PT wiring help needed.

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12bz7
Junior tube assistant
Posts: 14
(5/28/05 4:36 am)
Reply   PT wiring help needed.
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 I have a PT which is a pull from an old organ amp which ran 2 x 7868 output and 2 x 6au6 preamp tubes. The tranny is fairly large about the size of a typical fender 2 x 6L6 type (but standup not laydown)PT. I measured the secondary voltages and have come up with HT=192v no CT (these exit the trans on the primary side). 6.3volt with CT. A pair of wires that measure 14.5v and a black wire which is connected to no other ( this was connected to the chassis) so I presume this is a ground. Would this trans be suitable for a el84 or 6v6 amp? What sort of recitifier would be needed, SS or tube?what would the 14.5v tap be used for?
thanks for any help.
 
Tiny Daddy
I only work on Fender's
Posts: 1240
(5/28/05 9:18 am)
Reply   Re: PT wiring help needed.
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 I suggest a full wave voltage doubler on the 192 volts powering a pair of 7591 JJ tubes.
 
GroundhogKen
Moderator
Posts: 2789
(5/28/05 10:43 am)
Reply   Re: PT wiring help needed.
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 It might be cool the way it is. Electro-harmonix now makes a 7868.

Tiny Daddy's suggestion is also good. A 7591 is similar to 7868 except for the socket.

Ken
 
Tiny Daddy
I only work on Fender's
Posts: 1241
(5/28/05 11:06 am)
Reply   Re: PT wiring help needed.
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 Another note, if the 14.5V winding is a separate winding, use a doubler on it to get the negative bias voltage.
 
12bz7
Junior tube assistant
Posts: 15
(5/28/05 11:20 am)
Reply   Re: PT wiring help needed.
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 Thanks for the info much appreciated.
A close friend has asked me to build him a small PP amp and since he's on a limited budget and I have some spare el84s and 6v6s thought it might be cheaper going that path.
The voltage doubler sounds good but have had no experience with one. Looks like a bridge but with 2 x diodes and 2 x caps.
What type of diodes (1n4007 maybe)? what type and size caps (100uf/350v, 50uf/350v)?

thanks again
 
Tiny Daddy
I only work on Fender's
Posts: 1242
(5/28/05 11:30 am)
Reply   Re: PT wiring help needed.
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 You can use 1N4007 and 100uF/350V caps.
 
12bz7
Junior tube assistant
Posts: 16
(5/31/05 4:56 am)
Reply   Re: PT wiring help needed.
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 Thanks Tiny Daddy and GroundhogKen, now have ~530v peak to peak unloaded. Now I've got to find a suitable amp schematic.
 
 
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