14-07-2019, 10:37 AM
(This post was last modified: 14-07-2019, 10:38 AM by Mike Watterson.)
I'll do something. Likely get RF to detector (with an 1N60) working with ECH35 and EF39, then decide what to do next.
The coils and IFTs on mains sets are similar to battery models (valves).
The big difference is LT and bias. No self bias with cathode resistors. So short them all out and provide -Ve bias via grids, or run filaments -ve vs 0V. Mains /battery sets use series filaments to set grid bias, hence O/P last and audio preamp with grid leak is first. Parallel sets used to use a grid bias battery, lasts for shelf life, then used HT- current to get -Ve bias.
The only harder bit than say using 2V or 1.4V octal battery valves is the sockets. The only tricky bit on Rod Pentodes is AGC as they are sharp cutoff. One could just have a variable voltage to g2 for manual RF gain (done on some battery communication receivers).
Obviously HT wants to be 45V to 120V depending on location. I also have a Philips VHF tuner head for 2x EF80s. That will easily work with Rod Pentodes with suitable adaptation. Cathode feed is done by feeding filament via bifilar RF choke, the DC cancels and it's high impedance to the RF.
Even if I repopulate with original valves I may add the Philips EF80 tuner head. I doubt it tunes past 101MHz!
The coils and IFTs on mains sets are similar to battery models (valves).
The big difference is LT and bias. No self bias with cathode resistors. So short them all out and provide -Ve bias via grids, or run filaments -ve vs 0V. Mains /battery sets use series filaments to set grid bias, hence O/P last and audio preamp with grid leak is first. Parallel sets used to use a grid bias battery, lasts for shelf life, then used HT- current to get -Ve bias.
The only harder bit than say using 2V or 1.4V octal battery valves is the sockets. The only tricky bit on Rod Pentodes is AGC as they are sharp cutoff. One could just have a variable voltage to g2 for manual RF gain (done on some battery communication receivers).
Obviously HT wants to be 45V to 120V depending on location. I also have a Philips VHF tuner head for 2x EF80s. That will easily work with Rod Pentodes with suitable adaptation. Cathode feed is done by feeding filament via bifilar RF choke, the DC cancels and it's high impedance to the RF.
Even if I repopulate with original valves I may add the Philips EF80 tuner head. I doubt it tunes past 101MHz!
