Dx-20/hammarlund hq170 transmit receive switch

[N9axl]

I have a transmit/receive switch without instructions.  This is mostly obvious - coax receive to receiver, coax transmitter to transmitter.  There are four rca email plugs on the one side. I can't figure out how to power this relay which evidently requires 120 VAC.  I don't see that coming off the system socket on the 170. There's 6.3 volts off pin 8.  The muting relay contacts are on pin 3 and 4 of that socket. There's b+ and ground off the accessory socket but the manual doesn't specify what the B+ value is.

It looks like I'm going to have to wire some kind of accessory plug to rca connections?

Hate to ask so many question but I'd rather not blow up a perfectly working radio. I have some real concern that I will somehow overload the front end of the receiver.  What I'm doing now is simply putting the transmitter in standby and switching the antenna switch to the receiver for receive.  On transmit I switch the antenna switch back to the transmitter and put the transmitter on transmit. 

[Ed WA4NJY]

 I have one of those around here somewhere.  IF I remember right, two of the RCAs are for 115vac to key the relay.  The other two are for Normal Open contacts and Normal Closed.  They are used to mute the receiver.

Hope this helps.

Ed

[N9axl]

Yes. My issue is I don't see how to get 120 VAC from a DX 20 to power the relay.  It looks like I need to wire a power cord for this. On a Ranger or other transmitter of the period there was a 120 volts available to power the relay.

[k7mdo]

Depending on the "transmit" switch in the set you have a couple of options... if it is a toggle switch you could change it to a DPST and use the new pole to route line AC to rear apron of the transmitter for your antenna switch activation...   OR, if the switch isn't that easy then I have added a small relay inside the transmitter that is activated in transmit.  It's contacts then route the AC to apron on closure.
Tom


Tom

[N9axl]

Sounds like a plan.  Now, I just picked an nc300 today. Plugged it in.  BZZZZ.... Ok caps need replacement. That will be the next project after I get the Viking 2 CDC finished. Have the power supply caps on order, replace the silicon rectifier, and re tube since the 6146 and the HV rectifier is gone along with a few others.

Haven't worked on an NC300 before so this should be interesting. There seems to a little hitch in the smoothness of the tuner - restringing that won't be fun. The picture is terrible but it is just completely filthy inside.  Otherwise appears complete - even has the crystal calibrator option. The scary part is working on this without breaking that dial drum.  Not sure how to secure that safely. Perhaps tape some bubble wrap on it while the unit is out of the case and on its rear for servicing.  I assume face down on a blanket scrap like I normally do.