02-06-2023, 02:37 PM
Ron,
Thanks for the pix, overall it looks good!. Yes, solenoid orthogonal placed RF coils, O.K.
I do see that it is the single cone bearing tuning condensers.
There IS an obscure issue with certain tuning condensers, not just A-K. Although I have not directly experienced it, I believe Jeff of ARF has. The mixed metals and individual pieces that make up many tuning condensers that are nut/bolt assembled corrode in between the bits, the plates, the spacer washers and any connections to the wired circuits. So effectively, the tuning condenser at RF is not presenting the required capacity to tune the BC band.
This would be an easy check with a grid dip meter into any of the coils to find resonance or other means.
None the less the fix is to totally disassemble the tuning condenser(s) buff the joints, all of them, including the spacer washers. Buffing the entire surface of the plates is not required. Then, carefully re-assemble.
I would consider this only after eliminating any other possible cause of poor reception as it is tedious. The rust on the stator mounts seems to indicate this corrosion maybe present. A check with an ohmmeter is inconclusive as it is a DC measurement. Overall, deteriorated solder joints of 95 years old can create a similar poor RF joint despite DC measurements with an ohmmeter.
Since the radio will work with just the detector, directly feed the antenna into the 2rd RF plate circuit after disabling B+. The detector tuner could be cleaned up first, then tested for efficiency, expect it to tune broadly but it should be more effective.
The full procedure for rejuvenation can be found at many sources however, I use the method found in documents of the 20's which is repeated here:
http://www.nostalgiaair.org/References/A...lash08.htm
No matter who's procedure, do NOT connect the plate or the grid to anything during the process of flashing and ageing and do not attempt to measure emission at elevated filament voltage.
The reason: The thorium will be immediately stripped from the surface of the filament at the elevated temperatures of flashing and aging by potentials on the plate or grid. The Radio Fans restoration method the same applies that is why the B and C batteries are disconnected when in home use.
If your confident the emission measured by your tube tester is good then rejuvenation should not be attempted.
Initially, I used my tube tester to flash and age thoriated tubes. I used a tube base adapter (home made) in conjunction with an interposer (home made), of which connects only the filament to avoid any accidental connection to potential within the tester. It was tedious and required careful steps. The Jefferson tube rejuvenator solved all of that and has simply two steps flashing and aging, I do have to time the process...
The tube tester must test at 5 volts filament NOT 6...
It is also possible the RF stages are oscillating, since the OEM grid resistors should be 600 ohms, the current low value could be causing oscillation that would block any desired RF signal. One way to tell is bring an operating transistor pocket portable radio near any of the RF coils. turn on the A-K and then tune the transistor radio though the band listening for an abrupt "dead" air indicating oscillation on the transistor radio. The transistor radio could also whistle if it is tuned near a broadcast signal from hetrodyne. This oscillation should move when the A-K is tuned. Also, the A-K could pickup the oscillator of the transistor radio which could result in whistle on any received station or "dead" air in the A-K.
Further, when the A-K RF stages are working well, bringing a transistor radio near the detector coil and tune the transistor to the same station as the A-K the amplification of the A-K will bring the station in on the transistor radio quite loudly. There will be a slight drop in the A-K volume as the transistor radios ferrite loop absorbs some of the RF signal and slightly de-tunes the A-K.
A useful tool for a "sanity check".
Chas
Thanks for the pix, overall it looks good!. Yes, solenoid orthogonal placed RF coils, O.K.
I do see that it is the single cone bearing tuning condensers.
There IS an obscure issue with certain tuning condensers, not just A-K. Although I have not directly experienced it, I believe Jeff of ARF has. The mixed metals and individual pieces that make up many tuning condensers that are nut/bolt assembled corrode in between the bits, the plates, the spacer washers and any connections to the wired circuits. So effectively, the tuning condenser at RF is not presenting the required capacity to tune the BC band.
This would be an easy check with a grid dip meter into any of the coils to find resonance or other means.
None the less the fix is to totally disassemble the tuning condenser(s) buff the joints, all of them, including the spacer washers. Buffing the entire surface of the plates is not required. Then, carefully re-assemble.
I would consider this only after eliminating any other possible cause of poor reception as it is tedious. The rust on the stator mounts seems to indicate this corrosion maybe present. A check with an ohmmeter is inconclusive as it is a DC measurement. Overall, deteriorated solder joints of 95 years old can create a similar poor RF joint despite DC measurements with an ohmmeter.
Since the radio will work with just the detector, directly feed the antenna into the 2rd RF plate circuit after disabling B+. The detector tuner could be cleaned up first, then tested for efficiency, expect it to tune broadly but it should be more effective.
The full procedure for rejuvenation can be found at many sources however, I use the method found in documents of the 20's which is repeated here:
http://www.nostalgiaair.org/References/A...lash08.htm
No matter who's procedure, do NOT connect the plate or the grid to anything during the process of flashing and ageing and do not attempt to measure emission at elevated filament voltage.
The reason: The thorium will be immediately stripped from the surface of the filament at the elevated temperatures of flashing and aging by potentials on the plate or grid. The Radio Fans restoration method the same applies that is why the B and C batteries are disconnected when in home use.
If your confident the emission measured by your tube tester is good then rejuvenation should not be attempted.
Initially, I used my tube tester to flash and age thoriated tubes. I used a tube base adapter (home made) in conjunction with an interposer (home made), of which connects only the filament to avoid any accidental connection to potential within the tester. It was tedious and required careful steps. The Jefferson tube rejuvenator solved all of that and has simply two steps flashing and aging, I do have to time the process...
The tube tester must test at 5 volts filament NOT 6...
It is also possible the RF stages are oscillating, since the OEM grid resistors should be 600 ohms, the current low value could be causing oscillation that would block any desired RF signal. One way to tell is bring an operating transistor pocket portable radio near any of the RF coils. turn on the A-K and then tune the transistor radio though the band listening for an abrupt "dead" air indicating oscillation on the transistor radio. The transistor radio could also whistle if it is tuned near a broadcast signal from hetrodyne. This oscillation should move when the A-K is tuned. Also, the A-K could pickup the oscillator of the transistor radio which could result in whistle on any received station or "dead" air in the A-K.
Further, when the A-K RF stages are working well, bringing a transistor radio near the detector coil and tune the transistor to the same station as the A-K the amplification of the A-K will bring the station in on the transistor radio quite loudly. There will be a slight drop in the A-K volume as the transistor radios ferrite loop absorbs some of the RF signal and slightly de-tunes the A-K.
A useful tool for a "sanity check".
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
