Self Osc Problem
 

Andrew VK3BFA wrote:

and
didn't know there was a VR150(was it?)

That was before I added it. Strangely, it works about as well without it.

How about a photo of the latest metal attempt? - remember, if it looks
nice and neat, it doesn't really matter if it don't work too good....

I just posted one to http://schmidling.com/807b.jpg

Unfortunately, it now looks better than it works.

Hah! - silly man - NOW you have to get the VFO stable, as well as all
the other problems.

I faded out of ham radio because it was boring me to death once I "moved
up" to a rice box. My born-again career keeps me interested because
hardly anything works very well.

I finally gave up on keying the oscillator because of chirp but now it
drifts so badly, I still can't use it.

It's an interesting problem though that sort of defies my analytical skills.

When I turn on the osc, it drifts up several hundred cycles in a few
seconds and stops. I can find no voltage changing like that, I moved
all the hot stuff out just to test that and I am stumped. It seems like
it is in the tube itself.

I am now keying the grid bias of the osc and there is no chirp but it
does that several second climb that would be frowned upon.

Long term stability is another problem but in the noise at this point.

Do you or anyone happen to have a couple of 1000 pf zero TC caps? I am
using cheapo ceramics and they are not so good. Blowing on them through
a straw has a rather profound effect on the freq.

Interestingly, if I hook it up to a Variac, I don't get 200 hz change
until I get below 75VAC. This is rather amazing to me and points to a
temp rather than voltage problem.

BTW, this started out as an exciter for the 8000 rig but I have since
gotten the bug to make a CW rig out of it. Again, the rice box is too
perfect in that mode also for my interest.

js

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Self Osc Problem
 

On May 27, 2:02 am, Jack Schmidling wrote:


I just posted one tohttp://schmidling.com/807b.jpg

Unfortunately, it now looks better than it works.

And it LOOKS very nice...why no shielding around the vfo assembly? -
the sudden temp druft is possibly something suddenly stabilizing as it
warms up - BTW - polystyrene caps are a better substitute for disc
ceramics, especially old ones...


I faded out of ham radio because it was boring me to death once I "moved
up" to a rice box. My born-again career keeps me interested because
hardly anything works very well.

Good one- their the things that provide real satisfaction, the sort
that cant be bought...

good luck- keep us posted on progress.....

73 de vk3bfa Andrew

Self Osc Problem
 

Jack,

New chassis looks great, well done.

It looks like you have a white wire (Anode HT maybe) going to a meter
then through the chassis. This will need some serious de-coupling
(feed through cap) as it enters the chassis otherwise it is going to
radiate in the lower chassis which won't help with the stability
issues. A 'T filter' would be good here, 1mH above deck, a 10nF
feedthrough cap and 1mH below deck.

As Andrew mentions, you also have 'below deck' electronics 'above
deck' in the form of the VFO. This is going to need very tight
screening to avoid feedback and stability issues.

What frequency are you running this unit at - 14MHz ??

Any chance of some higher res photos looking from above the chassis
and from below ?

Regards,

Mark
On May 27, 7:49 pm, Andrew VK3BFA wrote:
On May 27, 2:02 am, Jack Schmidling wrote:

I just posted one tohttp://schmidling.com/807b.jpg

Unfortunately, it now looks better than it works.

And it LOOKS very nice...why no shielding around the vfo assembly? -
the sudden temp druft is possibly something suddenly stabilizing as it
warms up - BTW - polystyrene caps are a better substitute for disc
ceramics, especially old ones...

I faded out of ham radio because it was boring me to death once I "moved
up" to a rice box. My born-again career keeps me interested because
hardly anything works very well.

Good one- their the things that provide real satisfaction, the sort
that cant be bought...

good luck- keep us posted on progress.....

73 de vk3bfa Andrew