Muting HRO-50T

[WV9R]

I'm probably missing something easy, at least I hope so, I bought a very nice    HRO-50T receiver to use with my VikingII.      Can someone help me here, I cant figure out how to mute the receiver when I key the mic, there is mention of the BSW terminals on the back, and the switch on the front of the receiver, but when I turn the B+ off , using the switch on the receiver  and key the Viking I'm getting feedback from the receiver. So the sad truth is I'm missing something small I hope, or I'm just too stupid to figure it out  hihi

[WQ9E]

Ray,

There are a couple of terminals on a strip marked BSW.  You should run a pair of wires from these to a normally closed contact on your antenna relay and leave the front switch in standby.   It sounds like someone may have jumpered the leads on the back of your receiver if the standby switch is not cutting the receiver off.

It is considered preferable to place an additional switch in series with one of the leads from the relay to the BSW terminals on the back so you can place the receiver in standby for coil changing using this switch.

Rodger WQ9E

[WV9R]

Hi Rodger,  Thats how I have it hooked up, but when I key the mic I get a burst of feedback. It seems like the really isnt acting fast enough and I'm encountering a short period of TX before the receiver is muted. I havent had this problem with any of my other receivers when hooked up this way with the same switch. Is there something different with the HRO in the way it's mutes? I just picked the HRO up, it's in excellent condition and has the best audio out of any of my receivers by far so I'd really like to use it if someone can help me come up with a solution.
              Thanks, Ray  WV9R

[W3SLK]

Ray said:

Thats how I have it hooked up, but when I key the mic I get a burst of feedback. It seems like the really isnt acting fast enough and I'm encountering a short period of TX before the receiver is muted.

You might want to take a look and see if 'Hammy Hambone' wasn't in there with his (mis)soldering iron.  Mine works FBOM after I removed some of the mods. If memory serves me, you want to use N/C contacts when recieving. The B+ (350VDC??) comes off those terminals. That front panel switch is in parallel to the terminals, (or should be) Nothing more than 'goesouta' throught the contacts and 'goesinta.'

[WQ9E]

Ray,

The HRO-50 B+ switching kills the B+ to the RF, IF, and AF driver stage but leaves B+ on the HFO, BFO, and audio output stages.  A number of receivers work in a similar fashion and it should mute instantly.  I wonder, as the previous poster mentioned, if some modification were done?  If someone decided to hang and additional electrolytic cap on the switched side then it would take a little while for the voltage to decay and this could cause the problem.  You could take a look at the switched side of the line with a DC coupled scope (or I guess an analog voltmeter would work) and see how quickly the B+ decays.

I have never run into this problem with my 50T, 50T-1, or 60 using a standard relay for switching so something is not behaving normally in yours.

Rodger WQ9E

[KD6VXI]

Ray,

The HRO-50 B+ switching kills the B+ to the RF, IF, and AF driver stage but leaves B+ on the HFO, BFO, and audio output stages.  A number of receivers work in a similar fashion and it should mute instantly.  I wonder, as the previous poster mentioned, if some modification were done?  If someone decided to hang and additional electrolytic cap on the switched side then it would take a little while for the voltage to decay and this could cause the problem.  You could take a look at the switched side of the line with a DC coupled scope (or I guess an analog voltmeter would work) and see how quickly the B+ decays.

I have never run into this problem with my 50T, 50T-1, or 60 using a standard relay for switching so something is not behaving normally in yours.

Rodger WQ9E

I was thinking the same thing, about an electrolytic.

It was a common modification back in the 70s on Browning 2 piece CB radios, they even sold a cap called the "Browning Ping Mod".

Look for a cap on the "WRONG" side of the relay.

--Shane

[KC4VWU]

The best way I've found to mute the receiver is to switch the audio off at the speaker with a relay and load resistor. If you use a DPDT, you can also ground the antenna on TX. Switching the B+ on my dusty old boatanchors usually causes them to drift a bit.

73, Phil  KC4VWU

[w3jn]

Even better is to lift the ground end of the RF gain control and switch that.  It cuts off the RF and IF toobs but leaves everything else live.  It's best to add a 47K or so resistor across the terminals so there's a bit of DC return.  This is by far the best way to mute a RX.

I've not had great luck swithcing the audio; many times the relay just doesn't have low enough resistance and/or it gets dirty causing distortion, etc.

The worst and dumbest is switching the B+.  Dangerous, and presents unneeded transients into the power supply when you switch from standby - and the B+ can get too high in the PS with no load.

[WQ9E]

JN,

I agree with your muting scheme and I have done that with several receivers.  I put another variable resistor between the formerly grounded terminal and ground and this provides an "auxiliary" sensitivity control so the receiver can act as a sidetone monitor on CW.  I borrowed that idea many years ago after being inspired by an SX-88 schematic.

The HRO-50 scheme isn't bad since it leaves the B+ on the oscillators for stability and also the output stage is still connected and loading down the power supply.  This scheme was also used in the HRO-60 along with the NC-173 and later members of that family.  The standby scheme I really dislike is when the center tap of the B+ secondary is removed from ground for standby (the Halli SX-42 for example) so you get the nice surge of recharging the filter caps every time you go back to receive.  The Gonset G-76 is rather strange also, the associated power supply uses a relay in series with the HV DC output to switch it on for transmit.

Rodger WQ9E

[WV9R]

Hello all, I appreciate all of the input thats I get from you guys, I really can express how much I appreciate it. I talked to a friend here who is local, and into AM equipment. He told me he has run into the same problem with the HRO 60 he uses with his desk KW. His solution to the problem was use a relay to break the speaker lead. So I hooked up a relay with one of the speaker leads, and it solved the problem, no feedback or chirp of any kind. I'm all set to give the station it's madien voyage tonight, but as I tune arond between 3770 and 3885 all I hear is sideband, lots of sideband. So I'll wait till a quieter time to make my first contact, I hope to hear everyone on the air. Rodger you seem to have the biggest signal at my qth, but we arent really that far apart. Hope to talk to you all on the air, Thanks Again, Ray WV9R

[WQ9E]

Ray,

There is generally a group around on 3885 in the mornings; I won't be around tomorrow but you should find some fairly local strong signals and a group meets around 3875 each day at noon.  I look forward to contacting you on the air.

Just to be safe, you should connect a resistor of around 30 ohms (a couple of watts rated for safety) across the speaker terminals.  When you remove the secondary load you will create significant voltage possibly leading to breakdown of the output transformer.

I am still mystified as to why your HRO-50 is behaving that way; opening the B+ switch kills power to the RF, IF, and mixer stages and should instantly disable the receiver.  In a standard receiver there is no additional large capacitor which would discharge and keep these stages operating.

Rodger WQ9E