Planning PT for tube w low voltage G2 request - Is this rectify schem correct ?

[kagliostro]

Planning a new transformer for a circuit where the Power Tube require a lower voltage than B+

Think to tubes like GU50 - EL500 - 807 and so on

A tap to the correct AC voltage is planned on the PT and ....

is correct this rectify plan ?



Thanks

Franco

[chocopower]

I´m using this.

[kagliostro]

Ciao David

Unfortunately, for me the link didn't work 


Franco

[jjasilli]

This is a theory intensive question on Transformer & circuit design. I believe your proposed circuit, with a tap, will function.  You could go UL; or separate PT winding; or some circuit to drop B+ to the screens.


 FWIW:  The Stromberg Carlson APH-1100 is a 100W mono PA power amp, using PP KT88's:  600V plate, 300V screen.  It accomplishes this with a separate screen winding on the PT (not a tap).  (It also uses voltage doubling on both the plate & screen supplies.)  It sounds great for hi-fi with 5% THD @ 100W; 2% THD at 80W, from 20 - 20,000 Hz.

[DummyLoad]

see attached - g2 node (C3) will be approx 1/2 B+ node (C1). the example attached was designed for a pair of 6550. plates are 520V and g2 is 260V.


--Pete

[PRR]

Or without the frills, just this.

[kagliostro]

Many thanks to ALL

I belive all of you is right

I'm just arrived at home and walking around I was thinking to the circuit

If the G2 voltage is to be 1/2 of B+ I'll accomplish with you about the use of the CT as the G2 supply, like in this old Philips PA amp



But in some cases datasheet council is different, so an 807 at 350v B+ is to have 250v G2 and only 200V G2 if B+ is 500V

If I use a "standard" PT we have largely discussed how to obtain the needed voltage (PRR planned for me a Mosfet circuit to lower B+ to the exact G2 requirement)

But if I build my own transformer why not use a specific plan ?

So, walking, I've think to this solution (the previous I posted put on me the idea it is unsafe)



Do you think this will be the right way to have G2 and B+ independent values forom each other ?

Thanks

Franco


p.s.: Jjasilli the Stromberg Carlson APH-1100 schematic is missing on Doug's database

if you have it, please post it so he can add it to the database

[PRR]

That will work.

Since G2 power is much less than P power, it may make sense to just have dedicated windings. Especially if you wind your own. Then you can change the turns on the G2 winding without re-thinking and re-winding the P winding. Some of the big Ampegs did it this way. (VT40 with distortion feature)

[kagliostro]

If I understand correctly you PRR

you say that I can use a "sum" of the two windings voltages to supply the Plates

or have two windings that can feed, one the G2 and the other the Plate, without the necessity to stack them

100v + 200v staked

or

100v and 300v completely separated

Correct ?

Franco

You remembered me also Hiwatt has a similar circuit

[jjasilli]

p.s.: Jjasilli the Stromberg Carlson APH-1100 schematic is missing on Doug's database . . .   if you have it, please post it so he can add it to the database

Here's the whole service manual including schematic. I find these old manuals to be very instructive.


I've not been successful at getting Doug or other sites to post this schematic.  Maybe someone can get it done.


I have other Stromberg Carlson materials.  But, this is the best site for Stromberg Carlson:  http://www.audiophool.com/ with lots of other things, including references to sites for transformer design & theory which may interest you.

[kagliostro]

Many Thanks Jjasilli

Now I think Doug will add it to the database

Franco

[chocopower]

Ciao David

Unfortunately, for me the link didn't work 


Franco

Sorry. Try now.

[kagliostro]

OK David

now I can see, thanks

Franco