What do you call a short? The valve heaters and the dial lamp are naturally low resistance. If you find you get a "short" just by plugging in any valve, check again - it will be a few ohms, not a total short.

As Robbert said, the valve heaters are a quite low resistance, which you are describing as a short. This is why you are seeing a "short" when you replace the valves.

If there is a solder blob from pins 3 and 4, your HT is shorting to ground, either directly or via the 6V4 heater which is only a few ohms. What is the resistance from pin 3 to ground, both with the 6V4 in place and removed?

Harold

I had another look around the circuit. There was one loose connection on one the new capacitors and two small thin wire tails which looked like they were wrapped around each other. They appear to provide an earth for the light circuit.
I ran a jumper and everything came on, Lights worked 6V4 heated up but almost immediately R30 started to smoke and R27 got hot.
I checked the values and R30 has dropped to 200 ohms but R27 is still fine.
The photo shows the two small wires and R30 and R27. You can see the discolouration on the lower R30.

OK. Now can you tell me what resistance you measure between pin 3 and ground, junction of R30 and R27 to ground and junction of R28 and C31 to ground.

Clearly, there is far too much current and the above might help in seeing where the fault lies, HT1, HT2 or HT3 circuits.

Harold

Replacing the valves one by one, is not something I would do, in the circumstances; but if you were monitoring the B+ and nothing untoward happened.......

It would be somewhat obvious that if you were powering it (not plugging them in live) the last tube plugged in before the bum fell out of B+ is the one, with its socket shorting, grid bias missing, or its shorted, which is the problem.

Marc

So,
6V4 pin 3 to earth - OL
R30 + R27 to earth 35M
R28 + C31 to earth OL
however R25 started to cook and has climbed from 100 ohm to 140. But that is in circuit
C16 I noticed seems to be loosing some of it's innards.
Thanks

OK. Your 4 electros from pin 3 on 6V4 appear ok.

As Marcc commented, you need to find which stage is causing the excessive current, as your previous resistance measurements indicate there is not a short on the HT wiring.

Under the circumstances I would do the following:

1. Power off

2. All valves out except 6V4.

3. Connect meter to HT1 to monitor the voltage as 6V4 warms up. I would expect, with no other valves present, it will go up to maybe over 300V.

4. Keeping an eye on the meter, switch on and confirm that it does go up smoothly to this sort of level.

5. If it does, switch off, replace one valve, starting with a 6M5. Watching meter, switch on and you should observe HT1 go smoothly up to something like 260 or 270 volts. If it doesn't, your problem is around that stage, refer Marcc's comment. If this step is OK, repeat step 5 with the other 6M5 and so on through all stages. With both 6M5s in place, the voltage will be close to the specified 250V.

6. Hopefully this will get you close to where the problem lies.

Harold

Thanks Harold.
Just to check, leave 6V4 in and replace each valve one at a time or one in and one out.
I'm sorry I don't know what B+ is

B+ is a term to refer to the high voltage supply, called HT 1,2 and 3 in your circuit. It harks back to battery radios, where the A supply was for valve heaters/filaments, B supply was high voltage and the C supply was valve bias.

I would be inclined to leave each valve in place as each stage is tested, if the test is successful.

Harold

OK, Lights are working and 6V4 heats up.

But at HT1 voltage jumps to 50v then down to nothing. I tried another 6V4 I have, with the same result.

But at HT1 It jumps to 50v then down to nothing

Could you confirm that this is with just the 6V4 in place.

If this is the case, then the problem lies with the HT wiring or components and I would look for electrolytic caps in wrong way around or any cap with too low a voltage rating.

Because it does go up to 50V and then break down, it is unlikely to be a wiring short, as your previous resistance check would show this.

I am more inclined to think it is a component problem, based on your earlier comment.

I replaced the paper caps as I wasn't happy with the sound.

Harold

I am seeing methodology fails galore. What equipment do you have? I commercially fix so I have lots of toys.

Did you change the electrolytic caps as well as the paper? Putting electrolytic caps in backwards causes this issue the falling voltage may be an old or underrated cap. The electrolytic caps are chemical, if left unused they gradually fail. When re-energised they can and will present as a short circuit. You change out all of them.

Debris an large solder blobs can short. Sometimes a dead short heater to cathode can be picked up by an ohm meter: Tube out no fingers on the probes. IC clips are good for this and monitoring.

For games like this I have a capacitor reformer/ tester with stepped voltages. If there are no voltage dividers (which can be disconnected) I can use it to power the "B" rail with the tubes out and sets power disconnected; Step up the voltage. If there is a fault the regulator locks up. If the voltage holds "B" wiring is not at fault. I have gotten to the point that I test all Electrolytic caps before I use them: Allegedly new ones do fail.

You can do similar but not necessarily with batteries and a series globe or similar.

Do you have a Variac / Slide Regulator. Not a great believer in "Dim bulb" tester

Marcc

I am seeing methodology fails galore. What equipment do you have? I commercially fix so I have lots of toys.

I have a multimeter

Did you change the electrolytic caps as well as the paper? Putting electrolytic caps in backwards causes this issue the falling voltage may be an old or underrated cap. The electrolytic caps are chemical, if left unused they gradually fail. When re-energised they can and will present as a short circuit. You change out all of them.

no just the paper caps

Debris an large solder blobs can short. Sometimes a dead short heater to cathode can be picked up by an ohm meter: Tube out no fingers on the probes. IC clips are good for this and monitoring.

I have gone back over the solder joints with no blobs found


For games like this I have a capacitor reformer/ tester with stepped voltages. If there are no voltage dividers (which can be disconnected) I can use it to power the "B" rail with the tubes out and sets power disconnected; Step up the voltage. If there is a fault the regulator locks up. If the voltage holds "B" wiring is not at fault. I have gotten to the point that I test all Electrolytic caps before I use them: Allegedly new ones do fail.

I have started checking the caps. I have been de soldering one lead and checking with the multi meter



Do you have a Variac / Slide Regulator. Not a great believer in "Dim bulb" tester

No variac..
I don't do this for a living. When I left the RAAF, the last thing I wanted to do was more electronics. I knocked back a job with Boeing for that reason. It has been I long time since I have done stuff like this. I am just trying to get the stereo going so I can play my records. If I could find someone locally (Newcastle) to fix it I would.

I live in Cameron Park, not a million miles from Newcastle.

I disposed of my collection a few years ago, including all my test equipment, but I might be able to give some help.

My email is unhidden, give me a call.

Harold

I haven't seen a schematic, but I do wonder about those burning resistors and are they still intact.