MT-1 Cheyenne trouble...

[Alexander N. Gerli Sr.]

Hi, gang!

 

I'm working on getting an old MT-1 going. Having some real difficulty.

 

I've had to do a lot of chassis cleaning. Old Joe Ham who had it must have
been a heavy smoker. I've cleaned up a lot of nicotine. Looks pretty good
now.

 

Okay.I have cleaned all the switch contacts with LectraClean followed by
De-Oxit D5. Did the audio pot too. The wiring underneath is incredibly neat,
done with careful right-angle bends on components. I haven't seen lead dress
this nice in years. No mods that I can find, and I have a full manual to
check with.

 

All the tubes check out all right except the 6146 and I have spares of that.

 

Now.I can't get any grid drive at all.except a small amount in the PHONE
position, keeping the mic gain off. By a small amount, I mean .20 mA on the
meter (yes, the metering circuit is ok and the meter itself is ok).

 

I decided to try 15m as I have a small portable rx to use. On 21.3, lo and
behold, I get a very weak carrier peaked by both the drive and PA tune
controls.ok, the pi-net seems to be working.as is the VFO.

 

But there's got to be something in the 6CL6 buffer or the 5763 driver that's
wrong. Should I check the interstage coupling caps? There's a 100pF disc
ceramic between the plate of the VFO and the grid of the 6CL6, and a 47pF
silver-mica between the 6CL6 plate and the 5763 grid (this is, sadly, nigh
impossible to reach). But silver-micas are supposed to be pretty stable
anyway, right? If I can get at the 100pF disc ceramic, should I just swap it
out? Maybe use a higher value? There's nothing in the manual about what
signal levels to expect between stages, so I'm left with swapping components
which might be suspicious.

 

Appreciate any leads or suggestions!  73!

 

Sandy

 

Alexander N. (Sandy) Gerli, Sr.

4012 Bristol Road

Durham, NC  27707-5403

(919) 489-9638

 


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