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Author Topic: Hallicrafters SX100/ Johnson TR switch question  (Read 2914 times)
WA2DTW
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Posts: 91




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« on: January 02, 2009, 05:47:09 AM »

I am using the SX100 with a Johnson Ranger/Thunderbolt combination on 75M AM with a Johnson TR switch interface.   The SX100 loses sensitivity on 75 meters intermittently.  (Seems to be more so on 75 meters than other bands).  An exceptionally strong signal can sometimes get through but the sensitivity is extremely poor.   Sometimes tuning around to other frequencies results in a momentary restoration of sensitivity.  I tried changing most capacitors in the front end of the SX100, and thought many times that the problem was fixed, only to have it return.   Has anyone had this problem?   Could RF be leaking through the TR switch and killing the front end of the SX100?

Many thanks and 73
Steve WA2DTW
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KA5N
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Posts: 4380




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« Reply #1 on: January 02, 2009, 07:48:19 AM »

When this loss of sensitivity occurs have you ever moved the antenna directly to the input terminals of the SX-100?  If the sensitivity comes back up, then probably the cause is the T/R switch (maybe needs cleaning).  If RF is doing something to the front end of the receiver, I would suspect it to stay fried, not recover.
Allen
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K7UNZ
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Posts: 691




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« Reply #2 on: January 02, 2009, 07:51:18 AM »

Steve....you might wanna try checking the tube in the T/R switch.  It does act as a sorta pre-amp for the receiver, and may be what is giving you the problem.

Easiest thing to do would be to simply check the rcvr with a direct antenna connection.

Had exactly the same set-up in '63.....now just the SX-100 is still around (hi).

73, Jim/k7unz
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WA2DTW
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Posts: 91




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« Reply #3 on: January 02, 2009, 11:14:05 AM »

Many thanks.  So far, I replaced the first RF amplifier tube 6CB6 (although it had tested good), and also attached antenna directly to the receiver.  It seems to work alright.  And after re-connecting the TR switch it seems to work alright.  Let's see what happens with time?
73
Steve
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WB2WIK
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Posts: 20560




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« Reply #4 on: January 02, 2009, 06:21:59 PM »

The Johnson T-R switch is active, not passive.  It doesn't use relays, it uses a tube to shut off the receiver when you're transmitting.

It's a design from the 1950s.

From the symptoms you describe, the problem is not in the receiver, it's in the T-R switch.

WB2WIK/6
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W8ZNX
Member

Posts: 1




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« Reply #5 on: January 06, 2009, 09:22:02 AM »

wb2wik is right
its not the receiver it's the tr switch

the Johnson tube type tr switch
was famous for generating tvi
and
causing all kinds of screwy probs

its a pile
nobody but nobody uses the dam things

throw out / trade / sell that tr switch

make up something up using a relay

mac
get the hell off my lawn
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WA2DTW
Member

Posts: 91




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« Reply #6 on: January 06, 2009, 09:53:34 AM »

Thanks everyone for your help.  
I indeed tried using the Dow-Key relay for TR switching using the barefoot Ranger with the SX100 on AM, and there was no problem.  The extra contacts on the relay are used to mute the receiver and to provide the proper operating bias for the T-bolt.
Just a couple of questions.  a)  can a dow-key relay take the constant clickedy clacks of CW?
and b) more importantly- if I use the dow-key relay as an antenna relay for the T-bolt,  is that safe, or is there a danger that the T-bolt will go full power into the receiver or into nothing even for a split-second?   Is some kind of sequencing control needed, and is there an easy circuit that anyone can refer me to?
73
Steve WA2DTW
ps  Mac-  I'll definitely stay off your lawn!

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K7UNZ
Member

Posts: 691




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« Reply #7 on: January 06, 2009, 10:51:44 AM »

Steve, not sure what you mean about the relay being used for antenna switching of the amp.

As a T/R switch, it should work fine with the connections being just between the Ranger and the '100.  The RF output of the Ranger drives the T-bolt, which is, in-turn, connected directly to the antenna.  I'll have to assume that you have some kind of keying set-up between the Ranger and the T-bolt.  Been too long ago for me to remember if the Ranger, or T-bolt, had had any "built-in" keying line between them.  Without one you would have to manually switch the amp between send and receive functions.

If the relay you are going to use has a couple of extra sets of contacts, then that would solve the problem, and allow you to do both RX mute and amp relay switching.

Hope you can make sense out of what I said.....I'm not evcen sure I can (hi).

73, Jim/k7unz

If you are muting the rcvr when the Ranger keys, then it should already be muted when the amp kicks-in.

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K7UNZ
Member

Posts: 691




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« Reply #8 on: January 06, 2009, 10:57:18 AM »

Steve, not sure what you mean about the relay being used for antenna switching of the amp.

As a T/R switch, it should work fine with the connections being just between the Ranger and the '100.  If you are muting the rcvr when the Ranger keys, then it should already be muted when the amp kicks-in.

 The RF output of the Ranger drives the T-bolt, which is, in-turn, connected directly to the antenna.  I'll have to assume that you have some kind of keying set-up between the Ranger and the T-bolt.  Been too long ago for me to remember if the Ranger, or T-bolt, had had any "built-in" keying line between them.  Without one you would have to manually switch the amp between send and receive functions.

If the relay you are going to use has a couple of extra sets of contacts, then that would solve the problem, and allow you to do both RX mute and amp relay switching.

Hope you can make sense out of what I said.....I'm not even sure I can (hi).

73, Jim/k7unz

(Corrected copy)

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KA5N
Member

Posts: 4380




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« Reply #9 on: January 06, 2009, 11:37:25 AM »

Are you trying to use break in keying (QSK) with the DowKey antenna relay and its external contacts?  This is a bad idea without some sort of sequencer to prevent hot switching etc.  Usually one would use something like a foot switch to switch the DowKey and then key the transmitter/amp combo.  This gets rid of the clickty clack.
Back in the 60's I had a DowKey electronic relay with a single 6C4 tube and it worked well for several years.  I haven't seen one of those in years and had forgotten that Johnson made a similar unit.  DowKey has always made solid equipment but in 40 or 50 years almost anything will need repairs.  I notice that the Johnson unit has a number of components and I am sure that most of the resistors have drifted in value and the capacitors are probably leaky.
If you are going to use break in operation you would do well to have some setup with a sequencer and vacuum relays.
Allen
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WA2DTW
Member

Posts: 91




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« Reply #10 on: January 06, 2009, 11:37:38 AM »

Thanks, Jim.
The problem that I have with using the relay to switch between the Ranger and the Receiver with the antenna connected directly to the T-bolt is that the signal would not pass through from the antenna to the receiver in the "receive" position.  So it would appear that the relay would have to switch the antenna between the T-bolt and the receiver, with all of the output power passing through by the relay.  

Was just not sure if this is safe.  

73
Steve WA2DTW
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W8ZNX
Member

Posts: 1




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« Reply #11 on: January 07, 2009, 02:54:35 AM »

Steve
you don't want to try to run a Ranger T bolt
SX-100 lash up cw qsk
using a dow key relay

don't worry about the receiver or the amp
but
the dow key will be destroyed if hot switched

how do i run old transmitters / amps / recerivers

simple how you do it
transmitter connected to the amp
and a change over relay between
antenna / amp / receiver

have used all kinds of junk relays
to do the job
from old open frame jobs
to little potter and broomfield ice cubes

now if you want to realy  do it righ
you want to make the relay
fast make
slow break

root around see the AM web site on using
fast make slow break relays with the Johnson Desk kw

qsk
the only way i have ever got away with using qsk
with a lash up like Ranger and Amp
is to use a receive ant
and only use a relay that is hooked to the receiver
ant input
which opens the ant feed line to the rec
so you don't blow out the front end of the receiver

you don't even try to qsk switch a
old style tube lash up transmitter / Thunderbolt amp
im sure there are ways
but
i find it easier to run qsk with old gear
to use the receive antenna
and not bother trying to switch the ant
between amp/transmitte and receiver

non qsk
no probs
i just make sure the relay hangs closed
for a long time

their call, your call k

thousand one thousand two thousand three

relay switches
dow key relays are geting to expensive
to replace every 6 months because
the contacts are fried from hot switching

yours truly
mac

read or die
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WA7KGX
Member

Posts: 104




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« Reply #12 on: August 05, 2011, 06:10:17 PM »

I have an S-76 which intermittently had low sensitivity.
Sending an electrical spike through it would restore sensitivity for a while.


To make a long story short, it was an intermittent mica cap in one of the IF cans.
If the tuning on the IF can is funny or if adding capacitance to a lead on an IF can
increases gain, suspect an open cap across the coil.

This is the second time a mica has failed on me, perhaps the third.
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W8JI
Member

Posts: 9304


WWW

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« Reply #13 on: August 05, 2011, 06:21:37 PM »

Thanks, Jim.
The problem that I have with using the relay to switch between the Ranger and the Receiver with the antenna connected directly to the T-bolt is that the signal would not pass through from the antenna to the receiver in the "receive" position.  So it would appear that the relay would have to switch the antenna between the T-bolt and the receiver, with all of the output power passing through by the relay.  

Was just not sure if this is safe.  

73
Steve WA2DTW

Yes, it is safe. And yes, that is where it needs to be. It has to be on the output of the Thunderbolt.

The thunderbolt RF output goes into the normally open port of the relay, TX. The distant end connector out by itself goes to the antenna system. The normally closed rcvr port to the receiver.

The Ranger has no QSK. I don't know why the relay would  clack all the time. When the Ranger is on CW, TUNE, or PHONE the relay should key.

Or has someone changed the Ranger around??

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