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Author Topic: Unicord Power Plus 2X12 amp plus horn  (Read 6779 times)

galaxiex

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Unicord Power Plus 2X12 amp plus horn
« on: February 17, 2016, 09:45:09 PM »
I just won this amp on eBay auction.  :) .... for cheap.  :)  :)  :)  8)

A couple of searches yielded very little information about this amp.
I'm just trying to get a head start as the amp was listed as having issues and I'd like to find a schematic for it.

Here's the sellers words describing the problem.

"In terms of function, this Unicord powers on and passes signal.
But, there is a short somewhere causing squealing- you can hear the short if you tap on the top of the amp.
The reverb squeals as well and the pots have moderate static.
The horn in back does not pass signal."

Possibly an easy fix but of course I'll know more once I have the amp in hand.

Hoping that some of our (ahem) senior members might remember these, or even have a dusty old schematic tucked away somewhere.

Thanks for any help!  :)
If it ain’t broke I’ll fix it until it is.

Enzo

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #1 on: February 17, 2016, 10:03:29 PM »
Well, this senior member thinks your symptom description fits a loose connection, and a schematic may not help/  Flip the board over and resolder the jacks and controls and any other large components.  See if that helps.  After that, tap on the board or flex it with something to see what is sensitive to mechanical shock.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #2 on: February 17, 2016, 10:11:15 PM »
Well, this senior member thinks your symptom description fits a loose connection, and a schematic may not help/  Flip the board over and resolder the jacks and controls and any other large components.  See if that helps.  After that, tap on the board or flex it with something to see what is sensitive to mechanical shock.

Thanks Enzo! this advice will be the first things I try once the amp gets here.  :)
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #3 on: March 01, 2016, 07:05:24 PM »
Well the amp arrived today.  :)

The seller had already powered it up, so I went ahead and did that.

The non effect channel works fine, but the reverb/vibrato channel had some issues.... ::)

After removing the chassis from the box, a little careful poking around with a wood skewer and observing showed a couple electro caps looking kinda swollen.
BTW it all looks relatively untouched, no one been in here messin' wit stuff.

Some further investigation and I found one of the reverb transistors had a loose connection.

Soldered in 2 new caps and fixed the loose connection and YAY! The amp seems to work as it should.  8)
Nothing seems to get too hot

Now the tweaking begins....
The non effect channel sounds ok, but the reverb/vibrato channel has some harsh ice picky treble sounds.

Sure wish I could find a schematic....  ;)

Edit; good call on the loose connection there Enzo!  :)
« Last Edit: March 01, 2016, 07:08:00 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #4 on: March 02, 2016, 12:35:40 PM »
Wow, I have been digging and digging on the intergoogle thing and just cannot find much of anything on these amps.

Searching for "Unicord" gets lots of hits for "Univox" but nothing useful for tech info about this amp.
These seem to be forgotten/lost or more likely, only made for a few years so not many out there.

There does not seem to be an "equivalent" Univox model.

I did find a Unicord Power Plus brochure that is undated but probably from 1970 or so.
In the brochure this exact amp has a badge on the front "DELTA" but not the Power Plus emblem.
The ad shows a retail price of $372.00

I have the brochure in PDF format but don't want to post it cuz the guy that scanned and sold it might not like that.  ;)

So if anyone has some tech info and/or a schematic for one of these I'd be ever so grateful.  :)

Thanks!
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #5 on: March 03, 2016, 03:08:08 PM »
Well I'm holding little hope that a schematic will turn up for this, and really, I don't actually need it, but it sure would be handy.  ;)

Anyways... been playing it a bit now and the effects channel treble control is pretty much useless.
To get a decent sound I have to max the Bass control and keep the Treble on minimum.
Still has quite a bit of highs coming thru.
If I turn the Treble control to max it makes some very nasty harsh squealing noises.
So a quick look for the tone stack and what do I find.... this weird little 6-pin "thing" which I have possibly determined to be a multi capacitor device? (see pics)
You can see the numbers on it and I "think" the 134 is the EIA manufacturers code for Centralab who make caps, resistors and pots.
The rest may be the date code (year) 67, and (week) 32.
The JKE-2 is probably the part number.
Some google searching yielded no info.  :(

So it looks like I have to pull this thing and see if I can sub in some discrete caps for the tone stack.
Any hints on how I should test this thing to figure out how it is wired internally?
Or does anyone have some info on these devices?
I will have to draw a partial schematic to see how its all connected.

Other stuff...
The large metal can trimmers seem to be for bias adjustment and when I checked for DC on the speaker I had 9 volts!
Tweaking those "bias" pots resulted in an immediate improvement in sound, and DC on the speaker fell to 0.012V.  :)
Then a couple of small wipes back and forth and the amp is stable, as is the very low DC on the speaker.
I think they were just dirty/bad contact cuz I didn't move them much and the dirt on top allowed me to set them back to their original position.

Added a 3 wire grounded IEC power socket.  :)

Any help on the tone stack capacitor thingy would, as always, be much appreciated.  :)

Thanks!
If it ain’t broke I’ll fix it until it is.

Enzo

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #6 on: March 04, 2016, 04:18:15 AM »
The guy that scanned it and sold it, I bet didn't own the copyright to the material either.  What could he do to you?  I mean we post schematics and such every day.

J M Fahey

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #7 on: March 04, 2016, 06:33:16 AM »
Quote
I have the brochure in PDF format but don't want to post it cuz the guy that scanned and sold it might not like that.
Agree with Enzo, of course.

So the little thief is worried somebody will get not-his-stuff without paying him?
F*ck off  :trouble

As of tweaking tone controls:
1) if you don't like 60's EQ then stop buying 60's amps, period.
Or just exhibit them in a red velvet, crystal and polished mahogany showcase, under proper lighting of course.

2) yes, that's a multicap package.
Don't mess with it because you'll break it and end up with a unusable amp or at least lose a channel.

3) loved the devil-may-care exposed TO3 metallic transistor cases  :duh, obviously carrying +V voltage.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #8 on: March 04, 2016, 07:31:16 AM »
The guy that scanned it and sold it, I bet didn't own the copyright to the material either.  What could he do to you?  I mean we post schematics and such every day.

Quote
I have the brochure in PDF format but don't want to post it cuz the guy that scanned and sold it might not like that.
Agree with Enzo, of course.

So the little thief is worried somebody will get not-his-stuff without paying him?
F*ck off  :trouble

As of tweaking tone controls:
1) if you don't like 60's EQ then stop buying 60's amps, period.
Or just exhibit them in a red velvet, crystal and polished mahogany showcase, under proper lighting of course.

2) yes, that's a multicap package.
Don't mess with it because you'll break it and end up with a unusable amp or at least lose a channel.

3) loved the devil-may-care exposed TO3 metallic transistor cases  :duh, obviously carrying +V voltage.

Well, the guy that has these vintage brochures and catalogs charges a small "donation" fee.
I was merely "trying to do the right thing" ... as if I were the guy that had these things in my possession and went to the trouble to scan and make available, I wouldn't want some wanker to post them all over the internet so any schmo could have them for free.
I certainly was not worried about copyright etc.

But I see your point, this stuff was distributed for free back in the day so now that it's 30-40-50 years later and so much of this stuff is long gone it should still be free even tho he went to the trouble to make it available again....

Of course people do that every day with schematics and such, why should this jerk make anything from some ancient brochure?

Do you consider it a "rip off" to charge a small fee for that? Am I wrong for wanting to "trying to do the right thing"?

Sure, it's not all that likely there would be a massive download of the brochure if I posted it here.  ::)
How much would he "lose" if I posted it here...... maybe he's getting rich from this.... 


Pretty harsh words JM. Have I offended you?

It's not that I don't like 60's EQ.... it's that I think there is something wrong with this one, as the non-effects channel seems to be laid out exactly the same as the effects channel, and even has the exact same multi cap device.

Sorry I didn't mention this before, but the non-effect channel sounds fine and has a very usable range of tones.
Turning the treble control to max on the non-effect channel it gets very bright but unlike the effect channel where at max treble it makes harsh squealing noises.

Since the multi cap package is so-far made from unobtainium, I was hoping/looking for ideas to replace it so that the controls operate "normally" whatever that may be.
I can't imagine that the nasty squealing noises are normal. Maybe I'm wrong there too...

Anyway, my next step is to swap the 2 multi cap devices to see if the problem follows the device.
I have a good vacuum de-soldering tool and can get them out without much risk to the board, or to the device.
I'll report on that when I've made the swap.

Oh, and to show how much of a wanker I am, here's the brochure... ;)

Oh No! it's 5.4MB and the forum won't let me post it.  ::)

I'll see if there is some other way to show it.... or you could go here... http://www.musicmansteve.com/catalogs/OtherCatalogsEnew.htm

and pay the small donation for it.
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #9 on: March 04, 2016, 09:31:38 AM »
Well swapping the multi cap devices resulted in no change.
I actually expected this. The squealing noise with treble on max sounded too much like a failing semiconductor or other device.

So I started looking at the transistors (4) on the effects channel pre-amp board.
They are all Ge pnp.
There is no labeling on the boards except for on the solder side where they saw fit to include C-B-E markings.

The transistors all appeared to have the collector leg marked with a small red dot.
Closer observation showed the transistor closest to the multi cap device had the C and E backwards from all others!

The solder looked like it had never been touched so I assume it was installed wrong from day one.

A quick removal and flip it around and walla! The effects channel now sounds the same as the non-effects channel.
No more squealing with the treble on max.

Case closed. Time to button it all back up, after playing for a bit to ensure nothing else is amiss.

BTW, this amp has a true optical Vibrato circuit. The effect is relatively subtle but interesting.
You can hear the pitch change "warbling" sound better on the Bass notes.

I have never played with this type of effect before and not sure I like it as compared to Tremolo.
Maybe it will grow on me.  ;)
« Last Edit: March 04, 2016, 09:35:03 AM by galaxiex »
If it ain’t broke I’ll fix it until it is.

J M Fahey

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #10 on: March 04, 2016, 01:27:20 PM »
Sorry if it sounds harsh to you, definitely not the case, in fact the exact contrary, and I was trying to help you not waste time.
Maybe ignoring the fact that collectors want to waste time on something, my fault.

After all, "modding" something where the schematic is not available, the parts are mysterious and unobtanium, you have no clue how it works or how parts will change sound and the definite possibility of cracking the mystery part while grabbing one leg with long nosed pliers pulling it off the board (what for anyway?) ... what's the point?

And you are not repairing anything, jus don't like it as it is.
Am I missing something?

My answer was friendly, honest, and straight to the point.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #11 on: March 04, 2016, 04:44:31 PM »
Sorry if it sounds harsh to you, definitely not the case, in fact the exact contrary, and I was trying to help you not waste time.
Maybe ignoring the fact that collectors want to waste time on something, my fault.

After all, "modding" something where the schematic is not available, the parts are mysterious and unobtanium, you have no clue how it works or how parts will change sound and the definite possibility of cracking the mystery part while grabbing one leg with long nosed pliers pulling it off the board (what for anyway?) ... what's the point?

And you are not repairing anything, jus don't like it as it is.
Am I missing something?

My answer was friendly, honest, and straight to the point.

JM, sorry if I misunderstand you.

I think I need to make my intentions clear at this point.

I am here because there is no other forum dedicated to SS amps.
I'm am amateur at this.
I like to tinker. That is true. I have just enough knowledge to be dangerous,
but I like to learn more, and working on this stuff is fun for me. I don't make a living at it, it's just a hobby.

I like to take these old "worthless" cheap, ancient dinosaur amps, broken, not working, or working badly, and make something that is actually usable.
The folks here are friendly and have a wealth of knowledge and experience that they freely share.
In turn I try to share things I have learned from doing, and reading, and show the stuff I have worked on.

I have freely posted schematics of "nothing/worthless" amps, that I have painstakingly drawn by tracing the circuit layout and transferred to schematic program.
Any use to anybody? I don't know.
But those schematics might not be out there if not for my eccentric hobby.  :)
I know I couldn't find them, after extensive searches.

I also know I learned A LOT from doing that.

The threads I started for the National GA920P schematic and the Teisco/Audition amp schematic both have quite a few views.
Did those schematics help someone? I'd like to think so, else why so many views?

I don't mod every one of these amps that come my way.
Case in point; I have a National GA920P that I very much like the sound of, just the way it is.
I have another almost identical that sounds like sh*t.
THAT one will get some mods, for better or worse, my amateur hands will get in there and either make it sound better or muck it up so badly that no one can fix it.  ;)

I will take issue with this...

Quote
And you are not repairing anything, jus don't like it as it is.
Am I missing something?

In the case of this Unicord amp, I am indeed repairing it.
I thought that was clear from the first post where I said it has issues.

Tho I can see where one could misconstrue my intention when I mentioned "tweaking" it.

What I really meant was to tweak it to make it sound more like it should.
The harsh squeally treble could in no way be taken as "normal" esp as the other channel did not exhibit such behavior.
But you wouldn't know that, having not heard it.

So as my post above shows, I now consider it "fixed" and no more "tweaking" needed.
Turned out it didn't need tweaking after all.
Just some careful observation (which I have learned from this forum) and a transistor reinstalled right way round.  :)
And a good lesson for me, don't trust that the thing was made properly in the first place.

The amp now sounds fine, maybe not a great tone for me, but stick a pedal in front of it and it's great!
It does take pedals rather well. I won't be attempting to "make it better", it's already good enough.

What do I get out of it?
The satisfaction of having taken something that was otherwise worthless... and made it less worthless. (debatable)  ;)
It now functions (to me) as it should and what a great learning experience.  :)

One more thing...

I am (not to brag) excellent at getting thing apart with no to minimal damage.
I have excellent mechanical skills.
My job of 35 plus years as a transmission mechanic has taught me much about how to take apart tricky and complicated assembly's.
Getting delicate parts removed from a circuit board without damage is almost second nature to me.

I understand that you make a living at this, and for you, what I am doing must surely be a waste of time.
(worthless old crappy amps that sound like sh*t... why bother...)  ;)

Sorry for the long post, and Thank You for not wanting me to waste my time, but as you can see, all this is not a waste of time for me.
I LIKE doing this.  :) 
(Crazy stupid Russian)
« Last Edit: March 04, 2016, 04:46:19 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

cejay825

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #12 on: March 04, 2016, 04:55:20 PM »
Well said galaxiex......do what you want to do

J M Fahey

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #13 on: March 04, 2016, 08:24:34 PM »
Quote
for you, what I am doing must surely be a waste of time.
(worthless old crappy amps that sound like sh*t... why bother...;)
Well, I'm somewhat confused about what you are talking because I never ever said that about your amps , I dare you to show the post or shut up.

My answer was specifically about not messing with an unknown part , which does not look frayed or broken

I wonder what would you "repair" by substituting a working, factory set part by unknowns .

Changing a perfectly working part for something else to change the sound rates as tweaking/modding, not repairing, in my book and I guess in  most others.

galaxiex

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Re: Unicord Power Plus 2X12 amp plus horn
« Reply #14 on: March 04, 2016, 08:59:11 PM »
Quote
for you, what I am doing must surely be a waste of time.
(worthless old crappy amps that sound like sh*t... why bother...;)
Well, I'm somewhat confused about what you are talking because I never ever said that about your amps , I dare you to show the post or shut up.

My answer was specifically about not messing with an unknown part , which does not look frayed or broken

I wonder what would you "repair" by substituting a working, factory set part by unknowns .

Changing a perfectly working part for something else to change the sound rates as tweaking/modding, not repairing, in my book and I guess in  most others.

JM, I apologize. This >
Quote
worthless old crappy amps that sound like sh*t... why bother...  ;)


...was meant as humor and sarcasm directed at myself. Perhaps that wasn't obvious, in hindsight, I could have worded it better.

Sure I get that an amateur should not mess with an unknown unobtainium part.
Did you read the other post above where I carefully removed the 2 unobtainium parts and swapped them to determine IF they were the problem?
Discovered that they were NOT, and then found the REAL problem, fixed it and all is well?

I merely asked for advice/info about the unknown part and, OK, I did talk about changing it IF it were bad, but if you had bothered to actually read my post above, you would see... that...well... all is well.

Until I swapped them I didn't KNOW that the part was bad or not, and was kicking around for ideas about what to do to substitute for it, IF it WAS bad.

Do you not substitute parts to find a problem sometimes? In essence that is what I did.
It gave me a clue to look elsewhere for the problem.

And again, the sound from the amp was BAD,
not just junky old amp bad,
not just, "I don't like how it sounds so I'm gonna mod the SH*T out of it,
but "Broken part somewhere" bad.

Can parts not fail and still look ok?

I didn't know where to look, the weird part obviously had something to do with the tone stack, which is what I suspected all along, and it turned out to be a transistor installed wrong, right in the tone stack circuit. That transistor is probably the tone stack output buffer or whatever you want to call it. I have not actually traced the circuit but it IS hooked directly to that cap network.

Jeez get the bee outta yer bonnet. The amp is REPAIRED. NO MODS WERE DONE.

I was just askin fer chris sakes!
If it ain’t broke I’ll fix it until it is.