RCA MI-11302 (85-A, 85-X, 41-C, 41-B Preamps) Power Supply Schematic Wanted

[crazy]

If anyone has this laying around if you could post or pm me TIA

 

[mjrippe]

Or more to the point, do you have this power supply and need to repair it or are you looking for the PSU schematic to re-create one?

Unless you are doing a historic restoration, I would go with a more modern supply.  These items call for 180-250VDC at around 5mA, and 6.3VAC or DC at 0.3 or 0.6A.

 

[emrr]

I misread it the first time, sorry.  Do you have these amps?

Tangent, all originally most frequently drew B+ power from the associated program amps, and had stand-alone filament transformers mounted in the fuse panel at the bottom of the rack. 

 

[crazy]

@emrr Hey Doug, yep I have a 41b and a 87. I just finished getting the latter up and running and looking to get the 41b working. Didn’t see that power supply in the docs section though.

@mjrippe I’m not much of an engineer, more of a solder monkey. I read the original used a 5Y3-G rectifier with those specs you mentioned providing 180VDC on the plates. Is there a similar project that I could ping off that you know of? I was hoping someone might have the originals schematic laying around but I could work with something else for sure.

 

[emrr]

That original supply has two chokes and a power transformer, it's pretty standard in approach.  It also requires a pretty expensive power rheostat for voltage adjustment, I'd think you'd be looking at a $150 at least in parts just to get started, assuming you have an enclosure already. 

I have an 87-A and 41-B's as well.  I have seen DIY pairs of 87's done using original transformers, including a single original PT, so it would seem you could even consider tapping B+ from your 87 to feed your 41-B.  That would need an additional dropping resistor and filter cap, since there's about 240V at the PSU section output.  I wouldn't advise going higher B+ than stock on a 41-B since current feeds through the output transformer, with unknown current safety margin. 

As standalone, I would get the International Power regulated supply which covers that voltage range (about $60 last I looked) and be done with it.  If you put that in an enclosure and leave room for multiple power output connectors, it'll power a pretty large number of similar things, should you get more in the future. 

I track this old RCA in a database, love to know which model and serial # of 41-B, if you feel like revealing it. There aren't a lot of them out there anymore.  I put a bunch of data in another 41-B 41B thread here recently. 

 

[crazy]

As standalone, I would get the International Power regulated supply which covers that voltage range (about $60 last I looked) and be done with it.  If you put that in an enclosure and leave room for multiple power output connectors, it'll power a pretty large number of similar things, should you get more in the future.

I like that option the best. Would this be the one to get?

https://www.mouser.com/ProductDetail/International-Power/IHB200-012/?qs=0xCm9DOQnC7%252BW4SCa00vHA%3D%3D

Then just add a filament transformer that could keep up with adding a few other devices in the future. Should I elevate the heater supply or do anything else to it?

I’d be happy to pm that 41b info to you. Hey I saw your 87a in some photos you posted before. I have a few questions on that one. What did you use for your dial face for the gain control?

 

[emrr]

Yes that one is fine.  You can also consider going DC filament, the 5V supplies they make will turn up to about 5.8V and that works well with most small signal tubes like this. 

Could be worth elevating the heater, though usually I don't notice a practical difference. 

The face on my 87 is what came on it, it may be the original RCA, I'm not certain.