[Boatanchors] Globe King 500A tuning

[Charles Ring]

On 9/24/2012 0840, Charles Ring wrote:
> After a month of doing fine on 80. 40, and 20 CW, my Globe King won't
> tune properly on 80. On 80, plenty of plate current off-dip, but no
> proper dip at all, with minimum plate current and max output (less than
> 100 watts) at minimum plate tuning capacitance. Works great on 40 with
> 350 watts out and normal tuning. Somewhat degraded on 20 but functional.
> This is same on antenna and dummy load.
>
> My prior attempt to use it on 15 failed similarly with very low output
> and red 4-400A plate, but now 80 while 40 does fine? Does this make any
> sense? I have used Deoxit on all switch contacts.
>

Thank you to all who replied. I feel quite foolish now, since the GK500A 
is now working well with no real repairs done. The problem appeared 
while I was trying to move from 40 to 80 in the Classic Exchange event 
last Sunday after midnight EDT. It is possible that I left the VFO 
(Globe Electronics V-10) in the 40 meter position or I might have even 
put it on 20, being too tired that night to really have any business 
using gear like this. I am now getting 350 watts out on 80 and 40 as 
measured on a Drake W-4,  250 on 20 and 200 on 15, still a concern. 
Usually plenty of drive on all bands, but there might be something 
intermittent in the VFO output.

I got these measurements on the coarse loading caps on a Sencore LC-53:

2 - 81 pF
3 - 179
4 - 352
5 - 1050
6 - 862

I never use positions 5 and 6. The original manual that I have has 
handwritten corrections on the C27-C30 part numbers in the RF parts list 
page. I am not sure if the original or corrected part numbers are right.

The earlier problems that disabled my GK500A were a bad 6AG7 
oscillator/buffer tube, an open 6AG7 screen resistor, and several bad 2 
watt resistors in and around the final. All of the bad 2 watt ones were 
the grey colored type: 
http://www.flickr.com/photos/60576343@N00/8023776341/ I have seen that 
type resistor fail in other gear and I should replace all of them. The 
modulator deck also has problems but that is a low priority for me.

Here is its RF deck, along with other pictures of what I've been doing 
lately returning to ham activity:
http://www.flickr.com/photos/60576343@N00/8023298684/in/photostream/

-- 
*Charles Ring W3NU*