18-09-2017, 01:42 PM
Thank you Trevor for your posts concerning your pantry Tx. I find your videos' very interesting as well as your circuit. It has encouraged me somewhat as, although I don't have any 1j42a, my planned design uses a 1j37b dual g1 valve as modulator with RF input to one g1 and AF to the other. My oscillator is of the same type as yours, although follows the Russian circuits more directly and has a large resistor to screen from HT rather than a choke. And of course the anode tuned circuit tuned for the harmonic. I have just used a variable capacitor at the moment and on test tuned through several harmonics to get a feel. My supply is 40 or 50V but with decoupling the anode is at probably around 20V. This follows my Russian example, and also that a previous low voltage valve oscillator I have built worked very well with good stability in the power supply. I was momentarily tempted toward your approach, but on reflection, will continue as planned as my design is somewhat similar but different. I think that if I were to use an harmonic and modulate in the same valve it may work but almost certainly be 'dirty'. I do not plan to use a pa as I think the 1j37b should provide ample output in itself, especially as I am not planning for reduced voltage operation.
I do have some 6n16b double triodes, but because they use a 6.3V heater I am not planning to use these, and will stick with 1j24b or 1j29b for oscillator buffer and audio amp / driver functions.
I do note your advice about the heater supply. I don't think, in this case with probable fairly low useage, that 1.24V is an issue but looking to the future it would be good for me to sort now. Perhaps using my current supply with a small resistor or maybe even better with a wirewound resistor / resistive choke.
Another thing I have begun to look into is biasing. This is perhaps the main thing which is confusing me at the moment as, like most, I am far more familiar with indirect heating so separating bias and heating functions. My valve familiarity is almost all with post WW2 valves, and low power so I have no experience of circuitry using anything else.
Thanks Terry – I was aware of Mike's great input into this field. I do find, perhaps like with everything else, that a balanced approach works best so cross check a lot of facts anyway. I have found several times in the past that 'Chinese whispers' is rampant and, particularly in one specific power supply type circuit that I make good use of, maybe 95% or more internet reference circuits I have found appear to show electrolytic capacitors wrongly biased (as I have measured) giving potentionally dangerous results.
I like your explanation of electron velocity Nick. It reminds me of A level physics and a problem I had to workout then. A bit in the past, but a useful reminder, particularly toward the effects.
Thank you for all the links everyone. Many of them I have, but there are some that I need to follow up.
I do have some 6n16b double triodes, but because they use a 6.3V heater I am not planning to use these, and will stick with 1j24b or 1j29b for oscillator buffer and audio amp / driver functions.
I do note your advice about the heater supply. I don't think, in this case with probable fairly low useage, that 1.24V is an issue but looking to the future it would be good for me to sort now. Perhaps using my current supply with a small resistor or maybe even better with a wirewound resistor / resistive choke.
Another thing I have begun to look into is biasing. This is perhaps the main thing which is confusing me at the moment as, like most, I am far more familiar with indirect heating so separating bias and heating functions. My valve familiarity is almost all with post WW2 valves, and low power so I have no experience of circuitry using anything else.
Thanks Terry – I was aware of Mike's great input into this field. I do find, perhaps like with everything else, that a balanced approach works best so cross check a lot of facts anyway. I have found several times in the past that 'Chinese whispers' is rampant and, particularly in one specific power supply type circuit that I make good use of, maybe 95% or more internet reference circuits I have found appear to show electrolytic capacitors wrongly biased (as I have measured) giving potentionally dangerous results.
I like your explanation of electron velocity Nick. It reminds me of A level physics and a problem I had to workout then. A bit in the past, but a useful reminder, particularly toward the effects.
Thank you for all the links everyone. Many of them I have, but there are some that I need to follow up.
