Hi folks gr8 to be here
I have a Philips glidomatic I am repairing and restoring for a customer
the main power selector switch was siezed and not switching on and was broken on the wiper contact cork assy
i have since repaired it and now have 240vac primary switching on the transformer ok
the Phonogram is now giving sound but very quiet not a lot of volume
so I checked the supply at the capacitors and they where very low 120vdc instead of 250vdc so I did some testing and inspection and found the following conditions to be the problem

can I please ask for some assistance on a strange fault I have on the power supply of a 6v4 rectifier valve
i have 340vac 0vac 340vac secondary going to pin 1 HT1 & pin 7 HT2 on the 6v4 valve
i have replaced the 2 dual 50μF 350v capacitors with new dual 50μF 500v capacitors and all so replaced the leaking resistors soldered across them as the hold down stabilisers I
I all so replaced the b9a socket that was chared inside on the contacts and replaced the 6v4 with a replacment tested one from the valve store

on pin 3 I have B+ dc conected going to the c1 HT cap postive
and pin 4&5 going to the heater back to the transformer 5VAC

problem is I have no dc voltage at the capacitors no HT supply 250vDC as required on the schematic
when I check the supply with a dmm set to 500vdc and measure from the ground ref of the center tap and chasis black lead of meter and my postive probe lead on the postive of caps I get 200mv thats all
the tuner lights come on but no sound the all the valves heat up and look like they are on except the 6v4 no lights
from heater filiament I measure that there is 5.5vac on pin 4&5 no problem

iI am stumped why I have no DC HT voltage on pin 3
surely both 6v4 rectifier tubes cant be bad
thankyou for your assistance
i have a video of the repair work and the issue if you need it
LOOKS LIKE I MIGHT HAVE FOUND THE PROBLEM
The secondary AC is meant to have 350vac on both terminal windings and a center tap
measured today and found winding 1 HT 1.2vac 2 HT 21vac on a variac set at 17vac primary
so looks like the HT1 secondary winding is burnt out making sense now burnt rectifier socket pins and burnt out capacitor on the one that feeds DC from HT1 so I am guessing this has had a lighntning strike or massive power surge that took out the winding partialy on HT1 has high resistance on winding causing the low voltage
do you think I could be on the right track guys?

Hi, you have given me some confusing info on the problem, but we will try and help.

Firstly a model number would be handy, or at least a valve(tube) lineup.

5volts on the 6V4, should be 6.3 volts, is the primary selector in the correct position.

Have you measured continuity between centre tap and the two outer connections on the HT secondary winding.
Do they measure the same?

Can you measure continuity between centre tap of secondary and earth.
As this unit probably has a back bias resistor.
So, 200 ohms or less would be expected.

Awaiting your answers, JJ

Sorry, one answer....RF8
So, centre tap should be a direct connection the earth.
JJ

Remove the rectifier to prevent damage and to get a clearer picture. Shorted rectifiers & electrolytic caps, tend to be killers of transformers.

Irrespective of the thing being back biased, or not one would expect pins 1 & 7 to have roughly the same AC voltage to ground (Centre tap) or nearly the same ohms CT to pins.

Make sure that you are reading the socket wiring side correctly. Pin one is to the left of the wide gap and it's read anti-clockwise. Heaters are pins 4 & 5 (6.3VAC or slightly above off load) That electrolytic capacity seems overly high and can wreck the rectifier if it is.

This unit uses four 50μF electrolytics in the filtering circuit.
So, yes the 6V4 has a good load to look at on switch on.
Running two 6GW8's too.
JJ

Oh dear! Had a massive meltdown on a Thorn a while back (posted). As far as I can predict a 6GW8 went short that stuffed up the metal rectifier and that was the China Syndrome for the HV secondary which melted down.

It had a 5A fuse, which proved useless as they usually did. As there was no issue on the primary; if there was an RCD is was never going to trip in that scenario.

The Mystery has been solved !
it was the center tap winding had broken off under the coating and paper insulator to the lug
wow that was fun to find
thankyou so much for all your help in solving the issue
now onto the record player service

cheers

I've wondered if a smoke detector could be modified as the ultimate protection for old radios. But would be too expensive to implement on every radio, or even those most at risk.

100ma pigtail fuse inline with the HT centre tap goes a long way towards protection.. adjust value depending on current available from WES/Wagner

Wont help if already on fire....

Never leave them unattended

An 85 degree thermal fuse in fibreglass or silicone sleeving in series with the mains active and glued or strapped to the transformer winding provides excellent protection.

Don't forget, you cannot solder to them! For obvious reasons. Use crimp joiners.

I've wondered if a smoke detector could be modified as the ultimate protection for old radios.

Smoke detectors were just coming on to the market around the time I had a Kriesler 11-20 go up in smoke on me. They were a bit more expensive then than they are now though, which is why I didn't buy one. In the same situation now, I'd buy one, not just because they are compulsory but the building I lived in at the time didn't have a central fire alarm either. Just canvas fire hoses and soda-acid fire extinguishers. There were also no RCDs to speak of, as the switchboards were all E-frame ones with 6mm² wiring for the busbars, linked with Ross Courtneys.

All ancient stuff by today's standards and some actually older than the Kriesler.

As noted: In radios & such I have never found fuses, as supplied to be terribly effective, especially if the fault is on a secondary.

Back biased sets are good provided that the bias resistor to ground is "sailing with the wind" and when its wattage is exceed, it fuses.

That also applies to some sets where there are resistors of around 100 Ohm in series withe the tube rectifier plates (6X5 in particular).

One 55 Watt light here has some sort of PTC device as the current limiter for the battery. That may work in the radio secondary side?

NEVER: Forget that electrical apparatus runs on smoke: Should the smoke escape, it's likely stuffed (or seriously expensive to repair).