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Key line in a Lincoln II+??
- Thread starter 2NC995
- Start date
Check 8T on schematic. Measure with DMM to verify.
Mike
Mike
Ok, so I found a trace that’s positive on TX, but varies with the RF power adjustment from 4-14V. Not a huge issue because I keep it parked in one spot, but I wanted the key to work the same across the whole range. Otherwise, the trace is accessible, tinned, and ready to go.
I made a test circuit based around a 2N2222 and played with the value of the resistor until I had the transistor barely in saturation at lowest voltage. That seemed to work fine across the dial, and in all modes.
The problem is as I increase the RF power I start getting a delay in the relay opening. Not a huge one, I could probably live with it, but I’d rather it be timed a bit closer to unkeying the mic.
It’s not the trace I’m using, either. That cuts off immediately. It appears to be a problem with my circuit.
If anyone has any thoughts on what I can do to polish my plan, please let me know.
I made a test circuit based around a 2N2222 and played with the value of the resistor until I had the transistor barely in saturation at lowest voltage. That seemed to work fine across the dial, and in all modes.
The problem is as I increase the RF power I start getting a delay in the relay opening. Not a huge one, I could probably live with it, but I’d rather it be timed a bit closer to unkeying the mic.
It’s not the trace I’m using, either. That cuts off immediately. It appears to be a problem with my circuit.
If anyone has any thoughts on what I can do to polish my plan, please let me know.
I wonder if it's an rf issue? Try using some 103 bypass caps. Maybe one from the base to emitter of your transistor.
Mike is right. You really don't really need a relay for most amps. The transistor will handle the job for anything with a 12v relay. Looks like you're making good progress.
Mike is right. You really don't really need a relay for most amps. The transistor will handle the job for anything with a 12v relay. Looks like you're making good progress.
I wonder if it's an rf issue? Try using some 103 bypass caps. Maybe one from the base to emitter of your transistor.
Mike is right. You really don't really need a relay for most amps. The transistor will handle the job for anything with a 12v relay. Looks like you're making good progress.
If it’s RF it’ll only get worse when it’s off the bench and inside the radio. Lol.
Playing around some more, I think I’m just pushing the transistor too far into saturation. I ditched the second resistor, and upped the value of the resistor on the base to 47k. That helped a lot...definitely tolerable now, and perfect up to the sweet spot where I drive my amp.
I agree about the relay...I feel better having it there, but at the end of the day it’s a transistor controlling a relay whether it’s the one in the amp or one in the radio.
Because the voltage varies with the power control, chances are you are connected to the modulated voltage feeding the final or the DC control to the series pass modulator and not the 8 volt TX line.
Unfortunately, I’ve probed all over the board and can’t find 8v on TX anywhere.
Is there a reason I cannot (or should not) use what I’ve got? The voltage stays the same on every mode, modulated or not. It only changes with the variable power.
The 8 volt regulator should be the part mounted on the heatsink towards the front right in your photo. This part may not have an 8 volt terminal that turns on in TX only and that switching may be done by another transistor close by.
If the trigger voltage you're using now has not caused any problems, it's unlikely that a new one will develop as a result. However, I would confirm that the DC is not modulated by switching your meter to AC and modulating it. The DC meter may not show any change with AC audio on top of a DC voltage.
If the trigger voltage you're using now has not caused any problems, it's unlikely that a new one will develop as a result. However, I would confirm that the DC is not modulated by switching your meter to AC and modulating it. The DC meter may not show any change with AC audio on top of a DC voltage.
In that case, I have 8V there and it seems it’s on all the time.
And I think you’re right, in that I am on the power to the finals.
Back to the drawing board.
Look for the largest transistor on the PC board near that 8 volt regulator. One of those transistors around the regulator and towards the mic plug will be switching the voltage on in TX only.
Use Q125 collector pin, the center one. That's where your 8-Volt transmit-only 'trigger' source comes from.
73
73
Dang. Can't find Q125 anywhere. Cant even find it on the schematic, lol. I'm afraid this is an SMD, and leaves me stuck again.
I did find +7.5v on Q49, but I'm 99% sure this is modulated.
And I also found +6v at IC1 that drops on TX.
I did find +7.5v on Q49, but I'm 99% sure this is modulated.
And I also found +6v at IC1 that drops on TX.
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Ok, glimmer of hope.
The +6V on IC1 is steady in all modes and drops to .4V on TX. I'm guessing IC1 is an audio amplifier...I'm thinking for talkback?
Using that 6V as a + source and connected to the base of NPN transistor, I can use the other set of contacts in the relay and the test circuit seems to work. No delay whatsoever.
The only effect I can find is that the circuit is disabled in talkback mode...which is not an issue. It also does not function in PA...which is perfect.
The +6V on IC1 is steady in all modes and drops to .4V on TX. I'm guessing IC1 is an audio amplifier...I'm thinking for talkback?
Using that 6V as a + source and connected to the base of NPN transistor, I can use the other set of contacts in the relay and the test circuit seems to work. No delay whatsoever.
The only effect I can find is that the circuit is disabled in talkback mode...which is not an issue. It also does not function in PA...which is perfect.