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vacuum tube to pic -- how?

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tiny2

New Member
I've been working on a little novelty project to combine the two types of technology. Just wondered if anyone had any safe suggestions on how to interface the crystal oscillator to a pic CLKIN pin.

Here's what I have so far. The oscillator circuit was borrowed from an old shortwave receiver. The main difference between the circuit below and the actual prototype is the inclusion of a 1.5k resistor in the cathode. The tube used is the nearest equivalent I could find.


A picture of the prototype built on an old scrap chassis.


Here is the signal available at the anode. With approximately 130V applied, the measured current is around 1mA.


Across the cathode resistor is shown below, maybe I could fit a buffer transistor in there somehow ?


Any suggestions welcomed.

regards..
 

stevez

Active Member
Keep in mind that a short in C36 will make plate voltage available past that point. I know you might do something differently - just calling it to your attention.
 

ljcox

Well-Known Member
Another way to do it would be to wind a transformer and insert it in the anode circuit in lieu of the resistor. However, you will need the correct resistor in the cathode circuit in order to set the anode current.

The transformer could be wound on a ferrite ring. This would be the safest option for the PIC since there will be complete isolation between the primary and secondary PROVIDED THAT you don't wind the secondary directly over the primary.
 

Rolf

Member
750 Ohm ......

tiny2 said:
Across the cathode resistor is shown below, maybe I could fit a buffer transistor in there somehow ?


Any suggestions welcomed.

regards..
Why not drop the cathode resistor to 750 ohms and put a 5v zener diode across it for safety? This would clamp the signal to a safe level for the PIC. For additionally safety you could use capasitive coupling.
 

kchriste

New Member
Forum Supporter
Best not to even consider such an incredibly stupid and pointless exercise!
Now if only the OP had decided to drive a tube amp with PWM from the PIC for a richer higher distortion sounding BEEP..... :D
 

tiny2

New Member
Thanks all for replies. Not forgetting that this is just a novelty project; not to be taken too seriously !!

I thought that the optocoupler was a good idea, although I don't happen to have any here of adequate sensitivity to try. So I'll go with reducing the cathode resistor to give me the appropriate voltage. I had originally intended to use a miniature wire-ended pentode instead of the EF95, so maybe I'll implement that change first.

Thanks and regards
 
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