Circlotron questions

[atmasphere]

Originally Posted by nazaroo

Especially with a Circlotron style circuit,
where voltage references to ground may be ambiguous,
you absolutely must avoid an auto-transformer.

This is a death-trap,
just waiting for some child to tug a speaker-cable.

D.C. voltages stored in powersupply are just looking to empty themselves through some unforeseen or accidental connection.
The windings in the autotransformer will simply conduct DC.

Hydro would ban this, as would UL .

This will neither be legal nor moral.

Your second circuit is not much better.

This one also breaks the cardinal rule,
of keeping HV idle currents out of the secondary to speaker outs.

With a standard transformer you have 1kV of insulation/
protection from HV leaking to speaker lines.

This circuit defeats all the careful safety features of well-designed output circuits.

Please find a way to make it safe.

The original Circlotron had 2 kV transformer isolation from HV, in case of cap failure.

This is all bogus. If we can build an OTL based on these concepts (and pass UL and CE requirements) then an autoformer or transformer version will certainly pose no threat! Of course one must assume that there is no ambiguity about ground!

[Miles Prower]

Originally Posted by tinitus

and connected to opposite tube

When implementing a Circlotron with pents used as pents and not pseudotriodes, you have to cross connect the screens, as the finals are cathode followers. Pents only work as CF's if V2k doesn't vary. Not hard to accomplish if the cathodes are at AC ground.

If there's a signal at the cathode, then the screen voltage has to move in tandem with it to maintain V2k constant. Cross connected screens apply that compensating signal.

[revintage]

Check post #13. That´s where it all started as a DIY article in Funkschau. I have the complete article somewhere with winding data etc. etc.

You can also see the crossconnected screenfeeds that Miles mentions.

[tinitus]

hey, we got 'distracted', and now I can't remember if we settled on a schematic

and no, Im not into the 'impossible' high never ending
Im happy if it sounds ok and is reliable

and btw, in the meantime I have got a few 6n1p and 6n6p, for other project

[tinitus]

hey, the first, anode coupled, looks like it would be a natural for ccs on the cathode
but being a circlotrion, would it cause 'imbalance'

[banat]

Originally Posted by tinitus

hey, the first, anode coupled, looks like it would be a natural for ccs on the cathode
but being a circlotrion, would it cause 'imbalance'

Hi Tinitus !

ccs on cathode is not necessary to keep the working balance of output tubes , I think some low value of wire type trim pot in series with one of EL34 cathode resistor for adjusting perfect static DC & AC balance is good enough .
Any way since you already have your balanced OPT than stick with schematic nr.2 ( ecc81+ecc99(12bh7) & 2xel34 triode strapped ) with conventional cathode coupled Cirlcotron configuration .
That configuration have many advantage ,
1) allow both SE & balanced amp operation
2)You have applied on input tube cathodes circuit so called `` Current Feedback`` GNFB , with all advantages over so called `` Voltage Feedback ``GNFB configuration .
3) Cathode coupled Circlotron configuration of output power stage have natural low distortion characteristic since both EL34 tube work as CF .
Maybe just some little tweaking of that circuit is OK with adding of some small value of grid stop resistors in both grid of 12bh7 tube , with value of 1K , 2k2 or so .
and to remember , main power transf. need electrostatic schield between primary & secondary coil .

Best Regards !

[tinitus]

hi banat, thanks for staying with me on this

#1) I was thinking it might be nice to have both SE and balanced input option

Originally Posted by banat

and to remember , main power transf. need electrostatic schield between primary & secondary coil .

OK! I can get that from Toroidy, and means I can order any voltage I want

[tinitus]

Originally Posted by banat

.....electrostatic schield between primary & secondary coil .

I take it one trafo with double secondary will do ok
per mono channel ofcourse
but will each winding need each own electrostatic shield ?
or just one shield for the whole trafo ?

would also like to talk about heater winding(s)
or maybe its better with seperate heater trafo
they are beginning to become 'more available'
but takes up more space, with possible risk of more noise issues, etc
dont know

and I might consider regulated supply for small tubes, if it makes sense
but may not be possible at all, with this 'cross coupled' design

[tinitus]

well, I guess your schematic holds all the answers

[banat]

Just few more remarks :

1) If you connect OPT or autoformer middle point to ground than you don`t need that two 1K8/5W resistors on PSU to achieve ground reference point for output power tubes .

2) Have attention on correct relative phasing between All four main power transf. secondaries!!! ( warnings triangles and dots ) , they have to be connected ` in phase ` , since with correct relative secondary coils phasing you well achieve lowest possible generation of hum & noise from amp .

3) You don`t need any extra regulated B+ lines for small tubes since for input tube B + regulation is already done with two zener diodes string ( +260V stab.),
and diff.phase spliter ( driver ) tube anodes have to be bootstrapped from opposite ( B+) EL 34 anodes .