Friday, February 8, 2013

Twin Tube Operational Update

Been a while since I posted on the NoGA Twin Tube 80 (link opens the first article in the series, see Ham Radio Masterlinks for a list of all the articles), figured I'd post an update, and talk about some project ideas I have for this set up.
Not long after successfully using the transmitter, I ran into a difficulty. The next time I tried to use it, I powered the radio up, I got sparks when I keyed down! Hmmm, that's not right! I also was getting no power out.
I decided to give the rig a break for a lil' while, and focused my efforts elsewhere. Since I was going to be up, I took the transmitter back out, and began poking about.
2 months hadn't improved the situation, it still didn't work.
Power supply was good,
I suspected the transmitter had shorted something out when I tried to go poking about the last time I successfully used it, I wiggled wires, and mushed down parts. Still no dice.
I replaced the three 33pf capacitors and checked the 100microhenry inductor for continuity.
I then inspected the pins on the tube sockets, and sighed when I saw that pin 6 had a loose hookup wire.
hmmm, soldered that puppy down, made sure everything is bent to not short out, and closed the case back up. I think that the use of an Altoids tin in this situation is a mild gamble. It works decent enough, but there have been several times when I've come dangerously close to knocking something seriously out because the tin is somewhat flimsy when you begin poking holes in it.
I plugged the transmitter in, and things began to glow.
no Smoke, and no fires. That's a good sign.
Glow in the tube, antenna is a dummy load, DVM on, and keydown.
20V on the meter!
that's 1 watt folks.
we back in business!
The Thermionic Energy is Astounding!
These two glowing eyes
Voltage amplification
This is hollow state.

Of course, now I need to find someone to QSO with late at night on about 3582 KHz. The crystal is 3579.4 KHz, nominally, but it pulls a little higher in this circuit, I'm guessing that I need to add some capacitance somewhere to pull it back down. That gets me to my next point.
Back when I was building this thing, several suggestions for experiments were made to me, but it's not easy to swap parts out of this altoids tin. I've got a couple extra tubes that will work in this getup, and I'm thinking of building a breadboard that I can plug parts in and out of. I need some more tube bases first though.
The schematic is availble for view HERE. KL7H has done a great job of documenting this and Mike's 12 v regen project.
Any suggestions for substitutions?
Should I attempt to wire one tube as an oscillator and the other as an amplifier? (MOPA esque?)
Suggestions for boosting power?

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