Superb old Watkins amp with cabinet rattle ballache: give me some pointers

De Batz

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2,701
So I'm on something of a 'is it cool?' type trip at the moment. I've got hold of an old AC50 - updates later today - and dug out my father in law's old Watkins Powerbass amp. It's a 1x12, with a Goodmans speaker, 4 ECC83s with two input channels and a pair of EL84s. It sounds, frankly, awesome.

But: the cabinet is old, made of thin ply (9mm? 1/3"? it's really thin!) and has suffered from being in garages and cellars for most of its 50-odd years. I've improved the situation in one sense by tying some bits together, adding battens to hold joints, re-gluing some joints and so on, but I've got a rattle.

I'm inclined to think it's the cab, or a transformer, but I've also got one eye on the speaker as the source. Experts: what signs should I be looking for that constitute evidence for a particular diagnosis? I've so far managed to identify that it comes on with increasing volume and bass, is pretty static (it's always the same 'pitch' regardless of what I'm playing), it is most noticeable when notes are sustaining rather than when when I first hit them (could be the volume disguising the issue, though).

It's got the weird copper mesh stuff for the grille, which I've prodded a bit to see if it's vibrating and it doesn't seem to be that. A cursory listen close up made me think that it was the speaker (as in, it seemed to be coming off the cone) but I've never had a speaker fail and sound rattle-y before. The only one I've lost was to a voice-coil rub that made it sound 'fluffy'.

Ideas? I'll post a few pictures sometime this week as well. I wouldn't rule out getting a new cabinet made, but that (plus a new speaker) is close to being up to the cost of a decent old amp on its own.
 

Geeze

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2,424
Take the amp out of the chassis and play it plugged into the speaker. This 'should' help determine what the rattle is coming from. If it is the speaker with the cab and it only happens on specific notes the cab is reacting to a resonant frequency. Now comes the fun part. Sit on the cab and play it - rotating it until you find the resonant sides. You can try gluing in bracing similar to the sound board on an acoustic guitar in an effort to tame it. Otherwise new cab - some of these old amps were not designed to play full bore. Also - swap speaker.

Rattles in the amp you will need a helper to play the offending notes whilst you poke methodically with a chop stick.

Good luck!

Russ
 

De Batz

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2,701
So, to cut a long story short, the speaker and baffle board were all a bit shonky. Ply was separating on the baffle, speaker may well have been punctured anyway, but was rattling inside. New board cut, speaker replaced with a temporary beater, rattles have gone. So I'm going to have a go at patching up the cab and battening a few more joints, maybe get a replacement speaker of a more high quality and appropriateness, and then we're ready to gig and rehearse with it.

Even with the no-name (Peavey, possibly) speaker installed, it sounds out of this world good. It's not even that noisy.

And I will get that original speaker re-coned. Just not sure when, yet!
 

De Batz

Member
Messages
2,701
Now then... Have had what can only be described as lens fail this evening whilst trying to get this organised. I've managed to patch the cab up with a bit of love, tenderness and batten. It's got a slightly Frankenstein's-monster-ish look about it, with a few bolt-heads protruding from various places, but by God it sounds good.

The copper mesh grille stuff is absolutely beautiful but a total arse to attach to the baffle without it rattling everywhere. A few judicious screws seem to have sorted it.

As I say, pics to follow when the camera is less ballsed, or I might just do it with the laptop camera if the light's good tomorrow.
 




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