Masco MA-17P resurrection.

[bluzmn]

Hi, I'm new to the forum. I'm a professional musician; been playing guitar and harp for more than 40 years. Lately I've been more into the harp; I'm kind of bored with the guitar. Anyway, I've just recently started tinkering with amps; I bought a few "projects" on Ebay. First on the bench is a Masco MA-17P. I hooked it up to a speaker with alligator clips, brought it up slowly (over 2 hours) on a variac, and plugged in a mike; the tubes lit up, but when I tried to play harp all I got was scratchy sounds out of the speaker that did seem to correspond to the rhythm of what I was playing. What do you think is the problem? I know replacing the filter caps is usually the first thing you need to do with an amp this old, but I don't think that's the only problem; in my (limited) experience, old worn out filter caps usually cause a loud hum that doesn't get louder or softer with the volume control. Also, I'd like to install a fuse; is there a formula or rule of thumb one uses to decide the value?

[bob p]

Its funny that you should mention this today. I just noticed that these old POS lunchbox style Masco amps were fetching $200 on eBay, so I started a thread asking "why the madness?"

We've been talking about the obscene prices that some people are willing to pay on ebay for the old lunchbox style PA amps that are in non-working condition. It seemed to be the consensus of opinion that this type of project has become a fashionable thing to do today, and that a lot of people are taking on these projects without knowing all that they're getting themselves into. You've got a lot of work ahead of you and a lot of learning to do. Welcome to the site. You've found the right place to get help.

It used to be that this sort of activity was the exclusive realm of the electronics hobbyist. Now that there's been a fair amount of e-media attention given to this sort of thing, its become a vogue thing to do among musicians. The result is that the prices of these old pieces of salvage gear have escalated to a point that I believe is far beyond their net worth. The old Masco amps seem to be selling for prices that are 10 times what I'd be willing to pay for them. I just saw someone spend $200 to buy an MA-17 on eBay. Yikes.

These are the kind of devices that many of us would buy for $5 at a flea market, just to gut them and salvage the iron. The wiring inside of those amps is normally such a mess that the best thing to do is to gut them and to start over from scratch, building a totally new circuit into the chassis. That tends to be a lot of work. In most cases its faster to build a new Fender or Marshall or whatever circuit into an empty chassis than it is to completely restore an old PA amp that has crumbling wires and a point to point layout.

I have always thought that these projects were great fun if you could basically get the chassis for free, or next to nothing, and spend some of your free time reworking it into something useful. If you have to pay for a technician's time, these amps are best left avoided. But if you're going to fix the amp yourself, then the cost model changes dramatically. Free time is free, right?

Unfortunately the prices for this type of gear have risen to the point that the sunk cost of acquiring the project becomes so high that the projects may no longer be worthwhile. A lot depends on your acquisition cost and how much time you're going to have to dedicate to the project to get it finished. Having rebuilt more amps than I can remember, at the $200 price point I wouldn't take on this kind of project. I value my time and I have a strong desire to limit my losses. At those prices, I'll buy a blank chassis, cut the holes, and build an amp from scratch. Not everyone feels this way, so YMMV.

If I were in your position, I would make the decision on what to do with the Masco based on a few considerations. This post is already too long, so I'll break here and cover those considerations in the next post.

[bob p]

First, its very hard to troubleshoot an existing circuit if you're not familiar with electronics and you've never built an amp before. Troubleshooting a PTP amp is a lot harder than an amp with eyelet boards or turret boards, because the PTP wiring typically looks like a rat's nest. You've chosen to start off with a project that requires a higher level of proficiency.

Second, it may be easier for someone starting out to build a new amp from scratch using all new components of known quality. The prospect of repairing an amp where all of the parts are suspect is a challenging one. Things can become especially challenging if you're don't have test gear.

Third, it sounds like there are some basic electronics issues that you aren't familiar with. In some respects you're undertaking a real trial by fire with that old Masco amp. Good for you. Around here this type of project is traditionally considered a rite of passage.

Fourth, if I were in your shoes and I was determined to restore the amp, my first decision would be to make a firm decision on the application that I'm planning for the amp. Ultimately, these amps can be rebuilt any number of ways, and how you'd rebuild them would be different if you wanted to optimize the amp for harp vs. optimizing it for guitar. Although most of the guitar knowledge seems to be freely disseminated, I think that most of the harp mods don't seem to be as widely known. Maybe I've just never paid enough attention to know them. The good news is that there are people here who specialize in harp amps.

Now that you've got an amp that you're willing to work on, the first thing that you need to do is to get a schematic. I'd start by searching the web for the proper schematic or better yet, a Sam's Photofact for your amp. If you can't find one for free you can purchase one online. If you can't find one, then the next step is to trace the wiring through the amp and draw your own schematic. You need a schematic to really know what you're dealing with. Otherwise you'll be left with the monkey-see monkey-do approach to amp repairs.

For a fuse, nothing larger than a 2A slow blow.

Welcome to the site. Have fun!

edit: Oops. I just realized that this post is already in the harp amps section. I didn't notice that before. Please ignore some of the things I said.

[J M Fahey]

Sorry to say so, but the *very* short answer is:
"professionals won't touch them (unless payed very well) and ameteurs, usually, don't have the skills"
Besides that, repairing a tube amp is *way* more complicated than building a kit or following a (simple) Fender Tweed layout.
Sorry.

[bob p]

Once again, it takes me 1000 words to say what you can say in two sentences!

It it were my project, I'd gut it an build a pro.

[JHow]

Bluzman must have some electronic experience / knowledge, since he owns, or has access to, a variac. Not usually the fist piece of equipment you might acquire.

I'm sorry I'm no help on the schematic, but google searches and places like schematicheaven.com can usually turn something up. As a last resort, spend a few hours at a university library - if you are in L.A., UCLA Physics library, EE library and the Univ. Research Library used to have a ton of stuff, including Sams photofacts, at least they did some years ago. There are expert trouble-shooters here on the board. If you search the forum, there have been discussions recently on general topics, such as what books provide the best help, which web sites provide the most (free) info, discussions of suppliers, etc. To diagnose your immediate problems, they are going to need more information, however.


Oh, I think this site has schemo: http://blikethetubes.blogspot.com/

[bob p]

If you don't want to run to the library to do your research, Sams sells the photofacts online.

If you don't know where to start troubleshooting, Jack Darr's book is a good one. You can find it online.

That web link has some helpful information. Looking at the schem, I'm disappointed in the use of a 5y3 with 2x6L6. Its a cost cutting (cheap) design. He mentioned that some of the tubes for that amp are hard to get. He paid $40 for his Masco on Craigslist and gave up on restoring it. He ended up gutting it to build a 5e3. Great minds think alike.

[Bruce / Mission Amps]

Some of these have odd and difficult 7C7 tubes to work with and some are prone to ultra sonic oscillations that give novice builder/tweakers fits!

Masco Mark Simpson Company Inc., Long Island manufacturer

They aren't that hard to work on but can be a drag sometimes.

[J M Fahey]

You have seven Masco schematics in: Bargain Bin Heaven Amp Schematics - Airline Garnet Gretsch Hagstrom Kalamazoo Kay Magnatone Selmer Silvertone Supro
Yeah, they dare call them "bargain bin amps".
Not the MA17 exactly but having the 15 and the 18, plus an MU17, you can't be far from it.
Yours should be checked against one of those schematics, one of them must be practically the same.
Please post some pictures of the chassis inside.
Personal opinion: if you decide that you need a Masco schematic amp, and no Fender or whatever will satisfy you, you can design an eyelet board for that particular schematic; it's relatively easy, certainly compared to the herculean task of repairing one as-is, which involves for starters changing *all* electrolytics, *all* paper in oil caps, *all* cracking insulation wires, plus "mechanicals" such as pots and switches.
Even sockets, if it was stocked in a damp basment and they rusted.
Short answer? I would have *loved* to get one like this when I was 16, to practice my "skills" spending nothing .

[bob p]

You make a really good point -- I've been talking about how horrible it is to work on old, crumbly PTP wiring. With that said, even though we guitarists can't think of anything better to do than 'Wrecking an old Masco, for the harp guys these amps/circuits are really desirable. If you're willing to go to the trouble of restoring one of these, it would be a good idea NOT to rebuild it PTP. It would make sense to gut the chassis and design a Fender-style eyelet board, then rebuild the circuit from a clean slate. The build and the troubleshooting would be infinitely easier. Personally, I think that's the only sane way to approach a bowl of spaghetti.

[bob p]

Some chapters from Jack Darr's classic book

[bluzmn]

Thanks

Thank you all for your kind responses. To bobp- yeah, I think I got the last cheap Masco on Ebay. I'm also appalled by the prices these things are going for on Ebay! Even the 6, 8 and 10 watt Mascos are going for $150-200, and I've seen MA-17s and ME-18s going for as much as $300 or more. Luckily, I was cruisin' Ebay at 4am one morning, and the guy must have just posted the ad; it was on auction, but he had a Buy It Now price of $75. So, I thought I'd better snatch it; not $5, but a damn good price these days. And since it's an MA-17"P", it once had a turntable on top of it, so the chassis is 12"x 10" and the wiring is not such a rat's nest. If I can figure out how to attach it, I'll post a picture of the chassis. To JHow - you are correct, I do have some experience. I've wanted to know how to work on amps for a long time; about 15 years ago, I took an electronics course at a vocational school, but once we had learned all the basic electronics and it became clear that the rest of the course would be about transistors and there would be nothing about tubes, I dropped out. Around that time I got a BF Super Reverb; it had two 12" speakers in it and the Normal channel and the vibrato in the Vibrato channel had been disconnected. I got a 4x10" baffle and installed 4 Kendricks 10s in it; those mods were straight out of Gerald Weber's book, so I was able to reverse them. Also, I recently replaced the filter caps in a Kalamazoo Model 1 that I'd bought in a pawn shop. Oh, and I was a Boy Scout (their motto is "Be prepared"), so I got the schematics of the MA-17, ME-18 and a few other models I wanted to acquire of the internet (free); it seems you can find anything you want on Google if you look long and hard enough. And Mr. Collins, thank you for chiming in; I've been checking out electronics forums for a while, and I joined this one first because you are a member.

[bob p]

Don't go flattering Bruce too much -- he's still a humble guy and we like him that way.

$75 isn't a bad price if you've got good iron, a pretty chassis and tubes. I guess the screaming deals just aren't out there anymore. Now I'm starting to feel like an old fart.

I posted that link to Jack Darr's book. Its really worth reading if you haven't read it already.

HTH.

[Bruce / Mission Amps]

I've worked on a few of the Masco P models and after a good tune up and new filter caps, they sound just as good as any of the others... very good transformer iron in those too.
I'll have to ask Rick Davis if he has any pictures of the inside of his Masco after the many mods done... it works great with a single 12" speaker.
He has owned about a million "harp" amps and this Masco is one that he would probably never sell.
He is using one of my Chicago amps now and if you can get past his over the top enthusiasm, there are some good readings on his harp blog pages:

Blues Harp Amps

Just pick the stuff you choose to ignore.

[slacker]

masco mu17

i just finished getting one of these back up to snuff, the original PTP in this amp is really wacky, looks like it was laced by a 5 year old. all that said, it really sounds good now, 2 6l6 in class A. i can see where you'd pay 250.00 for this model