Bunch of dumb amp questions...

[danglybanger]

Well, it's finally here... the least covetted amp in Fender history, the tubeless, speakerless, knobless wonder... the 1970 Fender Libra! (of those three things, it ought only be tubeless... though I figure I've got enough knob myself for anyone :laugh2

Anyways, I know absolutely nothing about amps as it turns out... so before I stick speakers in here (leading me to my first question: they're 12"s, how should I know what kind of speaker to get?)

A few other questions so I don't blow myself up with all the switches. I don't know if these are generic amp questions or just ones that apply to this completely insane amp, but please help me out here...

First off... what the hell is this? (switch on left not power switch :smack I know it switches the grounds, but what ought to be the difference between 1, N, and 2 and why should I need to switch? How do I know when to do that?

two little jacks marked vibrato and reverb. Why???

Actually... maybe so these jacks can go into them?

But they also go into this... which is... uhh... what is this? :eek13: I've been told it's a spring reverb, and that makes sense because it makes a springy sound when you pick it up... This is how it was when I got it, hanging precariously on these two screws... is that really where it goes? Should it be tightened down at all? Why is the bottom of it lined with cardboard?

But how do I know which leads to put in which end, if that's how that goes? There are jacks labeled input and output, but the leads conveniently are not labeled at all. (And yes, the foam on the back is basically 70s Jaguar mute foam from the looks of it... and just as rock hard :laugh2 And why does it have its own pleather case

uhh... that ought to be about it. If you guys are nice I might give you sound clips. Maybe they won't sound like crap :laugh2:

thanks,

Slade

 

[Closed Eye]

Re: Bunch of dumb amp questions...

just...odd. What's it sound like?

 

[Gearjoneser]

Re: Bunch of dumb amp questions...

First, the ground switch is like a polarity switch, so if anything in the room is shocking you, like a microphone, you switch it the other way.

Once you put speakers, like Jensen or Eminence in it, and make sure the reverb tank is connected, turn it on. You can buy knobs at Sam Ash or GC for it.

Be honest, how much did you spend on it?

 

[danglybanger]

Re: Bunch of dumb amp questions...

thanks for the advice on not electrocuting myself...

Yeah, I know plenty of places to get solid shaft knobs... I'm thinking witch hats. Originally it had Bronco knobs, which were worth $25 a piece to the right person, which was the only reason my friend bought it...

After deknobbing it, it was sold to me for $100. It's worth the novelty to me anyways He bought it for $250 which was enough to break even on the knobs, and made $100 profit by selling the hulk to me.

So... those little jacks at the back don't really matter eh. Will hooking up the reverb tank backwards kill it?

on the plus side it's making my house smell like cigarette smoke

I need to break out the headphones to figure on how it sounds, but I'll try and pick up speakers tommorow anyways.

thanks,

Slade

 

[greco]

Re: Bunch of dumb amp questions...

Cool amp. I'll try to answer some of your questions, but please wait for a real amp guru to comment as I'm just a beginner and wouldn't want you to try things on my advice.
Hopefully ScottF or another true amp guru will read this.

I think that the 1-N-2 switch is a ground lift switch. Does it stay in the N (centre) position ? If it does than I'm not sure as Iv'e never seen a 3 way toggle used in this way...not that that is helpful or means much.

The RCA jcks on the back for reverb anf Tremelo might be fro a foot switch. Also, the reverb and tremelo might not work ulees the plugs are in ad turned on. You can do this by shorting the wires connected to an RCA plug ( outer ground shield to the centre connector) and then plugging them in (unless you got a foot switch with the amp). My Super Reverb is like that.

The reverb thanks often have cardboard under them. I'm not sure why,. Possibly just to reduce vibration from the amp ??? The covers are also typical. Possibly just to keep dust out...just guessing again.

The reverb tank has two wires ..send and return... they don't go into the reverb and tremelo jacks, but they have RCA jacks on them ...anyplace else on the outside of the chassis that has this type of jack in a pair side-by-side...they might be colour coded...which colour goes where will need to be answered by the guru I'm hoping will read this.

I think that most tanks have four screws. You might get some info. from the Accutronics site as they make several models of reverb tanks. Is there a brand name on the tank?

Did you Google for info about the amp? Like an owner's manual, ....or.....well......anything.

Keep us posted as to you progress with bringing it back to life.

Good Luck

I'll be following this to see what the other responses are.
Live and learn.

Dave

 

[danglybanger]

Re: Bunch of dumb amp questions...

heh... thanks. The only things I can find out about this amp are that they were made for less than a year, were semi experimental... it was the top of the line of the "Zodiac" series which had Taurus, Sagitarrius, Gemini, Scorpio amps etc...

No one knows anything :laugh2:

Yeah, the ground lift switch has an N center position that it sticks in. I've got another old solid state amp that has a similar switch, but it's only two places and I never learned how to use it.

So without the footpedals reverb and vibrato might not work unless I short something out? :smack:

Those two RCA jacks are the only two that are present on this amp... They will reach the vibrato and reverb inputs, but they'll also go in the reverb tank.

The reverb tank by the way has no names on it, and no mounting holes... It just seems to stick to the side of the amp by being wedged between two screws, and would be able to fall off if you knocked the amp wrong :smack: I'll look up accutronics.

Will keep you posted

EDIT: this is new since last time I looked: http://fender-freak.seesaa.net/article/8724222.html

Slade

 

[greco]

Re: Bunch of dumb amp questions...

heh... thanks. The only things I can find out about this amp are that they were made for less than a year, were semi experimental... it was the top of the line of the "Zodiac" series which had Taurus, Sagitarrius, Gemini, Scorpio amps etc...

No one knows anything :laugh2:

Yeah, the ground lift switch has an N center position that it sticks in. I've got another old solid state amp that has a similar switch, but it's only two places and I never learned how to use it.

I think that this should be the least of your concerns at the moment

So without the footpedals reverb and vibrato might not work unless I short something out? :smack:

That is what I think..the tremelo works that way on my amp for sure as I dont have a foot switch.
Those two RCA jacks are the only two that are present on this amp... They will reach the vibrato and reverb inputs, but they'll also go in the reverb tank.

Need to wait until someone else responds. Are you sure there are no other jacks on the chassis? Maybe some other type of connections for wires that are close to each other ??

The reverb tank by the way has no names on it, and no mounting holes... It just seems to stick to the side of the amp by being wedged between two screws, and would be able to fall off if you knocked the amp wrong :smack: I'll look up accutronics.

The pic looks like the tank has some holes in the flange. No ??

Will keep you posted
Thanks, cool amp at a good price. I bought an Italian FARFISA amp for $30.00 Canadian for a friend..( 2X12 Combo) it sort of works..but he prefers to use it as an end table. lol

EDIT: this is new since last time I looked: http://fender-freak.seesaa.net/article/8724222.html

Haven't looked at this. Will do.
Slade

Dave

 

[rainsong86]

Re: Bunch of dumb amp questions...

please don't turn on a tube amp with no speakers connected to it.. and a pair of headphones surely won't suffice for a proper load.. make sure when you buy the speakers you match the impedance.. you'll have to consider how you wire the speakers (parallel, series, or a combination of both).. you might have to wire the speakers JUST SO THAT you can effectively match ohms.. for instance if the amp runs at 8 ohms and you install four 8 ohm 12 inch speakers then you can wire two sets of speakers in parallel with one another (resulting in two 4 ohm 2x12s) and then wire those sets together in series (resulting in a total impedance of 8 ohms)

 

[J Moose]

Re: Bunch of dumb amp questions...

WOW!


I've NEVER seen one of those outside of a repro catalog!


Another CBS-era idea that went south...


Don't know anything about them! LOL


Speakers...hmmmm...are there any markings on the rear panel tha indicate wattage, ohmage or any of the other "standard" markings?

The two RCA jacks probably ARE for turning the vibrato & 'verb on & off and those might not work without something connected...

They might not work at all anyway! LOL

You won't blow the spring verb up if it's plugged in backwards...or at least you shouldn't. If it's backwards it should just not work.

 

[danglybanger]

Re: Bunch of dumb amp questions...

please don't turn on a tube amp with no speakers connected to it..

it's not tube But thanks for the info on ohmage...

I've NEVER seen one of those outside of a repro catalog!

for a minute thought you meant they actually reproduced these things :laugh2:

anyways, yeah... it says 105 watts, "min impedance on both jacks 4 ohms". Hmm... so that means I can wire 4 ohm speakers anyway I like basically?

So... to short out the jacks for the footpedals if it turns out I need them... just take an RCA jack and... short it out? or is it more complicated than that...

Should footpedals from other amps work too?

thanks for the advice, I'm slowly figuring out how to make this work

Slade

 

[Scott_F]

Re: Bunch of dumb amp questions...

A standard fender footpedal jack ought to work. They make several reproductions with rca jacks instead of modern 1/4 inch jacks.

Reverb tank hanging is a little odd, but tanks are specifically made with an orientation. Some hang like bats, some sit on the bottom like turtles, so I suppose that they make some that hang vertical like that. YOu can check the code versus the accutronics website. The reverb cables probably plug in underneath the chassis somewhere.

Plugging in the reverb wires backwards shouldn't matter, it'll either work or not. The jacks labeled vibrato and reverb are for pedal. See pedal comment above.

On the speakers, 4 ohms total minimum is what I think it's saying. Do not use headphones. Get 4 eight ohm speakers and wire up one pair in parallel, one in series and the combined impedance will be 8 ohms. What the warning is ssaying is not to plug in another outside cab such that the total impedance falls below 4 ohms. Im guessing it was originally shpped at 8 ohms on the 4 internal.

You can test the amp by just plugging one 8 ohm speaker in and seeing if it works.

Comments on the back jacks possibly needing a pedal to make the effects work are valid. Some old Fender amps had to have something plugged in there. Joe comments about rigging up a jack. I've got one here. I took an old crappy stereo patch cable, cut off each end with an inch or so of wire remaining and then took that one end of wire and soldered the core piece to the braid that surrounds. It's called a shorting jack and you use it to test the function effect and it eliminates the need to have a wired pedal hanging off your bench.

Sounds like you've got a little project on your hands. I wonder what the amp sounds like. My guess is that if they didn't make many of them there was a good reason. don't spend stupid amounts of money trying to make it sound like something its not.

 

[danglybanger]

Re: Bunch of dumb amp questions...

thanks Scott, the leads to the reverb tank aren't long enough for it to sit anywhere else as it turns out...

Good to know the pedals aren't made from unobtainium

Yeah... I briefly considered going for the original JBL speakers, but then I started thinking... how much is this thing worth anyways :laugh2: I'll pick up the cheapest 12"s I can find (and now I know how that whole ohm thing works... )

thanks,

Slade

 

[Scott_F]

Re: Bunch of dumb amp questions...

I think avatar speakers had a diagram for how to wire up four 8 ohm speakers for a total load of 8 ohms.

http://www.avatarspeakers.com/wiring diagrams.htm

 

[greco]

Re: Bunch of dumb amp questions...

Looks like you are getting lots of great advice.

I'm also feeling good that the advice I gave was not too bad for the most part. I'm just starting to study amp. electronics/building as a hobby.

Maybe someone will comment quickly on the cardboard and cover associated with the reverb tank, and more about the 3 way toggle switch (as asked in your original qustions with pics). I'm stiil very curious to know the correct answers myself.

Schematic Connection website lists the Fender Libra schematic for sale for $10.00 ....in case you need it.

Dave

 

[Scott_F]

Re: Bunch of dumb amp questions...

I'm not sure on the cardboard bottom to the tank. Seems fairly useless to me unless they were afraid that a bag might somehow make contact with the springs.

From my perspective, the reverb tank bag is a dust cover. It should also help dampen vibrations as well. Then again, I've seen a lot of new amps that have neither.

 

[J Moose]

Re: Bunch of dumb amp questions...

Yeah... I briefly considered going for the original JBL speakers, but then I started thinking... how much is this thing worth anyways :laugh2: I'll pick up the cheapest 12"s I can find (and now I know how that whole ohm thing works... )

Two words dude.


Radio Shack.



Kurt Cobain used to tour with them in his 4x12's...


But he also used to stick his guitar into 'em headstock first...

Soooooooo...

:laugh2:

But if 'ya want cheap that's a GREAT place to start. And who knows...maybe it'd sound rad with a Rat Shack speaker and fuzz pedal.

 

[WORSHIPTEAM]

Re: Bunch of dumb amp questions...

Two words dude.


Radio Shack.



Kurt Cobain used to tour with them in his 4x12's...


But he also used to stick his guitar into 'em headstock first...

Soooooooo...

:laugh2:

But if 'ya want cheap that's a GREAT place to start. And who knows...maybe it'd sound rad with a Rat Shack speaker and fuzz pedal.

+1
I had an old Kustom cabinet and head that I used 4 Radio Shack speakers in. It lasted for a couple of years worth of gigging before I sold it. You could tell the difference as opposed to more expensive speakers (I actually love Peavey Black Widows:27: ) but the are playable.

 

[danglybanger]

Re: Bunch of dumb amp questions...

thanks everyone for the good advice (And wow, someone DOES remember the libra enough to actually sell schematics for it...) Useful because I've heard these things uhh die alot.

hmm... radio shack... and I can be just like teh kurdtz :laugh2: Actually I headed by an amp repair shop today, who told me they would sell me some 12"s, but not while their techs were on lunch break. Can't come back later unfortunately (posting in class, shh!!) so I'll prob pick up some of those tommorow if I don't decide on shack speakers.

Slade

 

[greco]

Re: Bunch of dumb amp questions...

"VINTAGE FENDER LIBRA 4x12 GUITAR COMBO AMP--TREM REVERB $149.00"

Found this while surfing the net. The word "vintage" certainly takes this amp to new heights...the price doesn't seem to reflect the vintage entitlement

How is the repair work going?

Dave