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Old 23rd May 2008, 08:59 PM   #1
bigwill is offline bigwill  United Kingdom
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Question Generating big voltage swings without 'iron'

I've been looking at cathode follower based output stages and thus trying to figure out a way to generate the large driving voltage required. I saw something on John Broskie's TubeCad website that had some sort of arrangement with 6SN7-esque triodes in series to generate large swings, and counteract the max plate voltages of the tubes. I've been trying to find this but many google searches have turned up nothing!

What ways are there to generate such swings, say on the order of 400v p-p or more, without transformer or inductor loading?
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Old 23rd May 2008, 09:35 PM   #2
DougL is offline DougL  United States
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What ways are there to generate such swings, say on the order of 400v p-p or more, without transformer or inductor loading?
In order to get 400V p-p with a resistive or active load, the rule of thumb for triodes is to have a minimum 600V supply. Triodes swing about 2/3 B+. You also need a tube rated for an absolute minimum of 300V plate. The 6SN7 rated for 450V is a good choice, as well as some of the TV tubes have voltage ratings up to 550 V plate.

HTH

Doug
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Old 23rd May 2008, 09:38 PM   #3
bigwill is offline bigwill  United Kingdom
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Thanks for your reply Doug. With regards to max plate voltage, can this be briefly exceeded under transient conditions ie signal peaks? What actually happens if you go above this voltage?
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Old 23rd May 2008, 09:42 PM   #4
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What about something like the 6S4A
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Old 23rd May 2008, 10:05 PM   #5
DougL is offline DougL  United States
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With regards to max plate voltage, can this be briefly exceeded under transient conditions ie signal peaks?
The max plate voltage is the maximum DC voltage The tube can tolerate twice this voltage as AC.
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What about something like the 6S4A
I was thinking about that tube when I replied. However, I know there are different but comparable tubes across the pond.
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Old 23rd May 2008, 10:26 PM   #6
bigwill is offline bigwill  United Kingdom
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What determines the max plate voltage on a tube? Tendency to flash over, or is it a dissipation issue? I have some cheap russian 6SN7-alikes I'm not scared to try running at high voltages..
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Old 23rd May 2008, 11:01 PM   #7
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Quote:
Originally posted by DougL

I was thinking about that tube when I replied. However, I know there are different but comparable tubes across the pond.

ooh? pray tell what those might be what about 3D21A?
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Old 24th May 2008, 01:32 AM   #8
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I would suggest a bit of bootstrapped positive feedback, similar to what is done in the McIntosh driver stage. It's a good simple way to achieve large voltage swing, without having very high B+ voltage. Pentodes might be a better choice than triodes, as they can swing a large voltage more easily.
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Old 24th May 2008, 03:19 AM   #9
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Default Re: Generating big voltage swings without 'iron'

Quote:
Originally posted by bigwill
What ways are there to generate such swings, say on the order of 400v p-p or more, without transformer or inductor loading?
CCS loading. I had the same problem with an 845 design. That requires a swing of 310Vp-p to get it to max power. Here's a loadline. 6BX7 CC Loadline

Of course, without xfmrs or inductors, you will also need lotsavolts as well. In this case, I used a 6BX7 -- a vertical deflection type that can handle that. It operates off a +/- 410Vdc supply.
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Old 24th May 2008, 01:24 PM   #10
bigwill is offline bigwill  United Kingdom
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Just to throw a spanner in the works, how hard would it to be to generate large differential swings? Like a CCS loaded phase splitter...
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