[Hallicrafters] Hallicrafters HT-45 MKII Amplifier

[Al Parker]

Hi Robert,
    I got an HT-45 last Fall which had a similar mod.  Mine didn't come
with any docs either, and I didn't record the wiring on my schematic, but
did make some notes that might help you out.  I suspect that there's a bad
contact in the relay, or bad connection somewhere in yours that results in
an open ckt from input to output RF jacks.
    My notes indicate that for mine, TB-1 is used to contol the relay
coil, which in mine is 120vac. One terminal of TB-1 gets 120vac when the
"Plate" switch is on, the other to the relay coil.  The terminals are
shorted by the xmtr/xcvr relay and operate the relay which not only
switches the antenna, but also the bias to the tube.  So, in mine, there
is a set of relay contacts across R2 to change the bias, and R2 is not
connected to TB-1.  The 120vac to TB-1 comes from the junction of the
"Plate" switch and R12, the dropping reisitor for the "Plate" lamp.
    If you need a relay, Mouser.com is a good source, no min. chg, no
upcharges on shipping, quick service.
    I hope this is clearer than mud, you never know at this time of nite.
    My Loudenboomer gets weekly use on the Vintage Sideband net, 14.292
+-, 3PM ET on Sun., driven by an HT-32, rcvr is SX-115.  Hope to CU there.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.boatanchors.org
http://www.hammarlund.info

----- Original Message ----- 
From: "Robert Davis" <robertedavis at sbcglobal.net>
To: <hallicrafters at mailman.qth.net>
Sent: Monday, May 08, 2006 8:03 PM
Subject: [Hallicrafters] Hallicrafters HT-45 MKII Amplifier


> I recently purchased an HT-45 MKII amplifier to match my HT-44 and
SX-117.
>
>   Upon close examination, I discovered that it has been modified for
internal RF switiching, apparently so that it may be used with a
transceiver.
>
>   My attempts to "reverse engineer" the modification reveals that there
is a 12-volt DPDT relay used for the RF switching to direct RF input into
the amplifier circuit during transmit operation and to bypass it during
receive operation.
>
>   Checking the continuity of the relay contact, it appears that there is
no continuity between the input and output antenna connectors when the
relay is de-energized. One would expect that there would be continuity
when de-energized so that a transceiver can receive signals.
>
>   My question is the following:  I suspect that this may have been a
common modification to the HT-45. If so, there should be some articles, or
technical data on the modification.
>
>   1)  Does anyone have any information or source of information to learn
more about this modification?
>
>   2)  If the relay is defective, can anyone recommend a parts source?
>   Any and all good information will be appreciated,.
>
>   Thanks all.
>