Ampeg R-12-R Reverberocket Amp-What a mess inside

[shooter]

by grounding PIN 4 you are killing ANY input to V1 so you won't have guitar!


NO SIGNAL......remove the jumper on pin 4 and use it to jumper the VOL pot wiper to chassis....Got hiss?

[wsscott]

It goes dead quiet just like grounding Pin 4.  No sound.  When I remove the ground on the jumper it has hiss.

[shooter]

NO SIGNAL......Pull V1......Hiss?

[wsscott]

With V1 pulled, and no jumper between chassis and Volume Pot, No Hiss and very minor hum.

With jumper in place, then no sound.  No Hum, No Hiss, nothing.

[shooter]

NO SIGNAL.....put V1 back in, put Jumper from V1 Pin 1 to ground.....Hiss?

[wsscott]

Yes, Hiss.

The ground shield in the shielded cable from V1 to the Input Jack is disconnected.
But even if I connect it to chassis ground with a jumper, the hiss remains.

[shooter]

ok, my hand is getting all sweaty n clammy, read over those last few posts while looking at the schematic n tell me what you'd do next 

[SEL49]

NO SIGNAL.....put V1 back in, put Jumper from V1 Pin 1 to ground.....Hiss?

V1 pin 1 is the TREMOLO circuit. Maybe you meant to say V2 pin 1?

[wsscott]

Well I would swap this tube with the 6SL7 at the PI.  I think I've already done that. But I swapped tubes and still has the same effect.  With jumper on V1 Pin 1 to GND there is Hiss regardless of whether the jumper is connected to ground or not.

[wsscott]

If I jumper V2, Pin 1 to GND, only extremely little hiss when Volume turned all the way up.  When jumper is off the GND, then it has Hiss.

[AlNewman]

When you grounded pin 4 of V1 and it stopped the hiss, you isolated the noise to 8 different components, all between the input jacks and the 1st gain stage of the amp.  (I'm not sure why this didn't work when you did the same thing 2 pages ago, but anyways.)

Maybe some good high rez pictures of the input jacks and 1st gain stage might help.

[shooter]

V1 pin 1

  that told me there was no "cross talk" in V1, in other words the trem circuit wasn't influencing the 1st gain stage.


You "killed" the hiss at V1A, both into and out of, so V1A has a problem, socket, components, wire dress, solder connections, ya-de-da.
re-build V1A from the input jack to the output of the TS/VOL, you can do it Johnny Cash one piece at a time, or go nuclear and burn it all down n start new

[Willabe]

Did you try new tubes?

Tube could be noisy.

[wsscott]

Thanks guys.  Since I swapped tubes and everything is the same, I would say the tube is not the problem.

I"ve replaced all the components of V1A except for the 25/25 cap which appears to be relatively new and modern.

We've eliminated the V1B section.

So my gut tells me it's in the jacks or the Volume or Tone Pot.  The Volume pot is a 1M, but it reads 1.35M.  I don't know if that's the cause.  The Tone pot is a 500K, and it reads right at 500.

I've only got the middle input jack (as shown on the schematic), but it's the first Input Jack physically on the chassis, connected to the circuit.  I disconnected the other 2 jacks to eliminate them from the issue.

The wiring on the jack looks squirrely to me, and I've attached a photo of the one active input jack.  The jacks are all shorting jacks, and the schematic shows just standard jacks.  So I'm a bit confused on wiring them.

The two resistors attached to the active jack are a 4.7M vs. the 5.6M as shown on the schematic, and a 470K.

I'm also attaching another photo showing the wiring on the other 2 jacks.  The dangling red wire is what I disconnected and it had been soldered at the junction of the 4.7M, the 470K, and the shielded lead going to V1 Pin 4.  The black wire is on a jumper between the 2 lugs (which I think are the sleeve and switch) on the active input jack, and it connects to a ground eyelet on the circuit board.

Thanks for your help.

[wsscott]

SUCCESS!!  I did it.  I re-wired that first jack.  I realized that the 470K had been wired to the Pin 4 lead with the 5.6M resistor, and the jack needed the 47K resistor added to make it work.  So I wired the 470K from the Tip lug to the ground jumper between the sleeve and the switch lugs.  Then added a 47K to the Tip lug and connected it to the 5.6M and the Pin 4 lead.  Hiss is now barely there.  Maybe a new Volume Pot would clean that up.  Or maybe I should connect the GND shield from Pin 4 to a GND somewhere.  At the jack or somewhere else?

[wsscott]

Thanks fellas so much for all of your help and patience with me.  I couldn't have gotten this thing working without your guidance.  I guess one very important thing I learned in this process is that if an amp is a mess when you get it to fix, and nothing matches up with a schematic, then don't trust anything about the circuit or the work that had been previously done. Not even the simplest things-like the wiring of a jack. There were a lot of issues in getting this amp up and running again.  I still have the Tremolo and Reverb to work on, but since it's all been re-wired according to the schematic, and it has all new components, maybe this part will be relatively simple.  Famous last words!

[shooter]

I should connect the GND shield from Pin 4 to a GND somewhere.  At the jack or somewhere else?

a shielded cable is grounded at one end only and typically at "the source" of the "shielded signal" so in this case the shield should ground at the input jack, since that is the source of the signal


V1A is a hi-gain tube, I personally don't like the 1st stage to be hi-gain, I prefer higher signal to noise ratio. so there will always be some hiss, my "It's ok" level; with the amp VOL at 5, guitar VOL at 0 I start strumming and rolling the guitar VOL up, If the hiss is gone when guitar is at 1, it's normal, even 2 if it's a larger watt amp.  Then if the owner want better, you pay more for better 

[bmccowan]

I'm glad you got that straightened out. You are right that Shooter, Willabe and some others showed a lot of patience walking you through troubleshooting.
I am commenting on your "lesson learned" in hopes that it helps the rest of the process and others reach success with less pain.

I guess one very important thing I learned in this process is that if an amp is a mess when you get it to fix, and nothing matches up with a schematic, then don't trust anything about the circuit or the work that had been previously done. Not even the simplest things-like the wiring of a jack.

I think that is right, but it does not offer up an amended approach. From the beginning, multiple folks recommended and/or requested that you take the schematic closest to the circuit you had and go through the chassis marking up the changes on the schematic. You resisted doing that, and I think it cost you a lot of aggravation. The problem with the wiring of the input jack would have easily been found with that process. I think you said that dealing with tracing the circuit made your head hurt. I have to think your head hurt regardless.
You still have a ways to go, and I suggest you reconsider your process before Doug runs out of bandwidth

[wsscott]

Fair point.