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Any info on this old Telestar amp ?

Started by LJN, January 05, 2015, 10:03:27 PM

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LJN

Hi all. I recently picked up this odd little amp at a local pawn shop for 10 bucks. I've never seen one like it before and I wonder if anyone on here knows anything about it. When was it built, and who built it ?
It looks to me like it's been modified at some point. It has a built-in tremble circuit that looks home made,and three instrument jacks.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

Roly

{get a lot more light in there, better from two direction, use "flower" macro mode if your camera has it (most do these days)}


Impressions/observations.

The case most likely started out with some cheap Asian build, but it has been given a very major working over by somebody.  The name suggests the '70's, but could be anytime.

pic 139
Oh noze!  The speaker doesn't fit the hole!  Obviously not original, and the massive air leaks around it will be making the amp sound thin, and giving the speaker a hard time.  So it needs a speaker that fits (but you can use an external speaker cab for testing pro tem).

pic 140
This is certainly a home brew ring-in and the only way you are going to get the circuit is trace it, however five will get you ten it's a conventional Phase Shift Oscillator;



... the only real question is how it applies its output to the passing guitar signal.

Pic 139a
The main PCB is a corker.  Whatever it was supposed to be for originally, it has clearly been pressed into alternative service here, no components where there are overprints, components where there are no overprints, components that don't match their overprints.  Again its circuit trace time.  This page;

http://www.ozvalveamps.org/repairs/solidstateamprepair.htm

...may help by giving you some clues what to expect.

The Fender knobs are a cute touch.


I think you have two options with this $10 score (  :dbtu: ); try and make a silk purse out of a sows ear and "repair" what is there.  This means that you will really have to trace the circuit of each of the boards to get a handle on what has been done.  I read this as a "roughie" that has been done for zero dollars by somebody who actually is comfortable enough with electronics to re-purpose a PCB, so the actual circuit might be okay, you just don't know until you get a reasonable trace.  The upside should be that it will be very conventional, no real surprises once the arrangement used is recognised.

(and/or) The other path would be to measure the voltage(s) out of the power transformer and knock up some new modules to suit your tastes, small power amp, preamp, Fx, and give it a (documented) transplant.

HTH
If you say theory and practice don't agree you haven't applied enough theory.

LJN

thanks for the reply. the amp actually does sound pretty good, but a little too dark for my taste. it handles my bass extremely well. the tremors stopped working yesterday so I will have to repair that now. thanks again.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

J M Fahey

A friend bought a car for $100 and asked what preventive maintenance he could do.

Another (good) friend answered: "just *looking"at it is upwards of $100 and it will definitely need work done.

But it works perfectly so far, so my honest suggestion is you feed it gas, water and oil as needed, keep the tires inflated, wash it sometimes and plain use it.

The day it gives you any real problem (loss of oil pressure, engine overheating, etc.)  just park it somewhere, leave the keys in the ignition, doors unlocked, and a sign: "do not break windows to get in, this car is free for anybody who can use it".

Any similarity might not be a coincidence.

Roly

As it's working I'm inclined to agree with JMF.

Quote from: LJNtremors

That's what I get after I touch high voltage.  :lmao:   Tremolo here, but from the same Latin root tremulus "trembling".


The way it's built I'll bet a couple of component leads are touching that shouldn't be - might be obvious, just give it a very close inspect with your commonsense turned on.  Doesn't take much to stop an oscillator.


Quote from: LJNthe amp actually does sound pretty good, but a little too dark for my taste.

Without a circuit it is almost impossible to make any suggestions - almost.

If by "dark" you mean it has a tilt to the bass or away from the treble, then you could try applying a bit of top-coupling, and an obvious place to try this is at the volume control (which is very easy to identify), by adding a small cap, say 220pF to start, between the ungrounded (max, top) end of the pot and the (middle) wiper.  This might make it a bit brighter.  If it does but it's not enough, increase the cap, too much, reduce it. 

HTH
If you say theory and practice don't agree you haven't applied enough theory.

LJN

thanks. I built a treble booster to use with it. that was supposed to say tremolo,  not tremors.  sorry about the typo. I believe one of the transistors in the tremors circuit blew out. I pushed the amp a bit too hard. it still works, but no tremolo.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

Roly

It is effectively impossible to damage the tremolo oscillator no matter how hard you drive the amp.  The way it's built it is much more likely that two leads are touching that shouldn't be (close inspection), and if they aren't touching now then they may have damaged the oscillator transistor when they were.

Probe the three legs of the transistor measuring the voltage to ground.  One lead, the Collector, should be higher than the others and may be jumping around in value.  If so this suggests that the Low Frequency Oscillator (LFO) is actually working but its output isn't getting applied to the passing guitar signal.

Post results and we'll proceed from there.

It would be very helpful if you could post some crisp brightly lit (a couple of desk lamps from opposite sides) pix of both sides of the main board, square on view, full frame (use "tulip" macro mode if your camera has it).  A similar pic of the tremolo birds nest would also help with that.
If you say theory and practice don't agree you haven't applied enough theory.

LJN

If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL