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Old 1st March 2009, 07:23 PM   #11
jrebman is offline jrebman  United States
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Thanks, I'll take a look at those posts. I don't have a transformer yet, as I was going to have one made for this project.

-- Jim
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Old 1st March 2009, 07:27 PM   #12
jrebman is offline jrebman  United States
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Ok, took a look at those pages and see nothing. Maybe it's just a graphic, but I see no attachment, and my screen reader can't deal with graphics. This is the problem.

-- Jim
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Old 1st March 2009, 07:53 PM   #13
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Jim,

Let me provide some of the details. The LTP employs a 10M45S as the tail load, to force symmetry. The CCS is set for 9 mA. and the B- rail is 66 V. 43 KOhm/4 W. 6GK5 plate load resistors are called for. 300 V. is applied to the 6GK5 loads. The B+ rail voltage is 320 V. The C- voltage is 22 V.

Reply to the EMail I just sent and you'll get Poinz's gif, as an attachment.

As you are planning on monoblocks, 6SN7 LTPs would be OK, provided you use a line stage with gain. I suspect that buffering DC coupled MOSFET source followers are necessary. That would not be bad, as the 6V6 grid leak resistor value could come down.
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Old 1st March 2009, 07:54 PM   #14
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As far as your bias transformer goes, the Amveco 62035 (7 VA for a stereo bias supply) is also available as a 3.2 VA transformer for a mono application (62015). It's also available as a PCB mount potted version (that's what I used) as the following P/N's 70035 (7 VA) and 70015 (3.2 VA); both available from Digi-key. They actually give 44VAC with the secondaries wired in series.

If you use a primary transformer with a 50V bias tap (such as a hammond 300 series), you can skip the amveco xfrmrs above entirely and just use the bias tap, although if you want to energize the bias supply before the B+ comes up (start-up delay) a separate bias transformer gives a few more options.

You could also (I'm pretty sure) provide 320V B+ to both the 6GK5's and the 6V6's to simplify the PS design slightly, although the additional cap and dropping R are easy enough to implement. A Hammond 300 series (370DX or so) can do all the B+ voltages you need for a mono application.

What are the largest film cap values that you are planning to use in the PS?

I have just modified one of my PSUD PS schematics for this app with a 5AR4 and a 275V secondary transformer as a CLCLC supply but it is difficult to post the results here and still have them be legible. I can email a JPEG if you are interested.

To clarify, I believe that you can get the -66V and the -22V off of the bias tap (or amveco xfrmer) pretty easily. That's how Poinz did the EL34 version. I said "bias" above but it's actually the 10M45 voltage that comes off of the amveco in Poinz' schematic.
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Old 1st March 2009, 09:35 PM   #15
jrebman is offline jrebman  United States
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Eli and BW,

Thanks, now things are starting to make sense quite a bit more. Eli, I replied offline.

And yes, my plan was to use the monoblocks with a preamp.

Thanks,

Jim
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Old 2nd March 2009, 12:54 AM   #16
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You could also consider the 200 series hammond power transformers and use the Amveco for the -22V and -66V. The 200 series are less $$ and do not have the bias tap or universal input, so the cash saved can be applied to the Amveco (or other small VA transformer) and allow additional flexibility for start-up delay schemes, since you can apply the bias voltage and feed the CCS instantly upon startup and delay the primary side of the B+ transformer if req'd instead of having to deal with a start-up delay switching the secondary side.

The issue I'm presently having with the EL34 breadboard is alot of B+ overshoot on start-up due to SS rectification and a 385V transformer when the tubes are cold. I have have doubled-up all of the electrolytics in the PS to handle the voltage (close to 550V on start-up). It appears that there would still be some B+ overshoot even with tube rectification, although I haven't got that far.

With the 6V6 design voltages, 630V film caps, and tube rectification this will probably be less of an issue.
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Old 2nd March 2009, 03:03 AM   #17
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Jim,

These fine gentlemen have covered it very well while I was absent.  If you have further questions, don't hesitate to post me.  I tend in these fora to explain a lot of detail with .gif images, which of course don't help you at all, but I can pontificate at length as well, when prompted.

  :^)

Aloha,

Poinz
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Old 6th March 2009, 12:13 PM   #18
jrebman is offline jrebman  United States
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Thanks everybody, I think I have it under control now. I'll report back as things progress, but that will be in another thread, and ot for quite a while yet.

Best,

Jim
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Old 16th March 2009, 11:58 PM   #19
jrebman is offline jrebman  United States
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Poins,

YGEM.

Thanks,

Jim
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