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Author Topic: Muting the speaker  (Read 5378 times)
KD5TXX
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Posts: 82




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« on: April 01, 2012, 07:32:45 PM »

I am currently setting up a Ht 37 and Hammarlund HQ140x.  I have a Johnson T/R switch box between them.  How exactly do I wire these things up to mute the speaker when I transmit?  Please be exact because this is all new to me.  I don't see any terminals labeled mute on the transmiter so I need help.

Thanks
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AC5UP
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Posts: 3927




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« Reply #1 on: April 01, 2012, 08:43:17 PM »

If there is a mute connection it would be on the receiver...
The T/R box has a switch or relay and uses normally open / normally closed contacts wired to achieve two operating conditions:

* On TX the transmitter is keyed and the receiver is muted.
* On RX the transmitter is NOT keyed and the receiver is NOT muted.

The antenna is transferred between the two as needed. Have you looked at the book for the HQ-140X?
If not, there should a paragraph or two that explains what the receiver needs from a T/R box.......

http://bama.edebris.com/manuals/hammarlu/hq140x/

As for the transmitter:

http://bama.edebris.com/manuals/hallicra/ht37/
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W5RKL
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Posts: 894




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« Reply #2 on: April 02, 2012, 04:22:42 AM »

I am currently setting up a Ht 37 and Hammarlund HQ140x.  I have a Johnson T/R switch box between them.  How exactly do I wire these things up to mute the speaker when I transmit?  Please be exact because this is all new to me.  I don't see any terminals labeled mute on the transmiter so I need help.

Thanks

The Johnson T/R switch you are using does not have receiver muting connections. You will have to provide those yourself either by switching the HQ-140X's front panel's STANDBY/RECEIVE switch or a separate circuit as mentioned by AC5UP.

The Johnson T/R switch schematic can also be found on the bama.edebris.com website:

http://bama.edebris.com/manuals/johnson/trswitch/




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K1ZJH
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Posts: 1140




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« Reply #3 on: April 02, 2012, 06:57:41 AM »

If the HT-37 uses the same RF section as the HT-32, you may have a problem using a TR switch.
In the HT-32 the driver and PA stages are always biased into AB1;  note that the manual for the
Johnson mentions that some transmitters may have broadband noise on the output, even when
in standby.  Try it and see, but if your receiver noise floor is high, turn off the transmitter power
and see if it goes away.

I suspect they did this to keep a minimum load on the swinging choke power supply in the HT-3x
transmitters.

Pete k1zjh
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K8AC
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Posts: 1477




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« Reply #4 on: April 02, 2012, 08:10:12 AM »

If it were me, I wouldn't be using a Johnson T/R switch for SSB use.  There's no relay in the Johnson switch and as someone else mentioned, if there is current flowing in the transmitter final when you're not talking, you'll hear that as a high white noise level on receive.  I believe the HT-37 does have a switched output line on the connector on the rear panel, so you could use that to control a relay used to switch the antenna between transmitter and receiver.  We used to use a Johnson T/R switch for CW and that eliminated having to throw a switch when going from receive to transmit.  However, since there was generally no CW sidetone available at that time, we typically listened to our own sending on the receiver, which usually meant turning down the audio manually to save your ears.  Another common problem with the T/R switch approach was "signal suckout" which could reduce the signal level heard in the receiver.  T/R switch manuals often advised you to change the length of interconnecting coax to minimize or eliminate that.  Check DX Engineering for a box that meant to do the antenna switching in a properly timed fashion for old separate rigs.  There have also been articles in QST over the years for home brew versions of that.  I built one here years ago and it made using the old rigs on CW a pleasure.
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KD5TXX
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« Reply #5 on: April 02, 2012, 03:29:55 PM »

Thank you all.  I am actually trying to use the HT37 for AM, until I get the Valiant working again.  My problem is when I talk, I get really bad feedback from the speaker. 
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K1ZJH
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Posts: 1140




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« Reply #6 on: April 02, 2012, 06:10:00 PM »

 
On your HT-37:  is there an 11 pin accessory socket on the rear panel? On the HT-32, which is
basically the same chassis, pins 2,3 and 4 provide relay contacts  to operate an external antenna
relay, or for muting the receiver.  If you use an antenna relay, they often have external contacts
for muting the receiver as well.
 
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K1ZJH
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Posts: 1140




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« Reply #7 on: April 05, 2012, 01:43:50 PM »

BTW, I just tested my HT-32 and SX-101A combo with the Johnson TR Switch. As expected, the TX white noise
increases the receiver S Meter reading by about three S Units when the transmitter is turned on, and in standby.
This may not be a big issue on AM when the signals are strong. Try turning of the TX AC power when listening on
an unused frequency on 75 or 80 meters and see if your S meter and receiver noise doesn't drop appreciably.

Pete k1zjh
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W2WDX
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Posts: 188




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« Reply #8 on: April 29, 2012, 06:34:12 PM »

As mentioned before the HT-37 has relay contacts already for receiver muting. On the 11 pin connector on the back of the transmitter. You simply need to connect pins 2 & 3 to the mute connections on the Hammarlund & pins 9 & 5 to the Johnson switch and you will be good to go. Switch the switch to MOX and it will trigger the tube in the Johnson, and mute the receiver.

Fine business on the HT-37, have you performed the audio mod for AM?

John, W2WDX
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KD5TXX
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Posts: 82




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« Reply #9 on: May 17, 2012, 07:17:29 PM »

Bbusy with work and forgot to check here.....  I was given the Johnson relay switch so I have problem trying something else.  Anyone have any hints on where I can find something?  Been looking and I'm not seeing anything.  Do I need a Dowkey?  Remember, When I get this working it will be the first AM or boatanchor station I have seen in use.  In other words, I am teaching myself.
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W2WDX
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Posts: 188




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« Reply #10 on: May 17, 2012, 11:12:58 PM »

Hi again,

The thing with the Johnson t/r switch is its not a mechanical relay. It uses a tube (6BL7 I believe) as an electronic switch. The tube is setup as a cascode amplifier on the first stage and a grounded cathode type amplifier on the second. Simply put, it uses the RF voltage from the transmitter to create a negative bias which cuts off the two stages in the circuit. Also the second stages creates about 5dB of gain on the receiver side.

The thing about these is you need to make sure both tubes, the 6BL7 & the 6X4 rectifier, are good. Also check the filter caps, C25(a,b) for leakage, since this could cause hum on the receiver if it is bad.

As you already know you need to mute the Hammarlund. You simply need to connect pins 2 & 3 on the 11pin connector on the back of the Hallcrafters to the mute connections on the Hammarlund. The Johnson will do the antenna switching independent of this.

You could also use a standard relay as well using the HT-37, as long as it can handle whatever power output you are using. Any 30A rated contact relay will work, as long as it big enough were arcing will not occur. A Dowkey is better, but not always necessary.

Since you have the Johnson already, I would give this a try first of course.

John, W2WDX

BTW ... Here's me on my HT-37 on SSB on 80m. This is stock power with no amplifier. The transmission was made in central Westchester County, NY (Scarsdale) and the receiving station was in Central NJ. The receiver was a Flex with a 4.8kHz filter. The antenna was a 160' dipole at 90' high with balanced feedline, balanced tuner (Johnson Kilowatt). The mic was Neumann TLM-103.

W2WDX on HT-37 SSB 80m

Now on AM it is equally good. Here's Jeff, W2NBC (the same guy who made the recording above) on his HT-37 on 80m on AM talking to K2DK on his Collins 20V transmitter.

W2NBC on HT-37 AM 80m

The Hallicraters HT-37 is an awesome transmitter with transmit audio quality you cannot get from the modern stuff, on any mode. But you already know that, don't you! :-)

John
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K4RVN
Member

Posts: 788




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« Reply #11 on: June 04, 2012, 07:21:33 AM »

Not only do you need to mute the speaker but probably the b+ to the 140. You don't want RF getting into it. The standby switch would do that I think. Here is a link to the exact setup you mentioned that WD4AM has. He built a homemade
TR switch for his and you could email him from QRZ.com if interested in how he handles his station.

http://www.youtube.com/watch?v=Z_PKWIN4SzI

Frank
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AA4PB
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Posts: 12980




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« Reply #12 on: June 04, 2012, 09:54:10 AM »

The HQ140X has a set of mute contacts that, when opened, cuts off the whole receiver by biasing the AGC circuit. All you need to do is to control this with a set of NC relay contacts. DowKey made coaxial antenna relays that had an extra set of contacts to mute the receiver.

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K4RVN
Member

Posts: 788




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« Reply #13 on: June 04, 2012, 01:18:49 PM »

I found this on the net which may help. On the rear of the receiver are two pin jack receptacles. These are the mute (or Stand-By/Receive) pins. They are in parallel with the Stand-by/Receive switch as shown on Page 10/11 of the schematic of ther radio. We presume you have the manual.
 
There is high voltage on these two pins, they are NOT grounded in anyway. They break the HV to the IF chain, V5/V6 plates. That is how mine operates. The manual I have is dated January 1955.


The Dowkey relay I have used on my Multi Elmac transmitter is a coaxial relay with exposed contacts for muting. Mine is really old from the 60s. You can homebrew yourself a relay box to avoid contact with the high voltage and use any relay with a suitable coil voltage and contact ratings. I have made several for old rigs in the past and used a wall wart 12 volt transformer as power for the relay coil. Just depends on what you have in your junk box and what the voltage and current requirements are for your relay coil. I would also mute the speaker if necessary. There are several articles on how to do this for a HQ 140 on the net. Some add a resistor for the open contact going to the audio transformer to present a load for it.

Frank

« Last Edit: June 04, 2012, 01:20:24 PM by K4RVN » Logged
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