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Looking for a transformer compatible with an Altair 8800b linear PSU

jon1967us

jon1967us

Experienced Member
Joined
Jul 28, 2022
Messages
91
Location
Los Angeles
I thought I'd give the forum a shout to see if by some stretch of luck someone may have a spare. My system is only missing the transformer, which was removed by a previous owner. Otherwise, I plan to convert the PSU to switching supply units. I suppose I could cannibalize a "spare" Northstar system I have for one but that PSU circuit is very different and I'm concerned about compatibility, and I'd rather like to avoid turning an otherwise complete system into a parts donor.
 
Chuck(G) said:
Why not design your own PSU? Linear PSUs are easy.
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Well, I have switching power supplies that should work well in this application, should I not be able to locate a replacement transformer. My preference would be to keep things as original as possible
 
Chuck(G) said:
I've got my Altair Rev 0, so I don't know what the 8800B used. What transformer ratings are you looking for?
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The B used a beefier PSU than the A. I’m pretty sure both PSUs would work in either machine though. The transformer would need to handle 30A for the +8 and approx 2-3A for +/- 16.
 
The original Rev0 8800 PSU was pretty wimpy. At any rate, Surplus Sales might have something worthwhile. My Integrand box has a hog of a transformer--Integrand claimed that they wound their own. The 8VDC output is unregulated, BTW.
 
I've got two options for you, an original 8800B transformer out of a beat up parts unit, and a third party that IIRC lines up with the mounting holes.
 
glitch said:
I've got two options for you, an original 8800B transformer out of a beat up parts unit, and a third party that IIRC lines up with the mounting holes.
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I’ll take the 8800b, just for authenticity’s sake. I’ll email you. This is Jon, btw, the guy with the Vector ZCB. Thanks
 
deramp5113 said:
That was quick! Looks great.

Mike
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Thanks, Mike. Glitch miraculously had a spare and shipped that monster out to me. Luckily, the rest of the power supply seems to have held up, so it was just a matter of making the Molex connector and carefully reconnecting all the other leads. I gradually brought it back up on a isolation transformer/variac (Sencore Powerite) without any problems - both the giant cap and the xformer are completely cool to the touch.
I'm glad I could keep the PSU period correct.
 
jon1967us said:
Thanks, Mike. Glitch miraculously had a spare and shipped that monster out to me. Luckily, the rest of the power supply seems to have held up, so it was just a matter of making the Molex connector and carefully reconnecting all the other leads. I gradually brought it back up on a isolation transformer/variac (Sencore Powerite) without any problems - both the giant cap and the xformer are completely cool to the touch.
I'm glad I could keep the PSU period correct.
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Nice work! This one came from a really busted up Altair 8800B Turnkey that ended up being a parts unit -- no dress panel, no boards, major chassis damage, 3rd party backplane bolted to the bottom of the blue chassis half, backplate all cut up, etc. Can't save them all, but that's where the parts come from, right?

That new Molex connector looks good! I'm not sure why a barrier strip was installed on that transformer, but the rest of the machine was cut up pretty bad, so I guess it's par for the course.

The bulk +8V caps do often reform perfectly when brought up slowly or reformed out-of-circuit with a bench supply. The smaller ones in the cap multiplier/ +/-16V board often just need replaced. The only one I've had where the bulk cap didn't reform was one where someone clearly flipped the switch and it blew the vent plug out.
 
Actually, the barrier strip is standard. It let’s you choose from 3 slightly different output voltages to generate the 8v supply. The 8800b manual breaks them into 0-4A, 4-9A, and 9-18A ranges.

Mike
 
deramp5113 said:
Actually, the barrier strip is standard. It let’s you choose from 3 slightly different output voltages to generate the 8v supply. The 8800b manual breaks them into 0-4A, 4-9A, and 9-18A ranges.

Mike
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Yeah, but there was one on the primary side, too! Jon removed it and replaced with the proper Molex plug.
 
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