Later models of the HQ-145 had hard wired diodes in place of the 5U4
family. I found that out when I had bought a schematic and found some
discrepancies between what my HQ-145 had and the schematic. Then I
happened to find on the web a schematic that had the 5U4 in it, so
this was undoubtedly an evolutionary change in the production runs.
My schematic doesn't specify what diode was used and I'll have to
check to see if a dropping resistor was added. All my schematic gives
is a Hammarlund part number. Of course, with no Hammarlund Radio Co.
that is now meaningless. But I agree that garden variety high voltage
diodes would work. This certainly would cut down on heat in the radio
as the 5U4 is the biggest tube in it.
W3JT
On Sun, 30 Nov 2008 06:58:28 -0500, k3hvg wrote:
AKSWL wrote:
Is there a soild state replacement for the rectifier tube 5U4 in a
HQ-145xc?
Seems I remember such a tube being available for around $20 from an
internet source.
73
John
Many, if not most, of the smaller (read: 5Y3, 5U4, 5V4, etc.)SS
replacements do not have a dropping resistor molded inside the unit.
I/we use a series of SS replacements up to and including the 3B28 and
4B32. The latter two SS replacements do have the resistors owing to FAA
purchase specs, however. Just be sure and include resistors in your
replacement design. As far as filament "stripping", as alluded to by
another posting, some say its a big deal. If the unit is not being
turned on and off many times a day, every day, I can't see it being a
problem.
The simplest thing to do is get an old octal tube base and solder in two
1N4007's. If it pleases you, fill it up with some Home Depot epoxy or
the like, just like the commercial jobs. Remember to hook the diode
outputs up to the correct DC output filament pin, as the Hammarlund
schematic indicats. Leave the other pin vacant, of course. While your at
it, try and keep the a.c. input voltage down to where the mfgr says it
should be, or a few volts less. High line voltage can really add to the
spectre of failures of vintage equipment
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