[R-390] Differences between the various URM-25 generators?

[Flowertime01 at wmconnect.com]

Tom,

I hope you get a nice long response to your question with more knowledge than 
I have.

There were A, B, C, D, E, F, and a G.
There was also a civilian model.

There were many other flavors.

We should have a link to a schematic for each model on your R390 pages.
Maybe they should be an add on to the Y2K CD.

The tube set did vary from model to model.
The internal drum / tuning section / mechanical vary from model to model.

The later models are considered "better" than early models.

The best change is to solid state the rectifier tubes like we do with the 
R390's.
This of course changes the B+ and frequency. So you need to re calibrate.

This change does get a heat generator out of the case and lets the unit run 
cooler.

The D model are considered Good.

No problem keeping any of them running. Check the tubes every 4000 hours and 
calibrate whenever the signal gets so far off the dial number you cannot stand 
it any more. replace the dial lights as needed. Watch for the blue gas glow 
in the tubes. The tubes will still test good in a tube checker. But get them 
out of the signal generator. New tubes will drift. Just leave the generator on 
for several days to "cook the new off".

Microphonic and noisy tubes are my worst problems. You can hear the generator 
noise in the receiver headphones when you bump the generator around on the 
bench. This noise is not a problem. 

Roger AI4NI






> 
>