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Burt
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« on: January 26, 2013, 03:35:32 PM » |
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I have a Johnson Ranger that seems to work fine except it has an idling current that is almost as high as its transmitting plate current. Is this so? If so highly inefficent. I just switch it to standby and plate current is zero.
Also I was stupid enough to stick a lead in the mic connector and was shocked with 300 volts that is for the push to talk circuit. 300v on PTT, really?
Also there are several WA1HLR mods outlined in the manual but I do not know if they are actually implemented.
Burt
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WA3VJB
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« Reply #1 on: January 26, 2013, 04:12:43 PM » |
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If you saw it, it is so.
The one I use at K3RTV does not do that.
But yes, it does have a healthy spark on the PTT line.
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KC4VWU
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« Reply #2 on: January 26, 2013, 05:25:47 PM » |
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Check the clamp tube adjustment....  Phil |
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wa3dsp
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« Reply #3 on: January 26, 2013, 10:24:15 PM » |
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In a stock unit the clamp tube shunts the PA screen to ground or a very low potential when there is no or low drive to the PA. The shunt current (current through the PA screen resistor) is displayed on the PA current meter position and looks like plate current but it is really the current through the screen resistor and the clamp tube to ground. The stock resistor is 30K so the displayed current would be around 20-25 ma. with no drive.
In your case it sounds like the clamp tube is not working or the screen tap (tap on the big wirewound resistor under chassis) is either not making contact or is in a very wrong low voltage position. But while this tap feeds the screen of the clamp tube it also feeds the screens of the modulator tubes and is the method for adjusting the Modulator resting current. You don't adjust it to change clamp tube operation. You adjust the tap for 55-70 ma resting current (no audio) on phone. Of course you can't do this until you get the other problem fixed.
Check that there is about 250-300 volts on the clamp tube screen. I would pull the PA tube. Make sure the plate cap is not touching anything. Then you could apply a bias supply 0 to -80 volts the the grid of the PA tube. with a meter on the PA screen pin varying this bias should smoothly change the screen voltage. The more bias the more screen voltage. It should be very low with no bias. Keep the meter switch in th eoff position when you do this so the meter is out of the circuit.
While you have it open put a couple of 1n4007 back to back across the meter connections.
All of this assumes a stock Ranger.
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W2VW
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« Reply #4 on: January 27, 2013, 06:15:31 AM » |
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Some detailed photos would help people recognize the mods.
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Burt
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« Reply #5 on: January 30, 2013, 07:32:22 AM » |
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Thanks for all the help. I am currently laid up with a fever but will try suggestions when I get better
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wa3dsp
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« Reply #6 on: January 30, 2013, 12:52:16 PM » |
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Hope you feel better. Come back and tell us how you make out with the Ranger.
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Burt
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« Reply #7 on: February 02, 2013, 05:41:18 PM » |
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Some detailed photos would help people recognize the mods.
I pulled the 6AQ5 and the idle current went from 100ma to pin the needle. See any mods? |
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Burt
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« Reply #8 on: February 02, 2013, 09:02:30 PM » |
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In a stock unit the clamp tube shunts the PA screen to ground or a very low potential when there is no or low drive to the PA. The shunt current (current through the PA screen resistor) is displayed on the PA current meter position and looks like plate current but it is really the current through the screen resistor and the clamp tube to ground. The stock resistor is 30K so the displayed current would be around 20-25 ma. with no drive.
In your case it sounds like the clamp tube is not working or the screen tap (tap on the big wirewound resistor under chassis) is either not making contact or is in a very wrong low voltage position. But while this tap feeds the screen of the clamp tube it also feeds the screens of the modulator tubes and is the method for adjusting the Modulator resting current. You don't adjust it to change clamp tube operation. You adjust the tap for 55-70 ma resting current (no audio) on phone. Of course you can't do this until you get the other problem fixed.
Check that there is about 250-300 volts on the clamp tube screen. I would pull the PA tube. Make sure the plate cap is not touching anything. Then you could apply a bias supply 0 to -80 volts the the grid of the PA tube. with a meter on the PA screen pin varying this bias should smoothly change the screen voltage. The more bias the more screen voltage. It should be very low with no bias. Keep the meter switch in th eoff position when you do this so the meter is out of the circuit.
While you have it open put a couple of 1n4007 back to back across the meter connections.
All of this assumes a stock Ranger.
Replaced the 6AQ5 with one from a working Valient. The idle screen current went from 130ma to 150 MA The Modulator resting current was 55ma so I guess it was not the tap? |
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Burt
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« Reply #9 on: February 02, 2013, 10:08:49 PM » |
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In a stock unit the clamp tube shunts the PA screen to ground or a very low potential when there is no or low drive to the PA. The shunt current (current through the PA screen resistor) is displayed on the PA current meter position and looks like plate current but it is really the current through the screen resistor and the clamp tube to ground. The stock resistor is 30K so the displayed current would be around 20-25 ma. with no drive.
In While you have it open put a couple of 1n4007 back to back across the meter connections.
All of this assumes a stock Ranger.
As it turns out R38a,b,c screen resistor to 6AQ5 (3-33k resistors in parallel) were all open, when replaced with a single 7 watt 10K resistor, plate idle current dropped to 50ma, higher than what you suggest but better than what it was |
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Burt
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« Reply #10 on: February 02, 2013, 10:13:42 PM » |
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If you saw it, it is so.
The one I use at K3RTV does not do that.
But yes, it does have a healthy spark on the PTT line.
Why do they put 300v on a PTT line, any leakage in the mic switch is a shocker |
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wa3dsp
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« Reply #11 on: February 02, 2013, 10:39:29 PM » |
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Burt,
Glad to hear you found the problem. I was just writing to suggest you check that resistor!
The manual says 35-40 ma. I suppose what you are seeing is within reason.
The original PTT mod used a plate coil relay and ran it off the 300 volt B+ through a dropping resistor. Open circuit you are going to see the full low B+ on the PTT line. That is the way they use to do things! Perhaps the relay was more available or something that was surplus. Also when the Ranger was first made solid-state was in its infancy. Today you would just use a voltage doubler off the 6V filament line and a 12 volt relay which is very common.
Looking at the PTT mod on page 20 of the manual they show a voltage divider off the 300v line two 20K resistors, so the PTT should have no more than about 150v on it. I suspect you could lower the voltage by changing the divider values experimentally and see at what voltage the relay reliably pulls in. You are still going to have more voltage than you would like on the PTT.
I am in the process of upgrading a Ranger and I used 12V relays and also put the antenna relay inside but I also made substantial other changes. When I get it all documented I will let you know in case you would want to make some changes in your Ranger.
Doug
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Burt
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« Reply #12 on: February 03, 2013, 06:11:59 AM » |
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Burt,
Glad to hear you found the problem. I was just writing to suggest you check that resistor!
The manual says 35-40 ma. I suppose what you are seeing is within reason.
I am in the process of upgrading a Ranger and I used 12V relays and also put the antenna relay inside but I also made substantial other changes. When I get it all documented I will let you know in case you would want to make some changes in your Ranger.
Doug
There are so many old parts in it I am afraid to make any changes. Can you tell it on the air from a DX-40? Burt |
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