Vintage Impedence Selector Question

[alpha al]

Greetings! I'm servicing a vintage 1972 Marshall 50W Lead head. It's been in storage a long time, and there is a lot of corrosion in the chassis.

The impedance selector is not making a reliable connection. I've tried cleaning and retensioning it with no luck.

It is the older type, with the jumper plug that plugs in for the correct impedence.

Are these selectors available anywhere?

Also, does the newer type rotary switch with the screwdriver slot as used on current Marshalls fit these?

Thanks in advance.

 

[JP2036]

https://www.mojotone.com/amp-parts/Switches_1/Marshall-Impedance-Selector-Switch

If you're going to be wiring in a new one anyway the rotary style is the way to go.
You will have to widen the hole slightly w/a Dremel or similar to get the rotary one in there.
Ive done it to 2 JMP's not a huge deal.
I think i lost those old ohms plugs in the back seat of my 72' Firebird every gig i played in the 80's as i always forgot to remove it.
Those old plugs are a really poor design anyway.

 

[Matthews Guitars]

Buy this.

https://www.ebay.com/itm/Cole-Rotar...388075?hash=item2acff2472b:g:4OEAAOSwOfVdJiPk

Make a simple adapter plate to fit it. Just a chunk of sheet aluminum with one hole for the switch, two others for the mounting points.

Put a sturdy knob on it.


That's your new, no BS, reliable switch solution.

You could use the newer "coin switch" found on current Marshalls but they're overpriced and require you to enlarge the existing holes.

The original plug style selectors are probably the no. 1 cause of blown up output transformers. They are not reliable.

The best you can do for an original selector is to take it completely apart and retension the contacts and that'll make it work pretty well,
for a limited time. But eventually those contacts will get loose again.

 

[JP2036]

lol you don't need a "military/aircraft" grade switch/plate unless you're making the jump to light-speed.

 

[neikeel]

lol you don't need a "military/aircraft" grade switch/plate unless you're making the jump to light-speed.

True, but hogging out the back of the chassis and panel is a way of burning dollar notes for no reason (if you ever sell) so why not do the same job more sympathetically?

 

[Gene Ballzz]

True, but hogging out the back of the chassis and panel is a way of burning dollar notes for no reason (if you ever sell) so why not do the same job more sympathetically?

^^^^^^^ What he and @Matthews Guitars said! ^^^^^^^

Although, I agree that a "military/aircraft grade switch" is not necessarily needed! I personally like these, if there is room for them!
Switches https://valvestorm.com/Products/Switches They do appear to be getting difficult to find?



Just Sharin'
Gene

 

[Matthews Guitars]

Here's my installation. And those Cole switches are UTTERLY reliable. I have no issue putting 75 dollar mil-spec switches in, when they cost me 20 bucks or less to get them. That's cheaper than a replacement impedance selector so what are you complianing about?

 

[JP2036]

Slightly enlarging a hole isn't "hogging out".
Easy fix for a competent tech.
Your switch is way too fuggin close to the power tube socket.
The guy asked for solutions not alternatives.

 

[Matthews Guitars]

Nah, there's plenty of room there. I made sure.

Enlarging a chassis hole is always invasive surgery and non reversible short of rewelding the hole. (Which I've had done.)

Heck, there's no problem at all with just hard wiring each transformer tap to specific jacks. 16 ohm tap gets 1 jack, 8 ohm tap gets 2 jacks, 4 ohm tap gets 1 jack,
leave the dead original selector in place for appearance reasons.

 

[JP2036]

Yes you're right, your way is best.
What was i thinking ?
How dare i give the OP a good answer to his question.

 

[alpha al]

I decided to take Matthews Guitars advice, and make an adapter plate for this switch. I t looks like the same switch Gene Ballzz recommended. Mojotone stocks them.

Thanks for all the suggestions.

 

[Matthews Guitars]

Good choice, in my opinion. And you can always try a different solution if you want later. Literally, no harm done. Keep mods reversible. I guess that's one of my mottos.


Once you enlarge the hole, that's permanent unless you go to the huge effort to get it rebuilt by rewelding. I've done that, but honestly, who else does?

I have not heard of anyone else doing Marshall chassis restorations that involve welding up and filling in added and enlarged holes. I guess nobody else is nuts enough.

Well, it's good to own a niche market, I suppose.

 

[JP2036]

You're right again mods are for losers, nobody does mods.
Some of the worst ever advice i got here was "never drill on a Marshall".
Who makes that shit up & why ?
If folks never "modified" anything we never would have gotten to the Moon.

 

[neikeel]

enough holes drilled.
I think that most agree that a well done mod if necessary is fine
Gratuitous Swiss cheese or thoughtless, poorly planned or badly executed ones are not.
oversized and extra holes on a Saturn rocket have been shown to have poor results too

 

[Chrome]

I belong to a Marshall page on Facebook, dude named Alfie who is the administrator from London sells these. he states they fit in original chassis hole without having to cut away or file. I just purchased two of them yesterday, but will be a couple weeks before I get them from London. I paid 96.00 for two of them including shipping. if you or anyone is interested, I can send you his contact information

 

[Emtbreid]

I belong to a Marshall page on Facebook, dude named Alfie who is the administrator from London sells these. he states they fit in original chassis hole without having to cut away or file. I just purchased two of them yesterday, but will be a couple weeks before I get them from London. I paid 96.00 for two of them including shipping. if you or anyone is interested, I can send you his contact information
View attachment 87743 View attachment 87744 View attachment 87745

I also did this, but I got the plate itself from the guy that makes it (his name is Philip) and I bought the switch here in the states.

 

[Emtbreid]

I belong to a Marshall page on Facebook, dude named Alfie who is the administrator from London sells these. he states they fit in original chassis hole without having to cut away or file. I just purchased two of them yesterday, but will be a couple weeks before I get them from London. I paid 96.00 for two of them including shipping. if you or anyone is interested, I can send you his contact information
View attachment 87743 View attachment 87744 View attachment 87745

Most importantly @Chrome I can confirm it in fact fits, but only for that particular switch. That schurter switch has a little indent at the top that locks it into place. Original screw holes and everything.

 

[Seanxk]

That looks like a Schurter Rotary switch, there not so expensive last time I looked, I think about £5 each.

 

[Emtbreid]

That looks like a Schurter Rotary switch, there not so expensive last time I looked, I think about £5 each.

It is. Got mine for $13.99 here in the states.

 

[Seanxk]

It is. Got mine for $13.99 here in the states.

Yep, sounds about right, it was a while back when I looked.