Ekco U243, re. valve temperatures.

[Scotorvm]

Guys, I have been moving between 3 refurbs, this one the Ekco U243, I think is completed. Case is nice, just waxed it. Dial cord was snapped now replaced 100lb breaking strain green braided fishing line, works a treat, no slip etc..

I replaced 3 wax caps from NOS.
0.1uF at the mains.
2 caps underneath a 0.02uF and a 0.001uF

Fitted a new braided 3-core mains cable and earthed the chasis.

Set is now working well on all bands without any external aerial or earth.

Just a question re the temperature of the valves, brought the set up to 230v on the Variac, burst into life around 190v.

Using an infrared thermometer and safety glasses, I know it's not too accurate on glass but my fingers confirmed which one was hotter..

Valve 1 - 50 degrees C.
Valve 2 - 50
Valve 3 - 47
Valve 4 - 50
Valve 5 - 95+
Valve 6 - 50

Would this be a normal operating temperature for these valves after 30 minutes, or a component issue causing valve 5 to overheat, V5 is UL41, or the chasis being earthed, could this be an issue.

Cheers guy's.

[paulsherwin]

UL41s do run hot, I wouldn't be concerned if the circuit voltages are all OK.

You can reduce the output valve dissipation by increasing the cathode resistor. This will reduce the maximum volume somewhat but the effect won't be obvious in normal use.

[peter_sol]

Output valves and rectifiers always run hot.
You can't earth the chassis on a live chassis set.
Just make sure that the chassis connection of the mains lead goes to the neutral in the mains plug.

[paulsherwin]

This isn't live chassis. It's one of those odd early 50s Ekcos which use a mains transformer but a series string of U series valves.

Edit: This is wrong. See later posts.

[Nuvistor]

Hi Paul,
It’s a live chassis, I have just checked the circuit and the photos in post #1 shows a mains dropper.

Edit, if you increase the cathode resistance check that the heater volts on the DM70 does not increase.

[Scotorvm]

Originally Posted by paulsherwin

UL41s do run hot, I wouldn't be concerned if the circuit voltages are all OK.

You can reduce the output valve dissipation by increasing the cathode resistor. This will reduce the maximum volume somewhat but the effect won't be obvious in normal use.

Thanks Paul that's great, will take note of your comment re the cathode resistor for future reference

[Nickthedentist]

Yes everyone, this is a LIVE CHASSIS set with a mains dropper, U-series valves and NO mains isolation transformer.

I have two of them.

See here for info about the "live chassis" technique: https://www.vintage-radio.com/repair...ly-stages.html

Cheers,

Nick.

[Herald1360]

The photos show one new capacitor and two Hunts (NOS?) ones. Are the Hunts ones actually good- leakage resistance at rated volts 20megohms or more? I wouldn't trust them anyway. If one of them is the grid coupler for the UL41 it could be upsetting the bias conditions and increasing anode current and hence valve temperature.

[paulsherwin]

Originally Posted by Nickthedentist

Yes everyone, this is a LIVE CHASSIS set with a mains dropper, U-series valves and NO mains isolation transformer.

I have two of them.

You are right, apologies for the misleading post. I should have double checked first. Ekco radios of this era can be a bit confusing.

[Scotorvm]

Originally Posted by Nickthedentist

Yes everyone, this is a LIVE CHASSIS set with a mains dropper, U-series valves and NO mains isolation transformer.

I have two of them.

See here for info about the "live chassis" technique: https://www.vintage-radio.com/repair...ly-stages.html

Cheers,

Nick.

Hi Nick, thanks for that link, so what happened was, in the cabin working from the safety isolating tranny, the radio running fine with earth attached which I assume is what you would expect. Plugged into a non safety isolating circuit trips the RCD, earth going to be disconnected.

I did notice the voltage between the chasis and the earth point on a socket was 3Vac.

[paulsherwin]

Yes, if you earth the chassis of a live chassis set, it will almost certainly trip an RCD.

That's not why the UL41 is running hot though - that's just normal.

[Scotorvm]

Thanks Paul, great forum this, feels like a team effort to help. Hopefully one day I can help someone, no one hold their breath...a lot to learn.

[Sideband]

UL41's run too hot to touch. This is true of most power output valves. You probably won't be able to touch the rectifier (UY41) either since all the HT current is passing through this valve. Signal valves can be warm to very warm.

[Joe_Lorenz]

Hello,

if it was me wondering about a "valve under stress or not?" I would check the voltages first and then decide if further investigation is necessary. For that UL 41, at an anode voltage of 170 V and similar screen grid voltage you should be close to -10.4 V grid voltage. It is capable of drawing up to 53 mA anode current.

Here is a data sheet:
https://patric-sokoll.de/Museum/Auto...41_Philips.pdf
Regards, Joe

[Scotorvm]

Thanks Joe, nice link.

[Scotorvm]

You are correct Sideband, left the unit running longer and UY41 is running a lot hotter as well. Reading all the reply's this would appear to be normal, cheers.

[paulsherwin]

Indeed, this is completely normal. If output valves and rectifiers feel cool that usually suggests there's some sort of problem