Using mains transformer as output transformer

[revintage]

Did some minor adjustments for the proto to simplify the buildup. Also have to unwind a few turns on the secondary to get impedances right:

[Elias]

Hello,

revintage:
Why the extra tube? Can do the current mirror without it as well.

How about something like this. Throw the current mirror at the top.

R3 is selected so that Vcc-U1 > max anode swing.

C1 is the supply filter capacitor.

Can be no simpler, no?

Benefit is also that the saturation of the toroid initially is less because one direction current through toroid is only half of the bias current.


- Elias

[revintage]

Elias,
Your solution looks far out but interesting, I´m not sure it will work IRL. Anyway I will sim it for you to check.

The reason for using a second tube is that a cheapo tetrode do not need a heat-sink. It is also foolproof, would not trust sand with 300V over it to be so.

[Elias]

Hello,

Originally posted by revintage
Your solution looks far out but interesting, I´m not sure it will work IRL. Anyway I will sim it for you to check.

The reason for using a second tube is that a cheapo tetrode do not need a heat-sink. It is also foolproof, would not trust sand with 300V over it to be so.

May I ask what is IRL?

I think voltage rating is no excuse as there are more than plenty of choices of BJT that can handle easily more than 800V.

The dissipation of BJTs are no problem as they do not take over whole supply voltage and because the fact that the Ibias is split into two. I calculated about 5W per transistor, so no heat sink needed instead can bult them to chassis.

If your simulation fails, I'll build a proto

- Elias

[revintage]

IRL= "In Real Life"

It will not work, but if you want to waste your time, go ahead and build it !

[revintage]

Elias,
The idea of the current-mirror on top is very interesting and I will try to work something out of that one.

[revintage]

These two sim close to identical.

[Elias]

Hello,

I just realised my top current mirror concept approaches this very old idea from one patent. Mirrored current source imitates the choke. It was disscussed here earlier but I cannot locate that thread right now.

- Elias

[kenpeter]

Re: Rev Post #81.

Bypass C1 from Cathode to Cathode, instead of to ground.
Upgrade that current source into a brute force anti-triode.

[revintage]

The patent works with normal B+ because the ideal choke has infinite AC Z but minimal DCR. The effiency will theoretically be doubled but it will cost a lot since the choke will cost to much. Also something must be done to equal the DCRs and then you loose efficiency again.

If you want your circuit to work you have to double B+(6-700V ) for a triode-strapped EL34. Didn´t think so far when I said it wouldn´t work . Then you have to let the resistor above the triode take the heat. So in that sense it will work but what you win in less current adds in voltage. The efficiency will be the same as in my suggestion. So there are no free lunches......

In my eyes this is a lot more complicated. It might be worth if the halved current makes it sound better......

KenPeter: We could do like you suggest but it was not what we aimed for. What you suggest is a self-split PP and the &V& should then be substituted for another 2A3, but our aim was to make a SE. According to the sims I have done the uneven distortion doesn´t look to promising though.