[R-390] A few SP-600 questions

[James A. (Andy) Moorer]

----- Original Message ----- 
>
> How stable should the local oscillator  be on 6 meters?  I can tune SSB
> on 27 mcs with good stability, but the local 6 meter beacon
> warbles all over the place. SSB would be impossible to tune,
> the short term stability is just too bad.  Is this normal, or
> do I have a problem to solve?
>

I'll take a stab at this. You have a problem to solve if you really want to
use it on 6 meters.

After it warms up (30-60 minutes), it is pretty stable below 30 MHz. Above
30 MHz, it is real sensitive. If you just wave your hand over the VFO tube,
it will affect the tuning noticeably, even through the tube shield. Aligning
it in that range is an exercize in patience. If your VFO tube (the 6C4) is
the least bit noisy, it will wander about in the way you describe, so the
first thing to try is a new VFO tube. That will, of course, knock the
alignment of the high bands out a bit, so you will want to check the VFO
alignment. Other than that, any of the passive components around the VFO
tube can make the circuit noisy, especially the resistors. I use metal-film
resistors for the grid bias. I guess it helps a bit.

After the warmup period, a new VFO tube with new parts around it will drift
slowly back and forth as the temperature changes, but not so badly that you
can't receive SSB. The real problem up there is how twitchy the tuning is.
It really needs a vernier or something on that high band.

Hope this helps.

Enjoy!

James A. (Andy) Moorer
www.jamminpower.com