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Old 24th Jan 2021, 4:14 pm   #1
Sinewave
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Default Ekco A320

Hello, just a bit of advice if I may. I've moved onto this after sorting out the Bush.

Now when I started this, it was very quiet, almost nothing heard, so I cleaned up some joints, cleaned the switch out and tested the valve voltages, then it worked very well, nice strong signals throughout. Now all of a sudden it's quiet again, not even the strong static between stations on VHF. I'm getting some stations, not as quiet as when started, but it's certainly changed and I can't quite manage to find out why all of a sudded the change.

Any tips appreciated.
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Old 24th Jan 2021, 4:22 pm   #2
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Default Re: Ekco A320

Check the switch contacts again, and clean the valve pins and sockets.

Have you changed any components yet?
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Old 24th Jan 2021, 4:24 pm   #3
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Default Re: Ekco A320

Yes I'll go over those again.

Actually yes, grid coupling capacitor and some decoupling capacitors which looked like could cause trouble if were leaky.
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Old 15th Feb 2021, 11:11 pm   #4
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Default Re: Ekco A320

I've cleaned out the valve pins and it's improved, not quite as it was though. But the valve bases look dirty, so I need to figure a way of getting in and giving them a good old clean out and then work out why the radio has gone quiet if this doesn't help.
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Old 17th Feb 2021, 7:09 pm   #5
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Default Re: Ekco A320

Hi, I had one of those sets go quiet on me, after cleaning the switches (As Paul has suggested) and valve holders, just exactly the same as you've described the sound returned but was not as it was originally.

I eventually found that one or two resistors had suddenly gone high, on replacing those there was a further slight improvement, but i gave up eventually trying to further improve it, because there didn't appear to be anything else wrong, it's a tough one to get to the bottom of.

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Old 4th May 2021, 4:42 pm   #6
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Default Re: Ekco A320

I'm coming back to this, it's been on the bench for too long now. I haven't done a thing electronics bench wise for a while, so looking to return.

I think another check of resistors and caps, switches are ok, valve bases are no better than a poke about, as I can't get anything into them, but voltages measure just fine, which maybe they wouldn't if the pins weren't making.
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Old 4th May 2021, 7:57 pm   #7
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Default Re: Ekco A320

I remember a festival set giving me the runaround with low volume and it turned out to be tin whiskers inside the 'egen' volume pot.
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Old 5th May 2021, 4:55 am   #8
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Default Re: Ekco A320

I have a set with similar issues. I need to give the valves a wiggle and find the correct spot for it to work properly, b9a bases.
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Old 5th May 2021, 6:42 am   #9
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Default Re: Ekco A320

I use dental brushes dipped in contact cleaner for cleaning valve socket pins in the bases. They're available in lots of different sizes & some have a tapered brush, cheap too! Dirty contacts on wafer switches and valve bases have caused me some very odd faults in the past from low volume to totally dead.
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Old 13th May 2021, 4:35 pm   #10
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Default Re: Ekco A320

Dental brushes, there's a idea, going to try that now....
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Old 13th May 2021, 6:01 pm   #11
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Default Re: Ekco A320

I second the interdental brush idea. They come in sizes, the pink (smallest) works but you could go one higher I think. Also comes with the added bonus of being in the dental hygienist's good books
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Old 13th May 2021, 10:10 pm   #12
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Default Re: Ekco A320

Given the bases a good rodding. Still not pulling in many FM stations. I may revisit the FM alignment.
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Old 15th May 2021, 8:03 am   #13
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Default Re: Ekco A320

Quote:
Originally Posted by Sinewave View Post
I may revisit the FM alignment.
Have you tried a decent FM dipole? Re-aliening is a last resort for me. I lack the specialist equipment for FM aligning, its not simply a matter of peaking the coils.
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Last edited by crackle; 15th May 2021 at 8:09 am.
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Old 19th May 2021, 11:26 am   #14
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Default Re: Ekco A320

Yes I've got a decent antenna.

Update so far, I recleaned the valve bases and switches with the tooth brush/pick method and contact cleaner, then the FM came alive again.

Today switched on, quiet again.

I then noticed the ECC85 flickering/glowing with a buzz coming from the speaker.

More than likely poor emission from the ECC85 I guess?
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Last edited by Sinewave; 19th May 2021 at 11:31 am.
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Old 19th May 2021, 12:45 pm   #15
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Default Re: Ekco A320

If there are visible signs of distress then something is clearly amiss. The first thing to try is obviously fitting a new ECC85, maybe borrowing one from another set if you don't have a spare. It could be a bad valveholder though.
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Old 19th May 2021, 1:15 pm   #16
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Default Re: Ekco A320

Hi Paul. I don't have any ECC85s, I do have an ECC81/12AT7, it may not work entirely with one of those, but may prove a point if the FM band does at least something. At the moment it's entirely quiet.
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Old 19th May 2021, 1:28 pm   #17
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Default Re: Ekco A320

No, an ECC81 has a different pinout to an ECC85 quite apart from the difference in characteristics. You need an actual ECC85.
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Old 19th May 2021, 2:53 pm   #18
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Default Re: Ekco A320

From the datasheet I was looking at, they had the same, but I'll be best to get an ECC85.
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Old 19th May 2021, 3:09 pm   #19
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Default Re: Ekco A320

The heater arrangement is different for one thing - the ECC85 has a 6.3V heater, while the ECC81 has a centre tapped 12.6V heater which can be wired to operate on 6.3V.

http://www.r-type.org/exhib/aaa0241.htm
http://www.r-type.org/exhib/aai0246.htm
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Old 19th May 2021, 3:15 pm   #20
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Default Re: Ekco A320

Yes the pinouts may look the same but there is a subtle difference

Snips from r-type.org

It's all to do with pin 9, 4 and 5

On an ECC85 the 6.3V heater supply is between pins 4 and 5.

If you want to run an ECC81 at 6.3V you need to join pins 4 and 5 together and connect the heater supply between 4,5 and pin 9.

Otherwise you need to supply 12.6 V between pins 4 and 5

Hope that helps.

Cheers

Mike T
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Last edited by Cobaltblue; 19th May 2021 at 3:15 pm. Reason: Crossed with Paul
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