#4710 safety valve

Everything seems fine with the valve, it gets warm when it’s been on. I have noticed that the 27R does get really quite hot however further up the thread seems to suggest whilst this isn’t ideal it’s not awful.

Unfortunately I do not have a scope no, I really should grab one because it would make debugging things like this a lot easier, something to add to the list!

Think we’re on checking the circuit and components and continuity. It is very odd that it was working fine a few days ago but has decided now is the time to shit the bed!

CryoS: try putting some 51Rs in parallel instead of 27R to spread the load out.

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Unfortunately all I have are 47Rs that’s about as close as I can get. gets me to about 23R, they’re still getting far too hot and I’m still not getting any signal on the output with it turned on :confused:

EDIT: I do get some sort of signal if I bugger about with the valve pins around the back with my finger but only very short bursts.

Continuity test for everything to the opamp and past the opamp all seem to be fine too.

Far to hot for you, or for the resistor?

Two 47 ohm resistors in parallel would give you 12/(47/2+12.6/0.15) = 112 mA through the circuit, and each resistor sees half of that or 0.056×0.056×47 = 0.15 watt which is well within spec for a 1/4 watt resistor. See the graph here for how using more resistors lower the power dissipation for each individual resistor.

If you’re still concerned, you could try shorting the resistor. The valve can handle the full 12 V just fine.


If it’s well within spec then I have no issue, I just won’t touch them :grinning_face_with_smiling_eyes:

Going to order a scope so I can see what’s going on a bit better, have swapped out the opamp but that didn’t seem to make a difference.

Some scope discussion here

For not so cheap scopes I can recommend the Rigol DS1054Z.

I got this one that he also liked


pretty much the same price. Half the channels, 4x the bandwidth.


I will say… I don’t like it as much as my old analog tektronix scope.

Yeah, digital scopes are like modern cars…
Slim, efficient, but not as much fun as the old way…


I have exactly the same problems with mine.

@CTorp torp did you manage to solve this? im a little bit stumped to be honest. the status led on the front panel is wired straight to 12v via the switch im not sure why it would be doing such a thing apart from solder joints. which valves are you both us9ing??? maybe they are the same? and we could go from there?

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Not yet, but I haven’t messed with it. It’s an ECC83S.

Like I said before, I could never get the stripboard schem to work with it either, so I have a feeling it just won’t work with this tube. Don’t see where I could have really messed up this build haha


It works when you touch the tube leads? My tiny imagination can only think of 2 reasons for this:

  1. Something bad happened when you soldered to the tube leads (like something came loose inside and you’re wiggling it to touch
    (In the laser cutting world when you go to replace a CO2 laser tube they have all kinds of warnings about not soldering to the tube lead)


  1. Is it a grounding issue?

12AX7/ECC83 is just supposed to be a US/Rest of the World name thing.

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my tube is a JJ valves EEC83s , so they do work.

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I got mine working, the signal from my kosmo modules needed amplifying (probs around 3-5x is best) before going through the safety valve.

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thats rather odd. so in order for it to work you have to boost the signal of the oscillators etc? as in if you plugged in an oscillator straight in it would not work?

rather odd im trying to figure out why this might be the case, in normal function you plug in anything from a contact mic up to an oscillator it will make it louder, I dont think there would be an instance it would make it quieter as the boost circuit way beyond the headroom of the synth so im trying to work out why yours is not doing that

Just to add in mine, I’m not getting anything at all unless I fiddle with the valve pins, here’s my valve.

thats the same tube as in mine

hmm maybe there is another variable at play here. what power supplies are you all using?

is there a possibility the jacks have been soldered on the wrong side of the jack board?

I had that problem before cyroS it turned out to be a dry joint on the valve to the circuit board.

Yes, my external synths like microbrute, ms-20 have noticeable distortion and the led behind the tube lights up. With my kosmo stuff there is no distortion and the led doesn’t light, until I boost the signal. My diy valve distorting vca also doesn’t have this problem.

how extremely odd. what are you plugging into it? from the Kosmo modules