Help to repair Ever Ready Model B portable valve radio.

[AdrianH]

That suggests a problem that the set is taking too much current, what the resistor does is allow for a negative bias to the grid of V4.

Check C16 is not leaky as it could be driving the V4 valve into saturation if it is and would risk damging the audio transformer.

Adrian

[Cobaltblue]

That's worrying.

The only thing I can think of that might be passing that much current is C18 the tone correction capacitor.

Has that been changed yet?

Does it still get hot with all the valves removed?

You need be careful the filaments are pretty delicate to excessive volts.

Cheers

Mike T

[Simon Gittins]

Based on the resistor values given in Post 20, it looks as though you are using the ERT circuit rather than the Trader. If so, for C16 read C6 and for C18 read C15. Always causes confusion!
One thing that occurred to me, has the radio and power supply previously worked ok together? It is sometimes easier to get the radio working on batteries first.

[Pundles]

Thank you all, no other components replaced yet. I’ll try it again without tubes as soon as I can tear myself away from more pressing (She Who Must Be Obeyed says so), matters.
P.s. I came across a couple of BSR mono turntable pickup cartridges, if anyone feels in need.

[Pundles]

Next instalment as ain’t going out in this snow.
The resistor overheats with valves removed so I’m looking to provide a heater supply from a couple batteries.
Also I need to see if there is a potential between -HT & -LT from the PSU.
Just replaced the hardest electrolytic C13 (buried), and placed it across R12 on the tag strip. Only took me 1.5 hours.
C6 looks to have been replaced with a higher value, should be .01 but is .022. So plenty to do when the mood takes me.

[TonyDuell]

The power supply should be 2 separate supplies, just as the original battery pack was 2 separate batteries, one connected between LT+ and LT- and the other connected between HT+ and HT-.

So with the power supply disconnected from the radio you should not be able to measure any voltage between the HT- and LT- connections. It's like connecting your meter to the -ve side of 2 loose batteries, the +ve terminals of which go nowhere.

But when the power supply is powering the radio you will be able to measure a voltage between them.

Consider the LT supply first. The -ve side goes to the chassis . The +ve side goes via switch S1 (I'll use the Trader sheet references as that, I believe, is what you are working from) to the other side of the valve filaments. Thus the LT supply heats the filaments of the valves.

Now these valves are 'directly heated' types meaning that the filament is the cathode. So the cathodes of all the valves are at about the same voltage as the chassis.

Now consider the HT supply. Starting from the HT+ terminal of the battery/supply, for each valve the current passes through the anode load of the valve (for example the primary winding of the output transformer T1 for the output valve V4), then the anode-cathode path of the valve. And then where? The currents for all the valves combine and pass through resistor R12 (with C17 in parallel) and then to the HT- terminal.

The current through R12, of course, produces a voltage drop across this resistor. The 'bottom' end of R12 -- HT- is more negative than the top end -- LT- / chassis.

This was done so that R11 can provide a -ve grid bias for the output valve V4. The control grid of this valve needs to be negative wrt the cathode.

[AdrianH]

Try removing one end of the tone correction cap as suggested by Colbaltblue in post #22 that would give a direct path from HT to chassis with no valves in situ.

Adrian

[Pundles]

I’ll give that a try Adrian. C15 .005 350v. I can’t believe how hard it is to follow a circuit when you’re not dealing with a PCB.
Having moved C13 up to the tag strip, I’ve just realised I’ve doubled up the path to chassis.

[Simon Gittins]

C13 (ERT reference) should be fine directly across R12 with positive to chassis; I'm not sure what you mean by doubled up the path though, it should electrically be just the same.

[Pundles]

Originally Posted by Simon Gittins

C13 (ERT reference) should be fine directly across R12 with positive to chassis; I'm not sure what you mean by doubled up the path though, it should electrically be just the same.

The +ve end of C13 had two wires, one to chassis and one to Spkr.
I added a wire from chassis to +ve of the newly positioned C13 forgetting the strip already had a ground. Arhhh!

I’m always doubting my work but there’s rarely a mistake. Wiring Mr Javid’s house, I thought I’d forgotten the feed to the consumer unit only to discover two when I came to terminating to the MCB.

[Pundles]

Between -LT & -HT 4.31vac
That would explain why R12 was o/c and it was burning up it’s replacement.
Gonna need to drill them rivets to gain access to the PSU. Oh deep joy!

[kalee20]

How did you measure that 4.31V AC?

It's possible that stray capacitance in the internal transformer will give a significant reading using a very high-resistance meter. I'd connect a 10k resistor in parallel with the meter, and see what it is then - if it drops to a hundred mV or so, you can leave your rivets intact!

[AdrianH]

If R12 is 1,000 Ohms and doing a bit of V^2/R I would only get 0.0186 watts.

Are you using a DVM to measure the voltage as you may be seeing a bit of small leakage Voltage as a DVM will likely be of the order of 10 Meg resistance?

Just a thought.

Adrian

[Pundles]

Originally Posted by AdrianH

If R12 is 1,000 Ohms and doing a bit of V^2/R I would only get 0.0186 watts.

Are you using a DVM to measure the voltage as you may be seeing a bit of small leakage Voltage as a DVM will likely be of the order of 10 Meg resistance?

Just a thought.

Adrian

My trusty Fluke.
More disconnecting to do. kind of wished I’d passed on this one, oh well tomorrow’s another day and the snows getting thicker.

[Pundles]

Think I’ve found the culprit.
C15 .005 350v is leaky as hell.
It’s buried under the OP tx so couldn’t see it
I only have tiny ceramics. Do you think a 154 will be ok?

[Pundles]

Sorry meant 502

[Cobaltblue]

502 is the correct value being 5nF or 0.005μF but you will need a capacitor rated at at least 250V the tone corrector is the most stressed capacitor in the set.

Personally I like to use at least a 400Volt part in a battery set and 1000Volt in a mains set.

Cheers

Mike T

[AdrianH]

Well 502 is 5nF if the volts are high enough then yes it can be fitted.

if you are short of caps then they can be bought from the BVWS if you are a member, there is also a chance they will be on sale at Biggleswade if you were planing to go.

I typically buy batches of them so I have a few in my tubs.
Adrian

[Pundles]

Don’t think the ones I have would suit, typically 150v (I think).
Not used to these values.

[Pundles]

The radio is now working again.
I’ve replaced all the waxed paper capacitors and several resistors that were out of tolerance (one was plus 140%), rewired in places as EverReady used electrolytics as tag strips and added a small pcb to accommodate the ht supply terminals.
Despite Royal Mail attempting to thwart the project by losing orders, she is now ready to return to her owner.
It’s been a trip down memory lane as I’ve not worked on such old equipment for 50 years, but I’m glad to see my C&G Radio & TV qualifications weren’t wasted.
I can’t charge much for the work as the item is not the most valuable radio but the cost of parts plus a small fee.
Thank you all for your advice and suggestions.
Till the next time.
Andy