Masco MA 808 Mic and Phonograph Amp

[CJ]

fixing up a chassis from yesteryear,

anybody ever have anything to do with one of these>

 

[CJ]

it's two, two, two amps in one,

 

[CJ]

7C7  7B4  6L6GA and 5Y3 tubes,

mic and phono inputs, most of the mojo comes from the chicken heads, 

 

[CJ]

here is some verbage,

http://www.radiomuseum.org/r/masco_ma_808.html

speaker says Voice Coil 3.2 Ohms  295707  S1000C-5  188

 

[CJ]

schemo>

 

[pucho812]

I'm working on a masco ma-17 for a harp player.  Dude wants a cab to match his ma-17. Also wants it so he can store the ma-17 inside it for transport. kind of like in your photos.

 

[CJ]

cool!

yes, this is also for a harp player,

1947 means we should have a look at the output transformer,

here are some pics,

 

[CJ]

this is a single ended xfmr for a 6L6-GA, 75 EI, butt stacked with no paper in the gap.

 

[CJ]

structure is a simple pri-sec affair that seems to run pretty flat,

 

[CJ]

freq response>

 

[CJ]

Henries vs frequency>

 

[lassoharp]

I've got an MA 8 that looks about the same as yours.  7B4, 6SJ7, 6L6, 5Y3.  That thing has been one heck of a recording amp for guitar.  Sounds better than most Champs I've heard with the right speaker.

I've gigged with it a lot too pushing a Marshall 4 X 10.  Perfect sound for small venues.

Had to remove some plate to plate FB to get it to quit humming.

Also pulled the tone controls out but left the 270K mix iso resistor in line as a huge grid stopper.  I bypassed it once and it got way too toppy - maybe OT ringing?

Great little amp.  Haven't tried the field coil speaker yet. 

 

[pucho812]

Very Nice work as usual CJ

 

[CJ]

thanks!  i guess the harp players really like the MA 17, plenty of youtube stuff, those amps get the Little Walter break up,

here is a guy who works on them for too much money>

http://skipsimmonsamps.com/amps.html

 

[CJ]

note that the MA 808 heater circuit could be improved by un-grounding one end and running 100 ohm resistors off each leg to ground or better yet, installing a hum pot to balance the 60 Ha, a welcome addition to any SE amp as hum is a bigger issue than with a push-pull circuit,

here is the Masco  MA 17 schematic, grid leak again>

 

[CJ]

time to rewind the 67 year old choke,

 

[CJ]

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