subminiature tube radios
The Local oscillator works but the mixer does not seem to.
sorry about the bad schematic I made it on paint :P
Measure the plate current of the mixer, which from the schematic provided I think is null, because you do not have proper bias.
Myself I would place a decoupled cathode resistor and gate bias resistor. Check the net for different bias topologies for tubes.
Jeez, tubes, huh? Well, back before the earth cooled......
I do not see any components on here for biasing up the tubes properly. A mixer is a non-linear element, and you want to control the tube bias to maximize that non-linearity. That means you want to control the grid DC voltage, or have some sort of self-bias scheme (resistor-capacitor) between the cathode and ground. That is probably the extent of my help on this. Suggest you find a HAM radio forum and ask there. Here is one quick explanation:
http://www.hans-egebo.dk/Tutorial/Superhet-2.htm
Added after 6 minutes:
BTW, do we need to remind you to keep your hands off of the Anode supply? One hand testing, the other in your pants pocket!
Thanks for your replies.
I have seen many topologies, yet I have found a little info on pentode mixers.
These are sub-miniature tubes and the filament and anode supply rating is only 26V !
Which gives a noce idea for low voltage tube receiver without degrading the tube performance.
I think the ceramic filter solution (cheap one) would work ok right?
I have tried the resistor/capacitor cathode bias but it did not seem to work
I would appreciate some info about the grids bias topology as I do not know any ham forum to ask.
Check the site of JF1OZL for a lot of homebrew tube radios:
http://www.intio.or.jp/jf10zl/5vssb.htm
Also I found this book which may give you more information about tube receivers.
?Radio Receiver Design ? Sturley, 1943?
http://rapidshare.de/files/46358613/..._1943.rar.html