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Need info: Stewart Warner 950 - Printable Version

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Need info: Stewart Warner 950 - BrendaAnnD - 04-01-2015

I have a Stewart Warner 950 with no top cover. Also no tubes.

In looking up the schematics on N/A, I find several different versions of this set. This one appears to be a later model AC version. The AC version in the schematics uses 24A's for the RF amps, this one does not. Whatever it does use has no grid cap. Does anyone have any information on this version? The chassis seems to be in very good condition, and after installing an 80 rectifier, all sockets have voltages on the plates, so I really want to try to get this one going.

Thank you for your time.

RE: Need info: Stewart Warner 950 - Radioroslyn - 04-01-2015

Got any pic's of the chassis??? How many pins do the RF tubes have? And what do you have for filament voltage??
Terry

RE: Need info: Stewart Warner 950 - BrendaAnnD - 04-02-2015

Didn't think to check filament voltage, but the sockets are 5 pin. Tube complement appears to be 80/45/45/27/27/27/27/27. All filaments except the 80 are 2.7V no load. Forgot to check them under a load when I finally found my long lost stash of 27's.

What's really amazing is that the doggone thing actually makes radio noises! I can get just one stations right now, but that's not bad considering I haven't recapped it yet nor are the coil shields in place! (I'm trying to straighten out some dents in them).

The power transformer has been replaced, and I'm pretty sure that the B+ voltage is way high, so I may have to do something about that.

RE: Need info: Stewart Warner 950 - Radioroslyn - 04-02-2015

Back in the early days there weren't many choices!!! A little odd as I don't think I've seen a TRF set w/227 as the rf amps.  The 24A was just coming out as the superhets were slowly becoming popular, about 1929. In a set it was a big selling point having these new fanged SCREEN GRID tubes. And have a screen grid meant having more gain. Mostly seen in TRF sets 226's 24A's and 201's and 222 on the battery sets.
Have fun chasing electrons!
Terry

RE: Need info: Stewart Warner 950 - BrendaAnnD - 04-02-2015

I figured it out. This set must be an EARLIER version, as it uses 27's. I wonder how crazy it would be to upgrade this set to use 24A's? The sockets are the same, after all. I would basically need to add the screen grid circuit components and connect the tuner sections to the grid caps instead of the sockets.

RE: Need info: Stewart Warner 950 - Radioroslyn - 04-02-2015

Hey if you have a few 7 pin sockets why not try some 3AU6's??? Neutralize that!!!
Terry

RE: Need info: Stewart Warner 950 - BrendaAnnD - 04-02-2015

I'd rather keep it looking original. If I could modify to use 24A's, it would technically be an upgrade rather than a frankenradio. Icon_smile

RE: Need info: Stewart Warner 950 - BrendaAnnD - 04-03-2015

My turn to be perplexed...

Been working on this Stewart Warner 950. It's the early version, 7 227 tubes, an 80 and a pair of 45's.

Tonight, I slid the coil shields into place and checked out the reception (yesterday I had checked it out without the shields in place, and got just one station and of course lots of oscillation). It played pretty well, for a while. After a bit, it started sort of sputtering and then went away completely.

I did some troubleshooting and found that the large voltage divider resistor was open on both halves (it had some tell-tale corrosion in spots). I subbed in some temporary replacements... B+ on each tap now, but still no sound.

Began tracing things out. Good B+ on the 45's, but none on the driver tube. Darn, I thought to myself.. the interstage transformer must have opened up. Check B+ on the other side of the input.. hmmm.. nothing there, either.

Checked the B+ on the plates of all the other 27's.. none there either. Curiouser and curiouser. Especially since according to the schematic, there's nothing but a solid wire between the divider resistor and the bus that goes to all of those plates.

Tracking where that open is will be a MAJOR PITA, since the wiring harness has this beautiful truss holding it all together, and to trace the wire from the divider to where ever that bus is will require that I remove that truss. Icon_sad

Sooooo... I decided to jumper in a 10K resistor between the proper tap on the divider to the B+ side of the interstage transformer (which should, and did, put B+ onto all those other plates as well). Turned on the radio and VIOLA! (as I brought the voltage up on the variac it made a noise not at all unlike an out of tune string instrument.), there was sound again.

Next, I bypassed that extra 10K resistor and everything is working very well indeed.. better even than it was before.

So much for the troubleshooting.. now I'll have to actually trace down the open circuit.

RE: Need info: Stewart Warner 950 - KCMike - 04-03-2015

Sounds like the Stewart Warner is quite a challenge. Looking foward to your continued posts on this one. Good luck.

RE: Need info: Stewart Warner 950 - Ron Ramirez - 04-03-2015

(04-02-2015, 07:18 PM)Radioroslyn Wrote:  Hey if you have a few 7 pin sockets why not try some 3AU6's??? Neutralize that!!!

A little tube rolling, eh? Hmmm...I may have to try that sometime. Maybe some 6AU6s in place of 36 or 77 tubes.

RE: Need info: Stewart Warner 950 - BrendaAnnD - 04-03-2015

I could always try making socket adapters and use some sort of octal triode or a heptode wired as a triode.. but day-um, the gain would be ridiculous compared to a 27, and I'd probably get nothing but oscillation. I could probably replace both 45's with a 6SN7.. Icon_smile Oops.. nope, wrong filament voltage..

RE: Need info: Stewart Warner 950 - BrendaAnnD - 04-03-2015

BTW, this set doesn't even seem to have any neutralization adjustments.. just some fixed caps in each stage.

RE: Need info: Stewart Warner 950 - Radioroslyn - 04-03-2015

There is a military metal tube 16** that has 2.5v filament that some folk rewire to use as a 45. It's a tetrode or penode I forget.
Terry

RE: Need info: Stewart Warner 950 - BrendaAnnD - 04-03-2015

Terry,

I actually have a dozen or so of those. Be cheaper than 45's, too. Will have to look up the filament currents for both tubes, though.