HP 200CD oscillator restoration

[Randall]

Ok, so this isn't about amp per se, but it is about a vintage hand wired, point to point piece of tube gear. I picked up what I think is an old Navy HP 200CD 5 - 600K HZ generator to restore. I have two questions about it. The small fine tuning knob that turns the large wheel is hard plastic, spring loaded to contact the back of the aluminum tuning wheel. Surely, there must be something missing, as hard plastic doesn't grip very well. Maybe a fiber, felt or rubber washer of some type. What would be a good way to get this function to work again, and to quiet the hard grating noise it makes when turned?

And, what are the two 12v lamps next to V1 and V2? I can't imagine they are for lighting inside a metal enclosure. So, are they current limiter maybe? And if so, why would this piece need them?

Thanks!

[martin manning]

Pictures? Schematic?

[ToneMerc]

Seems Google would have been a great place to search for info first.

http://www.vintageanalog.net/attachment ... 1314128799

TM

[martin manning]

Nice piece of gear!

[Randall]

I have about $90 into it. The vernier dial was seized, but I got it freed up and now she's workin' slicker 'en a smelt! Thanks to TM for landing the docs, from them I glean that the vernier assy is indeed stock as I find here:

http://www.qservice.tv/VPASP/shopexd.asp?id=10060

I just don't get it, hard smooth plastic driving smooth aluminum? Something surely is amiss here. I was hoping some of the old school would know about this, that is why I posted here first.

I still don't get the RT1 and RT2 lamps.

[Prairie Dawg]

I would head on over to the antique radio forums for test equipment and see what you can learn there. The bulbs are part of the bridge circuit. You can see them on figure 4.1 of the manual.

That's about one of the best pieces of test equipment there is. by the way.

[Randall]

Here's where I am: http://s668.photobucket.com/user/Randal ... t=3&page=1

[boots]

I wonder if the two lamps are intended to produce enough heat to keep the oscillator stable? Some old-time radio transmitters had crystal oscillators with the crystal mounted in an enclosure (crystal oven?) to keep the temp, and thus the frequency, stable.

I imagine frequency stability would be even more important in a good piece of test equipment.

[alvarezh]

Page 5-3 of the manual:

"amplitude stabilization lamps"

All the best!

[xk49w]

The 200A used them as temp stabilization of the wein bridge oscillator amplitude.

[Randall]

I got it up and running almost good as new I think. Very smooth, very nice. The vernier adjustment is now working very well, just needed to get in there and lube everything. Looks really rock solid on the scope, with the slight exception that the dual sealed AB Amplitude pots is a little jumpy, but not too much, and only when being adjusted. I can live with it until or if I find a nice replacement. I want to keep it stock as possible.

So, I am very pleased with my eBay adventure, and I have you kind and experienced folks to thank for it. Love the good stuff!