Amp got da buzz

[Roosterman]

Need a little help here fellas...

Iv just taken an amp in to fix for a friend, but before I tear it apart, I just wanna check my thinking - and show yas some pics of this little beauty! lol
By the way, these arnt the pics of my mates, but its exactly the same... and nearly as clean!

Its a nice little WEM Westminster combo which he bought brand new in the late 60s / early 70s. Its in relatively good condition, but crackles and pops no end. As far as I can tell (from the stamp on the big red cap), it was last checked in 1973!!

Iv tried spraying switch cleaner into the pots and its no different, so Im thinking next step is replace the pots entirely. Trouble is, I cant tell what size the pots are... they dont seem to be marked.

Any tips on rebuilding the pots?

[Ted Crocker]

I wouldn't immediately start replacing parts. First thing I would do is remove the tubes one by one, check the prongs for oxidation or other gunk and then replace them, paying attention that they seat correctly. The prongs can be cleaned with a pencil eraser. You can also visually inspect the tubes for signs of burnout. If those 2 large tubes are the same, you can also try swapping them.

A quick trip to the interwebs reveals these 2 models which look similar, what does the back on the one you have look like?

MID 1970's WEM WESTMINSTER 10 WATT AMPLIFIER (Mk IX)

c1974 WEM WESTMINSTER BASS AMPLIFIER

As always, always unplug the amp and be very careful poking around inside. If reseating the tubes doesn't work we'll do some more digging and find what's wrong. I'm sure schematics are available that'll give the pot values as well as cap values.

Good luck!

[JKevn]

If it crackles and pops when adjusting the control pots.....thats likely where the problem is. Switch cleaner is a good start...if spraying and repeated operation of the pot...back and forth...doesnt help, a high quality cleaner/solvent may be needed. Thanks to the EPA, and the evolution of electronics, some of the best cleaners have gone the way of the dinosaur...

I wont argue with Ted's advice....but a sleepin dog is a sleepin dog....no need yet to poke it with a stick. Check with a TV repair shop for a high quality control cleaner...or try this one:
http://store.caig.com/s.nl;jsessionid=0a0101431f4364330cb893864a29b...
sorry...this link...http://store.caig.com/s.nl/sc.2/category.188/.f

[Roosterman]

Thanks Ted.

The model is the Mk9 Guitar amp (with the split back piece).

Well, I pulled the tubes out and they looked pretty clean, but I give them the once over just to be sure.
However, the 2 larger tubes do look to have 'scorch marks' on the glass... could this be the problem?

Iv not really worked with tubes before so its a bit new to me.

Il try it again now its cleaned and see what gives :o)

Ted Crocker said:

I wouldn't immediately start replacing parts. First thing I would do is remove the tubes one by one, check the prongs for oxidation or other gunk and then replace them, paying attention that they seat correctly. The prongs can be cleaned with a pencil eraser. You can also visually inspect the tubes for signs of burnout. If those 2 large tubes are the same, you can also try swapping them.

A quick trip to the interwebs reveals these 2 models which look similar, what does the back on the one you have look like?

MID 1970's WEM WESTMINSTER 10 WATT AMPLIFIER (Mk IX)

c1974 WEM WESTMINSTER BASS AMPLIFIER

As always, always unplug the amp and be very careful poking around inside. If reseating the tubes doesn't work we'll do some more digging and find what's wrong. I'm sure schematics are available that'll give the pot values as well as cap values.

Good luck!

[Roosterman]

Thanks man! Yup, theres the values right there :o)

Naz Nomad said:

+1 what Ted says ... it's unlikely the pots would be noisy across the whole sweep of the pot.

This page has a shedload of WEM schematics ... http://www.vintagehofner.co.uk/britamps/watkins/schematics/wemwire....

[Roosterman]

Thanks mate.

Iv had a liberal spray of the switch cleaner to no effect.
Theres crackling all the time, which changes when any of the pots are moved, so I figure its maybe a deeper problem?

JKevn said:

If it crackles and pops when adjusting the control pots.....thats likely where the problem is. Switch cleaner is a good start...if spraying and repeated operation of the pot...back and forth...doesnt help, a high quality cleaner/solvent may be needed. Thanks to the EPA, and the evolution of electronics, some of the best cleaners have gone the way of the dinosaur...

I wont argue with Ted's advice....but a sleepin dog is a sleepin dog....no need yet to poke it with a stick. Check with a TV repair shop for a high quality control cleaner...or try this one:
http://store.caig.com/s.nl;jsessionid=0a0101431f4364330cb893864a29b...
sorry...this link...http://store.caig.com/s.nl/sc.2/category.188/.f

[juju]

Hi Ben just had a look at the schematics and it states the valves are 2x ECL82 and one ECC83

heres what i have found for you pretty cheap
http://cgi.ebay.co.uk/Electro-Harmonix-6BM8-aka-ECL82-Valve_W0QQite...

http://cgi.ebay.co.uk/Electro-Harmonix-12AX7-aka-ECC83-7025-Valve_W...

wort thinking about for what they cost
juju

[LJ]

Last time i had scorch marks on the glass of my output tubes. they were arching on the inside. youll probably find the glass loose on the tubes. scorchin means archin.look at it when its making that noise you should be able to see it arching.Tube depot. Everybody says groove tubes. i have been using electro harmonix.

Roosterman said:

Thanks Ted.

The model is the Mk9 Guitar amp (with the split back piece).

Well, I pulled the tubes out and they looked pretty clean, but I give them the once over just to be sure.
However, the 2 larger tubes do look to have 'scorch marks' on the glass... could this be the problem?

Iv not really worked with tubes before so its a bit new to me.

Il try it again now its cleaned and see what gives :o)

Ted Crocker said:

I wouldn't immediately start replacing parts. First thing I would do is remove the tubes one by one, check the prongs for oxidation or other gunk and then replace them, paying attention that they seat correctly. The prongs can be cleaned with a pencil eraser. You can also visually inspect the tubes for signs of burnout. If those 2 large tubes are the same, you can also try swapping them.

A quick trip to the interwebs reveals these 2 models which look similar, what does the back on the one you have look like?

MID 1970's WEM WESTMINSTER 10 WATT AMPLIFIER (Mk IX)

c1974 WEM WESTMINSTER BASS AMPLIFIER

As always, always unplug the amp and be very careful poking around inside. If reseating the tubes doesn't work we'll do some more digging and find what's wrong. I'm sure schematics are available that'll give the pot values as well as cap values.

Good luck!

[LJ]

That is one cool amp. I love it. and so clean

[juju]

I've just started to get into valve amps , bought a Rat Rod Special the other month (brand New) but decided i wanted to see what all the fuss was about with the NOS (New Old Stock ) Mullard Valves - so i bought some Mullard El84 Output PowerValves and a Mullard Ecc83 Pre amp and a Jan Philips military 6L6gt rectifier tube and
WOW does it really sing now as standard my amp is rated as a great sounding amp but now it's
fantastic then i added a Hand made Webber VST Blue Alnico Magnet 8" Speaker (USA) so now it propper Rocks the only problem i have now is i'm a crap player lol! - but next time Bluesbeaten Redshaw comes round i'm gonna get him to do a demo while i video it Heres the parts i changed

i love messing around with these valve amps so much that i have seen a Kit that i'm going to buy - chuck myself in at the deep end and give it a shot , would be a cool project to make the amp and build a Cab to house it all in juju.

[Ted Crocker]

WOW juju, like dropping a big block into a mini cooper...

Keep us posted on the kit build, I'd love to do the same thing.

[juju]

hehe! thanks Ted the it's got a all round fantastic sound and the harmonics are just to die for - the power scale control rules you can run the valves into overdrive but turn the power scale down and whisper above it - fantastic for home /bedroom /night use - would love to hear it plugged into a 4 x12 cab :-)

this is the kit i've been drooling over
http://www.ampmaker.com/ak01x.asp
sounds like a good little Amp to start with
juju

Ted Crocker said:

WOW juju, like dropping a big block into a mini cooper...

Keep us posted on the kit build, I'd love to do the same thing.

[Roosterman]

Wow, thats great! Thanks mate.... seems we are all spending too much time on ebay with this bad weather huh? lol

juju said:

Hi Ben just had a look at the schematics and it states the valves are 2x ECL82 and one ECC83

heres what i have found for you pretty cheap
http://cgi.ebay.co.uk/Electro-Harmonix-6BM8-aka-ECL82-Valve_W0QQite...

http://cgi.ebay.co.uk/Electro-Harmonix-12AX7-aka-ECC83-7025-Valve_W...

wort thinking about for what they cost
juju