I was able to find an NOS KL-25 (a BK-36 replacement), but when it was installed in the Receiver, the filament(s) burned brightly even at 80VAC (voltage was brought up slowly using a Variac), cracking the glass envelope of the tube. The tube now does not work at all.
When the abortive test was made, the dial-lights (which I think are connected to the KL-25 circuit) did not illuminate. A few questions arising:
i) Am I right in assuming that the brightness of the filament in the KL-25 signifies a 'short' somewhere (in one of the other tubes--though these have been tested and seem OK)?
ii) If not in the tube, where else could the short be?
iii) Maybe the route to go would be to use a Resistor Tree to replace the K-25 (I can't keep going through those at this rate). I've had very full information on this, but still do not really know what resistor value(s) would be connected to ALL the relevant pin sockets. Any 'duh' point-to-point guidance would be appreciated.
iv) If the KL-25 'overloaded' through a short, would the filaments of the other tubes be damaged?
v) My EC-2 came with the AC plug wire de-soldered from the circuitry. To which pins of the KL-25 socket would the live/neutral AC wires be attached?
Sorry to be so...plodding in working this out.
Cheers,
Leslie Sheldon
I see that from the schematic as well but (and excuse the dumb question), would any part of the AC input cord be attached to 'Ground'? Would that not electrify the chassis, making it 'live'?
There a couple of 'mussed' solder connections on the BK-36 tube socket pins, but of course that could have been done by a previous owner.
If it helps, I'll try to see which connections these are; pins 7-8, I think...maybe it was badly wired in the past, which might explain why the ballast tube lit up like a light-bulb.
Cheers,
Leslie
Yes, it's a " hot chassis " Very common thing in radios with no transformer. Be careful with that. Use an AC plug with the Big pin connected to the chassis side of the cord. Keeps the hum down as well.
I'm getting there (on this part at least). If the wire from the big AC 'blade' connects to the chassis, from your reading of the schematic where does the other wire connect on the BK-36 socket? Pin 2 or 3?
Many thanks.
The schematic don't show a pin out for that tube. But it does show three resistors in series .. With an ohm meter read the pins. From the two pins with the most resistance would be the clue. One end to the heater string, the other to the AC "hot side" line.
Hi again,
So to 'recap': i) the large blade ac plug wire attaches to the chassis; any particular location, or just anywhere near the power cable inlet hole?
ii) I can do resistance tests on the tube pins (not the socket, yes?); the tube may be damaged, though, so I'm not sure whether the readings will be useful. By 'heater string' do you mean the connection between the KL-25 ballast tube and the other tubes in the set (especially the next tube in the series, the 25B6GT (the rectifier)?
A kind individual previously gave me some resistance values between the various pins, so that a resistor tree could be built to replace the ballast tube. Just to double check; I have 30Ohms betgween pins 7-8, 30ohms between 8-2, 106 ohms between 2 &3, and then 166 between pins 7-3. Does this seem correct (I also came across other values in my research, though, so I'm not sure which are correct)? And when I build the resistor tree (using resistors of the right wattage of course) do I simply solder them from socket pin to socket pin, or is there any particular way of 'arraying' them?
Anyway, thanks for your input, which is certainly getting me there...
Leslie
Hello again Leslie. I would say the 300 ohms between pins 3 & 8 is the total resistance as shown in the schematic. The hot lead of the AC line to pin 3 then pin 8 would go to the 25Z6 heater. The Big blade of the AC line goes to the on off switch first, then from the switch to chassis ground. Dial lamp #1 pins 7 & 3 ..Dial lamp #2 pins 2 & 3 .. That seems the way it all should go .. Also notice the hot AC lead wire goes through the stand by switch, then to the plate of the rectifier tube 25Z6 .. Good luck
How about using an unpolarized electrolytic capacitor as a ballast and use a small resistor in parallel with two series connected back to back zener diodes and connect the pilot bulbs across this.
Dick
Hi Dick,
Thanks for that. I've nothing against using a different solution from the obvious 'resistor tree'. Can you give me a lead on any of the specs. for the caps/resistors/diodes?
One of the first problems, whatever ballast equivalent I use, will be in working out why the KL-25 ballast tube burnt like a light-bulb to begin with (which it's not supposed to do). I'm guessing there's a short somewhere, though all the other tubes were tested and replaced where necessary.
Have a great day.
Leslie, check the wiring of the tube heaters on each sock and if correct, tubes removed and radio unplugged, you should measure infinity on ohm meter from the chassis to pins 2 & 7 (pins 7 & 8 on 6SC7)on all sockets except 6H6 where either pin 2 or 7 should be zero.If any socket varies start checking there for short(s). Last place to look will be ballast socket but I don't kinow the pin out but with the lamps removed readings should be infinity between chassis and all pins on that socket. Next check for short to chassis on any lamp socket terminal. If no shorts, possibly one of the heater elements in a tube shorted which would bring up voltage on remaining tubes and balast that caused it to glow. Resistance on all 6.3 V tube heaters should be about 21 ohms hot and on25 V tubes it should be 83.3 ohms hot. Cold you can only measure the resistance and use comparison to each other but it will be low, not near hot resistance. PL