[R-390] bottom 200 kc dead

[Todd Bigelow - PS]

John Page wrote:

>     My Collins R390A just suddenly developed an odd ,to me, problem. 
> It suddenly decided it would not receive anything from X.200kc down. 
> This on ALL bands. Really didnt have a clue as where to start as 
> signals from 200kc up were great. It was as though you flipped a 
> switch when you tuned below 200kc on any band. I did check all tubes. 
> Just to try something. All checked good. Thought a cam had slipped so 
> I compared it with my stewart Warner which works great. All seemed ok.
>     Had a occasion to be talking to Jim Garland W8ZR this evening and 
> he thought I should check out the PTO. Jim knows his stuff so I went 
> home and decided the easiest check was a new PTO tube.
>     WOW it works. Old tube still checks good and returning it to the 
> PTO brings back the problem So Thanks Jim, you fixed it. Not sure why 
> that happens but at this point, who cares.
>     Just wanted to share this with the group. Might be some newbys to 
> 390's like me on here.
>                            John 


Thanks for posting this, John - these are the kins of things you'd 
(we'd?) not normally associate with this behavior (I was thinking 
something along the lines of a crystal problem). Just goes to show, you 
can never trust a tube even if it checks 'good'. There's a reason why 
they list "substitution with a known-good substitute" as being the best 
method for testing a tube or given circuit.

73 de Todd/'Boomer'  KA1KAQ