Baffling Magnatone MP-1

[gktamps]

Hi Friends,
I was given a Magnatone MP-1 that had been poorly stored, and had mice living in the cabinet. I have cleaned and scrubbed it, re-capped it, changed out some bad resistors, replaced the power switch, re-wired it to work with either EL84s or 7189A tubes, (not ONLY 7189A tube which have pins 6 an 9 internally connected, unlike EL84s with no pin 6 connection) and replaced some dodgy wires, cleaned and tightened pots, as well as cleaned, serviced and replaced mounting foam on the reverb tank. Voltage checks look good, the tremolo seems to work. The front panel light strip does not illuminate, but I guess I have to live with that.
I've run into a couple of other problems:
First, the speaker is reading 125k ohms, though that fluctuates. I've connected my probes directly to the coil extension wires, but I fear the speaker is kaput.
The other problem is the pressboard baffle is falling apart, so I need to make a new one, and the grill cloth is filthy.
Sooo, what say you?
1. Make new baffle out of plywood, or pressboard like the original?
2. Anyone know what grill cloth would be correct? It looks a bit like Fender cloth, but not exactly. Is it even possible to get the original style?
3. Any suggestions about what replacement speaker to use in this amp? I've never played this or any other Magnatone.
Thanks!
Greg

[martin manning]

based on this http://www.magnatoneamps.com/MP1.html picture, it looks like Fender "wheat" grille cloth would be a pretty close match. Reading on that site the original speakers were probably ceramic magnet Jensens. As long as you're making a baffle, make it plywood. I gather luminescent panel material suitable for use in MP-series amps is available from these folks: http://www.luminousfilm.com/el_lamp.htm

[gktamps]

Thanks very much, Martin!
Greg

[xtian]

One of my two DMMs often cannot get a read on a speaker coil resistance. The other always works. Confirm before you toss the speaker.

[teemuk]

With such an old amp I would personally try to change as little as possible because every change will be robbing on its historical value. And often value in plain money as well.

How badly broken is the baffle? Can it be fixed with additional bracing instead of replacing it completely? Is the grill cloth's condition beyond washable? Is there any other reason to replace it than a cosmetical one?

The vintage kinda washes off if you merely replace everything that's broken.

My 2c.

[gktamps]

Xtian, yes, I considered that and used two different DMMs but will use an analog meter next. Voice coil moves to the 9V battery test...

Teemuk - thanks for the comments. Concern over originality is exactly what is why I was on the fence over additional changes. The existing baffle has separated where the speaker mounting screws pulled through. I could use epoxy to try to glue the board back together, I suppose. Cleaning the grill cloth is also something to consider - might work well enough.

cheers,

Greg

[Default]

Consider building a replacement cabinet. I recently picked up a mid sixties Guild Thunderbird amp and it is constructed of sawdust and glue too. I plan to build a cabinet for it as soon as I get moved into the new house.

Heavy AND fragile? Not fun!

[gktamps]

Stripped off the grill cloth and the baffle pretty much fell apart in my hands. So, it's time for a plywood baffle, and I'll just keep the old one for a future owner to use as a template if they want a pressboard baffle. I get the whole keeping it original thing, but the amp wasn't broken originally, which is why I've done all the other repairs, so there doesn't seem to be too much value in an amp that has a flatulent speaker/baffle, I'd say.

Not so sure about the grill cloth. It's soaking right now, but the mouse urine and fecal pellets definitely HAD to go! However, I don't care about dirt and a couple of holes - matches the old cab, which is still tight but beat up.

I probably won't invest the time and money in making a cabinet at this point, but would consider it if I fall in love with the amp. Probably just new baffle, old cloth, see if the old speaker works, and let the old Maggy do her thing, whatever that sounds like. Now I'm getting really interested in seeing how she sounds.

Thanks for the comments.

Greg

[joshdfrazier]

I see no harm in replacing the baffle as long as you are able to keep the original grille clothe. There are some freaks like me who actually prefer vintage gear in deplorable condition! mint and clean stuff doesn't do it for me. post some pics!

[gktamps]

A bit late posting photos, as I'd finished this several weeks ago, but got busy again with work, and started a new Rocket build. Gut shots are on my laptop, so will be posted tonight.

The grill cloth cleaned up really well in the laundry sink with a little light detergent, and the plywood baffle was a big improvement. The reverb tank is soft-mounted with foam weatherstip, which had all rotted away. I replaced it with larger strips of high-density weatherstrip after cleaning out the filth. Reverb sounds lush and full.

Everything but the light strip works now, and with some nice NOS tubes, this amp sounds really, really cool - cleaner than most of my amps, and not really loud, but it does break up nicely, and has a tone unique from my other amps.

The tatty schematic pasted inside the cab was actually for an earlier version, but there was no evidence that the amp had been updated, however there was a lot of amp hackery that I fixed or reversed; wrong tubes, wrong switch, unsafe wiring, etc.

I was disappointed to find out that this model came with an amplitude shifting tremolo, not pitch-shifting! Now I'm wondering if it's possible to splice in a switchable pitch-shifting trem, or if it's just time to look at a pedal.

Cheers,

Greg

[xtian]

Man! That looks minty!