i think i have the layout figured out, waiting on the fingernail paint to dry.
oh crap, missed a trace, glad i looked again.
oh crap, missed a trace, glad i looked again.
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TRC-57 restoration
- Thread starter TM86
- Start date
Wow! You're faster than a Chinese PCB manufacturer with a Party Member breathing down their neck for missile parts!
I think I got it done. I slopped a little UV mask on it with a paint brush, probably shouldn't have, looked better without it. I haven't tested it yet, but if I get time yet tonight, I will see if I have a coil to put across it. I need to unlock the clarifier on a 959B first, told 1408 NM I would have it done this weekend.
I made a 1uH coil and it did not oscillate. I have poked at it for a little while and know what I need to do to make it work. Gonna need another day on that.
Take your time with it. I've got plenty to keep me occupied between my day job, the XYL's business, and the pile of radios from that estate sale last month. I'm just grateful you're taking time that you could be using to work on your own projects for this.
I did get it oscillating last night using some leaded parts tacked on.
I think what's happening is the J310 has a higher Idss and transconductance compared to the older 2SK19. Online research suggests the older JFets tolerate being directly connected to the coil like that because of their lower gm and Idss whereas the J310 and other newer JFets needs a gate isolation capacitor (they are more sensitive to bias conditions, signal amplitude and loading). Thanks to a video I just watched, I know the shape of the waveform is sensitive to the value of that isolation cap and it can output a pretty clean waveform if that cap is set right so I will be adding a trimmer to isolate the gate from the coil and a 1Mohm resistor to hold the gate at 0v. When I get home. This is fun stuff!
edit: Etched a new board last night, will try to populate it after work.
I think what's happening is the J310 has a higher Idss and transconductance compared to the older 2SK19. Online research suggests the older JFets tolerate being directly connected to the coil like that because of their lower gm and Idss whereas the J310 and other newer JFets needs a gate isolation capacitor (they are more sensitive to bias conditions, signal amplitude and loading). Thanks to a video I just watched, I know the shape of the waveform is sensitive to the value of that isolation cap and it can output a pretty clean waveform if that cap is set right so I will be adding a trimmer to isolate the gate from the coil and a 1Mohm resistor to hold the gate at 0v. When I get home. This is fun stuff!
edit: Etched a new board last night, will try to populate it after work.
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Received the replacement On/Off Volume control. It On's, it Off's, and it volumes. Which is two features more than the old one.
Replacement VR7 installed. Turns out what I ordered was not quite what I thought, it was a bit smaller. So I had to "extend" one of the legs to one side.
Tiny piece of perfboard to the rescue. Used that to attach the pot to, then soldered the wiper to one of the legs so it works like the original. Leads from the perfboard to the original mounting holes and seems to be good.
Sure it's kind of hard to tell without a working VCO, but no fire came out so I'm pretty happy about that.
Tiny piece of perfboard to the rescue. Used that to attach the pot to, then soldered the wiper to one of the legs so it works like the original. Leads from the perfboard to the original mounting holes and seems to be good.
Sure it's kind of hard to tell without a working VCO, but no fire came out so I'm pretty happy about that.