[Boatanchors] Resolved: De-chirping a Globe Chief Deluxe?

[Richard Knoppow]

----- Original Message ----- 
From: "Charlie Cheney" <ccheney3686 at charter.net>
To: <boatanchors at mailman.qth.net>
Sent: Tuesday, December 28, 2010 11:13 AM
Subject: [Boatanchors] Resolved: De-chirping a Globe Chief 
Deluxe?


> Thanks to all who took the time to respond to my request 
> for help. After
> being assured that the GCD should be capable of chirp-free 
> operation, I
> checked components in the area of the 6AG7 and found a 47K 
> resistor that
> had drifted up to 60K. I got a significant improvement 
> from replacing
> that as well as the 6AG7 (the one in there was "mfd for 
> Globe
> Electronics" so presumably the original tube), but chirp 
> was still
> noticeable especially listening to the low beat frequency 
> I prefer for
> CW operation (~500 Hz).
>
> I measured the plate and screen voltages on the 6AG7 and 
> found it was
> operating well above the max rating for screen 
> dissipation. (This
> appears to be as-designed, I'm guessing as an economy 
> measure to keep
> down the cost of the resistive divider?). Worse, the 
> screen voltage was
> changing from 380V key-up to 240V key-down. Regulating the 
> screen
> voltage at 150 with an under-chassis OA2 pretty much 
> cleaned up the
> remaining chirp, without using any non-period components 
> or making any
> mechanical changes, so we're good to go.
>
> Thanks again for the help. I hope to make a lot of 
> contacts with this
> old timer on SKN.
>
> 73,
>
> Charlie K1LDZ

    I should look at the schematic before commenting but my 
first thought is that running the screen high is more likely 
to get the output of the tube up rather than to save the 
cost of a resistor or two.
    Keyed oscillators do tend to chirp. It may be that a 
different design could be used such as an electron coupled 
oscillator. The same tube type will work but the output may 
be too low. When the plate and screen voltage _ratio_ are 
chosen correctly an ECO is almost immune to voltage 
variation over quite wide range and the isolation of the 
output from the frequency determing circuit gives it a good 
deal of immunity to frequency variation with load change. 
The cleanest CW comes from letting the oscillator run 
constantly and keying the following stages but then you may 
have problems with backwave especially if using true 
break-in.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com