PT Hack .... is this possible ?

[kagliostro]

A friend has a 340v-0-340v PT that he has wind, now he would like to use it for 4 x 6v6 in PP and 340v is too much ...

he told me he want to unwound the windings till 315V but being a PT with CT I think this isn't very simple

I had an idea (assuming there is enough space for some further windings on the transformer)

the idea is to add a single 25V winding and connect it to the CT in counterphase

as to have the 25V subtracted from the 340V

Do you think this method can give the hoped results or is a crazy idea ?

BTW as load it will be better a 3.3K or 4K OT with 315V AC rectified using diodes ?

Thanks

Franco

[VMS]

340 is not necessarily too much.

That PT and about 4k OT and you have output section similar to jim kelley amp.

[eleventeen]

Wouldn't it be easier to employ the zener-diode-on-CT trick? I also agree, 340-0-340 is not too much. Probably turn into 440 VDC under load.

[kagliostro]

340v * 1.4 = 476v

. a drop of 36v under load .... may be, but I don't know how much current is disposable on the PT

. use a zener ..... may be an amplified zener as to avoid the use of a big one

Jim Kelly amp .... is a schematic disposable ?

--

The reason for which I've think to the additional winding was an association of ideas as recently I discussed about to decrease the voltage on a toroidal transformer and there (single secondary without CT and no lamination to be dismounted) the thing is easy to be done

I would like to know if this method can be applied also to a CT secondary using a single addon winding connected to the CT

Franco

[VMS]

Jim Kelly amp .... is a schematic disposable ?

Here is one:

http://el34world.com/charts/Schematics/files/_Miscellaneous/jimkelly_facs.pdf

Kevin O'connor has kelly project in TUT5 that uses hammond 273BX PT and 1650N OT.

[kagliostro]

Many thanks for the schematic

I've the TUT5 but forgot about this schematic

Franco

[PRR]

> add a single 25V winding and connect it to the CT in counterphase

How does that work?

The two ends of the CT winding are in anti-phase. A single winding counterphase to one must be in-phase to the other.

[trobbins]

K, you would need to wind two new windings, and buck the ends of each of the 340V windings.  But that seems a horrible path to take.


A non-dissipative way to drop some B+ is to use a CLC filter, where the first C is only small (eg. 4uF poly) and L can be low (eg. 1-4H).  It does take up some space, but provides a smoother B+ ripple with less rectifier noise.  Easy to see using PSUD2.

[DummyLoad]

A friend has a 340v-0-340v PT that he has wind, now he would like to use it for 4 x 6v6 in PP and 340v is too much ...

he told me he want to unwound the windings till 315V but being a PT with CT I think this isn't very simple

I had an idea (assuming there is enough space for some further windings on the transformer)

the idea is to add a single 25V winding and connect it to the CT in counterphase

as to have the 25V subtracted from the 340V

Do you think this method can give the hoped results or is a crazy idea ?

BTW as load it will be better a 3.3K or 4K OT with 315V AC rectified using diodes ?

Thanks

Franco

why not wind another?


--pete

[kagliostro]

>>> A single winding counterphase to one must be in-phase to the other.

Yes, that way it didn't work

>>> But that seems a horrible path to take

Yes, I see

>>> A non-dissipative way to drop some B+ is to use a CLC filter

Good I'll remember this

>>> why not wind another?

Seems he would like to use that, but I don't know if there is a particoular reason

Thanks to ALL

Franco