Repair and overhaul of a Selmer Zodiac 100w Combo


Fault - dead the customer had said it had died with a burning smell


Not in fantastic condition however it must be nearly 50 years old


From the rear 2 different speakers fitted

A close up of the speakers - both Celestion units but not the original drivers, also the Celestion on the right is only rated at 30w

Looks like 50 years of dirt and a couple of completely blown EL34s - original Mulard Valves











See also an IEC Mains socket fitted in the old Bulgin connector round  hole just hanging !

See below the chassis removed from the cabinet after a good going over with the air gun to get the crap off.

The small signal valves exposed 

Apart from the dirt dust and grime, found this switch pot combination falling apart, this is part of the tone control

After some investigation found that a new replacement was going to be difficult to obtain, so after cleaning all the internals and applying some contact spray/lube and reassembling the potentiometer and switch were working perfectly 


Removed all the EL34s - not even I could fix these, so installed 4 reasonable modern matched replacements and set the bias.

Yes - even modern valves glow in the dark !


As is always advisable with and amplifier that is getting on for half a century old all the resistors and capacitors should be checked 

See above and below a couple of resistor replacements the pictures on the right had side have the new resistors fitted, there were some more bits and pieces replaced but you get the general idea, you can also see the refitted tone control/switch bottom centre.

Somebody had already replaced the big smoothing capacitor for a couple of more modern replacements, 2 x 450 volt 100uf in series to make 900 volt at 50uf,  and fitted them under the chassis on an antique bit of strip board, however they checked out just fine so left them in position, also see the IEC mains socket fitted properly using a square punch and screwed securely to the chassis, if you look very carefully at the bottom right you can also see the new standby switch fitted 

See the top of the chassis showing the hole blanked off neatly a very good job - I wish I could take the credit

See the amplifier on its side having the chassis re- installed 


All done - working perfectly

I did advise the customer that his non standard speaker replacements were not powerful enough to handle 50w each (100w total), however he rarely if ever runs this amp flat out so they seem to be coping ok, all in all a nice amp, good for another 50 years - Made in England built to last.   

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