Precision 920

[Buzzsaaw]

Howdy,

I started working on my 920... found some bad Potentiometers. I've been searching for replacements but have found nothing so far. Here's what I found in the TT:

R14 300ohm clarostat pot (1 11/16" in diameter and wire wound)
R13 40ohm pot also wire wound.

The larger one, R14, was really fried and very smelly.. it took a lot of heat at some point.. and no.. it wasn't me doing the fry job. (grin)
The 40 ohm was missing it's cover and would sometimes work but most of the time not. It had been subjected to a lot of moisture.

I just hope that whatever caused this is gone.. and that this isn't too expensive to fix.

Schematic for the 920 is here:
http://oldradios.50webs.com/precision/

Anyone knows of a source for these high wattage Pots I'd appreciate the info.

Buzz aka Da Fried Pot Collector

[bandersen]

Any idea what the wattage is ?

I'd check with Playthings of the Past: http://www.oldradioparts.com/pg2a22.htm

They have several 40 ohm pots at 2, 3 and 5 watts. Also some 300 ohm at 2 watts.

There's also ebay.

Here's a 300 ohm 25 watt: http://cgi.ebay.com/OHMITE-300-OHM-2...-/400092214166

It seems 40 ohm are a little harder to come by.
Here's a 40 ohm http://cgi.ebay.com/300B-211-845-Nob...-/270495697121

[Buzzsaaw]

Hi,

I did see that 40 ohm Pot on Ebay before. Wow, quite expensive. The 300 ohm should work and thanks for finding that. I don't have a clue as to the wattage of the pot that was in there. The 300 ohm, as I mentioned was very big but the 40 ohm was just regular size. Both are wire wound.

That schematic drawing program is kinda fun!.. (from the Variac post) I'm still looking for a switch. I think I have to just draw one out.

Buzz

[bandersen]

I just remembered that I have a 920 too!
The box it's in doesn't look quite right as there's only a little box with lid up top - no lid for the while tester.
No marks where there might have once been hinges either

I do believe it is working though.


I can pull it out if you'd like to compare the insides to your tester.

[Buzzsaaw]

Howdy,

I took some pics for ya and everyone too.

The case is the nicest part of this tester. It was refinished by the person I bought this from.







And some pics of the insides. Notice the first pic and the holes that mount the power xformer. The weight of the xformer caused the panel to dent. I'm trying to figure a fix for this without breaking some of the near by sockets.



The panel is bent or tweeked in other areas too.



Also, this unit must have been subjected to moisture or perhaps a battery that might have been left in the case. (I don't know where the 4.5v battery was to be stored as the leads were just left dangling)



I used some red tape as a temporary hook up as pictured.



LOTS of rust and even though this plate is removable, it has quit a bit of wiring on it including that 4 pin socket. Maybe after I get it all working.



Just an overall inside shot.



And lastly, I removed the Roll apparatus just for protection during the operations. It rolls well and looks great even though there's some rust on the hardware.

So that it!..

I did find some pots at the "play things of the past" site. I haven't called and ordered.. Heehee.. I'm still trying to attain the 20 buck minimum order. He's got some nice books and manuals.. Maybe that will fill the gap.
I had to download each TXT file and stuff it into my Works program, then I could search and cut and paste to another blank doc file. He's got an incredible inventory.. Wow!

I did order another tt from Ebay. That BK 667. Hope it works.

Buzz

[bandersen]

Nice cabinet! Clearly mine isn't even close - not even any dovetails. Odd though 'cause it fits well

I wasn't aware there was supposed to be a 4.5 v battery. I think it's for the ohmmeter mode.

Here are some pics of mine.

[Buzzsaaw]

It's had a hard life..I'm think'n..

I notice the little storage area has a door.. Mine doesn't.
Also the pot that's located on the same plate as the V tube doesn't have a cover.. I thought that was a fault in mine. I wonder if there all like that?



(the second pot to the right of the Vacuum tube in your photo above)

No rust in yours either. Nice!

Kinda fun comparing. Too bad we don't live closer cuz we could combine the two into a good unit.

Buzz .... -aka The Tube Tester Rust bucket and burnt Pot locater...

[bandersen]

I'm keeping my eyes open for a cheap one that's fried but has a decent cabinet. If I find one, you're welcome to whatever parts you need.

[jeyurkon]

I have a Precision 10-12 which is very similar. I'm pretty sure the 300 ohm pot is 25 watts so the eBay one should be a good choice. Radiolaguy offers a 250 ohm 25 watt pot. Line Adjust

John

Originally Posted by bandersen

Any idea what the wattage is ?

I'd check with Playthings of the Past: http://www.oldradioparts.com/pg2a22.htm

They have several 40 ohm pots at 2, 3 and 5 watts. Also some 300 ohm at 2 watts.

There's also ebay.

Here's a 300 ohm 25 watt: http://cgi.ebay.com/OHMITE-300-OHM-2...-/400092214166

It seems 40 ohm are a little harder to come by.
Here's a 40 ohm http://cgi.ebay.com/300B-211-845-Nob...-/270495697121

[Buzzsaaw]

Wow.. Thanks Bandersen,

That's mighty nice of ya...

I did find a 300 on Epay, but I missed it and it ended on me.

More will come along. The 50 watt Rheostat on Epay was too large in diameter. I'll keep looking. I'm going to try and clean up and adjust the 40 ohm WW pot and maybe it will work.
Thanks guys!

Buzz

[Buzzsaaw]

I'm still looking for a 300 ohm and about 25 watt POT for this 920. I missed one on Eflea waiting for a note from the seller on it's dimension. Rats! I wrote "play things" website guy and no reply. He lists several Possibilities so I'll keep waiting.
In the mean time.. the rain keeps falling. Two days and nights of nothing but light rain.. then heavy rain. This semi-desert area is going to turn tropical (grin). Hay! If I plant a banana.. will it grow?

Buzz

[Findm-Keepm]

Originally Posted by Buzzsaaw

I'm still looking for a 300 ohm and about 25 watt POT for this 920.

Are you looking for one pot, or are you looking for two pots? Following the thread, it's hard to decipher what value/wattage pots you need.

The 25 watt would not be a pot, but a rheostat - Ohmite, Angstrom, and Clarostat are the big three when it comes to rheostats. Angstrom is now part of Vishay, and their 25 watt rhoestats are smaller in diameter (38mm)than Ohmite and Clarostat devices.

If you are looking for a 300 ohm, 25 watt rheostat, the Angstrom RT25 series are what you need - 350 ohms is standard, but you may find a 300 somewhere. Allied Electronics lists Vishay/Angstrom as a line they carry. Mouser carries a 220 ohm, and a 470 ohm, both a bit away from your 300 ohm value.


Cheers,

You can also check fleabay or some of the surplus places to see if they might have what you're looking for.

[Buzzsaaw]

Hi,

Sorry about the confusion. The 40ohm pot, I believe, I'll be able to clean up enough to get back to work.

The 300 Ohm Pot/Rehostat at 25 watts... I finally managed to find a replacement for.. I hope. We'll see when it gets here. I'll post of pic of it.

Buzz