info on old gibson ss amp

[bballkvn]

i just bought this old gibson amp from my friend for 50$ The model is Gibson Plus 50. ive done alot of looking around the internet and all i have found out is that.

it is a ss slave amp
50 watts
2x10 speakers
1966-1967
made in Kalamazoo Michigan by maestro
it was probably used for both guitar and accordion

there is a wiring diagram on the gibson website.
http://www.gibson.com/Files/schematics/Gibson%20Plus%2050.pdf

if anyone could tell me anything more about it would be awesome. heres are some pics.










thanks for any info you have

[teemuk]

it was probably used for both guitar and accordion

No. Like you said, it's a "slave" amp: You plug it into the line level output (or maybe even the speaker output of another - in this case Solid-State - amplifier) and it works as an additional, rather transparent power amplifier and speaker cabinet. This is why it doesn't even have tone controls and stuff – they are in the "master" amp. As is, it won't work (properly) with a guitar since there is a terrible impedance mismatch and likely not enough gain either. I never played accordion through an amp and I'm not familiar with its input properties so can't comment on that. It's a nice amp I'm sure, but without modifications it is not suitable for the tasks you hoped to use it in.

I'm sorry to be the messenger of bad news.

[bballkvn]

yeah its really bassy sounding. i plugged in a distortion pedal with top boost and managed to get a good distortion sound out of it.

this is the oldest amp ive ever played on do you think i should worry about blowing the speakers because im thinking it might be worth some money?

how exactly do i connect it to another amp with just a regular guitar instrument cable from the output? right now i use a vox valvetronix 30watt amp but if i could use this i might not have to mic my amp if i play a gig.

[nashvillebill]

Okay, I hope you come back and read this reply...

On the back of your Vox there is a jack labelled "line out" (I think, I couldn't find the manual for the 30 but I found the manual for the 60).  Plug your cable into it.  Plug the other end of the cable into the jack on the Gibson marked "input".  I think your Vox has a knob by the "line out" jack labelled "level".  Use this to adjust the volume on the Gibson.

DO NOT plug the cable into the "Speaker Out" jacks on the Vox.  DO NOT plug anything into the "Output jack" on the Gibson.


Caution.  This Gibson is 40+ years old.  It almost certainly needs to have some internal components replaced.  These components, called "electrolytic capacitors", start to dry out and fail after many many years.  If you hear a hum from the Gibson, it's because it needs these capacitors replaced.  This is commonly referred to as "recapping".  The caps themselves aren't terribly expensive but shop labor rates will make this cost around $150 or so (maybe more).  Unfortunately, all amps of this vintage will need new electrolytic caps.   And to make it worse, these caps can fail quite catastrophically.

[teemuk]

Nashvillebill, it's good that you brought up the issue about electrolytic caps drying out. It's definitely a thing that should be fixed in amps that are as old as this one. Also, it's not the only thing that may have gone south so a complete overhaul is likely required. It may be that some component values are drifted and the bias adjustment is definitely worth checking out. Unfortunately the schematic doesn't state any required reading for it. Do some cleaning of the internals and some visual inspection of the components. If the thermal paste of the output transistors looks old and "chipped" it might be wise to renew their whole contact to heatsink.

If I have understood correctly this is a "combo" amp and the speakers are permanently fixed to the output stage. If you look at the schematic, it shows that the output jack is simply wired in parallel with the input jack. Makes sense considering the overall "slaving" concept.

The comments I read concerning this amplifier state that it is indeed used by connecting a coord from the external speaker output of the master amp to the input of the amp. Sounds odd and risky, I know. If this is done with a tube amp it should be made sure that a plug in the external speaker jack does not disconnect the tube amp's own low-impedance speaker load. Anyway, that advice is based on hearsay I don't know how accurate the information is. Back then stuff like "line level" outputs was not that common either. Thus I would try it with line level signals first (from the "line out" jack or something similar) and only if the gain doesn't seem to be sufficient I would try the speaker output trick.

[nashvillebill]

Argh, I shoulda looked at the schematic,   teemuk is indeed correct that the input and outputs are in parallel, so my original post ("don't plug into the output of the Gibson") was in error.  Sorry...and as teemuk said, it *may* be possible to plug this into a speaker out but definately try using the line out of the Vox first.  Then, and only then, if you can't get acceptable volume, use the speaker out of the Vox.

[bballkvn]

The comments I read concerning this amplifier state that it is indeed used by connecting a coord from the external speaker output of the master amp to the input of the amp. Sounds odd and risky, I know. If this is done with a tube amp it should be made sure that a plug in the external speaker jack does not disconnect the tube amp's own low-impedance speaker load. Anyway, that advice is based on hearsay I don't know how accurate the information is. Back then stuff like "line level" outputs was not that common either. Thus I would try it with line level signals first (from the "line out" jack or something similar) and only if the gain doesn't seem to be sufficient I would try the speaker output trick.

so i want to use a cord from the line out from the vox to the input on the gibson??

edit: i just tryed it, sounds beautiful. i get no sound out of the vox though....so bacially its just using the gibson as a cab that it doesnt power??? so i dont have to worry about blowing my vox. is it acting like a preamp?

[teemuk]

It looks like that at least in Vox AD30VT lineout = headphone out. The feed for this jack is taken straight from the preamp and thus it also – and unfortunately - disables the signal path to power amplifier section along with the Valve Reactor circuit. Valvetronix design is quite silly on that remark and this issue has been a grief for many people. So yes, you pretty much (and literally) use the preamplifier of the Vox as the preamplifier and the Gibson as the power amplifier (yep, Vox does not "power" this, it only provides the input signal). Not a very optimal set up, I'm afraid, as it sort of beats the purpose of having a "slave" amp for sound reinforcing.