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

[wsscott]

A buddy was recently given this amp from the early 1960's, and we opened it up to see how it looks.  What a mess.  No power cord, the reverb tank cord is cut off, no Output transformer, a very rusty chassis, some wiring broken loose from solder points, spliced wiring in several connections, and only 2 of the 4 can filter cap nodes are wired into the circuit with the other 2 never being touched and it appears to be a relatively new cap can.  This is just based on an initial inspection.  Who knows what the values of the resistors and caps are!

So where would you start?  Throw it out, or start down the rabbit hole.

If the rabbit hole, would you just take it outside the house, plug it into a Variac and dim bulb tester with no tubes installed, flip the power switch and see what happens?  Or is there a wiser approach?  I guess my initial concern is whether the PT is any good.

Thanks.

[wsscott]

Here's a photo.

[BrianS]

If someone brought that into my shop, I'd turn down the repair.  Massive hackjob by whomever had there hands in that amp previously. 

If it's a "labor of love" and the cabinet is good, rebuild the circuit! 
FYI, Mercury Magnetics makes some very exacting Ampeg replacement transformers.  You may have to call them to get one though.

[wsscott]

I agree with you wholeheartedly!  It's more of a project/challenge for a friend.

[bmccowan]

Funny, I was going to say, that's not a mess, its a challenge.
If a hobby, the process is fun, no need to tally the time expense. If it were in my hands, I would:
Make sure the friend will pay for the parts.
Test the PT as you suggested. If not familiar, you should read up on safe procedures.
I would leave the reverb out of the circuit until I got the basic amp working.
If its as bad as it looks, I'd document the connections and free-up and remove the board.
Give everything a good cleaning - it sucks to work on filthy electronics.
Obtain an OT. There are much cheaper options (Hammond for one) than MM.
Go over the schematic checking it against your circuit.
Replace all electrolytic caps. Test the others.
Replace any resistors that are wildly out of spec.
Clean and test all the tube sockets.
Clean and test the pots. reinstall and rewire the board.
Obtain a spare set of tubes.
Once the basic amp is working well, tackle the reverb and trem.
I've worked on worse - electrocuted mouse in the chassis, teeth still on the B+ wire

[wsscott]

I'm curious about the wiring on the cap can.  It has two 40uf nodes and two 20uf nodes.  Neither of the 20uf nodes are wired to anything.  Any idea why?  The circuit has 6 nodes in it, ie. A-F.  Why use a can like this if you only need/want 2 caps?

[mresistor]

Do you know which model this is the? 7591 or 6V6. 7591 model has solid state rectifier.


Figuring out why all the caps in the can aren't used is part of the journey in restoring the amp. You have the amp in front of you and can diagnose it.

[wsscott]

The Power Transformer checks out fine.  I unwired it from the circuit, then tested  the windings for continuity and shorts to case and that was fine, so then I hooked up the Variac and tested the windings for proper Secondary voltages.  All read perfect.  So one good thing.  Hopefully more.

The amp is missing its Output Transformer.  It wasn't attached to the chassis, but there are holes with grommets on the PT side of the chassis where the wiring to/from the OT would go.  Do you know where the OT would have been mounted? On the speaker, or someplace on the cabinet?

[wsscott]

Its the 6V6 model since it has a tube rectifier.

[mresistor]

Here's a pic    I would say the OT was mounted on the chassis..   This is the 7591 model though it should be very similar. Notice the reverb pan was mounted vertical on a side panel.

[mresistor]

Here's the 6V6 version with tube recto..    you probably could find close ups of one of these if you look around on the net. 

[BrianS]

try this for the 3rd time...

[BrianS]

Pics of my '62 Reverberocket. Still needs restoration.  Pics show OT mounting.  Hope this helps.

[wsscott]

Brian-Thanks.  Now I see the 2 empty mounting holes on the chassis.  Great!

[bmccowan]

Good news on the PT.
There are a lot of muddy schematics for this model out there. But Joe Piazza drew up really clear schematics, and the attached is likely your amp. With the 6V6s you will have your choice of many OTs.

[wsscott]

I've seen this schematic before and it doesn't match my amp.  My amp has 7 tubes, not 6, and the 100K plate resistors shown in the schematic are both on V2, where mine has 1 on V2 and the other one on V3.  So mine is still a bastardized build from the factory.

It's interesting that the 6V6 builds are supposed to have the tube rectifier, and the 7591 have the bridge rectifier.  The Ampeg tube tag in the cabinet shows the 6V6's scratched through with ink, and handwritten above is 7591.  My buddy who was given the amp in this condition said it didn't have any tubes in it.

So I've got to see if the pinouts on the 6V6's and the 7591's are the same.  If not, then I've got to figure out another mystery in addition to the cap can that never had 2 of its nodes used!   

[mresistor]

They have different pinouts.. 

[wsscott]

I just pulled down the spec sheets. Yes, not interchangeable.  Okay, now I need to see how this amp is wired--probably save this task for tomorrow.

[wsscott]

bmccowan-You're right about Joe's schematic.  I forgot that V7 is the rectifier tube.  So that schematic has the right tubes and it looks like my amp is wired for 6V6's.  What's left to resolve is the conflict with the wiring of the 100K Plate resistors connecting to filter nodes E and F.  My amp has them connecting to different tubes while Joe's schematic has them both connecting to the Plates on V2.  I'll leave it be until tomorrow.  Thanks again for your help on this.

[bmccowan]

Have you seen this thread. Might be of some help as it documents an information search on the model.https://www.tdpri.com/threads/ampeg-reverberocket-r-12-r-diy-project.1102984/
Those minor changes in plate resistors are pretty common. Sometime intentional, sometimes just a lunchtime joint.

[shooter]

You're right about Joe's schematic.

His re-draw of Ampeg's SET (super echo twin) made a world of difference for a repair I did.


while it was a nightmare crawling around inside the chassis, once I plugged in for a test run, you will forget all the sailor talk you had,
she's melted butter to whatever "sound" you play.
I've fixed 1/2 dozen fender twins n supers, they are like cold hands, sterile, compared to the sound of the Ampeg.

[HotBluePlates]

... I've got to figure out another mystery in addition to the cap can that never had 2 of its nodes used!

The attachment to this post is a layout diagram for the 1962 Reverberocket with 6V6s.

You may need some time to get used to how it presents things, but it will show "what parts should be where, connected to what" well enough.

[shooter]

FWIW
the SET i worked on had one side blown, bad tube, bad OT, couple other pieces;
owner had a donor 6V6 amp, so I stitched in a 6V6 "side" one one channel, left other side 7591 based
this is my 6V6 side schematic

[wsscott]

The wiring in this amp seems under-gauge with poor insulation.  Is that just me worrying, or is that something that should be changed.  The Heater filament 6.5V wiring isn't even twisted once it leaves the PT.  I really do want to change that even though it may not be necessary.  Any thoughts on adding a terminal board to run the lead from the PT to, and then wire off of it to the pilot light and another separate lead to the heaters?

[Willabe]

The wiring in this amp seems under-gauge with poor insulation.  Is that just me worrying, or is that something that should be changed.

      Not enough information.

[acheld]

The wiring in this amp seems under-gauge with poor insulation.  . . .  Any thoughts on adding a terminal board?

Some thoughts:  Many builders worry about wire size, but in reality 22AWG wires are fine throughout most of our tube amplifiers, even the heater circuit, as the ampacity is in the range 7 Amps.

Your wiring does look the worse for wear, though I bet the insulation itself would be fine.  The splicing and prior repairs would be a big concern for me.

Nothing wrong with adding a terminal board, but not sure if your carcass (chassis) has the space.  I've used these insulated turrets https://www.ebay.com/itm/362043934117 for this purpose from time to time.  They work well, and take up a little less room than a board would. 

Looks like a fun project! 

[wsscott]

Thanks.  I guess the wire gauges in question are no smaller than the wire on a cap or resistor and that works fine.  So I think I'll focus on the ones with bad insulation or splices.  Looks like the terminal board won't be feasible.  So I'll just run new wire for the 6.5V heaters.  Some amp builders I"ve seen on Youtube don't like to run that heater wire directly to the pilot light, and then from there to the heaters.  They connect elsewhere, like to a terminal board.  I don't know what's the issue.  Do you?

[wsscott]

The mystery of the cap can is developing.  The can appears not to be original.  It is a CE with setup as 40/40/20/20 at 525 VDC.  The two 20 nodes appear never to have been used.  Maybe the tech just gave up when he got to that point.  But what's interesting is that each of the 40 nodes have 2 connections to them going to different parts of the circuit.  The schematic of Joe's shows there are six 20uf caps in the circuit.  So maybe the prior tech was using the 40uf nodes as dual purpose to cover 2 nodes each.  Does that make any sense?

[bmccowan]

The mystery of the cap can is developing.  The can appears not to be original.  It is a CE with setup as 40/40/20/20 at 525 VDC.  The two 20 nodes appear never to have been used.  Maybe the tech just gave up when he got to that point.  But what's interesting is that each of the 40 nodes have 2 connections to them going to different parts of the circuit.  The schematic of Joe's shows there are six 20uf caps in the circuit.  So maybe the prior tech was using the 40uf nodes as dual purpose to cover 2 nodes each.  Does that make any sense?

Agree - certainly not original. If you look at the layout that HotBluePlates referenced you can see how Ampeg implemented the 6 20uf caps. a 4x20 can and two axial 20uf caps. Those components are all readily available.
Did how the last "tech" wired it make sense? Well, no. As you work on this amp, I suggest not trusting that any of the previous work was done correctly. Instead follow proper procedure. You don't want to blow anything up, especially yourself.

[wsscott]

I think I'm going to loose my mind on this one!

Ok, so V-1 is the Tremolo stage
V-2 is the Pre-amp Gain stage
V-3 is the Reverb
V-4 is the PI
V-5 & V-6 are Outputs

The Problem:
V-2A is wired for the PreAmp, but V2B is wired for V3A Reverb.
V-2B is wired for V3A Reverb and V3B is wired for Reverb.

So 1/2 of V-2 is wired like 1/2 of V-3; and 1/2 of V-3 is wired like 1/2 of V-2.

Even though they're both 6SN7's, the connections are not the same.  For example, there's a 22K resistor between V-2P's 3 & 6; but V-3P's 3 & 6 are not connected together.

Plus the schematic may show a connection on P-2, but it's wired to P-5, etc. Ok, they're both Plates, but still.

And it looks like it's factory wiring.  How could this possibly be?  How could it have ever worked properly.  Maybe it didn't.  Who knows.

Pardon my venting.  IF it were 5 o'clock it would be cocktail time!

[bmccowan]

It's 5:37 in London - so you are safe.
1/2 or V1 is the tremolo stage - other than that, yes that's what the schematic shows.
I'm having a hard time following the rest of your comments - but I understand you are venting.
My suggestion is that you decide which schematic best matches your amp - hopefully the Joe Piazza version as it's clear. And then follow it.
You likely need to approach this project as a rebuild rather than a repair.
I sympathize with your frustration - not that it helps, eh?

[SEL49]

1/2 of V1 is the input preamp and the other half is the tremolo oscillator. V2A is another preamp gain stage but it has two outputs. The plate output is connected to the grid of V3A which is the reverb driver. And the cathode output is connected to the cathode of V2B mixer.

Ampeg has a different way of mixing the dry and wet reverb signals together, but the circuit works just fine on the schematic. That 22K resistor between V2 cathodes is the dry signal input to V2B mixer. The reverb recovery signal is on the grid of V2B and the combined wet/dry signal leaves V2B plate headed to V4 paraphase inverter. Tricky to look at for the first time but simple once you understand.

If you wire the amp according to the schematic it will work properly.

[wsscott]

Thanks guys.  London is a great city.  Maybe it will be a G & T tonight!  Yes I"m going to use Joe's schematic and looks like its going to be a rebuild.

SEL49, yes my amp has the first 100K connected at V2-Pin2, but the other 100K that's shown on V2-Pin 5 on the schematic is connected to V3-Pin5. And of course some of the other components have been switch around between those 2 tubes.  And on my amp, that 22K connects between the cathode on V2 and the cathode on V3.  So that connection is not between cathodes on the same tube

No telling what else I'll find. I don't think this will be done by Thanksgiving--but maybe Christmas!

[SEL49]

Maybe you should be looking at this schematic... It's a bit different than the Piazza schematic.

[bmccowan]

That schematic is for a SS rectified version with much higher value filter caps. But the amp in your hands could easily be a transition model. Ampeg and everyone else did that, including Fender.
The important thing is to pick the closest one and follow it. If you try to follow multiple schematics you may be looking at April Fools Day, let alone Christmas.

[wsscott]

I'll check it out, but I feel pretty comfortable with Joe Piazza's schematic.

I also found these 2 YouTube videos.  Both are very good, and the one from Psionic Audio is exactly what I need.  I actually surprised myself in that I was going to start out doing exactly what he did, ie. cleaning up the area around the PT, cap can, and resistors.  Fingers crossed.

[bmccowan]

Lyle is meticulous - so good find. Notice he mentions that the amp on his bench matches none of the schematics, including the JP. As he says, "what the Hell, Ampeg."

[shooter]

"what the Hell, Ampeg."

That's what happens when you hire the engineers Gibson fired 

[wsscott]

You guys are great!

[shooter]

 
naw, just crazy from too many years crawling around tangled wires.
while you're tackle'n this one, keep your eyes n ears open for it's big-bother the SET.
Ampeg managed to put 2 of your amps in the same chassis   

[HotBluePlates]

The mystery of the cap can is developing.  The can appears not to be original.  It is a CE with setup as 40/40/20/20 at 525 VDC.  ...

Agree - certainly not original. If you look at the layout that HotBluePlates referenced you can see how Ampeg implemented the 6 20uf caps. a 4x20 can and two axial 20uf caps. ...

Below is an original Reverberocket.

The silver in the bottom-right corner is the 4-section can capacitor.
The brown tube on the right-edge is a 2-section can capacitor.
There are your 6 filter caps.

[wsscott]

Georgeous!! Is that how it was when it was brand new, or is that its condition now?  If the latter, I assume there was a restoration?  Anything of interest develop in the course of that?  If that's yours, lucky guy.  Thanks for sharing.

[wsscott]

I was looking at the Layout for this amp that's referenced earlier in this topic, and I noticed that the two 20uf electrolytic caps C5 and C6 are shown has having their + leads connected to the GND terminals on the Cap Can.  Is this correct?  Shouldn't they be connecting to that point with their - leads?

[Willabe]

I was looking at the Layout for this amp that's referenced earlier in this topic, and I noticed that the two 20uf electrolytic caps C5 and C6 are shown has having their + leads connected to the GND terminals on the Cap Can.  Is this correct?  Shouldn't they be connecting to that point with their - leads?

It would really help the guys greatly if you post the drawing so they don't have to look for it. 

[SEL49]

Shouldn't they be connecting to that point with their - leads?

yes

[wsscott]

I was wondering, since I'm working right now on the power supply side of the amp, would it be worthwhile putting a fuse or diode in the circuit to protect the PT from something going wrong with the rectifier?  I don't have much room to work with.  If so, how would you recommend wiring it into the circuit?  Thanks.  Oh, and Happy Thanksgiving to everyone.

[wsscott]

Well I got the wiring finished on the Power Supply section of the amp. I wired in new green 6V filament heater wires from the pilot light to the V6 Power Tube, and then ran a colored red & green twisted pair from V6 to V5 and to V4 filaments.  I left the remaining filament wiring on V3-V1 in place since it tested ok. I added a power cord, after testing the PT and it showed everything was fine, I wired it into the circuit. Got the can Filter Cap A (40uf) node and the B (40uf) node wired into circuit.  Installed a new 250 ohm bias cap. The 6V6's are partially wired, and I'm waiting on a OT.  With no tubes installed, I plugged it into a dim bulb current limiter which is connected to my Variac and brought it up to full voltage, and no shorts. Then I shut it off and installed the 5Y3 rectifier tube, and turned it back on.  No shorts or issues.  It is putting out about 450-475 VDC.  I checked the voltages at the can A and B nodes and through the rest of the Power Supply part of the circuit, and everything is where it should be.  The only thing I noticed was when I turned the power on after installing the rectifier tube I only got high voltage on one leg of the cathode, but after a couple of minutes it was reading equal voltage on both legs of the cathode pins 2 & 8.  Maybe it just took some time to charge up the cap node.

So for the moment, I'm waiting for parts to come in. As I said, an OT, a set of tubes, a few electrolytics, and some coupling caps are the main items.  So maybe by next weekend some more progress will have been made.

I'm still struggling with figuring out the wiring for the rest of the circuit.  I can't figure out what the amp builder was doing.  There are some tubes that are wired in reverse, ie. the wiring on A and B nodes of the tube are flipped.  Some wiring that is shown in the schematic as being wired on Nodes A and B of just 1 tube, are split between 2 tubes, with it wired to A node on tube 1 and B node on tube 2, or maybe A node on tube 2.  So it's really hard for me to trace things.  I guess I'll just assume it's wired correctly since the wiring looks original and it must have worked since someone bought it.

[shooter]

I can't figure out what the amp builder was doing.

 
See reply #37


consider the times in which an amp was built


Vietnam, Hippies just getting started, guys avoiding spending a few years in the jungle, Collège became a social construct rather than an educational one, sex, drugs, early rock n roll

[wsscott]

Yea, those were some really great times.  Plus the best music ever!  I never did drugs other than alcohol, and I had a high draft number so I didn't see the jungles but I respect those who did.  No one can appreciate those times other than those of us who lived it.

[wsscott]

I decided to replace the 6 coupling caps and started working on it today since I had replacements on hand.  The ones on the board are covered in glue of some kind so it's hard to read them, but the schematic shows 0.02 uf's for all 6.  I removed 3 of the old ones, and ALL 6 of them are 0.1 uf's--no not 0.01uf!!  Surprise, Surprise!  So I replaced them with the 0.02's.

Who know how this will affect anything.