17-07-2020, 09:17 PM
(This post was last modified: 17-07-2020, 09:19 PM by Mike Watterson.)
The rectifier Anodes (AC inputs) are pins 1 &2.
The common Cathode (DC HT out) is pin 3. That is the DC power to everything.
The heater is via pins 4 and 5. Pin 3 and Pin 4 (Cathode and one side of heater) can only be connected to each other if the EZ81 has its own isolated heater supply. Older rectifiers that even had an indirect cathode sometimes had one heater pin and the cathode internally connected. If the HT+ is less than the heater-cathode breakdown insulation voltage, then 3 and 4 can be separated, but the heater pins ( 4 & 5) would need to use the main heater supply which can't be floating. But pin 3 needs to feed the main smoothing cap (Reservoir). If the EZ81 has its own heater supply, then one side of it has to be connected to somewhere, not floating. Similarly the 6.3V supply for all the other valves needs either one side, or a centre tap, or a 1K pot with slider to chassis so it's not floating. If a heater supply on a transformer doesn't somehow connect to something it can have a high parasitic voltage to Earth/Chassis or HT.
Your EZ81 must be on a separate heater winding or else all the heaters would be sitting at +HT with pin 3 & 4 connected. Some radios with an EZ80 or EZ81 do have a separate isolated heater supply for it, and then it makes sense to connect one side of that isolated heater supply to HT+ at the EZ80/EZ81.
Really old rectifiers had no indirect cathode. Just the filament as cathode.
The common Cathode (DC HT out) is pin 3. That is the DC power to everything.
The heater is via pins 4 and 5. Pin 3 and Pin 4 (Cathode and one side of heater) can only be connected to each other if the EZ81 has its own isolated heater supply. Older rectifiers that even had an indirect cathode sometimes had one heater pin and the cathode internally connected. If the HT+ is less than the heater-cathode breakdown insulation voltage, then 3 and 4 can be separated, but the heater pins ( 4 & 5) would need to use the main heater supply which can't be floating. But pin 3 needs to feed the main smoothing cap (Reservoir). If the EZ81 has its own heater supply, then one side of it has to be connected to somewhere, not floating. Similarly the 6.3V supply for all the other valves needs either one side, or a centre tap, or a 1K pot with slider to chassis so it's not floating. If a heater supply on a transformer doesn't somehow connect to something it can have a high parasitic voltage to Earth/Chassis or HT.
Your EZ81 must be on a separate heater winding or else all the heaters would be sitting at +HT with pin 3 & 4 connected. Some radios with an EZ80 or EZ81 do have a separate isolated heater supply for it, and then it makes sense to connect one side of that isolated heater supply to HT+ at the EZ80/EZ81.
Really old rectifiers had no indirect cathode. Just the filament as cathode.