Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on May 25, 2017, 03:56:55 am
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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 ?
(http://i.imgur.com/IiA51OL.jpg)
Thanks
Franco
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I´m using this.
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Ciao David
Unfortunately, for me the link didn't work :dontknow:
Franco
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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.
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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
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Or without the frills, just this.
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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
(http://i.imgur.com/15NtYAi.jpg)
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)
(http://i.imgur.com/YazPCaR.jpg)
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
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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)
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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
(http://i.imgur.com/vgJgbr6.gif)
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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/ (http://www.audiophool.com/) with lots of other things, including references to sites for transformer design & theory which may interest you.
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Many Thanks Jjasilli
Now I think Doug will add it to the database
Franco
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Ciao David
Unfortunately, for me the link didn't work :dontknow:
Franco
Sorry. Try now.
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OK David
now I can see, thanks
Franco