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Old 31st December 2010, 10:55 PM   #11
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I haven't tried the 6LQ6 specifically because it is not cheap and I like to use cheap sweep tubes. They should do nicely and require less voltage across them than the typical 6L6GC or 807 pass tube. I was planning to use 6LW6's since I have a fair collection of them. I since scored the motherload of 35LR6's at a hamfest so I have been using them for experiments. I have no plans to build a power supply since I got the HP.

Your power requirements fit with the typical Kinght - Eico - Heathkit - whatever type bench power supply that uses 4 X 6L6GC. I have an old Knight KG-664 that goes from 0 to 400 volts and is rated for 200 mA. It will crank out 250 mA for an hour or so before the transformer gets hot and 300 mA for short periods of time. It has been shorted out dozens of times and I have not had the cover off of it yet. It was my main bench supply before I got the Fluke 407D. I got it at a hamfest for $25. They can still be found cheap at hamfests but go for too much money on Ebay. There are also versions that use 2 X 6L6GC and are rated for 100 mA. I have one of them too, same schematic.

It should be possible to build one, but you would need to kludge something together for the power transformer. It uses one raw B+ winding (about 500 VAC), a seperate floating screen supply winding (about 250 VAC), and yet another winding for bias (about 250 VAC). There is a filament winding for the tubes inside the supply and two more for external use. The circuit is similar to all of the bench supplies from that era (1960's). It uses an 0A2 and an 0B2 for reference, a 6DK6 control tube, and 4 x 6L6GC's for pass tubes. I have seen zeners for reference and 6CB6's for the control tube. Sweep tubes can be used for the pass tubes but the floating screen supply will need to be about 150 volts instead of 320 volts.

I have the manual with schematic scanned to PDF. It is too big to attach here (700K). I can email it to you if you want.
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Old 1st January 2011, 03:03 AM   #12
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Quote:
Originally Posted by mashaffer View Post
Are the tubes I mentioned like 6LQ6 and other Horizontal Sweep tubes reasonable performers as pass tubes? A pair of 6LQ6 in parallel ought to be able to pass quite a bit of current.
The TV HD finals will work just great as series pass regulators. Although, if you have 6LQ6s, I'd save those for audio final duty. It would be nice if these were more common and cheaper, but just esssss-loads of 6LQ6s got poofed in illegal CB equipment, and there was also a commercial amp that used them as well.

You can find lots more common TV HD types that'll work, aren't excessively pricey, and available.
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Old 1st January 2011, 03:43 AM   #13
taj is offline taj
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Hmm, just thinking... I have a couple dozen 500V/26A FETs (IXFH26N50) in my junk box. I wonder if they'd work for pass duty if I found an appropriate supply circuit. http://ixdev.ixys.com/DataSheet/91525.pdf

I can send someone a few if they want to play with designing a circuit.

..Todd
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Old 1st January 2011, 07:50 AM   #14
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Originally Posted by taj View Post
Hmm, just thinking... I have a couple dozen 500V/26A FETs (IXFH26N50) in my junk box. I wonder if they'd work for pass duty if I found an appropriate supply circuit.

I can send someone a few if they want to play with designing a circuit.

..Todd
No reason why they shouldn't. As with anything else solid state, pay attention to heat sinking requirements, and make sure you cage those heat sinks as a shock prevention measure.

Just be aware that SS is a lot easier to poof than HS, so be sure to avoid short circuits.
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Old 1st January 2011, 07:57 AM   #15
RE 604 is offline RE 604  Germany
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Hello ,
more power supply circuits , but in german language :

Verschiedene Roehren-Netzteile und ihre Schaltungen

Regards and a happy new year ,
Alexander .
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Old 1st January 2011, 02:20 PM   #16
Doz is offline Doz  United Kingdom
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I kept mine simple...

5VAC, 6.3VAC

Variac feeding a step up transformer to give me up to 550VAC at an amp.

Current metering via a homemade current transformer.

All this is AC, so you can play with rectification/regulation scheme in the amp itself.

Just my 1p's worth..
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Old 1st January 2011, 05:09 PM   #17
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Thanks George. You have mail.

I probably should sell the 6LQ6s and use the 6SJ6 instead. I guess I should knock up a test jig of some sort and do a quick manual gm test to make sure that they are at least functional. I have a tube tester but it has not been restored to usable condition yet. I suspect that plotting some data points by hand would be a more accurate measure of condition anyway.
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Old 1st January 2011, 07:48 PM   #18
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Quote:
I have a tube tester but it has not been restored to usable condition yet.
I have two tube testers. I quit using them because I kept finding tubes that tested good but didn't work in a real circuit. One is a popular Gm tester (I don't remember which one since it has been in the warehouse for years). The other is a programmable (12 slide switches) creation that probably seemed like a good idea at the time but isn't too repeatable today.

I have found that even small signal tubes can have good transconductance but show high distortion in an audio amp. I sorted a big box full of 6U8's and 6BL8's for distortion and was going to investigate this effect but never found the time. Big output tubes and sweep tubes can show normal transconductuctance at the power levels seen in a tube tester, but fail misaeably when asked to produce big power. On the other hand if the tube tester says it's dead, it usually is.

I emailed the manual a few minutes ago.
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Old 1st January 2011, 07:53 PM   #19
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What I ought to do (but probably never will) is convert the tube tester to a curve tracer for PC input. Thanks again BTW.
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Old 1st January 2011, 10:11 PM   #20
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i thought i'll give some inspirations to frontpanel, this is my HV PSU, use analog meters if you can, much easier to see when things goes wrong..

Click the image to open in full size.
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