Help with Reverb/Tremolo wiring Gibson GA15-RVT

[devilsindetails]

Hi..new to this forum but have been browsing and learning from it for a little while.

My problem is a Gibson GA15-RVT.

The trem/reverb footswitch was all messed up so I took a stab at rewiring but quite frankly the schematics don't make a lot of sense to me when I am looking at the actual wiring layout.

So maybe someone here would be kind enough to look at the attached schematic and then at my attached rendering of how I wired the inside of the pedal and set me on the right path or tell me this part is ok as I have it.

I'm trying to approach this one piece of the puzzle at a time. Thanks in advance.

[Firestorm]

The dotted lines you see coming off the Pin 2/3 connection represent the shield of the footswitch cable. The center conductor of the cable connects to Pin 3; only the shield connects to Pin 2. Pins 2 and 3 are not connected together. Pin 2 is a ground; Pin 4 is a ground. When the reverb switch is off, it grounds out the reverb signal. When the tremolo switch is on, it grounds one end of the frequency pot, which makes it work.

Rewire your footswitch with that in mind and it should work (assuming the rest of the circuits are functional).

[devilsindetails]

Thanks Firestorm...must be amusing to watch a newbie stumble around

Now to part two of my problem..I don't know if the reverb tank plug nearest the footswitch plug on the top of the chassis is for the output to the tank or the input....I'm guessing it's to the output plug on the tank..yes...no....?

The other plug from the chassis to the input on the reverb tank seemed to be wired through a whole in the chassis (I've circled in red on the last chassis pic) but wasn't connected to anything...was just a brown wire hanging loose near the numbered tag board )pic also attached.

Where does that wire go to exactly? Somewhere on the tagboard? Or is it supposed to be wired to one of the 6EU7 tubes?

[Firestorm]

Yes, the output of the tank goes to the RCA jack nearest the footswitch jack. The input to the tank comes from the yellow end of the 10uF cap (eyelet 26 it looks like). The brown wire should originally have been soldered here.

[devilsindetails]

Thanks again Firetorm...I will give it a try!

[devilsindetails]

Ok no luck with the rewire:

Wired reverb input jack wire to negative side (yellow end of 10uf cap) at eyelet 26.

I checked continuity from the reverb tank input/output plugs to their respective chassis wiring connections, soldered braided pin 2 wire to shield and checked continuity to chasis ground from pin 2 and pin 4, all check out fine.

I also checked the continuity from foot-pedal plug ends on pins 3 and 5 to foot-pedal reverb and trem switches...continuity is fine.


Bare braided wire soldered to shield
White pin 3 ( - reverb)
Black pin 4 (ground bridged to - tremolo and - reverb switch)
Red pin 5 (tremolo switch +)

So far so good?

I have checked all tubes
2X6EU7s
1X12AU7
2XEL84

I have output, volume, bass and treble control off instrument jack 1 but neither tremolo or reverb with tank connected.

Swapped out the reverb tank for another...same result...

I substituted another 10uf cap for the existing at eyelet #26 on the tag board observing correct polarity...no change

QUESTIONS.

Are the footpedal switches actually reversed from one another in the schematic in terms of orientation. Do both + - poles sit parallel to each other or are they supposed to be diagonal..does it even make any difference?

Is there any type of legend or template I could refer to regarding the tag board? It seems that when I touch eyelet 27 with a probe connected to the input reverb and touch it repeatedly I get some tremolo.


Anything obvious jump out at anyone? Other than my inexperience, of course.

[tubeswell]

The layout in that amp is terrible. Does it work without the footswitch plugged in?

[Phil_S]

Tubeswell: This series of amps were generally low to medium gain and for reasons that defy gravity, generally they performed OK in spite of the poor layout. I own a GA20-RVT, sort of a 2-channel variation on the GA15-RVT pictured here. It had terrible hum problems that I finally solved by reworking how the interstage transformer was grounded. I'm posting a picture of it after I molested it and after the cap job. I left most of the board as I found it and you can see that Gibson must have thought the layout was OK. I'm not defending it, just saying its what they did.

Curiously, I tried a number of times to draw a better layout that would fit into the same amount of space and finally concluded that I couldn't do it; that it would take a combination of a new board, relocating the big filter cap, and attaching some components directly to the tube sockets to reduce loading of the board.

Yes, these are a sorry looking lot of amps.

[devilsindetails]

The layout in that amp is terrible. Does it work without the footswitch plugged in?

I'll try that...thks...ok so the layout is terrible....be that as it may any troubleshooting ideas?

[devilsindetails]

Tubeswell:Yes, these are a sorry looking lot of amps.

Ok, but any ideas regarding troubleshooting my problem? I tried to layout what I've done so far as well as some questions I have..any input on that?

Thks. Leon

[Firestorm]

Reverb should work without the footswitch; tremolo will not. Make sure you have the correct reverb tank; the ones designed for Fender circuits will not work here. Try to read the numbers off the tank.

[devilsindetails]

OK...reverb works without footswitch plugged in...I do note that with reverb input jumpered to #26 eyelet (negative side of 10uf cap) there is no increase/decrease using reverb pot. Is this correct...or an indication that something is amiss.

Volume control, Bass, Treble pots operate as they should.

What should I be looking for next?

[Phil_S]

I am not good with switches, which is why I didn't answer earlier. They confuse me if they have more than two terminals and I don't know why that is. It looks to me like shorting terminals 4 and 5 will turn the tremolo on. That's why it won't operate without the switch because the closed position is on. The reverb is opposite, with the closed position grounding the signal, turning it off.

[tubeswell]

I am not good with switches, which is why I didn't answer earlier. They confuse me if they have more than two terminals and I don't know why that is. It looks to me like shorting terminals 4 and 5 will turn the tremolo on. That's why it won't operate without the switch because the closed position is on. The reverb is opposite, with the closed position grounding the signal, turning it off.

And that's where we need to get to, which is why I asked about the footswitch. So get a R-meter and put it on the footswitch lead plug contacts, and work out whether you have DC continuity where you need it, and that you don't have it where you don't want it, in order to get the reverb part of the footswitch to be 'open' when you want the reverb on, and the trem part of the footswitch to be 'closed' when you want the trem on. And that should take care of the footswitch. Any other problems are most likely inside the amp chassis (unless its a bad tube).

[devilsindetails]

First of all. thanks to everyone taking the time to bear with me....and my sometimes muddled descriptions and explanations.

I guess what I require, however, is for someone to answer my questions as I pose them...

I attached the original foot pedal schematic originally along with how I thought the connections are hooked up.

This is a five pin plug at the end of the pedal

Pin 1 (blank)
Pin 2 (bare braided wire connected to socket shield)
Pin 3 (ground to reverb off)
Pin 4 (ground to reverb and tremolo off)
Pin 5 (to + tremolo switch)

IS THIS CORRECT ?

I have checked the continuity of the pedal wiring from 5 pin plug ends to reverb/trem switches

Pin 1 (no continuity)
Pin 2 (continuity at socket shield only)
Pin 3 (continuity at reverb off)
Pin 4 (continuity at reverb and tremo off)
Pin 5 (continuity at tremo on)

IS THIS CORRECT

Checked continuity of chassis reverbtrem footswitch socket.

Pin 1 (no continuity)
Pin 2 (continuity to chassis)
Pin 3 (continuity to C15)
Pin 4 (continuity to chassis)
Pin 5 (continuity to frequency pot R33)

IS THIS CORRECT

Know when I had no footswitch installed and the reverb was working I noted that I was unable to vary the reverb at the reverb pot...

is that correct I would have assumed that I should be able to vary the reverb...it seemed to make no difference whether I had the reverb input plugged into the tank or not...that doesn`t seem right to me..