Ekco A239/1

[Graetz_1022]

I have been working on an Ekco A239/1. I changed all the Hunts capacitors,and some others. I aligned the radio as per instructions. It performed well for a few days, then I heard a few popping sounds and it went a bit low. Since then FM has been a bit down. The valves test OK on a valve tester (Mercury 2000). How should I localise this fault?

Thanks.

[Nuvistor]

Is it just FM that is low or the other wave bands affected?
Dirty valve pins, bases and wave change switch can cause popping noises and could possibly reduce the volume, clean those if not already done so.
Then if all wavebands are affected check the audio circuits first. If only FM check the voltages on the IF valves and tuner.
That should give you a start on finding the fault.

[Graetz_1022]

I have measured the voltages and I thought I had posted them to the forum. If not I will do it again. There were some discrepancies from the Data Sheet.

[Graetz_1022]

Here is a list of Voltages measured::
ECC85::Pin 1/122v Pin6/135v. Spec:::Pin 1/209v Pin 6/117v.
ECH 81 Pin 1/101v Pin 6/238v Pin8/60v Spec:Pin 1/86v Pin6/245v Pin8/95v.
EF85 Pin7/225v Pin8/82v Spec::Pin7/220v Pin8/85v.
EABC80 Pin 9/66v Spec Pin 9/85v
EL84 Pin 7/243v Pin 9/218v Spec::Pin 7/231 Pin 9/217v.
EZ80/267v. Spec/260v.
Which of these are of most concern.
Thanks.

[Nuvistor]

Is it just FM that is low output.
There are a few discrepancies that could be valves that have lower than best emissions, ECH81 and EABC80 but not that bad.
The one to investigate is the high anode voltage on pin1 ECC85, I presume it was switched to FM when you took that reading. That portion of the valve does not appear to be conducting, it could be the valve, they are a known possible problem but obviously other parts of the circuit could be causing it.

[Graetz_1022]

Pin 1 in the Spec Sheet shows 209V, it is measuring low. I have seen discrepancies before with ECC85 valves.

What would cause this?

[Nuvistor]

Should have put my spectacles on, yes I read them the wrong way. I will check if I have a circuit.

[Graetz_1022]

I see what you mean about the trader sheet. The trader sheet shows a DM70 magic eye, which was in the earlier A239. My radio (A239/1) has the EM80 magic eye, and the 56k resistor is 27k.

[Chris55000]

Originally Posted by Graetz_1022

Pin 1 in the Spec Sheet shows 209v,it is measuring low.I have seen discrepancies before with ECC85 valves.
What would cause this.

Hi!

It may be leaky ceramic h.t. decoupling capacitors in the f.m. front–end, particularly if they're the feed–through type!

The ECC85 is well noted for causing strange faults as well as low FM gain, if you've not got one, either ask in the Forum or alternatively you could try an ECC88 which is also listed as a VHF double–triode, and might be a bit easier and cheaper to get!

Don't forget that Ekco's figures were taken with an analogue meter, AV0 8 most likely, if you've used a DMM then you can expect about 2–5% higher readings – there's nothing overly wrong with the voltages in general, but V.H.F. instability can play havoc with D.M.M. meter readings – try a 1000p disc ceramic rated at 400V across your DMM terminals if possible!

Did you measure pin 1 at the valveholder tag or the anode end of the anode–circuit h.t. decoupling resistor?

The r.f. stage bandpass coil can be ignored as regards d.c. resistance, so a reading at the h.t. decoupling resistor will be the same as that at the pin 1 anode tag of the ECC85.

Chris Williams

[Graetz_1022]

I didn't know about the Multimeter problem,so that is a good possibility.I changed capacitors in the FM Tuner section,(C2,C4,C5,C9,C52)and I left the legs long.Would this matter.Also FM reception is from a 50 Mile distant transmitter.I use an amplified indoor ariel(Radiotop type).Without this,reception is poor,with it,noise is a factor.
Are there test points,where a signal level could be checked,besides C51.
I cannot see any on the diagram.

[Nuvistor]

Not looked what those capacitors do but in a VHF tuner try to keep the build as similar as possible to the original, noting that components will be of a later type.

It’s quite possible that those long leads have detuned the circuits.

[Herald1360]

Long leads and even the precise orientation can matter in the FM front end.

Wire has about 1nH per cm which isn't trivial at VHF.

[Graetz_1022]

I rechecked the alignment,and I had made a few mistakes/omissions.I did it correctly this time,and the radio is performing quite well.I found C49 to be missing.It doesn't seem to matter.Should I install it.