Manny's Vocal/Instrument Amplifier

[tigerzilly]

I just picked this up. Its a PA head with four channels and spring reverb. It has SS preamp with two 6CA7 power tubes and a single 12AX7 for the reverb. I'm not sure what drew me to this amp, but who knows, maybe it will sound good.

[Leo_Gnardo]

Kool find. Manny's was one of the big music stores on 48th Street in Manhattan. Legendary, all the big rock stars went shopping there including Jimi Hendrix. But anybody could walk in, try out whatever, and buy it. I know I did, same story at Sam Ash just a couple doors away plus a lot of smaller but also now legendary stores, most went out of business by the early 2000's, or moved. Nothing much left of old Music Row just off Times Square.

This piece looks like it might be patterned off a Bogen PA - they were right across the river in Paramus NJ. Looks like you have a nice straightforward clean-tone amp right there, once typical maintenance is done for vintage amps. What to do with 4 identical channels though? Kool big meter on the panel, gotta love that. Where did you find this relic?

[tigerzilly]

Kool big meter on the panel, gotta love that. Where did you find this relic?

I can't stop looking for more amps. This was FB marketplace. I figured what the heck for 100 bucks. My quick search found the same about the legendary music store, which is cool. The big meter on the front did catch my eye. Something about big meters. It has feet on one end as well as the bottom with a handle one the other end. So it stands like a tower.

The ss pre-amp is a drawback. Any recommendations? I'm not thinking this needs to be kept original.

[Leo_Gnardo]

It has feet on one end as well as the bottom with a handle one the other end. So it stands like a tower.

The ss pre-amp is a drawback. Any recommendations? I'm not thinking this needs to be kept original.

Handle one end & feet on the other - meant to be handy for carrying around. I wouldn't operate it standing on end, as heat from one output tube would rise to bake the other output tube extra krispy.

Looks like they have a bias adjust pot, another handy feature.

I'd leave the transistor mic mixer alone for the nonce, just do the usual for the rest of it: replace hi voltage filter caps, excise the death cap, put on a grounded AC cable, maybe a fresh set of output tubes plus driver tube, clean pots & switches. Old film & disc caps often get leaky too - I'm thinking it would be cheap & useful preventive maintenance to replace caps supplying signal to the output tubes' control grids. Plus any other small-value caps in the power amp circuit if you wanna be super safe.

This could make a dandy monitor amp for low volume rehearsals, also a keyboard amp especially for someone who has up to 4 instruments. Want a little music in your rec room, workshop, garage, patio - as long as you can accept glorious mono, you're all set.

Comes a day you insist on going tube for the mixer, two 12AX7 or AY7 should suffice. Replace the transistor PC board with a metal sheet, punch a couple holes for tube sockets, add a couple tie strips for point-to-point wiring, you're off to the races. I'd hazard a guess the stout looking power transformer could spare 600 mA filament current to run those tubes, and add another stage or two of filtering to the hi voltage supply to power your pre tubes' plates. Search for schematics of early 70's Earth or Plush brand PA amps - in function very similar to your Manny's - but they had tube mic pre's - very similar to the pre's on Fender guitar amps nothing out of the ordinary. The "speech filter" - hi pass - switches could be left alone, or converted to input pads.

OR you could wire up a whompin' stompin' tube overdrive pre, there's 4 volume knobs & 4 switches, you could go to town with that. Turn a mild mannered old PA amp into a screamin' banshee.

Does that meter light up? Whether it does or not, you could fit it with some blue LED light for the ultimately kool McIntosh vibe, sure would ice the cake .



The blue glow that assures world-class quality!

[tigerzilly]

Well Manny's amp lives. Replaced the caps and installed a new power cord. Decent signal coming through two channels. Nothing on the other two channels. Reverb not working yet. Looks like I still have more to do. Theres a screw terminal strip to select speaker impedance, but I'm not sure which is which.

[tigerzilly]

This piece looks like it might be patterned off a Bogen PA - they were right across the river in Paramus NJ.

I just noticed the markings for the speaker impedance settings. Also see a manufacturer name...Audio Products, Inc. Ever hear of it?

[Leo_Gnardo]

I just noticed the markings for the speaker impedance settings. Also see a manufacturer name...Audio Products, Inc. Ever hear of it?

As generic as it gets. Back in those times there was a cab builder in Queens or nearby Long Island by the name of Wachuwan - like "What you want?" in New Yorkese. Sam Ash carried a couple of their stock cabs, and of course you could contact them directly and order - what you want.

If 2 of your input channels aren't working, check the associated preamp tube. Is it lighting up? Pins clean & shiny for good contact? How do the voltages compare on the working vs non working tube.

[tigerzilly]

If 2 of your input channels aren't working, check the associated preamp tube. Is it lighting up? Pins clean & shiny for good contact? How do the voltages compare on the working vs non working tube.

Well if it had tubes for the preamp section, I would do that. Sadly this has a SS preamp. I got the third channel working after finding a transistor lead crossed over to another trace. Signal looks clean, just not great volume with a guitar.

[tigerzilly]

Correction. There is one 12ax7 in the preamp section. I thought that tube was for reverb, but when I pulled it, I lost everything. Signal seems to go through separate transistors for each channel, then all channels go through the 12ax7. Looks like a couple transistors for the reverb.

[The Dude]

That 12AX7 is most likely the PI tube.

[tigerzilly]

That 12AX7 is most likely the PI tube.

Ok that makes sense. Well I lost signal through it. I replaced the 12ax7 and signal came back. Then I lost it again. Something seems to be messing with th PI tube now.

[Enzo]

Something? When you have lost signal, start at the start. You suspect the PI? Look close, are both heaters glowing? Check voltage on pins 1 and 6, got B+? Cathodes on pins 3 and 8, got a reasonable voltage? Does signal appear on the plates? Heck does signal appear on the power tube grids. Speaking of which, make sure you have B+ on pins 3 and 4 of the power tubes.

Touch the grid pins of the PI with a meter probe, leaving the black probe unconnected. Or maybe a small screwdriver. Point is to inject some hum into the system. Does it come out the speaker?

[tigerzilly]

I finally got my head back into this amp. There is a problem with the power switch. Its a 3 position switch..off-standby-on. I did see burns marks on the chassis around the switch. I took it apart and its not working correctly. I dont see how it can be fixed. Not sure how easy it will be to find a replacement.

[Leo_Gnardo]

I finally got my head back into this amp. There is a problem with the power switch. Its a 3 position switch..off-standby-on. I did see burns marks on the chassis around the switch. I took it apart and its not working correctly. I dont see how it can be fixed. Not sure how easy it will be to find a replacement.

Very easy, lookee here:

https://www.tubesandmore.com/product...ion-play-stdby

$5.25 very affordable.

I've used hm, maybe 30 of these so far - they work as advertised & no failures.

[tigerzilly]

Very easy, lookee here:

https://www.tubesandmore.com/product...ion-play-stdby

$5.25 very affordable.

I've used hm, maybe 30 of these so far - they work as advertised & no failures.

This one has three layers of switching going on. I still have to do some testing to figure out whats what.