Super Junkbox 6S19P SET - diyAudio
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Old 17th March 2008, 06:33 AM   #1
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Default Super Junkbox 6S19P SET

I've got a couple 6DJ8's, more than a few 6S19P's, four noval sockets, two 120:12V 20W wall-warts, one 35VA 1:1 isolation transformer, and one 35VA 12V filament transformer.

I thought it would be funny to make the cheapest single-ended amplifier that I possibly can.

My plan (detailed schematic to come):

Use a B+ of a whopping 150V derived from the isolation transformer, preferably solid-state regulated. Use the 120:12V wall-wart transformers in parafeed, as 800:8 output transformers. The choke loads would be Hammond 193C's at 20H 100mA 181R. I'm new to parafeed; would these be all right? I would use smaller cheaper ones but B+ voltage is precious and I need a lower DCR.

The 6S19P's would be biased using a constant current source holding them at 40mA. This would allow +- 40V swing in a pretty linear region, as the plate curves show. I was thinking of using the CCS found here: http://diyparadise.com/yhlmccs.html but the greater bias voltages seem like they might be a problem.

The input stage would be a standard SRPP. The 6DJ8 seems pretty happy with only 150V total B+. With 330 ohm top and bottom resistors, at 5mA total, I get +- 43V, with a bias at -1.63V. I'll want a volume potentiometer! I could also probably use a 12AT7 for a bit more headroom but I don't have any and am poor. I'd probably need to use one if I ever wanted to implement NFB.

So what do you think? Am I crazy, or just very cheap? Does this amp have a chance of working?

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Old 17th March 2008, 09:31 AM   #2
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Oops, bad loadline.

I just realized that I'm burning off 40V or so in the cathode resistor for the 6S19P, so my B+ needs to be about 170V. This is a lot closer to 1.414*my house AC which is usually around 125-127V... Good stuff.

A SRPP using 6DJ8's at 170V should be able to provide the +- 25V pretty easily.

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Old 17th March 2008, 09:55 AM   #3
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Uh-oh. Just realized that some small 10W SE outputs from Edcor cost less than the plate chokes, and are a more "sane" impedance. Oh well, maybe I'll save the wall warts for some kind of headphone amp.
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Old 17th March 2008, 03:29 PM   #4
ilimzn is offline ilimzn  Croatia
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Default Re: Super Junkbox 6S19P SET

Quote:
Originally posted by sorenj07
...Use a B+ of a whopping 150V derived from the isolation transformer, preferably solid-state regulated...
The 6S19P's would be biased using a constant current source holding them at 40mA. This would allow +- 40V swing in a pretty linear region, as the plate curves show.
You have a crytical error in your reasoning.
The loadline will be that of a current source only if there is no actual useful load to the circuit, which kind of defeats the purpose
Secondly, at a whopping cost of one capacitor, you can double the B+ voltage.
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Old 17th March 2008, 04:39 PM   #5
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Yeah my reasoning was not very good. I've learned a bit since then, including to make a reasonable design. Feeding the isolation transformer into a doubler for 300V to bias in the following new way is the way I'm doing it. 2.5K load (10W Edcor OPT)

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Old 17th March 2008, 05:34 PM   #6
Fuling is offline Fuling  Sweden
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Quote:
Feeding the isolation transformer into a doubler for 300V to bias in the following new way is the way I'm doing it. 2.5K load (10W Edcor OPT)
Seems like a much better circuit than the +150V - 800R option.
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Old 17th March 2008, 08:03 PM   #7
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Thanks. I'm very tempted to try and put this one together. Unfortunately I have a ton of other stuff on my plate. Once I finish some commission work I should have enough scratch to cover the few parts I need. I want some kind of metal cover to hide the un-belled isolation transformer and the toroidal filament supply
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Old 17th March 2008, 08:41 PM   #8
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Semi-final schematic. Can't wait to try it.

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Old 17th March 2008, 10:32 PM   #9
Vlauga is offline Vlauga  Russian Federation
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Sounding of a tube 6S19S is very similar on the transistor amplifier. But considerably smaller power))

There is other tube from this series of tubes for application in stabilized sources. It 6S41S.
http://forum.cqham.ru/download.php?id=2702
Its power disseminated by the anode 25 watt.

In this series of lamps there is one more reputable lamp because of the uniqueness. It 12S42S.
http://www.next-tube.com/DataSheets/tubes/12s42s.djvu
Its power on the anode of 120 watt! Its current catode 1.2А!
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Old 17th March 2008, 11:01 PM   #10
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Quote:
Originally posted by Vlauga

In this series of lamps there is one more reputable lamp because of the uniqueness. It 12S42S.
http://www.next-tube.com/DataSheets/tubes/12s42s.djvu
Its power on the anode of 120 watt! Its current catode 1.2!



- ?

I've never seen one, is it still a top-secret tube for military use only?
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