Ekco A274 - Project No 2

[Sideband]

Originally Posted by Barnjet

Great thanks - I'm thinking this may be the simplest path to take.

thanks

I'll sort out a couple of used ones with the valvetester and put a good one aside in case you need it. Personally I think you just need to change the EL84.

Another point to bare in mind, the capacitance test on a standard DMM will be confused by leaky paper capacitors and show the value as much higher than what is printed on the capacitor. Hence why your tone corrector is reading approx 100 times higher than expected. The capacitor will be leaky so just replace it anyway. It's unlikely to make any difference to the present fault.

[Barnjet]

Originally Posted by Sideband

Personally I think you just need to change the EL84.

Originally Posted by Leon Crampin

The EL86 is not a suitable substitute for an EL84. The anode current is much higher with the same bias and screen voltage, and the anode load will be mismatched.

Absolutely spot on! Sidebar very kindly supplied a nearly new EL84 and the cathode voltage now reads 5.7V, and with the grid bias resistor testing at 176ohms, that means that the cathode is carrying a much more respectable 31mA. Top result - many thanks Sideband and Leon

However, I now detect a some distortion which gets worse with increasing volume. Sideband helpfully suggested I test the audio output on another known good speaker, and double-check the new components I installed are of the correct values. And if that doesn't rectify the distortion, then post some pin voltages.

[paulsherwin]

The first thing to do is to connect some high quality audio from something like a CD player or FM tuner to the gram sockets, and see if the distortion is still there with that. The gram switch is at the back.

31mA is actually a bit low. If the resistors around the EL84 are within spec then you may have acquired a tired valve. Some ex equipment EL84s have led a hard life. Did Sideband test it on a valve tester?

[Barnjet]

Sideband has done it again! I connected the audio output to a different speaker and instantly the distortion disappeared! This confirms there is some fault with the Ekco speaker(s) which are wired in parallel. See photo

I'd appreciate some steers on what to look out for.

Thanks

[Barnjet]

Originally Posted by paulsherwin

The first thing to do is to connect some high quality audio from something like a CD player or FM tuner to the gram sockets, and see if the distortion is still there with that. The gram switch is at the back.

31mA is actually a bit low. If the resistors around the EL84 are OK then you may have acquired a tired valve. Some ex equipment EL84s have led a hard life. Did Sideband test it on a valve tester?

Crossed with my post. Sideband did test the EL84 and it's running very well

[paulsherwin]

Good.

Remove the speakers from the baffle and examine them closely. Check that the cones move freely.

You can disconnect the speakers one at a time to identify the bad one. I can't remember if they are in series or parallel, but it should be pretty obvious (from your photo, it looks as if they're parallel, but it's not completely clear). The radio will work perfectly well with only one speaker connected - both are full range drivers. Two are used to give a wider, more diffuse soundstage - a sort-of pseudo stereo effect.

[Nickthedentist]

Mine did this too, one of the speakers had a rubbing voicecoil. Disconnecting the faulty speaker is one option, but you can often flex the speaker chassis and get it working as intended.

[Sideband]

Originally Posted by paulsherwin

Did Sideband test it on a valve tester?

Well we know there is a faulty speaker causing the distortion now but to answer your perfectly valid question Paul, yes I did test the EL84 before I sent it to Max. I particularly selected one that I knew the history of and tested it on the Avo Two Panel tester to make sure before sending it. I didn't see the point of sending an unknown pull that 'worked ok' and possibly creating more confusion.

The EL84 I sent was a Sovtek (Russian) manufacture that had been rebranded as Marshall. It was recovered from a new but damaged guitar amplifier about 15 years ago. It had had virtually no use since the control PCB was split and the amp had never worked properly.

The valve, not surprisingly, tested as new.

[Sideband]

One of those speakers doesn't look original. The wiring is new and the manufacturers wouldn't use a 'chock block' connector. I suspect the round one is the interloper. Check the simple things first.....where the blue and white wires are passed through that hole in the speaker casing, make sure they are not touching the cone....I've had a similar thing before. If the wiring is OK, do what Paul suggested in post #86

[Nickthedentist]

I think those speakers are original, though the choc bloc has been added, of course

[paulsherwin]

Originally Posted by Sideband

Well we know there is a faulty speaker causing the distortion now but to answer your perfectly valid question Paul, yes I did test the EL84 before I sent it to Max. I particularly selected one that I knew the history of and tested it on the Avo Two Panel tester to make sure before sending it. I didn't see the point of sending an unknown pull that 'worked ok' and possibly creating more confusion.

The EL84 I sent was a Sovtek (Russian) manufacture that had been rebranded as Marshall. It was recovered from a new but damaged guitar amplifier about 15 years ago. It had had virtually no use since the control PCB was split and the amp had never worked properly.

The valve, not surprisingly, tested as new.

No criticism was intended.

I agree with Nick that the speaker drivers look original.

[Sideband]

None taken Paul! It was a perfectly reasonable question that required a perfectly reasonable reply!

Ref the speakers, yes I suppose they could be original. I just noticed the cloth in front of the round one is smaller than the one in front of the oval suggesting that the speakers were different types although exactly why remains a mystery.

[paulsherwin]

Ekco deliberately fitted different speakers. I think the idea was that the different speaker characteristics would enhance the pseudo stereo effect. It does work to some extent.

[Synchrodyne]

The use of – and benefits from – two close-coupled speakers in parallel has come up previously. For example, see the latter part of this post: https://www.vintage-radio.net/forum/...1&postcount=11. I’d say that Ekco was seeking somewhat better than typical performance for a table receiver of the time, but without venturing very far beyond the standard bill-of-material.


Cheers,

[robreddog]

hi,i repaired an ecko a274 last year that had a scratchy, distorted round speaker, i tried but could'nt sort it out, a forum member kindly offered a very simular one that i could fit. Sounds quite good.
Rob.

[Barnjet]

Lots of advice and personal experiences - thank you!

Originally Posted by paulsherwin

Remove the speakers from the baffle and examine them closely. Check that the cones move freely.

Speakers removed. Examined the cones very closely - no tears, holes or obvious weaknesses. Cones moved freely under light pressure with no evidence of voice coil rubbing (no sounds or resistance to pressure) See photo 1

Checked them again as a pair before checking them individually and........... no evidence of distortion. So tested them against a known good sound source and again no distortion. Perhaps not the speakers at fault then?

What I did notice was, and here I am showing my inexperience for not identifying this earlier, was that the level of distortion, ranging from none to moderately intrusive, appeared to be dependent on where I was standing in relation to the external FM aerial! Further investigation by jiggling the aerial's wires had the same effect. See photo 2

The current arrangement (or lash-up) involves matchsticks for the external FM and I believe I need to improve the aerial arrangements in order to provide a consistently good signal. The aerial socket accepts a 2-pin plug of different pin sizes - see photo 3

[paulsherwin]

Yes, you have an FM reception problem of some sort. There may well not be a fault with the radio.

I thought you said the distortion wasn't present with a different speaker? I guess it could just have been a confusing coincidence.

[Barnjet]

Originally Posted by paulsherwin

Yes, you have an FM reception problem of some sort. There may well not be a fault with the radio.

I thought you said the distortion wasn't present with a different speaker? I guess it could just have been a confusing coincidence.

When connected to a different speaker I was standing in very different place and there wasn’t any distortion. It could be coincidental. But I should try to eliminate FM aerial reception issues by improving the aerial connection arrangements.

I suppose tinning the copper tails of the FM aerial will be good start? How can I clean the pin sockets on the aerial connector itself? Cocktail stick to remove fluff, then roll of fine grade Emery paper?

[paulsherwin]

The main factor will be the positioning of the aerial - tinning the ends won't make any difference. All indoor aerials are a compromise, and you have to experiment with them to get the best results.

[Sideband]

Yes this is where experience can identify different types of distortion. A rubbing speaker sounds very different from distortion caused by a poor FM aerial. If you can sort out the aerial then you should have a good sounding radio.

Now when you replace the speakers here is something else for you to be aware of. Both speakers should 'work together'. They are in parallel so it seems all you need to do is connect them in parallel and all is well.....Not quite as simple as that! When I say 'work together' that means both speakers must work 'in phase' with each other. That means both cones moving forward and backwards together instead of one moving forward and the other moving backwards. OK so how do you do this? Well there are only two connections on each speaker so you have a 50-50 chance of getting them both right first time. What you need to do is find yourself a 1.5V battery and connect the battery briefly across the speaker terminals and observe if the cone moves in or out. It doesn't matter which way it moves. Lets say you check the round one first and the cone moves in. Mark the terminals + and -. Now check the oval speaker and do the same. If the cone moves out, reverse the battery and mark the terminals + and -. Now the blue and white wires from your transformer can go to either terminal BUT it should be the same colour for both speakers so if you decide to put the white wire to + make sure it goes to + on both speakers.

Why is this important.....well you will get better sound (bass response) if both speakers are in phase otherwise you get a cancelling effect and bass response is impaired.

If there was only one speaker it wouldn't matter which way it was connected.

Hope all that is clear....