# Symphonic



## ezcomes (Jul 28, 2008)

...so this isn't so much of a Build, as a rebuild...

this is my dad's amp...best i can ascertain is Symphonic amp model MA-13 circa 60's...based on the design...no info found using google...three tubes...12AX7, 35W4(rectifier) and 50C5 (power tube)...roughly 5W of mind blowing power...he wants to use it again to try to amp up his acoustic a bit...ideally, not the best amp, but...we'll see

the amp hums like a ba$tard...so...the tubes are new...so that leaves caps...but...since it is apparently highly unsafe...there will be some mods made...

the caps will be replaced (yes, all THREE of them...hahaha)
i will add an isolation transformer, and
add a grounded plug

in the process of this...i think I'm going to remove two of the three inputs (i don't really think they are required) and this will free up some space to work...

I'll post as i work...but here's something to get started as i order parts...apparently iso transformers aren't readily available around here...

also...any helpful hints/ideas would be welcomed


----------



## bsco (Dec 7, 2012)

Hi. New to the forum. I have a question for you...How did you make out with your amp after??Did you solve all your issues?? I had a friend drop off on of these amps to me last night to fix up for him....same problem...very bad hum and not very safe...did you find a suitable power transformer??? 
Cheers,
Bernie


----------



## ezcomes (Jul 28, 2008)

at this point...its on the shelf...got a 18W kit on the go, and it took priority...

here is the isotransformer for you though...
http://www.alliedelec.com/search/se...,Ro:0&Term=N-68X&SearchType=2&fromsearch=true


----------



## bzrkrage (Mar 20, 2011)

ezcomes said:


> at this point...its on the shelf...got a 18W kit on the go, and it took priority.../QUOTE]
> Did you ever get this amp up & running?
> I have noticed a hum in my M-8, was wondering what to do. Yes it still has the 2 prong.


----------



## ezcomes (Jul 28, 2008)

no...its still on the shelf...haven't even looked at it to be honest...


----------



## dcole (Oct 8, 2008)

The hum, if loud typically indicates that the filter capacitors have gone in these amps. Take them to a qualified tech and have him troubleshoot the problem.


----------



## Electraglide (Jan 24, 2010)

This is my MA 1....early 50's as far as I can tell. And as far as I can tell, all original right down to the 2 pronged plug. Tho it does have a 12ax7 in place of the 12sq7. Not too sure when that was changed but the amp sat for years before I got it. The tube are, 12ax7, 50l6gt and 35z5gt. And it hums
http://s1000.photobucket.com/user/Electraglide49/media/symphonic1_zpsa39a6059.mp4.html
It sounds very similar to some of the old tube AM radios I have when they are off station. There's an RF oscillation in there and this is one of the amps I have that does at times pick up radio signals. One of the things that affects the hum is my cell phone. I tried to take a video with the phone and as I got near it, the amp got very noisy so I had to use an actual camera. Picking up and strumming a guitar doesn't affect the hum and neither does the florescent lights. One of these days I'll go thru my old tubes and see if putting a 12sq7 back in the amp changes the hum.
nb....I just checked a 12sq7 and it's different than a 12ax7....not interchangeable so I imagine that the tube change was possibly made at the factory.


----------

