HW-16 Final Tube Meltdown

[Robert Wood]

Thank you Ken,

a. I measured pin 3 and there was a positive voltage.

b. I removed the 6GE6 turned it back on, and receiver began working fine.

c. I measured pin 3 to discover no voltage.

d. I measured opposite side of the RF choke attached to pin 3 and found -150vdc.

e. I removed the RF choke and checked continuity to discover it is open.  I
inspected it, and it looks fine... Must be related to being 34 years old.

f. I will not begin finding a replacement .5mH RF choke.  Hope my junk box has
one...

Thanks for everyone's help.  This was my first rig my parents bought me back in
1974 after getting my novice license.  I want to use it this winter.  I will
send an update once I find a replacement part and install it into the rig.
Thanks to everyone's technical assistance I got using this website, and please
let me know if there is anything you need from me!

Thanks,

Robert Wood
K5MBA

-----Original Message-----
From: Kenneth G. Gordon [mailto:kgordon2006 at verizon.net]
Sent: Friday, September 05, 2008 11:45 PM
To: Robert Wood
Cc: HEATH at LISTS.TEMPE.GOV
Subject: Re: HW-16 Final Tube Meltdown

On 5 Sep 2008 at 17:51, Robert Wood wrote:

> All,
>
>
>
> I am encountering a very unusual problem with my HW-16.  All was
> working well, and I operated it for about a week during the evenings.
> Last night when I turned it on and monitoring 40 meters, the final
> turned red hot.  I moved the switch to the current position, and
> noticed it was drawing current.

How much? Pegged?

>  I removed the 40 meter xtal and key
> and turned it on while switching bands and encountered the same
> issue.  I shut it off and retired for the evening.
>
> After getting home from work this afternoon, I decided to test the
> 6GE5 in my Syncore tube tester.  I was hoping the tube may have a
> short, but the tube tested ok.  I put the it back into the rig with
> same results. Before I tear into the rig, does anyone have any
> suggestions?

It sounds to me as though your grid bias is missing. Measure the
voltage at the grid with the key unplugged. Do this quickly so you don't
ruin the tube. The voltage at the grid with no key plugged in, or with
the key UP, should be around -150 VDC.

If it is zero or positive, then you have something between the -160
VDC line and the Grid that is open, or some other problem.

If the voltage is zero, perhaps L-15, a 0.5 mH choke, which is
connected right at the grid, pin 3 of the 6GE5 is open.

IF there is a high positive voltage on the grid, then the 100 pfd
coupling cap coming from the driver plate and which is also connected
directly to pin 3 of the 6GE5 may be shorted.

Measure the voltage at the grid of the 6GE5 and report back.

Do this very quickly so you don't ruin the tube. Connect your meter,
set it at a safe setting, then turn the rig on. 6GE5s are very rugged
tubes, but no tube of that sort lasts very long with a red plate.

Ken Gordon W7EKB

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