Re: Artificial centre tap for GG 3CX1200
|
Quote: ¡°I've also heard of using the secondary winding of a totally separate transformer that does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap.¡± ? Yes I have done this and it works very well.? Using the resistors for a fake CT will add a variable bias as the cathode current varies which will hurt the IMD performance.? Also as suggested, you might be able to make your own CT.? Try probing the secondary winding with a DVM fitted with a pin to see if you can find the ? voltage point.? I have also done this and found a CT at a very easy point to get to between the two layers of the secondary at the physical end between the two layers. ? -Chuck K1KW
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of va3dxv
Sent: Friday, December 01, 2023 1:57 PM
To: [email protected]
Subject: [ham-amplifiers] Artificial centre tap for GG 3CX1200 ? Hi, I've been trying to gather parts for a 3CX1200D7 build. I had trouble locating a sufficient filament transformer. Tube requires 6.3V @ 25A. Ended up finding one for 6.3V @ 28A - Would like to have more overhead but thought it would be the best I'd find, and only $50 brand new! Perfect!
BUT In my haste to complete an order of needed parts, I wasn't paying close enough attention. It turns out that it doesn't have a CT. (it's dual secondary - parallel is 6.3V@28A and series is 12.6V@14A) - D'oh!
Now what... when I used to play with guitar/audio amps, a semi-common thing to do would be to take a pair of low value resistors, put one end of each to each end of the filament winding, and ground the joint in the middle for a fake CT. Unsure how this will affect a cathode bias.
I've also heard of using the secondary winding of a totally separate transformer that does have a CT, and using it in parallel across my filament winding, then using that transformers centre tap. Further, I've heard of using a pair of diodes, each anode to each end of my filament winding and tie the cathodes together in the middle... or maybe that was t'other way around... either way I dunno about this either.
Anyways, obviously the best way forward would be to actually use a proper transformer, but since I can't find one and I already made this oopsie... I'm wondering what the next-best-way forward is? :)
Thanks :)
|
