[Hammarlund] Fw: [BoatAnchors] (BA List) Hammarlund HX-500 Transmitter... (Halp!)

[David Thompson]

Please help Jack if you can
73 Dave K4JRB

----- Original Message ----- 
From: "Jack Harper" <jharper at secureoutcomes.net>
To: <boatanchors at theporch.com>
Sent: Saturday, April 27, 2013 2:39 PM
Subject: [BoatAnchors] (BA List) Hammarlund HX-500 Transmitter... (Halp!)


Greetings to the List...

I am hopefully bringing back "up to snuff" a
really nice Hammarlund HX-500 transmitter. If I
can get this beast into top-notch shape, I plan
for it to be my primary transmitter (CW) with the R390A "forever".

The HX-500 is a large rack-mounted 85-pound beast
(oh, my aching back) with 21 tubes - two 6146s in
parallel for the final - support for CW, SSB, DSB, FM, FSK/RTTY 80-10 
meters.

Hammarlund brought the HX-500 to market in 1962
or so - not many were built - 600 or so. Mine is s/n 294.


It is in excellent cosmetic condition and, I
think, "almost" HI working, though there are a few problems :)

First thing that I did was to install a modern three-wire power cable etc.

Second was to go through and replace the
electrolytics and the several paper capacitors.


I did power the transmitter up - there is no
output power and the 6A slow-blo fuse pops after about a minute in STANDBY.

I am at the "Check Resistance" values stage now -
I am a bit surprised to see that almost all of
the 150+ specified resistance points are solidly
within 10%. There are, however, six that are off.

The first two were simple to correct: #1 was
caused by a modification recommended by
Hammarlund in the first audio amplifier to
eliminate a source of distortion. That checked out.

#2 was another Hammarlund recommended modification, which also checked out.


However, bad resistance #3 is a bit
different.  V8 is a 6U8 used for anti-trip-relay
control. Pin #8 is the cathode and the schematic
shows (and the physical circuit agrees) three resistors in parallel from 
Pin-8:

R54 is a 2.2K to ground from Pin-8.

R56 is a 47K to +300VDC line. The +300VDC line at
that point measures 18K to ground after it settles (electrolytics).

R55 is a 470-ohm to the "operations switch"
(SO-2A) which is "OFF" for the published
resistance measurements. In OFF, R55 floats and,
therefore, should not be a factor in the measured resistance.


The Hammarlund published resistance measurement
for Pin-8 is stated to be 350-ohms. But, I
measure it in the physical circuit at 2.3K.

Calculating the expected resistance from the
schematic comes up as 2.1K or so - which is
within 7% of the actual measured value.

I think there is an error in the Hammarlund
published resistance chart, but I may be missing
something. The stated 350-ohms should, I think, really be about 2.1K.


Also, if you assume that the Operations Switch
grounds R55 (it doesn't in OFF, it floats and I
measured the resistance and it is not grounded),
then the calculated value comes out to about 380
- close to the stated expected value - or some
such - I wonder if Hammarlund errored...

Advice and Counsel greatly appreciated.  I hate
the idea of leaving Pin-8 totally out of published spec without a reason...

Thoughts from a List Member that has tackled a HX-500 before???


Regards to the List on a beautiful Saturday afternoon...

Jack, WØYJ ("Friend to all things Hammarlund")
Evergreen, Colorado USA





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