06-10-2016, 05:58 PM
Hi.
Indeed Michael you are right about these being the oddest of the Rod Pentode valves, In fact they are the oddest valve I have ever come across.
I have thrown the valve theory books in the bin and looked at these valves from a different perspective.
I spent about an hour and a half with one I'll use for experimentation and without regard for valve theory.
On the bench I had an AA Ni-Mh cell, PP3, a 22ohm resistor a few small value caps and assorted resistors 100k and above, high impedance phones and other bits and bobs.
I only used the 1j42b as I'm now quite familiar with the other types and their idiosyncrasies.
Initially I wanted to try it as a simple audio amp, after trying some combinations I found that using the G2 as a control grid with about 1.2v positive bias and the anode as the output I got around 4x gain, very odd indeed. I then tried using the valve as a leaky grid detector, results were pretty poor no matter what combination was tried. Next was a simple crystal osc, simple feedback from anode to G1 this works well but the bias is touchy and how it's connected, it must be between Filament - and needs to be 1-1.2 v to work reliably, a 44mhz crystal started and ran as good as a 200khz one I have, anode load was a choke for the 44mhz and a 100k for the 200khz crystal, connections are conventional but the G2 produces nearly the same op as the anode, a very high value of resistor (1meg up to 8.2meg) increases the output, G3 damps the op if connected to either polarity of the filaments on the 200khz crystal and stops oscillation on the 44mhz crystal. As an RF amp I was getting useful gain at 100mhz but using the G2 as a control grid got more gain than using the dual G1's how very odd.
I'll be doing more tests over the next few days but have to say if anyone is experimenting expect the unexpected!!!!!
Indeed Michael you are right about these being the oddest of the Rod Pentode valves, In fact they are the oddest valve I have ever come across.
I have thrown the valve theory books in the bin and looked at these valves from a different perspective.
I spent about an hour and a half with one I'll use for experimentation and without regard for valve theory.
On the bench I had an AA Ni-Mh cell, PP3, a 22ohm resistor a few small value caps and assorted resistors 100k and above, high impedance phones and other bits and bobs.
I only used the 1j42b as I'm now quite familiar with the other types and their idiosyncrasies.
Initially I wanted to try it as a simple audio amp, after trying some combinations I found that using the G2 as a control grid with about 1.2v positive bias and the anode as the output I got around 4x gain, very odd indeed. I then tried using the valve as a leaky grid detector, results were pretty poor no matter what combination was tried. Next was a simple crystal osc, simple feedback from anode to G1 this works well but the bias is touchy and how it's connected, it must be between Filament - and needs to be 1-1.2 v to work reliably, a 44mhz crystal started and ran as good as a 200khz one I have, anode load was a choke for the 44mhz and a 100k for the 200khz crystal, connections are conventional but the G2 produces nearly the same op as the anode, a very high value of resistor (1meg up to 8.2meg) increases the output, G3 damps the op if connected to either polarity of the filaments on the 200khz crystal and stops oscillation on the 44mhz crystal. As an RF amp I was getting useful gain at 100mhz but using the G2 as a control grid got more gain than using the dual G1's how very odd.
I'll be doing more tests over the next few days but have to say if anyone is experimenting expect the unexpected!!!!!
