Ekco U29

[benjamin77]

Apologies first. What a ! I took the reading for Valve 4...CY31 Now checking the other things BRB !

[Boom]

Originally Posted by benjamin77

Apologies first. What a ! I took the reading for Valve 4...CY31

It's the red one on the left Ben

[benjamin77]

Thanks David but I am colour blind as well as dopey....

With my wealth of amature knowledge I located the problem. F1 has decided to give up..!

Next are 2 questions .......
Are they easy to get hold of and apart from old age making it blow is there a fault that I can look for that made it "pop"

Cheers

[Steve_P]

Well it could have gone through old age or there may be a problem. Get several.

I don't have one of these sets, so I don't know what fuse it is, but try here:

http://www.thefusecompany.com/index.php?cPath=36

If it blows again, I'd go for C54 (Manufacturer's Data) / C11 (Trader) or the smoothing caps.

Cheers,

Steve P.

[Boom]

Fuses blowing.....

If it uses the same mains input filter as mine you will have several wax caps straight across the supply. Change the lot! They are buried behind the loudpseaker.

I also have an earth isolation waxxy. If you have an earth socket so will you have.

This one has been tough going but is now complete apart from the dial pointer which Alan is kindly helping with.

There are two EF39's in my one and I have had to rebuild the red covering on both valves using aluminium foil. The paint is drying now.

The Missus wants to borrow the set to cook the brekky on.

[benjamin77]

David Sounds like you are a little ahead of me .... I have changed all the wax caps as i never trust any of them. Also the Electrolytics have been replaced with new ones.

I am just going to check that I wired in the main smoothing caps correctly. Although I am sure I have otherwise would it not have resulted in a bang...

Anyhow guess I will just have to wait untill the shops open to get some fuses...why cant there be a 24hr electrical/electronics supplier in every town

[benjamin77]

Ok popped in a new fuse and switched on via the lamp limiter. The bulb dimly lit . All valves lit as did the scale lamp bulb. No stations could be tuned.

Left running for a couple of minutes so switched to full power. Still no stations after a few more minutes F1 blew as did the scale lamp bulb.

I re checked the main smoothing caps to make sure they are wired correctly and I think they are ...if they where wired the incorrect way round

i.e say 24uf had been wired to the 8uf and vice versa what would happen?

[yestertech]

F1 + scale lamp suggests there is a problem on the HT line somewhere. Or it could be a faulty CY31. Check the resistance from CY31 pin 8 ( cathode ) to chassis, it should be > 500K
Alternatively, with voltage applied via the limiting lamp CAREFULLY check the voltage drop across L14, the HT choke. when the limiter lamp is switched out.
This should read about 15 or 16 volts - Much more and there is something pulling too much current from the HT line elsewhere.

Do check the smoothing cap wiring again, in case these are the cause of the extra current. Although using 24 microF as the reservoir might put a straiin on the rectifier, I can't see it actually blowing the fuse.
Best to check anyway.

Andy

PS it is possible that L14 has some leakage to chassis and this could be the cause of the excess current. Measure the voltage at C36 which should be around 245v DC with the lamp limiter switched out.

[benjamin77]

Ok took a reading from pin 8 of CY31 and it measures around 131 kohm. I have rechecked the the wiring for the smoothing caps but just to make sure they are as wired as follows.
C30 red wire to pin 6 on Pen453DD yellow wire to tag board near F1C29 red wire to pin 8 on Cy31 yellow wire to tag board near F1
Although I replaced the main smoothing caps with 10uf and 33uf as this was the closest I could find .

I took reading accross the pins of L15 HT choke with the limiting lamp out and its 16-17v.

[Boom]

I was a bit confused by Steves comments on the lamp blowing as well as the fuse but checking the circuit the lamp is in series with the entire neutral feed of the set HT as well so this is to be expected if something like the CY31 is sparking over is happening Ben.

I've also just realised that the original mains filter caps' in my set were 600VDC ones and I replaced them with 600VDC ones which might not be a good idea. While this could blow fuses though it wouldn't blow the lamp if you have done the same thing.

[Steve_P]

Right - try disconnecting the HT at various places and see what happens. Don't lift wires on the EBL31, they are rare enough as it is.

If the capacitors are wired wrong, then it could cause this. Have you got another CZ31 that you can try?

Cheers,

Steve P.

[Boom]

EBL31 Steve? I've been trying to work out what the number is as the markings are missing from mine but the EBL31 has a 6V 1.2A heater (Valve museum) so it can't be that one although it looks identical complete with the small red metallic strip.

The PEN453DD as per the circuit has a .2A heater but doesn't look right. Far too fat and wouldn't fit in.

[Steve_P]

I've got the data up now. It is in fact CBL31. Sorry. But the CBL31 is a version of the EBL31 and yes, they are as rare.

And my eyes need to be tested.

Cheers,

Steve P.

[benjamin77]

I have not got any other replacement valves to try. As I have increased the UF of both the smoothing caps as mentioned previously would this have caused the problem ? From what I described as to how they are wired is this correct ?

Reading the valve data i think mine has the CBL31 as the volume pot is not grounded but returns as described to R13/R14.

[Boom]

It won't be the extra uF doing it. Try disconnecting the CY31 anode (pin 5) and see if that stops the fuse blowing. That will narrow it down to a HT or AC problem. The only spare CY31 I have is faulty and gives a fireworks effect in use. I'd have thought that if yours is that bad to blow fuses it would give off sparks too.

You did replace ALL of the rubber wiring didn't you? I had to check several times that I had all the bad stuff out.

[benjamin77]

I didnt carry out a complete re wire just anything that had gone stiff and looked bad. This was mainly around the dropper resistor as well as the top cap wires to valves 1 and 3.

I will try disconnecting pin 5 of the CY31 and report back with my findings.....guess i had better buy some more fuses....!

[yestertech]

Hi Ben, this is looking suspiciously like a problem with the CY31
( Possibly h-k short as it warms up. )
From your measurements the HT current flowing through the choke L15 is about right. The DC resistance of the HT line to ground is also about right, as there is a potential divider across the HT line which brings it below the >500k ohms I mentioned.
2 further tests you could do. Remove the connection from pin 8 of the CY31 so that there is no load on it. Power up and measure the voltage at pin 8 both with the lamp limiter and without. Is it stable or does it fluctuate ? Does the fuse stay intact ?
Also, you could insert your meter on the ma range between pin 8 of the CY31 and the rest of the set ( ie wire runnning to C29/L15 ) The current drain should not exceed around 45ma. This reading would decrease ( as would the voltage ) if there is any internal problem with the CY31.

Andy

PS I have a spare - just need to test to see if it's OK

[benjamin77]

Hi Andy I will try those things you have mentioned tomorow. I do hope that its not anything more serious.....

[benjamin77]

Ok.....I removed the connection from Pin 8 as suggested and switched on results are :-

With Limiter Lamp
after 3 mins 9.8-10v
after 5 mins 43-42v

Without Limiter Lamp
74v
99-100v

Tha scale lamp stayed illuminated at the correct brightness and F1 did not blow. I left it running for approx 5-7 mins and nothing strange happend...

I would say then Its a rectifier problem.....agreed ?

[Boom]

I still would have thought the CY31 would protest with some sparks or blue glows if it was that bad. You can lash a 4001 diode with a 100 Ohm series resistor in place of the CY31s anode and cathode connections.