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Old 27th June 2007, 05:12 PM   #1
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Default 813 Project has begun !

All,
So I made the official dive into a monoblock 813 SE project, and plunked down hard-earned cash for a set of output transformers from Heyboer. They should be arriving this time next week; so I will be sure to submit some photos.
In review, I will be using a 2C22 (7193) tube as my driver; although if I feel the need for higher gain I was thinking of going two-stage with a 6SN7. Any thoughts on this ? I figured that I would start with the 2C22 on the breadboard and see what I think...
The Output Transformers are 6k, with a 40% UL tap.
For the power supply, I will be using a 400/0/400 400VA unit from Antek (which makes great stuff IMO), wired in series. The 800v will go into a bridge, into a CLCLC filter for around 900v. I had originally planned on using a full bridge of 6W4's, but perhaps I should use a hybrid instead ? Two damper diodes (for slow start), and two pieces of sand. Thoughts ? Suggestions ?
I'll take the 400v out of the CT to use for my driver tube B+.
A question here: How do I determine the voltage that I will be getting out of the CT (so I can plan my filter stages, and load line for the driver tube B+) ? Will it be 400v, or 1/2 the output voltage of the bridge ?
The chokes (10H and 8H) are custom wound from Heyboer as well.
I will be using a SS regulated supply for the heaters on the power tubes.
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Old 27th June 2007, 05:26 PM   #2
Gluca is offline Gluca  Italy
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Ciao.

Been there. My (triode strapped) 813 was running at 900V/100mA, parafeed with 10K OPT. I was getting something like 15W out of it.

I suggest you stay with a 2 stages amp. I used a 801A and a 1:2 step IT. An option can also be the 3C24 by EIMAC.

My first PSU was 700V (CT) into an hybrid GZ34 bridge for 750V or so. I switched to 2000V CT and mercury half wave rectifers into LCLC. Much better I'd say.

OH! You are using PSUD... not sure I got your Q properly.

SS for the filaments are going to be very hot, use a very large heatsink. Now I am using a LC there too.

Ciao
Gianluca
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Old 27th June 2007, 06:14 PM   #3
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Thanks for your help. I will take your advice and stick to a single driver stage. I think I will parallel the two stages of the 6SN7.
As far as the power supply goes, I really want to say with 6.3v heated rectifiers. Also, I do not want to go much higher than 850v on the secondaries, as I need to filter down the CT to no more than 400v.

Thanks again,
Steve
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