28-09-2017, 06:23 PM
(This post was last modified: 28-09-2017, 06:26 PM by Mike Watterson.)
(28-09-2017, 04:39 PM)Murphyv310 Wrote: Hi.No, i'd not in this case
I hear what you say Michael but the proof of the pudding is in the eating, would you not agree. Using just one valve with a proper tank coil and tuning I get a useful range of 10 meters, with traceable signal 50 meters from the shed.
All the theory is well and good but often in practice the theory is disproved.
Theory is disproved if it's wrong.
Yes, what you are doing works. BUT with the same parts it would work far better connected correctly. It's not theory, it's how it works. You can easily test and prove it with two pots from a -9V to drive the g1a and g1b and meter the Ia and Ig2. You'll see it works exactly as I describe, not like a heptode, hexode, nonode, dual grid or dual gate FET.
No separate LO valve is needed. Even the 1j24b can be a Mixer / Osc (see early superhets before Hexode) with no extra valves, though for stability a SEPARATE valve LO was ALWAYS used, hence Triode - Hexode is far superior to a single tube mixer/osc or modulator based on heptode/octode/nonode.
The 1j37b and 1j42a are based on a unique Russian design, it's working as a modulator purely because you are using it in a non-linear mode. The circuit I describe is far lower IM distortion for RF to IF mixer, or AF to RF modulator, which is why the actual Russian radios used those devices that way.
It's not a dual grid valve. It's the single grid of the 1j24b used in two parts.
Obviously if you are happy with what you have, don't bother trying to do it better. But anyone that hasn't built one, is better first building the proper Russian design and understanding it.
The Internet is full of stuff "that works", but is actually misleading, less than good or plain wrong. Hence people buying old transistor sets and cutting out the Germanium output transistors to make guitar pedals. Or using Litz speaker wire. Those "work".
