Gibson Plus 50 /What Is This?

[plexi50]

Looks like trouble to me. Havent had time to turn it on yet. I was told it squeals like a pig with wings

[archaos]

Looks like trouble to me. Havent had time to turn it on yet. I was told it squeals like a pig with wings

With wings ?

Well, that's not so common, is it ?

 

[Geezer]

Gibby sand state probly just needs a cap job... 

[P Batty]

I had one of these back in the 60s.  It is an amp booster, 50 watts into 2 pretty good 10" speakers. Made a Champ nearly as loud as a Twin.    You could piggyback these and make an insanely loud stack.   I ended up using mine with a clock radio!

[plexi50]

I turned it on and major hum. Has a pulsating vibrato effect going on as well. Goes to show how bad caps can effect tone. I'll work on it tommorrow. Interesting old piece and yeah cool speakers

[plexi50]

Tacted in 2 1000uf  PS caps. Turned on and still very loud hum. This has been tinkered with in the past. Probably needs a lot of parts replaced

All ceramic resistors read good and within there values + -

[HotBluePlates]

I ended up using mine with a clock radio!

You must have a really hard time waking up in the morning if you needed a 50w clock radio! 

[PRR]

Check for DC on the output.
Replace _all_ the electrolytics.

EDIT: see http://www.el34world.com/Forum/index.php?topic=15111.msg145583#msg145583

[plexi50]

Check for DC on the output.

Replace _all_ the electrolytics.

Yes Sir!

A giant clock radio? You could wake up the entire neighborhood with just the hum it produces

[eleventeen]

The Sylvania "ECG" output transistors are, as you say, a clear sign of a previous repair. Plus it would appear like they have a "92" date code on them.  Transistor amps can be tough. Stick a scope probe in there and most everything has the same or very similar waveform. Very often, if the driver transistors for the outputs go out, they blow up the output elements.

[PRR]

It has a driver transformer.


http://www.istockphoto.com/stock-illustration-12307190-flying-pig-with-wings.php

Changed my mind.

Verify that the rectifiers and two large caps deliver + and - 30V (or so). If you have a couple 100 ohm 10W resistors, load both sides and see if it still delivers the voltage (slightly sagged).

Then get a LM3886T amp kit: a chip and a PCB, ready to apply power and rock-out.
http://www.ebay.com/sch/i.html?_trksid=p4634.m570.l1313&_nkw=LM3886T+kit

You don't want stereo, you don't want a heatsink, you don't need the big capacitors (unless that is easier than re-capping the existing PCB). Screw the big chip to the Gibson aluminum L-bracket, wire the wires to power supply and in/out jacks.

This is, apparently, an amp booster, not a complete geetar amp. It goes to the EXT AMP jack on many older amps. It would probably take speaker level from a clock-radio, if you wish. If you want a preamp so as you can play guitar, study Peavey and other adequate chip-based guitar amps and plagiarize a front-end.

[plexi50]

Look at the non existant terminal strip and parts on this other Plus 50. Interesting!
The back panel is on again. I cant see right now if this was added on by someone as some kind of mod.
The high resolution picture shows the wiper of the pot going straight to the board

[plexi50]

I found an hole that someone drilled on the front panel under the volume knob and to the left. Ive been busy all day putting in a new washing machine and i just noticed it. Taking panel off later this evening and wiring the wiper of the pot right and bypassing that weird circuit

[plexi50]

Finished and sounds very LOUD and deep. Depending on the volume that is. Nice balance between amp i used to patch the booster. Sure weighs a ton though

[P Batty]

Now just plug the headphone out from your clock radio into it and you'll never oversleep again!

[plexi50]

It has a place with a dolly or shopping cart if you want to get that dimensional two way tone. I think just A/B ing two different amps is the only way to go for me. A princeton reverb and my Classic 50 Peavey head using a 2x12 cab is heavenly through a stereo chorus pedal

[PRR]

> terminal strip and parts on this other Plus 50. Interesting!

One-transistor preamp. Gain about 10, input Z under 100K.

Not enuff to bring a normal guitar up to the level this power-amp probably needs.

> Finished and sounds very LOUD and deep.

Well, good on you then.

The more I looked at that antique, the less I liked de-bugging its acquired and intrinsic flaws.

Bias is guess-and-gosh (and smoke). There is NO short-protection. Distortion numbers are probably not what you expect in today's gear. In every way I am SO glad those days are behind us.

But if it works, it's good.

[plexi50]

It's a good thing i started looking for completed sales on Ebay. Thats where i found good high resolution pics. None of them had that funky terminal strip. Sounds more like a full blown PA at medium to full volume levels. One thing i can say is you wouldnt know it is on when it is. Very silent until plucked