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  #1  
Old 12-15-2004, 03:09 PM
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Nick_the_'Nole Nick_the_'Nole is offline
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These should be simple questions...

...but no amount of searching will turn up a straight answer. And sorry if this is a little bit more on the DIY side, but I figured I might get better answers from the antique radio guys.

I am trying to build a battery eliminator for an old Atwater Kent 30. Theoretically simple enough, yet I can't seem to make heads or tails of it. First of all, how in bloody hell are you supposed to hook this thing up? I got that the A+ supply is 5v, the B+ is +90v, then you have a +67.5v and a +22.5v, and a -4.5v C bias as well. No problem there. But the A- lead is also labelled B- and C+? WTF, how are you supposed to hook that up?

Basically I need to know what all this translates to in building an AC ps for the thing. Right now I'm thinking I just need a + and - filament hookup (with the - just being a return to ground in the PS), a + for each of the plate supplies, and a - for the bias (possibly even just a lead hooked to the - side of a battery)?

Also, for the higher voltage supplies, would it be wise to just run voltage dividers directly off rectified/filtered wall power? If so, what kind of current draw am I looking at on those?, since resistor values are dependent on that bit of info and it is nowhere to be found...

Last edited by Nick_the_'Nole; 12-15-2004 at 07:48 PM.
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Old 12-15-2004, 05:35 PM
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Nick_the_'Nole Nick_the_'Nole is offline
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Ok, a bit more checking and I have decided to just do voltage dividers, it's a lot easier and cheaper than making battery packs or anything, but I still am not sure on the current draw I'm looking at. I found a little bit of info indicating it's around 10ma per tube, does that sound right?
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Old 12-15-2004, 09:26 PM
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Tom Bavis Tom Bavis is offline
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Al the supplies share a common terminal - B-, A- and C+ all hook to the same terminal. The high voltage should come from a transformer - a 30W isolation transformer will do, $15-20 at Allied, Mouser etc. Or tie two lower voltage transformers back-to-back. You can use a regulator for high voltage - TI part number TL780 can take 200 V or so.
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Old 12-16-2004, 10:36 AM
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Nick_the_'Nole Nick_the_'Nole is offline
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Ok, overnight I looked a little more, and I didn't realize that the batteries were originally connected together. Knowing that, now it makes a lot more sense. I was ultimately planning to get an isolation transformer, but I semi-frequently run across 'em for free if I look for 'em, so I was just gonna run the whole deal off a separate line conditioner box until I could find one.

But for any of this to work, I still need to know the current draw from the HV lines so I can get the resistor values right... I found some generic info for making battery eliminators for later farm radios, but there is some bad math in those, and I'm still left back at square one.
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Old 12-16-2004, 11:02 AM
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Chad Hauris Chad Hauris is offline
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Here is a link to the schematic of the AK 30: http://www.nostalgiaair.org/PagesByM...8/M0039388.pdf
The 01 A tubes it uses have a plate current draw of 3 milliamps each according to tube manual. Max plate voltage 135 v.
The 01 A filaments are 5.0 volts DC at .25 amp (250 ma.) each.
It appears to use 6, 01A tubes.
There is also a 71-A tube used as the 2nd AF tube: it has a plate current of 20 milliamps at zero signal. Max plate voltage is 180. Filament voltage is 5.0 volts at .25 amp (250 ma).
Keep in mind that the first digit in the tube number (say 301-a) is a manufacturer's number only and can vary. The real standard designation used in the tube manual does not include that prefix number, and thus is 01-a or 71-a, etc.
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Old 12-16-2004, 12:05 PM
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Nick_the_'Nole Nick_the_'Nole is offline
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Ya, I know that the tube numbering standard changed in 1934 or so, and I already got that schematic but can't make out most of the numbers and such on it... The 3ma each is what I needed on the 01a's but I have a 12a in the last audio stage in place of the 71a, so I believe the 12a would be significantly lower draw?

Also, how much variation should I reasonably allow in the 22.5 and 67.5v lines? I hear anywhere from 10% to 30% allowable margin in voltage, and while I'd like to get it spot on if I can, if I do end up with some error, how far off is reasonable? I know these things aren't extremely precision, but I'm trying to get a feel for what would work best...

I really need to find a good source for such info, I don't have a book that covers the early tubes and Google doesn't really give me anything except price lists at online stores, even when I use every conceivable variation on the numbers... Any suggestions for a good reference in the future?

Last edited by Nick_the_'Nole; 12-16-2004 at 12:12 PM.
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Old 12-17-2004, 06:17 AM
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Chad Hauris Chad Hauris is offline
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12a tube yes is lower plate current, manual states 7.7 ma at zero signal.
filament is 5.0 volts at 250 ma current. Max plate voltage 180.
The GE tube manual is what I have here from 1973...it has all the common old 1920's tubes listed. Just about all tube manuals seem to have the vital specs on the old tubes...the older manuals likely have more detailed data on them.

As far as plate voltage, as long it is under the recommended maximum value for the tube (and negative bias is at least as much as recommended) I don't think it is terribly critical. Filament voltage, though, should be kept closely to the recommended value or very slightly less for good tube life.
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Last edited by Chad Hauris; 12-17-2004 at 06:20 AM.
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Old 12-17-2004, 01:09 PM
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Nick_the_'Nole Nick_the_'Nole is offline
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Alright, sweet. That's what I needed to know. I do have a Sylvania tube manual from the late '50s but it doesn't cover some of the early types for some reason. I didn't realize that wasn't normal. Maybe I'll keep an eye open for a different book at the flea markets and such...

My filament supply is going to be run through an LM338 (or whatever number it is, I can't remember offhand) 5v regulator, so I should be fine there. Looks like I might even be able to get the PS put together this weekend.

The only obstacle after that is the dial pulleys. The potmetal ones are long gone, and somebody replaced 'em with some very badly done wooden ones... I have an interesting idea on making new ones easily and cheaply, and since it seems to be a fairly common problem, I'll post a tutorial if it works. (I don't have easy access to brass ones out of a junker radio.)

Thanks again. Hopefully I can get this thing working pretty soon...
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