, will this have any chance to work ?

CFB coupled interstage driver

 

[tinitus]

thinking about Power Buffer amp
could be kind of CFB too, right?

this is inspired by Broskie

 

[tinitus]

looks strange