Shure Vocal Master

[Dave_P]

Picked this guy up off of CL today for $10!


Slightly disappointed because I thought it was a tube amp from the quick research I did, also the ad said it was but I can see how he thought it was, the "tubes" are actually 2 light bulbs


they are clearly there to look like tubes because there are no back-lit buttons

I'm not gonna lie it's in rough shape


Someone made a padded top out of vinyl and some fake wood paneling

That was the first thing to go

I've been told it still works but the sound is distorted, I haven't tried it out due to the extremely poor condition of the power cord.
The plan is to clean it up and trouble shoot the issues, not sure if I'll hang on to it though.

First order of business will be replacing that power cord so I can evaluate the sound

I'll keep you posted as work progresses

-Dave

[darwinohm]

Dave, is this basically a tone shaper or does it have some effects? I am not at all familiar with it but it looks to be no later than 70s. It could be an interesting project. If it is all solid state some pot clean up and caps may fix it right up.-- Darwin

[blargfromouterspace]

That's an interesting piece of gear Dave. What is it exactly?

Looking forward to seeing this one progress.

[Dave_P]

Thanks for the responses, it's actually just a PA head, if I remember correctly it came out around 1967ish and was pretty state of the art at the time, one of the first portable PA systems available. Originally it came with a pair of speaker towers. It's 100 watts rms, solid state, has built in reverb and "anti-feedback" filters.

Darwin I think you are right, it won't take much. So far I've identified at least one component that needs to be replaced, a thermistor that prevents the speakers from popping when you turn it on, it's actually almost disintegrated so that was an easy one to identify. The part is $2.56 from Mouser, I had planned on ordering a few items from there anyway but now I'll have to wait til I go through it completely. Grabbed a new power cord while I was at work today, one benefit of working in A/V is all the IEC cables you can carry, I literally have a milk crate full of them, so I'll clip the end off and wha-la! new power cord

Unfortunately I'm all out of solder, so a trip to the store is on the list for tomorrow.

-Dave

[bassman]

I own one of those dinosaurs! A Shure Vocal Master!
It was our PA head back in the 70's They were state of the art for local bands in the late 60's early 70s.
It's about 90 watts and it came with two column speakers with about 4 8's and 2 10's in each.

One word of warning- DO NOT TURN IT ON WITHOUT SPEAKERS BEING CONNECTED! It will SELF DISTRUCT!

The power transistors will pop one by one without a speaker load. I remember that repair.

It's not a bad guitar amp if I remember correctly, I haven't connected mine and powered it up in years.

The two light bulbs illuminate the volume controls for the 6 channels. The orange and yellow switches are notch filters to help control feedback and tune the sound to the room. You also have volume, reverb and tone for each channel.

Most of them were made for Hi Z microphones, but later ones were Low Z and most of these had a VU meter in the front. You can tell if there are cannon connectors in the back or just phone jacks. I think yours is a high impedance model.

[Dave_P]

One word of warning- DO NOT TURN IT ON WITHOUT SPEAKERS BEING CONNECTED! It will SELF DISTRUCT!

Thanks for the warning!

I haven't had any time to work on it yet, it's slow at work the next couple weeks so it may follow me there. You're right it is the High-z model (1/4" jacks), the labeling on the front is all distorted, it looks like it was printed on a vinyl overlay, which is now coming off.
Since this will probably end up in my practice space(save some mileage on the big PA amp) I may just strip it right off and paint/re-label it. I appreciate all the info, I'm hoping the last guy didn't turn it on with no load, if he did at least I know where to start.

-Dave

[Dave_P]

Finally made some progress on this today

Replaced the power cord


and replaced this thermistor with a jumper wire


when I finally get around to placing a parts order I'll get the proper replacement but the manual said I could substitute the jumper, just have to remember to turn the volume off before I turn it on.

Also, as Bassman had said, the light bulbs back-light the controls, the labels are printed on a vinyl overlay and there are slots cut out of the face plate to light them


this ruins my plan of stripping off the vinyl and repainting it, the overlay is in bad shape and you can't really even read most of it anyway, I'll have to be inventive.

Haven't actually hooked it up to anything yet, I was told by a friend these old amps have the potential to blow out your speakers if the transistors are bad. Not sure on how true that is, but I've been reluctant to hook it up to the PA speakers especially since they are not mine.

Can anyone verify if that's true?

Thanks,
Dave

[bassman]

I think the amp will self destruct before it blows anybody's speaker cab. Its only about 100 watts, so I don't think that can happen.

I would suggest connecting it to a bass cabinet or two and then power it up to see if you can get any sound out of it.

It will either work or not and you may hear nothing or a lot of noise if the filter caps are shot.

I don't see it blowing speakers unless you play it too loud through some low wattage cabinets.

I also can't see any modern PA cabinet having any problem handling what a Shure VM can put out.

I think it wants to see 8 ohms on each side, so go with that.

Bassman

[yowhatsshakin]

Reading the Vintage Guitar magazine has made me aware that impedances on older equipment is sometimes 'out if the ordinary'. So in trying to verify bassman's factoid I found this little nugget. Bassman's right. And the author is 'vaguely' familiar .

- Jos

[Dave_P]

Thanks for the info guys! Just what I needed, that post by Boogie Bill was excellent. I have a pair of 8ohm 12" EV speakers I could try out, they handle around 300w rms each so should be safe. No work tomorrow, left the amp there, but Wed. I'll fire her up

-Dave

[nickdawes]

hi there, I have just picked up a vocal master, I have quite a hum but other than that everything works fine. I also have a broken thermistor and would love to know what the replacement part is..

[Dave_P]

hi there, I have just picked up a vocal master, I have quite a hum but other than that everything works fine. I also have a broken thermistor and would love to know what the replacement part is..
hi there, I have just picked up a vocal master, I have quite a hum but other than that everything works fine. I also have a broken thermistor and would love to know what the replacement part is..

These should help you out! the second link is for the replacement part info

http://edmullen.net/manuals/Shure_Vocal ... 300_ug.pdf

http://shure.custhelp.com/app/answers/d ... l%20Master

-Dave

[kylevaughan]

I know this post topic is ancient now, but just thought i would chime in. the sure vocal master does make a pretty decent guitar amp. the clean is not too bad but I have been using mine as a power amp for my digitech 2120 rack effects for years, easily enough power to gig with, and i run it through a marshall jcm 900 4x12. the low end on it is pretty awesome and can stop all over a bassist if dialed in right. the only thing it really lacks is the tone and characteristics of a good tube amp. but for 10$ definitely a good score. I got mine with bother column speakers for $175 CAD about 6 years ago. It has served me well. Also not too sure about the whole blowing up the amp if no speakers are plugged in. Ive done that many times with mine and its never given me a problem. only problems ive ever had with mine is that the pots have gone dirty so now im down to 1 working channel, but for guitar thats all i need.

[Elwood]

Also not too sure about the whole blowing up the amp if no speakers are plugged in.

Tube amps don't like infinity ohms ,sorta like running a motor with frozen wheels.

With solid state it is usually not detrimental , the thing not to do is to hook it up with a very low total impedance , like running a motor downhill in first...it'll heat up and fail eventually ( I've done that at least once).

and...

Welcome to the boards Kyle


elwood

[Boogie Bill]

My, my.....that article WAS well-written, wasn't it?

Brilliant!!!

Bill