ECL86 PP Amp - Very low frequency clicking - diyAudio
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Old 26th October 2012, 12:02 AM   #1
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Default ECL86 PP Amp - Very low frequency clicking

I recently brought an old home brew push pull ECL86 based amp. fairly good condition, but when I fired it up, one channel produces a very loud clicking sound (from the speaker).

I've tried swapping the tubes around, the click still remains on the same channel. I've tried swapping all the signal caps around (from one channel to the other) and it remains on the same channel.
and of course I've swapped the speakers.

Anyone have any ideas what this could be? I'e never encountered anything like it before.

Kind regards,

Matt
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Old 26th October 2012, 10:00 AM   #2
DF96 is offline DF96  England
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This may be motorboating. Possibly caused by a decoupling electrolytic drying out and reducing in value, thus allowing unwanted feedback via the supply rail. Do you have a circuit diagram?
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Old 26th October 2012, 12:11 PM   #3
TheGimp is offline TheGimp  United States
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How often does it click?

Can you pull the input tube from the offending channel and still hear the click?

Schematic please.
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Old 26th October 2012, 06:00 PM   #4
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That was sort of what I had thought, hence the swapping them out. Given this is a flea market jobbie I don't have a schematic for it sorry.

The clicks are about every .8 of a second.
It doesn't have a driver tube as it uses the triode built into the ECL86 (not exactly HiFi...)

Might I just be wise to replace all the coupling and decoupling capacitors and just see what happens? Still seems strange that the problem didn't replicate itself when I swapped caps from the other channel.

Thanks for your help.
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Old 26th October 2012, 07:12 PM   #5
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You could change everything, or you could fault-trace and change only what is wrong. Be aware that when changing everything the most likely outcome is the introduction of new faults. Have you swapped every cap between channels? You said 'signal caps' in post 1, which could mean all or just coupling caps.

The first step is to check DC conditions. After that, do you have a 'scope or an analogue meter - to look at the oscillation?
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Old 26th October 2012, 07:17 PM   #6
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Yes, I swapped every cap between channels. Hence my confusion as to why the fault remained on the same channel.
theres only three or four in each I think.

Yes I have a scope, long time since I knew how to use it though.

Given its age, I think I'm better to just replace them all, rather than leave some semi-dodgy ones in there- dont you think?
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Old 26th October 2012, 07:28 PM   #7
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If changing the caps makes no difference then it may be a resistor. Check resistor values, and DC voltages. Phase shift, the cause of oscillation, needs both C and R.
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Old 27th October 2012, 04:37 AM   #8
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Found it!

I went through every component and tested it with my crappy old DMM. Found a component that was earthed that shouldn't have been. Where and old fibre washer had torn. Really simple!

Replaced the washer, and now its running like a champ! sounds excellent given the price. Just putting some decent RCA jacks and Binding posts, then I'll tidy the case up, and away we go I think! Maybe new filter caps too, we'll see.

you can see the tiny tear in the side of the washer, and where the nut that was on it was shorting.

Thanks very much for your help.

Matt
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Old 27th October 2012, 04:48 AM   #9
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Old 27th October 2012, 05:02 AM   #10
TheGimp is offline TheGimp  United States
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ECL86 can make for a beautiful sounding amp. Too bad they are so expensive.

I'd leave the mustard caps and change the power supply filter caps, as well as any other electrolytics.
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