Masco MA-17

[Brad1]

Another fine garage sale find. Will describe a bit, and then some questions. (I may post some pics later. I'm going to do some "before" and "after" pics.)

Saw this one from the street. "Hmmm...an old 50's-looking speaker box! I should check this out."

It was a two-piece, two speaker box that hinged on the bottom and pulled apart to separate. I popped it open to peek inside at the speakers...and the Masco amp was in there. It was mounted on a square board, and slid out of the front half of the speaker box to remove.

"Hmmm...this is interesting". The speakers are a pair of Jensen P10S, in relatively decent condition, though there is a slight tear in one. If I'm coding this right #220650 is December 1956?

The amp is in pretty good condition, cosmetically, considering. The speaker cabinets are not terrible, but have some scuffs and worn corners. I figure a soft brush, some mild detergent...and maybe even some brown KIWI shoe polish might liven them up a bit?The metal painted grill clothes are dirty with brown spots, but I may be able to clean them up. Tarnished brass hinges and latches...no big deal. The cardboard-rolled-leather covered handles are in bad shape, but, whatever.

The thing DOES smell pretty musty, and the plywood board the amp was mounted to is separating. I guess years and years of Kansas humidity/damp basement storage, and smoky auctions is bound to do some damage. (The guy said his Dad used it in the 50's-to-late 60's for an auction PA.)

Asked the guy how much he wanted. He said "Well...I'm sure it still works, but I don't have the microphone. How about $6?"

"Uh...OK!"

NOTE! To be resumed later. I just lost 1/2 hour of crafting a post, hitting "Submit"...and then being told I had to "Log In". I did, and the above "Auto-Saved" content is all that was left! That kinda bugs me!

Will get into the questions later.

Thanks,

Brad1

[Brad1]

OK...back at it.

7C7, 7F7, 2x6L6 and 5Y3G tubes, all strong except a slightly weaker 7F7. Definitely needs caps. Will rewire any cloth-covered wiring that I can, because the existing stuff is kinda...fuzzy (presumably from moisture/mildew). The choke and OT paper are also kinda funky-looking, but they are dry, and they measure fine. I THINK the power transformer may have been changed a some point, because it looks like they had to slightly cut and fold the chassis hole to accommodate it. Still, definitely old.

So, I checked everything, plugged it into a Variac, and turned it up slowly. Got it up to 115V, no problem.

(Downloaded schematics from a search of this site. Thanks, Bruce Collins!) http://music-electronics-forum.com/a...oma17schem.pdf

Actually fairly quiet (self-noise) with signal generator connected to "Phono" input. Also, not very loud (naturally).

Way more noisy connected to "Microphone" input. Hopefully, all new caps and a grounded plug will cure most of that. (Definitely needs at LEAST those...touching the chassis produces way more hum, and is kind of worrisome.)

So, knowing it kind of worked, I rigged my Strat up to the "Microphone" input. (This has the old screw-on mic connector for that, and a terminal strip for the "Phono" input.) There's some tone under all that noise...and it's surprisingly loud through those speakers! And, those speakers seemed to take it with no problem.

Now then, some questions. I know blues harp players seem to love these things. Would it be sacrilege to mount a 1/4" jack in the front. (That's actually really close to the tube pin where it connects, anyway.) I've seen people put them in the back, but I think it would be handier on the front, and there is plenty of room in there. Should I leave the back screw-on connector connected (with a new cap) and install a front jack, with the same value cap? Would a different component setup be better for guitar? If so, would a switch installed to toggle it from the "Mic" to the "Guitar" setting be out of the question, with the components for each.(To use as a harp amp, or guitar amp.) Does it even matter?

What to do with the "Phono" circuitry? Obviously, it's much lower. Would it make sense to install a 1/4" jack for that, and maybe run a boosted signal into it? Maybe, "Y" the guitar, one going straight to "Mic" input, and the other going through a boost/preamp/etc...and maybe even through something like my Fender Reverb Unit? Set the Fender wet, and dial in the amount underneath the straight signal? Maybe, run an overdrive under the straight signal, and mix to taste? Can that be done? Would it make sense to try?

I assume I'll just leave the speaker sockets on there, and parallel a couple 1/4" jacks by them. The system still has the funky old speaker plugs, which I'll rewire with new (non-cracked) wire, and use when I use those speakers with it.

About the speakers, am considering mounting some feet tall enough to clear the handles, so I can set on top of the other. That would make the "stack" about 40" tall, and get the top one up a bit. (They are so light, though, I wouldn't put any amp on top.) Am wondering, even, about installing some board on the backs of one, or both, to make them semi-closed? (That'll be easy to goof with, before doing it.)

One other thing. I've read that those 7#7 tubes are a bit funky, and a lot of people change them to 6S?7 (along with the sockets). I'm going to try to keep it what it is for now. I can always screw with that later. But, what is the main advantage of changing those out?

Any ideas or comments appreciated. Any "NOOOO...DON'T do THAT!", also appreciated.

Thanks,

Brad1

[MWJB]

Some blues harp players love them. Skip Simmons customised MA17 being the more desirable.

There were different versions with different preamp tubes, inc. 6SJ7 (deemed most desirable tonally) some had 6SL7 PI tubes.

Your phono input has less noise because essentially there is no preamp, input goes straight to the input of the PI.

It is common practice to replace the screw on concentric inputs with 1/4" jacks.

[Bruce / Mission Amps]

I have two of them Brad and I hate them both.... different strokes-different folks.

[Brad1]

I have two of them Brad and I hate them both.... different strokes-different folks.

Well...for a $6 initial investment, plus a few more $$ in parts...I can always just clean it up, quiet it down, and get rid of it. Maybe I'll just get one of those screw-on to 1/4" adapters for the input, and not replace/drill for a jack. I think I will go ahead and install a couple 1/4" speaker jacks, though.

What is it that you don't like about them, Bruce? You don't like them for guitar, or you just think they suck on everything?

Brad1

Before and after speakers, after cleaning and using KIWI brown shoe polish, and cleaning grill screen and painting with Krylon Gloss Almond:





Other images:

[Bruce / Mission Amps]

Brad yours are totally different then the ones I have... I'll shoot a picture of them.... they're kinda buried under a pile of tweed 2x10 cabinets right now though.

[Brad1]

You can probably see the reason I wondered about putting the input jack(s) on front. Both the present inputs are flying clear across from the back to the front, anyway. If I even use that "Phono" input at all, that may get disconnected completely from the back terminal strip. I am wondering about doing the parallel "Microphone" input thing, to provide a standard 1/4" jack, but also have the availability of the screw-on connector, in case someone has an old mic and cable they want to connect? Use one or the other? I'm thinking some shielded cable from the inputs, closer to their destination, couldn't hurt...instead of running over all that other stuff. I guess I'd have to put the jack(s) over by the lamp. Plenty of room, closest to the connection points, and about as far from any transformers as they can get?

I think I'll start by replacing only the old orange caps, and that odd silver 25uF Mallory, which I'm not quite sure yet what it is. It doesn't appear on the schematic, but I haven't gotten real deep into this part, yet. (Been dealing with a lot of background and security paperwork and stuff for a possible new job, as well as school.) See how that works, and go from there.

I suspect that silver Mallory was added with what is obviously a different power transformer. I tried to search for the transformer, but couldn't find anything. The only things printed on it are "6K45 HB" on the top cover, and "1005005" on the bottom cover, with no stampings, etc. Looks like that little aqua-blue .01uF cap was replaced, also.

Brad1

[Bruce / Mission Amps]

Beside a basic tune up and mild mods, here is what I did to the Masco owned by Rick Davis of the Blues Allstars so he could plug into the front.... I used a piece of shielded cable to the jack, of course.

[Brad1]

Doing some cosmetic work, while waiting for parts. Figured, "What the heck...this ain't no old vintage Marshall, Fender or Vox that I will completely destroy the value of by doing stuff to it."

Removed the MASCO badge, and cleaned it up nice and shiny. Cleaned the cover and gave it several coats of the Krylon Almond, and a couple clear coats, to match the grill screens of the speakers. Took a small piece of the speaker covering (from the inside, and shoe-polished) to the hardware store, and found some Rust-oleum Leather Brown gloss enamel paint that matches nearly perfectly. Am going to paint the amp chassis with it, once I get all the parts removed. It'll give it an old two-tone "dark brown/light tan" look, and match the speakers perfectly. It also blends in the control plates and dried-blood-red chickenhead knobs nicely.

Heck with it. Might as well make it look kinda classy.

About that "Phono" input, and volume pot? I'd like to figure out a way to make use of it. Maybe as a parallel effects loop? Not sure if it could be pre-preamp tube, or post, and what I might be able to do. If I did it pre-preamp, somehow, would I have to buffer the input because it would load the input if anything is plugged into the loop? I've been looking at a bunch of different parallel loop ideas, and am not sure where something like that might be best placed, as far as before or after preamp tube? I figure, split it off at the input, run it through an effect, and blend it back in right before the tube, somehow? Seems like that would be simpler than after the tube, since anything I'd want to run through it would be a guitar-level effect, anyway.

Trying to keep it so it can be pretty much used as "original", or able to plug in, say, my Fender Reverb unit, to blend in some of that (or even some other thing(s), if used for guitar...delay, etc.)

Not looking for anyone to go through any trouble diagnosing the thing, and writing out a solution (unless it's super easy). Just wondering, for now, if it could be done, with not too much in extra parts and trouble. Maybe even if I have to use a bit of SS stuff? Here's a link to the schematic, in case anyone wants to take a peek, and say "can't be done", or "it'll be easy...just add this and this, there and there."

http://music-electronics-forum.com/a...oma17schem.pdf

Just wondering.

Thanks,

Brad1

[Brad1]

Was wondering about utilizing (changing) that "Phono" circuit on this MA17. I just hate to have a knob with little use on there!

I had several thoughts, but a few seem to be a bit tricky. I had thought adding a couple jacks and incorporating a parallel FX loop, so I could run my Fender Reverb Unit through it. I've looked at several SS and tube things, and they look a bit tricky, not to mention that to do it properly, I'd have to add yet another pot (to get pre-out level and return level adjustments). I just want to utilize that one knob...not add any more. I realize I could just add an "out" or "in" level...but...

So, looking around, I found that it may be just as easy to just add a different preamp circuit to it...assuming the PT would handle it. Here's something I found:

Weber Mod Kits

It's the "General Purpose Gain Stage", using a 12AX7. (JPEG attached).

It seems I might be able to just add another 1/4" jack, build this up, and connect the "Output" to the same spot at the phase inverter?

Maybe give me a different characteristic, while being able to pretty much use the "Mic" input as the "harp" input, as original? Just added functionality, while keeping original characteristics? May even try to figure out a way to switch the tone circuit, later ("Harp/Guitar")?

Anyway, just got my basic parts to recap, add 1/4" input and speakers jacks, etc. (Still have to reinstall transformers, since I removed them to paint the thing). First thing I'm going to do is to see how it works as original (with just caps changed, and one "Mic" input jack added, and speaker out jacks).

Does it look like adding a different preamp circuit would work? If that's not feasible, I guess I could just run that as a "Line Level" and pump it up with an external preamp.

Would, as it is, running two devices be in phase, if I split a signal, ran one into the "Mic" input, and another through, say, my Fender Reverb Unit (set "wet"), then an external preamp, and into the "Phono" channel, to mix in with the original (or replacement) pot?

Would adding a tube preamp in the amp keep them in phase to run, say, direct to the "Mic" channel, and through the outboard effect, then into the "Phono" channel to mix in? Or...

Could I eliminate a 1/4" input jack, (and not worry about running effects in parallel), and maybe just put a switch for "Mic"/"Both"/"Phono", and just run effects to input, choose one or the other, or both, and mix preamp outputs?

Just some thoughts. I want to keep (as close as possible) the original "Mic" channel usage, but just add some more variety, if possible. I've heard these don't sound particularly "great" on guitar (especially with the 7C7/7F7 instead of the 6Sxx tubes), but it may sound good as original for harp, and sound good with an added 12AX7 for guitar duties? I just hate to see a knob go to waste. This is one of the first things I've gotten so cheaply, and that isn't going to be "sacrilegious" to experiment on to learn more. (Plus, I caught the Curt Thomas "just can't leave anything original, can ya!" bug! Not like it's a '57 Bassman I'm trying to hack, right?)

Thanks in advance for any advice.

Brad1