Tristar 777 no rx/tx

[SiriusHardware]

i touched it with a plastic part of a pen, no change, and the metal screwdiver test it goes up 1 watt

It sounds like this is just a matter of the circuit reacting to having a bit of extra circuitry - namely, the long metal shaft of the tool and possibly your body - connected to the metal wiper of the pot.

I tend to use these:-

https://uk.rs-online.com/web/p/trimmer-tools/0543434

They are almost entirely non-metal, with only a very short embedded metal blade on the very end.

Someone (RS?) used to do a short bodied plastic trimmer with two different sized flat brass blades at each end and the smaller end (suitably filed to size) is a good fit for the coil cores in typical TOKO can coils etc. I've just looked high and low and I can't seem to find those anywhere now.

[John M1JWR]

i have some plastic trimmer tools, think they were ck ones and another double ended one which i think is aluminium, back to the job at hand.
the 270r was soldered on the solder side of the board to start with, i removed 1 leg, no light, i tried 2 resistors, 2.2k and 10k, no change, currently it has a 10k resistor on the board where the 270r was and the other 10k one is back inline on the wire from the band switch, voltages have changed red wire at board 10k is now 5.20v and white at 10k from band switch is 6.99v

[SiriusHardware]

When you had the 270R out and no other resistor in its place the LED went out, but with the highest replacement value you have tried so far it is still too bright. Conclusion: You need a higher value resistor than 10K.

Do you have a collection of preset resistors or potentiometers? Try picking one with a marked value of let's say 47K or 100K, solder a couple of short wires to one end leg and the middle leg and insert it in place of the 'extra' inline 10K resistor. Wind the value up and down and see if you can find a point at which the LED does dim but doesn't go out.

At that point, power off, disconnect the pot and measure the resistance that the pot is set to. Replace it with the nearest standard resistor value.

[John M1JWR]

might take a bit of time as i have to rob scrap board, i take it that i am the leave the 10k one in place that goes to the band switch and trial and error the one where the 270r one was.
i will try the trimmer pot idea aswell, again i will have to rob scrap board for one

[SiriusHardware]

As the 270R and your extra resistor are in series, their values are added together so it is up to you which one you replace with the preset, but the important thing is to definitely have a resistor in series with the preset, whether it is the 270R or the 10K one.

This is because the value of a pot can go all the way down to almost no ohms, and if you run the LED from 12V with no series resistor at all you will definitely damage it. My suggestion is to leave the 270R in its original position and replace the 10K with the variable one - or with a selection of ever higher value fixed resistors, but using a preset / pot would allow you to arrive at roughly the right value within a matter of seconds.

[John M1JWR]

Found a 200k trim pot on scrap 121 board was rv11, with the 270r in position and the end reading on that test was 112k for good light level similar to original, so now i need to find a resistor of around 112k

[SiriusHardware]

Try adjusting the preset to read 120K and if that still looks acceptable, 120K is a standard resistor value. If it's too dim at 120K try 100K. If that's too far the other way, you should be able to buy 110K resistors but that is a 'modern' resistor value and you won't find any in your scrap chassis.

[John M1JWR]

looks like quite a wide spectrum all the way to around 200k, around 150k looks about best, i have one or two mini disc deck boards with more various sized resistors but of course smaller in psyical size

[SiriusHardware]

As you probably realise, the 270R in series with ~ 150K is making an insignificant amount of difference to the overall resistance so if you wanted to make it neat you could just fit a 150K in the position where the 270R was originally fitted and revert all wiring back to how it was.

Or, leave the 270R where it is and just add the 150K to it if you think there will ever be a chance that you will find an original lamp to put in it, that will make it easier to revert it back to as-built.

[John M1JWR]

probably just fit the 150k in place of the 270r, found one on the scrap 125 board, R61

[John M1JWR]

all installed, so hopefully that is the end of that.
one thing i would like to ask, am has backwards swing, what is that all about

[SiriusHardware]

You mean the RF output meter is dipping when the TX is being AM modulated?

If the unmodulated supply to the RF driver and PA is correctly set to about half supply ~ 7V then the process of AM modulation should lead the supply voltage to be reduced and boosted in equal measure.

One reason why this might not happen in some radios is if the unmodulated supply has been wound all the way up to maximum in an effort to give the radio more power on AM, but this is counterproductive as it then means that the modulator can only decrease, not increase, the supply voltage to the RF driver and PA, leading to distorted AM modulation.

From what you've said earlier you are aware of this as your unmodulated AM output is much less than the FM output, just as it should be.

I would tend to say that as long as the transmitted AM audio sounds OK, don't be too concerned about the meter quirk.

[John M1JWR]

From what i can make out from another radio am sounds good, so hopefully this one is near or at the end of its ressurection, all in all it only took 7 years !
many thanks of course, i will put it on soak test for a bit on rx as i currently have only the 80m di pole to plug it into just now, 10m area has always been a deadish area on it, if cycle 25 ramps up like some people say that wont matter too much, as i remember back in the early 80's on am in two cars not far behind each other being wiped out by yank truckers, and back in the early 00's i took the 10m black shadow to a ham friend a G4 who is unfortunetly no longer with us, and whilst setting it up, he was picking up the usa on some co ax only and he said see that, sensitive radio this, a single band radio wins every time.

[SiriusHardware]

The late seventies / early eighties sunspot high doesn't seem to have been equalled since, or maybe it was just that I was very keen on radio in those days and spent a lot more time listening / observing. I can clearly remember using a pair of low-spec walkie talkies and not being able to get a word in edgeways due to a multitude of Italians swamping their only channel.

At the time I could not imagine why there would suddenly be so many Italians all crowded into one space and on one frequency here on suburban Tyneside but I was, in reality, hearing Italians from all over Italy on a little one-transistor superregen receiver.