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.
Last edited:
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.
Sorry for the delay, last night got busy.
I made the changes I mentioned, but it still struggles to oscillate with my J310s.
An amazon M102 through-hole tacked on will oscillate, but it is still not a good waveform, nor is it stable. Before I go measuring the bias and trying to adjust for the Jfets I have, I figure I would first try pulling one from an old radio and seeing how that behaves in this circuit. I will hopefully have it figured out by this weekend sometime.
If I can find an equivalent jfet in SMD form, I will get them. I could use some small signal RF jfets around here anyhow. monday through thrusday I work 12s so I have little time to tinker until friday.
I made the changes I mentioned, but it still struggles to oscillate with my J310s.
An amazon M102 through-hole tacked on will oscillate, but it is still not a good waveform, nor is it stable. Before I go measuring the bias and trying to adjust for the Jfets I have, I figure I would first try pulling one from an old radio and seeing how that behaves in this circuit. I will hopefully have it figured out by this weekend sometime.
If I can find an equivalent jfet in SMD form, I will get them. I could use some small signal RF jfets around here anyhow. monday through thrusday I work 12s so I have little time to tinker until friday.
Yeah, no worries. You've already gone above and beyond what I would ask anybody to do.
I may start working on something else. Doesn't mean I've lost faith in your abilities. Just means impatience on my part. Maybe a touch of ADD, too.
I may start working on something else. Doesn't mean I've lost faith in your abilities. Just means impatience on my part. Maybe a touch of ADD, too.
Made a little progress. Got the J310 to oscillate. I measured the voltage across the 470ohm resistor and found most of the 8v was dropping across it, so I added a 220ohm resistor at the source and bypassed it with 100nF and boom, got a nice waveform at the source.
I am not done yet though. I have the sig gen set to output PWM at 10kHz to drive the active filter to simulate the PD pulling it. When I bring the duty cycle above 32%, the signal amplitude starts to drop. Works great from 0 to 32% duty cycle. The drain connection at C82 is not sinusoidal like the source so I need to sort that out too. Ill have to do some math and figure out the ideal bias and play with the feedback a little. Not knowing where your coil is tapped, I might have to add an adjustment for the feedback somehow.
If you beat me to a clean-running VCO, my feelings will not be hurt lol. Im having fun. I admit though, I thought it would "just work", so guess I really dunning kreuger'ed this one. I'm slowly getting there though.
I am not done yet though. I have the sig gen set to output PWM at 10kHz to drive the active filter to simulate the PD pulling it. When I bring the duty cycle above 32%, the signal amplitude starts to drop. Works great from 0 to 32% duty cycle. The drain connection at C82 is not sinusoidal like the source so I need to sort that out too. Ill have to do some math and figure out the ideal bias and play with the feedback a little. Not knowing where your coil is tapped, I might have to add an adjustment for the feedback somehow.
If you beat me to a clean-running VCO, my feelings will not be hurt lol. Im having fun. I admit though, I thought it would "just work", so guess I really dunning kreuger'ed this one. I'm slowly getting there though.