[Hammarlund] Send receive swtich

[ve4feb at gmx.ca]

Nice info guys.Ive read about manual tr switch back in the day and im familiar with the send recieve schematic on my 145a. It does make sense to use manual tr switch, before the fancy and expensive rf sense stuff today.I just find it hard to imagine a us navy operator listening for cw on the hammarlund and then reach for the send/receive swtich to answer back. It is even more strange at least for me with the hammarlund 145 having send-rec-cw. RegardsFernan------ Original message------From: Richard Knoppow<1oldlens1 at ix.netcom.com>Date: Thu, Dec 5, 2019 15:36To: hammarlund at mailman.qth.net;Cc: Subject:Re: [Hammarlund] Send receive swtich    The send/receive switch on most receivers is connected to
terminals on the back. Its purpose is to desensitize the receiver
when transmitting. Usually it is connected to a pair of contacts
on the transmitter which also operate the antenna relay.
    On some receivers, such as the HQ-129-X, the switch cuts off
the B+, usually by opening the center tap of the power supply
transformer, in other receivers, such as the Super-Pro series and
SP-600- it cuts off the screen or plate supply to the RF stages.
The Super-Pro cuts off the plate supply, the SP-600 cuts off the
screens (much better way to do it). The external relay contacts
go across the S/R  switch on the receiver.
     The SP-600, except for some very early receivers, does not
have terminals at the back, it was meant mostly for receive only
use. However, one can attach wires to the switch and bring them
out to the S/R relay.
    Some receivers have a bias to cut off the RF section, for
instance one version of the R-388 (Collins 51J-3) has an internal
relay for "break in" which controls the bias on several of the
tubes. It also has a B+ connection on the back.
    I used a BC-779 (Super-Pro) with minor modifications for my
station receiver and used its send/receive terminals connected to
my antenna relay. I also had a small auxiliary relay right across
the antenna terminals to short them when transmitting.
    Almost all tube communications receivers have this sort of
set up.


On 12/5/2019 1:03 PM, ve4feb at gmx.ca wrote:
> Hi allNow that my hammarlund has become my main receiver i have some curiosity questionsSend/receive swtich - back in the day how did people use this? Seems to exist since super pro series so must have been useful.RegardsFernan
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--
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL
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