04-08-2022, 05:52 PM
(This post was last modified: 04-08-2022, 05:59 PM by Murphyv310.)
Hi.
Thanks Michael for the info. A closer look at the 41.5Mhz crystal revealed some rust at the leads at the body, perhaps its O/C internally.
Some interesting developments on the modulator this afternoon. For some reason I decided to reverse the grids on the vision modulator and lo and behold I don't need the positive bias to give me a positive going signal! The down side is it needs a lot more drive so its left as was.
Also I have modified the audio stage slightly by adding a 1K resistor between the earth side from the input audio transformer to ground bypassed by a 25μf cap and connecting the HT supply negative to the transformer, this giving the audio section of the 1ZH37B some negative bias (approx 1.95v) this increases the depth of modulation and reduces distortion. I think I'll be doing this mod to my 1ZH37B pantry transmitter.
I've updated the diagram. Total HT current is 1.95ma.
rpentodech1upd.pdf (Size: 380.31 KB / Downloads: 10)
Thanks Michael for the info. A closer look at the 41.5Mhz crystal revealed some rust at the leads at the body, perhaps its O/C internally.
Some interesting developments on the modulator this afternoon. For some reason I decided to reverse the grids on the vision modulator and lo and behold I don't need the positive bias to give me a positive going signal! The down side is it needs a lot more drive so its left as was.
Also I have modified the audio stage slightly by adding a 1K resistor between the earth side from the input audio transformer to ground bypassed by a 25μf cap and connecting the HT supply negative to the transformer, this giving the audio section of the 1ZH37B some negative bias (approx 1.95v) this increases the depth of modulation and reduces distortion. I think I'll be doing this mod to my 1ZH37B pantry transmitter.
I've updated the diagram. Total HT current is 1.95ma.
rpentodech1upd.pdf (Size: 380.31 KB / Downloads: 10)
