Need some help restoring my Masco MA-50 amp

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blackba

blackba

Well-known member
I am restoring a Mason Ma-50 PA amp from the 50's that was the grandfather's. I want to convert it into a guitar amp, right now I am just trying to get it working.

Here is what I have done so far:
1. Changed power cord to 3 prong and removed death cap
2. Changed jewel light to Fender style (only socket was shot and jewel was smoked)
3. Replaced all electrolytic caps
4. Replaced all inputs with shorting when open 1/4" jacks
5. Tested all the tubes, replaced the 7F7, I have backups for the others

I used a variac and ramped up the voltage for the first time yesterday, but that just yielded cracks and pops through the speakers. Here are my questions with the amp?
1. 3 of the 6L6's have a blue hugh to them. I tried the original set of 6L6GA's and the new TAD 6L6GC's I have, both did the same thing. What is the most likely issue?
2. The 500kohm pots are super scratch, I was going to get replacements as I think they are beyond cleaning. Should I get 500kohm audio taper for the volumes and 500kohm linear taper for the bass and treble?
3. The filter caps in the power supply were a mix of 8uF and 16uF. I replaced them with 20uF. Is that okay, given the amp has 2 5U4G rectifier tubes?
 
Aww man I thought you would have knocked that out by now. Mine is on the slate for a rebuild here shortly. I may gut the entire thing and do an 18w or similar.

Good luck and let me know how it turns out!
 
tweed":1brkke67 said:
Aww man I thought you would have knocked that out by now. Mine is on the slate for a rebuild here shortly. I may gut the entire thing and do an 18w or similar.

Good luck and let me know how it turns out!
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Just too many projects for me to complete it myself. Skip thinks it will be a better Bass amp, than guitar amp. One channel will be more tuned to bass, the other to guitar.

I will provide updates once I get it back. I am sending it out this week. Its a heavy little beast.
 
Update, my grandfather passed away on 6/10/2010. :( I would have liked him to see the final product, but he was in pain at the end and is in a better place. I got to see him 12 days before he passed away. My grandfather was a WWII vet, repaired radar in the war. He used to fix tube radios and TVs back in the day. RIP Grandpa

Got my Masco MA-50 back yesterday. I will post some before and after pictures soon.

Skip combined the 2 mic channels. One channel is very dark, the other is bright and the tone controls don't do that much, so I just dialed in the treble/bass with the volume knobs. This amp crunches like an old Marshall. It gets loud and crunchy fast. The volume pots are 500k, I am wondering if I can change them to 1meg audio taper, like is on a BF Fender. I swapped a 7N7 for the 7F7 and that helped tame the volume a bit, but not much.

So far the amp is really cool, but just too loud for much of any kind of home playing. I run it into my 212 with 2 CL80's. I am a bit concerned about blowing my 212 with G12H30's or my 212 with 2 30Watt Weber 12A125A's. Its got 4 6L6's but is cathode biased. I measured the plate voltage at 340VDC, ~50-60mA depending on the tube.

Next step is to try it with my Jazz bass and look into some other pots to help with the volume.
 
Did some more testing. The power tubes still have this blue color to them, not sure if I should be concerned about that.

I did try the Masco with my bass and its a bit too crunchy and doesn't handle the low A and below very well. I tried my Ampeg SVTIIIpro with the preamp out into the phono input, that sounded pretty good. Still not doing below low A well though. I am thinking that a Tech21 character series pedal would sound great through the phono input. A used Masco amp might also be a good option for those Axe-FX guys who just want a cheap amp to run it through, as the phone input is pretty transparent.
 
Finally some pictures. The nuts are where the can caps used to be. They are just to fill the holes, as you can't buy caps in that form any more. Still testing out cabs.

IMG_2590.jpg


IMG_2589.jpg


IMG_2587.jpg
 
For cabs so far I have tested. Vox 212BN with anni G12H30's, Marshall 1936 212 copy with CL80's, and Fender Bandmaster 212 open back with Weber 12A125A's.

The Vox with the G12H30's is by far my favorite. It just has a nice chime and warmth to the tone. The Fender cab with the Webers was a little bright and thin. The 1936 with CL80's was just kind of plain, not very warm.
 
After doing a bunch more speaker tests, I still like the anni G12H30's the best with the Masco. I am going to look for some 50Watt WGS Reaper HP or Scumback H75 65Watts speakers.

I haven't decided if I am keeping the 212 closed back or making it closed back.
 
:rock:

Very nice. I just stumbled onto a MA-25P late last night. It's the same thing with a turn table on top......crazy. It looks like a cool little project with a lot of potential.

Masco_zps3bf0e527.jpg
 
Very nice Riffraff, I hope you get yours up and running. They are cool, well built old amps. The original 'lunchbox' amps.

My MA-50 is super loud, in fact Skip said he had only done a few MA50's, most of the time it was an MA-25 or MA-17. I have done one gig with the Masco and it did great.
 
It looks like it's going to be a fun little project. I picked it up last night and my car failed to start when I went to leave. I was stranded about 70 miles from home (I have a really long commute and the amp was by my office). F#%kin' Nissan and their keyless ignition system! This is the second time in 4 months I've had this happen to me and they replaced the brake switch the last time but that is a rant for a different place. I ended up having to call a tow truck. My wife drove out to pick me up and we didn't get home until after midnight. Good times..... :confused:

Right now the amp is in my trunk at a garage. Once I get my hands on it I'll test it out to see if it's working. It doesn't look like it's been used in many years so I expect the caps will be toast. I don't have a variac so I will use the poor man's version....light bulb wired in series with the supply voltage to bring it up slow in an attempt to reform the caps. I'm hoping to avoid having to do a complete gut & rebuild because that will push this project out a while with the auto repair & towing expenses I'm now facing.
 
Riffraff":1jjgwt9v said:
It looks like it's going to be a fun little project. I picked it up last night and my car failed to start when I went to leave. I was stranded about 70 miles from home (I have a really long commute and the amp was by my office). F#%kin' Nissan and their keyless ignition system! This is the second time in 4 months I've had this happen to me and they replaced the brake switch the last time but that is a rant for a different place. I ended up having to call a tow truck. My wife drove out to pick me up and we didn't get home until after midnight. Good times..... :confused:

Right now the amp is in my trunk at a garage. Once I get my hands on it I'll test it out to see if it's working. It doesn't look like it's been used in many years so I expect the caps will be toast. I don't have a variac so I will use the poor man's version....light bulb wired in series with the supply voltage to bring it up slow in an attempt to reform the caps. I'm hoping to avoid having to do a complete gut & rebuild because that will push this project out a while with the auto repair & towing expenses I'm now facing.
Click to expand...

That sucks about the car, hopefully the repair is not that expensive. My Van has recently been in for service a lot, it hasn't left me stranded thankfully. Car breakdowns are a pain.

I would replace those caps before you even fire the amp up. If you are just going to wing it, at least you are ramping up the voltage slowly. When I need a variac, I borrow one from work. :)
 
Well total cost on the car repairs with towing was $1200. :doh:

On a happier note, I've got the Masco in my hands again.

MA25P_zps80215c69.jpg


I popped the hood on it this morning to see what I will be dealing with. It is 100% original. I was expecting a rat's nest but that's not the case at all.

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Look at those crazy dogbone resistors! I've never seen those before. You don't see wirewound types mounted that way in amps much either. That actually looks pretty smart but cheaper options replaced those several decades ago. This thing looks so cool inside I want to try to change as little as possible.

OldSchool_zpsb6a97da5.jpg
 
Very nice. I was able to find a schematic for mine, but had to pays little for it. I can't remember where I got it now.
 
*** Update ***

I ended up sending mine to Skip too. He did his usual Masco mods to mine as well. It came out really well.....a lot like a '50s Tweed Bassman. The tone control on mine is actually quite usable. I put anourht jack in the back which is connected to the phono channel. Since it has one less gain stage it makes a pretty good line in for running an external preamp. I put a pair of RCA black plate 6L6GC's in it yesterday and it sounds incredible. It has nice chimey clean tone, outstanding bluesy edge of break up tone and crunches nicely when boosted. Here's a little clip which starts clean to bluesy then I stop on a SD1 for something dirty. ;)

 
Sounds great riff. I wish the tone control on mine worked better. I am now using my ma50 into an Alex attenuator to tame the beast a bit. I can now get some great edge of breakup tones.

I am getting some intermittent crackle and pops in mine, but that seems to go away if I use it more. I actually have a couple of other amps doing that, but they are most consistent. Very annoying actually.
 
Sorry about the cackling. Did you try swapping preamp tubes? It could be a microphonic tube. Some of those octal preamp tubes are often microphonic.
 
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