Mesa Boogie Subway Rocket - Where does this red wire go

[mikeydee77]

Can anyone help me with the correct location of the red wire coming from the FET on the right over towards the orange relay. It doesn't quite reach to the foil.

Why didn't I take a pic?

[DrGonz78]

I looked at other gut shots of this amp online and couldn't see any red wire. Looks like it could be a factory mod. Or it's just a wire that hangs their hoping to effect the tone somehow through mysticism and good luck.

[mikeydee77]

Ha ha, yes I good scout around on the web and found several pics without the wire. Fishing antenna could be the answer or perhaps for picking up remote tone updates to the vactrols from head office. I think I might check in with MB HQ and see if they can provide any guidance.

[Chuck H]

FWIW I did the same looking around and couldn't find the red wire either. Or any wire coming off something like that floating circuit on the board in this post. It may be part of some kind of modification, factory or otherwise. I had a Subway Blues (two actually) and when one started to exhibit hum problems due to the effects loop "cube" (the notorious black epoxy block that was not serviceable). Mesa had me send them the board for repair. They replaced the whole board free of charge even though I wasn't the original purchaser. At that time there were a couple of mods posted on line to solve the issue. One was a Mesa factory effort. You could look around to see if those floating components may have something to do with that.?. Though this would have been something like twenty three years ago.

EDIT: I don't expect that red lead terminates at the foil because the foil looks to be on the ground plane and the floating component circuit where the red lead starts looks like it's probably a voltage supply.

EDIT2: (random stream of consciousness) Look at the shape of the solder at the end of that red lead. It's flat. It doesn't look like it was attached to a component leg or through hole. In fact it doesn't look like it could be or was attached to anything it could reach. So I might guess that it was tacked with hot glue to that capacitor just to keep it out of the way.?. So maybe it was attached to something, but now, for whatever reason, isn't supposed to be anymore. But then why tack it to the capacitor rather than just snip it off? Just thinking out loud.

[g1]

Agree with Chuck that it looks flat like it broke off it's connection, not like it was de-soldered. I guess you found it to be disconnected like that? Your mention of not take a picture 'before' implies you may have done something? What kind of work did you do? It doesn't look like it would reach around to the bottom of the board, but is that a possibility?

[Helmholtz]

Does the amp work properly with the red wire floating?

Is there a schematic?

[Pedro Vecino]

I think itīs original from the company. Both the resistor and the capacitor, wire and the silicone itself. I would like to see if the transistor is a J175 for switching purposes. Maybe it's related to a temporary mute around the reverb or an associated gain adjustment.. The wire could simply be used for testing purposes and they didn't bother removing it.
It must be a Reverb rocket . Here's a photo of one that doesn't have that.

[Pedro Vecino]

Is there a schematic?

Now yes

[mikeydee77]

Thanks Chuck... second pair of eyes always appreciated and some of your thoughts got me back on track. Main thing... swapped my eyes for a phone magnifier and now I am making progress.

From pouring over the schematic the only mention of J175 is in the switching circuit (I don't think the schematic I have is the correct version as I have op amps in the FX loop whereas the schematic does not have any). Pretty normal for Boogie I suppose but I can't find a match.
Checked some voltages as well... pic 1 but it does confirm that with 12v on it unlikely to be headed for a ground connection. It also shows that signal is on the FET channel so presumably some signal grounding function in the switching circuit.
Then I noticed the vactrol... it has three pins and one is broken off. My eyes are terrible but spotted it with a phone magnifier.
The red wire lands perfectly on the Vactrol. Feels like this is the answer.

I'll see if I can repair the connection on to the Vactrol but really it needs to be replaced to get a reliable fix.



Schematic that I have...
mesaboogie-subway-rocket-schematics.pdf

I have contacted MB today...

[mikeydee77]

Agree with Chuck that it looks flat like it broke off it's connection, not like it was de-soldered. I guess you found it to be disconnected like that? Your mention of not take a picture 'before' implies you may have done something? What kind of work did you do? It doesn't look like it would reach around to the bottom of the board, but is that a possibility?

I had lifted the board to check for dry joints etc and also replace the DC heater supply caps that were suspect. It is quite possible that in flipping the board the wire broke. But it is also consistent with the original fault symptoms of lacking drive on the dirty channel. I usually photograph amps where there is a doubt about replacing cables or anything like that but didn't seem neccessary - Doh!

[mikeydee77]

Does the amp work properly with the red wire floating?

Is there a schematic?

It does work but apparently the tone is not what it should be. Since making a little progress by chipping away at the Vactrol and connecting the wire temporarily it does sound really good and each voicing has distinctively different levels of drive so I do suspect that this wire had broken off before I got in there but really cant say for sure.

There is another residual fault with cutting out where the signal from the input socket seems to get interrupted on its way to the V1 grid... seems to be a bad joint but had enough boogie fun and games for one day.

[mikeydee77]

Now yes

Thanks will study this one... Is a Reverb Rocket another name for Subway Rocket?

[mikeydee77]

I think itīs original from the company. Both the resistor and the capacitor, wire and the silicone itself. I would like to see if the transistor is a J175 for switching purposes. Maybe it's related to a temporary mute around the reverb or an associated gain adjustment.. The wire could simply be used for testing purposes and they didn't bother removing it.
It must be a Reverb rocket . Here's a photo of one that doesn't have that.

There is a rocker switch on the chassis of the amp that seems to be a mute socket presumably for when using the headphones jack socket. Perhaps it is part of that circuit? I will investigate and post findings.

[Pedro Vecino]

That already makes a lot more sense. In two dimensions identifying these things becomes a guessing game. What is obvious is that this connection requires a more flexible wire that does not retain mechanical tension.
The opto looks recoverable. Using a fine dremel tip removing a millimeter of the thickness of the plastic casing would allow a secure connection (using another type of wire).

Subway Reverb Rocket is the model with reverb. Yours has it, so it must be that one, although it is obvious that it is not the same as the ones I have known.
They actually have a small rocker selector at the bottom of the chassis to mute it.

[mikeydee77]

That already makes a lot more sense. In two dimensions identifying these things becomes a guessing game. What is obvious is that this connection requires a more flexible wire that does not retain mechanical tension.
The opto looks recoverable. Using a fine dremel tip removing a millimeter of the thickness of the plastic casing would allow a secure connection (using another type of wire).

Subway Reverb Rocket is the model with reverb. Yours has it, so it must be that one, although it is obvious that it is not the same as the ones I have known.
They actually have a small rocker selector at the bottom of the chassis to mute it.

Yep, I have dug into the vactrol base with a scalpel to expose a tiny bit of lead and then attached a tiny single strand mylar insulated wire (it is like a strand of hair) and it works OK. I just need to find a way to stop it from moving around but it is functioning well enough.

Yes correct on the rocker switch I think that is for when using the headphones. Thanks for sharing the schematic info.

Mike