1966 Gibson Explorer GA15 Amp

[DetroitBlues]

I've been offered this amp as a trade.  

But I know nothing of the amp.

I know its a tube amp, has Reverb and Tremolo.  Three inputs.

I don't know much more than that.

What I should look for or what problems these amps are known for, if any?

Thoughts?

[rockabilly69]

good background and demo towards the end..

 

[tsp17]

8 hours ago, DetroitBlues said:

I've been offered this amp as a trade.  

But I know nothing of the amp.

I know its a tube amp, has Reverb and Tremolo.  Three inputs.

I don't know much more than that.

What I should look for or what problems these amps are known for, if any?

Thoughts?

All I know is that I played though one of these once and liked it.  That's not much help, I know, but it was memorable enough to mention it.

[212Mavguy]

The deviations from the schematic often present in these Gibby amps could be a bit problematic for the casual hobbyist.  If you know a tech that is familiar with how Gibson did their stuff this design has some great tone potential.   The lack of printed circuit boards (Yay!!!) makes this one easily repairable and also tweakable.  As the tech explained, in the video, a lot of signal gets thrown to ground, that can be changed to less loss by a good tech. The 10 inch speaker and small output transformer might provide less bottom end than what one might want, but since IMHO this is not a sacred amp platform and not hugely expensive to purchase now or in the future, it could be turned into a customized grab and go little tone monster to have and hold onto.  There are a lot more good sounding 10 inch speakers being produced today with greatly varying price points.  The fact that it has a pair of speaker jacks allows some real flexibility in cabinet choices.  While the demo was playing my conure parrots were screaming and dancing, they liked it a lot.  There is great harmonic content. the reverb and trem sound great.  

This vintage cheese amp design is begging to be taken to the next level of awesomeness.  Compared to a modern Chinese printed circuit board design , this is way more flexible to allow the great things to happen and could be done for a reasonable dollar outlay.  Could definitely become a werewolf in sheep's clothing with the right love. 

YMMV... 

[DetroitBlues]

23 hours ago, 212Mavguy said:

The deviations from the schematic often present in these Gibby amps could be a bit problematic for the casual hobbyist.  If you know a tech that is familiar with how Gibson did their stuff this design has some great tone potential.   The lack of printed circuit boards (Yay!!!) makes this one easily repairable and also tweakable.  As the tech explained, in the video, a lot of signal gets thrown to ground, that can be changed to less loss by a good tech. The 10 inch speaker and small output transformer might provide less bottom end than what one might want, but since IMHO this is not a sacred amp platform and not hugely expensive to purchase now or in the future, it could be turned into a customized grab and go little tone monster to have and hold onto.  There are a lot more good sounding 10 inch speakers being produced today with greatly varying price points.  The fact that it has a pair of speaker jacks allows some real flexibility in cabinet choices.  While the demo was playing my conure parrots were screaming and dancing, they liked it a lot.  There is great harmonic content. the reverb and trem sound great.  

This vintage cheese amp design is begging to be taken to the next level of awesomeness.  Compared to a modern Chinese printed circuit board design , this is way more flexible to allow the great things to happen and could be done for a reasonable dollar outlay.  Could definitely become a werewolf in sheep's clothing with the right love. 

YMMV... 

I don't think anyone could have metaphorically described the amp better than you.

[zguitar71]

It’s a cool amp with potential. Start watching Uncle Doug YouTube Videos and open that chassis up and make it a monster. https://m.youtube.com/user/Stratosaurus1
 

I have taken two amps in trade in the past. One I ended up selling the other became one of my main giging amps. I got the amp here at HOC as a partial trade with a guitar and some $$$. It was the best move I think I ever made. It opened my eyes to different stuff and then spurred me on to learn new stuff in life. I didn’t know anything about amp tech before the trade and the desire to modify the amp and a lack of money to get it done pushed me to figure it all about and get it done. Now I can do a little side work fixing amps and I’m in the process of making three amps. I cannot urge you enough to get that amp, you may not go the route I have but vintage and different amps are just so cool on there own it is worth it. 

[DetroitBlues]

I never got the amp.  The person offering kept changing his mind then starting to demand money from me.  Big nope, I’m good.

[Warren]

Most old tube amps (over 10 years old) will need all of the electrolytic capacitors replaced with new caps.  Electrolytic capacitors have some liquid in them which dries out over time.  This drying out makes the old electrolytics resistive which throws off the entire design of the circuit as a voltage drop now exists across the bad caps.

That means the filter caps, the bypass caps, and the coupling caps will have to be replaced if they are electrolytic.

Easy to do if you do just do one at a time.  Many of these old amps are wired "point to point" without circuit boards.  Literally each component is soldered to the next component in the chain.

Capacitors are very similar to batteries in that they can store electrical charge.  Caps (bypass and coupling) don't pass direct current so they are used to route signals around inside the amp.  Filter caps though are used explicitly to store electrical charge and as such can deliver a large shock in not handled correctly.

A lot of old amps also utilize a two wire power plug and "death cap" across the hot and neutral.  The "death cap" is there to reduce noise but puts the guitar player in danger.  If this cap goes bad by shorting out it can deliver the wall current to your guitar strings and kill you since your strings, bridge, etc will suddenly become "hot" and you might present a low resistance to ground.

Ever find a scratchy pot that you can't fix with DeOxit?  That is likely the failure of a bypass cap.  It has failed in its mission to block DC and DC on a potentiometer will make the pot sound scratchy when adjusted.  No amount of cleaning will fix it.  The BOX OF ROCK pedal says "crackle ok" on the Drive pot because it's designed to have DC on it.

Old amps are cool and sound great. I have a 1960 Gibson GA5 which really sounds amazing - after I replaced all of the electrolytic caps and installed a 3 wire power plug.  Without doing this maintenance they sound bad or not as good as they should and can be dangerous.