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Johnson 500 Keyer




 
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Author Topic: Johnson 500 Keyer  (Read 2939 times)
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Dave K6XYZ
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« on: March 19, 2013, 10:35:44 PM »

Recently I acquired a Junkston 500 and it works great....except the keyer is not adjustable.
The rig can be keyed ok but the adjustment pot has no effect.
Yes...the pot is good.
The keyer does not conform to the schematic I have.
Apparently I have an early model but a later schematic...and I believe there has been some additional haywire changes.
Can anyone help me out with the early schematic?
All I need is a .jpg of the keyer area......or a location to dwnld the early schematic.
I think the early schematic will show a 4-250....


Dave
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ke7trp
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« Reply #1 on: March 20, 2013, 12:09:39 PM »

I will ask around for you Dave. Mine was made in 1958 so it is the later model.

C
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WQ9E
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« Reply #2 on: March 20, 2013, 05:37:01 PM »

Dave,

The Johnson keyer circuit was nearly identical across all of their gear, the only differences were in the values of some resistors based upon the B+ and bias voltage levels produced in a specific line of gear.  The Valiant preceded the 500 by a couple of months according to the advertisements I have seen and the Valiant keyer is the same across production and is identical in design to that used for the Ranger.  My Viking 500 is from 1957 and its schematic shows a 4-400A although the block diagram shows a 4-250 instead. 

I have worked on a couple of early 500 transmitters and I don't recall seeing anything different in the keyer circuit.  The standard keying circuit shows up at least as early as 1954 in official Johnson literature; the keying modification from Johnson was dated 10-28-54 and this predates the 500 official introduction by over a year. 

I wonder if the differences in yours are from modification by a previous owner?
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Rodger WQ9E
Dave K6XYZ
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« Reply #3 on: March 20, 2013, 06:53:00 PM »

Dave,

The Johnson keyer circuit was nearly identical across all of their gear, the only differences were in the values of some resistors based upon the B+ and bias voltage levels produced in a specific line of gear.  The Valiant preceded the 500 by a couple of months according to the advertisements I have seen and the Valiant keyer is the same across production and is identical in design to that used for the Ranger.  My Viking 500 is from 1957 and its schematic shows a 4-400A although the block diagram shows a 4-250 instead. 

I have worked on a couple of early 500 transmitters and I don't recall seeing anything different in the keyer circuit.  The standard keying circuit shows up at least as early as 1954 in official Johnson literature; the keying modification from Johnson was dated 10-28-54 and this predates the 500 official introduction by over a year. 

I wonder if the differences in yours are from modification by a previous owner?

Hi Rodger....thank you for your comments....I always read your stuff.
This is a bit confusing so I'll try to avoid too many words.
It's always a crapshoot buying a used rig....in this case, the changes were documented but I had to dig for them a bit.

The keyer pot had no effect.
The radio keyed ok and seemed to be operating normally on CW.
In looking over the keyer componants I noticed that there were some differences in this unit and the schematic I have.
My manual is different in several ways from the BAMA manual which is a PARTIAL reprint of the earlier manual....note dates on pages.
I assume the earlier manual to be the one that shows the 4-250 in the parts list and on the tube lineup.
I will not confuse the issue any more by mentioning any of the other changes I noticed.....This thread is only about the keyer.

The resistors on the parts list in the new manual shows a change on 3 resistors from the old manual.

OLD             NEW
R113 10K     R113 4.7K
R114 68K     R114 4.7K
R116 33K     R116 DELETED

See fig 12 Keyer Wiring in manual.
I used fig 12 in the old manual and the schematic of the new manual to determine the new physical connections.

See pix of the changes and hand scrawled wiring pictorial.

I just tested the rig and it works correctly now.
I should mention that the paper caps C131 & C136 have been replaced with the good stuff.

So....if anyone else is unable to adjust the keyer and is interested enough to dig in there and fix it....this is it.

On my hand drawn pictorial....remove strap from 8>9 if present.
Add insulated strap from 4>8.
The terminal strip is TS115.
The lugs count from left to right.

Dave





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WQ9E
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« Reply #4 on: March 20, 2013, 08:01:58 PM »

Dave,

I am glad you got it figured out!  I know what you mean about figuring out some of the changes in used rigs and one is really lucky when there is any documentation.  I just got through working on a RCA ACR-155 that was owned by one of the RCA engineers at Rocky Point and fortunately he did document what he did but I have been through several other adventures without a map of the changes.

For future reference, if you experience hum on the VFO signal it is often from heater/cathode leakage in the keyer tube.  Only a very slight amount of leakage will hum modulate the VFO. 

I know you are familiar with the keyer circuit but for those not familiar with the keyer if you monitor the VFO without the final operating you may hear what sounds like a chirpy signal.  The VFO will chirp when keyed but the keyer circuit allows the VFO to key quickly while the rest of the exciter chain is slightly delayed so the start-up chirp of the VFO isn't amplified and transmitted over the air.  The VFO is held on for a short time after the key is released so the rest of the exciter chain cuts off first and any clicks or frequency change on VFO stop is also not transmitted.  So this is a case where the transmitter should be operating at full power into a dummy load to monitor the true signal characteristics such as when adjusting the keyer pot.  The keyer adjustment is fairly critical when adjusting for minimum chirp on 15 and 10 but it is not very critical on the lower bands.  VFO frequency change issues on 40 meters for any of the Johnson internal VFO rigs of this series (Ranger, Valiant, and 500) are generally due to RF getting into the VFO.

Dave, while you still have the 500 out of service you may want to address possible problems with relay RY-302 known as the slow release relay which controls the external T/R relay and prevents hot switching.  This relay, located in the modulator/power supply section, apparently depended upon residual magnetism to cause a slight delay on release and this effect diminishes with time.  You can easily add a small electrolytic capacitor across the coil along with an isolating diode to restore this delay feature.  Alternatively you can use a T/R relay with slow release on return to receive like that used with the Desk KW or a tube type electronic T/R relay.  PM me if you want details about the capacitor/diode solution.
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Rodger WQ9E
Dave K6XYZ
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« Reply #5 on: March 20, 2013, 08:43:56 PM »

Dave,

I am glad you got it figured out!  I know what you mean about figuring out some of the changes in used rigs and one is really lucky when there is any documentation.  I just got through working on a RCA ACR-155 that was owned by one of the RCA engineers at Rocky Point and fortunately he did document what he did but I have been through several other adventures without a map of the changes.

For future reference, if you experience hum on the VFO signal it is often from heater/cathode leakage in the keyer tube.  Only a very slight amount of leakage will hum modulate the VFO.  

I know you are familiar with the keyer circuit but for those not familiar with the keyer if you monitor the VFO without the final operating you may hear what sounds like a chirpy signal.  The VFO will chirp when keyed but the keyer circuit allows the VFO to key quickly while the rest of the exciter chain is slightly delayed so the start-up chirp of the VFO isn't amplified and transmitted over the air.  The VFO is held on for a short time after the key is released so the rest of the exciter chain cuts off first and any clicks or frequency change on VFO stop is also not transmitted.  So this is a case where the transmitter should be operating at full power into a dummy load to monitor the true signal characteristics such as when adjusting the keyer pot.  The keyer adjustment is fairly critical when adjusting for minimum chirp on 15 and 10 but it is not very critical on the lower bands.  VFO frequency change issues on 40 meters for any of the Johnson internal VFO rigs of this series (Ranger, Valiant, and 500) are generally due to RF getting into the VFO.

Dave, while you still have the 500 out of service you may want to address possible problems with relay RY-302 known as the slow release relay which controls the external T/R relay and prevents hot switching.  This relay, located in the modulator/power supply section, apparently depended upon residual magnetism to cause a slight delay on release and this effect diminishes with time.  You can easily add a small electrolytic capacitor across the coil along with an isolating diode to restore this delay feature.  Alternatively you can use a T/R relay with slow release on return to receive like that used with the Desk KW or a tube type electronic T/R relay.  PM me if you want details about the capacitor/diode solution.

Thanks Rodger....I didn't think to test the keyer on the upper bands but I'll do that right now.
I DID add the slow release mod and it works as advertised....in other words....great!
You can really hear the problem if testing on a dummy load and monitoring with a non-switched receiver...ie...the rx on a cliplead and not muted.
Upon release of the PTT, the PA tails off slowly as the HV filter discharges....obviously, this causes the decades old hot-switching problem. FYI....this 500 has not arced yet.

Right now...I'm preparing a board with the K6AD mod trans secondary flyback killer as shown in Electric Radio some time ago.

I intend to get it on the air to see how it sounds before any audio mods...gonna try to make it by the first Wednesday of next month.

ONE MORE THING....those with the 500 check your modulator arc gap.....the OLD manual says to set the gap to .040"...page 28.
Note the date on the bottom left of the page.
Now look at the later manual from BAMA page 28.
The new manual says set the gap to .018".
Note the date on the bottom left of the page.

Be advised that if the unit has a 4-250......use the old manual to set the bias....again....check the page dates.
If your unit has a 4-400.....the bias settings are different in the later BAMA manual.
Read both manuals and compare carefully.

Thanks to all.

73

Dave

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WQ9E
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« Reply #6 on: March 20, 2013, 09:22:33 PM »



ONE MORE THING....those with the 500 check your power supply gap.....the OLD manual says to set the gap to .040"...page 28.
Note the date on the bottom left of the page.
Now look at the later manual from BAMA page 28.
The new manual says set the gap to .018".
Note the date on the bottom left of the page.


Dave,

Excellent point about setting the gap properly!  In one part of the manual the owner is instructed to slightly increase the gap spacing if nuisance arcing occurs.  I imagine more than one person tried that advice when their delay relay begin losing its delay and that was the first step on the path towards creating arcing at the much maligned power connectors because when hot switching occurs the voltage will find a place to arc across and once the safety gap is wide enough the interconnects become the next arc-over point.  With the transmitter operating properly and the power cables properly secured the voltages are well within the capability of the connectors.

My novice rig was a Valiant but while studying for my novice ticket I spent a lot of time looking through my father's old Radio and TV News magazines.  The full page ads introducing the Valiant and 500 appeared a few months apart and once I saw the 500 advertisement I knew one day I had to have one.  Getting mine involved a trip from IL to AZ including driving over 1,000 miles one day but it was a really fun experience.  Once I retire in a couple of years it will be time to take another long vintage gear excursion but since I am planning to buy a C7 Corvette as my retirement present from me to me I guess I will have to limit that vintage acquisition to something smaller and lighter than a Viking 500.

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Rodger WQ9E
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« Reply #7 on: March 21, 2013, 09:18:46 AM »

Dave,

Thanks for posting the information on the early 500's with a 4-250 in the final. Too bad both manuals are not on BAMA.

WD8KDG
Craig
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Ham radio is now like the surprise in a box of "Cracker-Jacks". There is a new source of RFI every day.
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