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

[wsscott]

Shooter-I was tracing the signal through the schematic that we've been using, and I can't see how a "clean" signal gets to the PI without going through the Reverb circuit which is shown as wired through V3.  Is the footswitch the answer?  Ie. if the footswitch is closed then the signal goes to Ground, and not into the grid of V3, and that ground sends the signal on to the bottom of the Dimension pot, and then out the Center lug on the Dimension pot to the PI?

Can you tell me how the signal would flow?  Thanks.

[wsscott]

No, I'm sorry, I misspoke.  The signal goes into the grid of V3 and out the Plate, but if the footswitch is closed the signal doesn't go on through the Reverb Tank, the signal goes to ground, and then on to the bottom of the Dimension pot, etc.

[wsscott]

Shooter, I checked the Output voltage at the speaker.  It reads 2.25Vac.  I had a 1K signal at 135Vrms input at the input jack.  I turned the Tone pot to midway, and the Volume pot to about 8. 

No tube is in the V3 spot since I have packed it up for return.  I should add that the Footswitch which is wired into the circuit and not connected with a RCA jack, was cut off from the circuit board--literally cut off.  So there's just a dangling footswitch wire.  Would that turn the Reverb ON?

I had a dummy load in the speaker output jack.  I connected the + lead of the DMM to the + lug on the output jack, and the - lead to chassis to get the reading of 2.25 VAC.

[shooter]

once you eliminate all other possibilities, the problem will be come obvious

keep going, you'll eventually get there 


once the sockets have been eliminated you're one step closer
I would "rebuild" that circuit, new R's n C's for grid, plate, cathode and next stage coupling. $3's well spent.

[SEL49]

May be helpful...

[wsscott]

SEL49-Thanks so much.  I had everything but the cross-over through the 22K between the cathodes.

[bmccowan]

once you eliminate all other possibilities, the problem will be come obvious

Shooter, that's one of the best quotes I've seen in a while. I'm saving that for re-use.

wsscott, I see that you plan to have the sockets re-tensioned over Christmas, as you have identified that they are not making solid contact. To me, that's like working on an amp with a bunch of loose connections. You can only get so far until you fix those. You may have reached that point.

[shooter]

best quotes

I stole it myself, might be a Sherlock Holmes variation


I used it a lot talking with other Field engineers "Once you eliminate all the good parts, only the bad parts remain"

[AlNewman]

Did you ever check for DC voltage at the grids?

[Willabe]

.... There's 177vdc going into the resistor, but only 20vdc coming out and making it to the subject plate.

That's with the tube in, yes?

Take the tube out and measure the dcv at the tube socket. It should now read the same dcv on both sides of that plate R. Does it? 

So the resistor reads good, but it's losing a lot of voltage at that point.  Why is that?  Could the resistor read properly but something else in the resistor be causing the drop?

I'd change that R, if you haven't yet. 

Yes, the R could be bad internally. Sometimes 1 of the leads is not connected fully to the R's body, you can't see it, R can be cracked inside, you can't see it.

Also, it could be a bad solder joint, bad resistor, bad tube or tube biased wrong, so it's drawing too much current.

It's dropping 157dcv across that plate R, while only drawing a mA or so of current, can't be. Like shooter wrote. The more current you pull/draw through a R the more voltage gets dropped across it. Pretty common for a tubes plate R to drop 1/2 or so the the dcv across it.   

Or is the Node F voltage of 177vdc too low?

The nodes dcv is fine. That's not the problem.

[wsscott]

Thanks everyone for the input. I did replace that .005uf cap that ties onto the 100K resistor, but haven't replaced the resistor yet. I delivered the amp this morning to my buddy who was given the amp, and he's going to work on the tube sockets.  So I'm out of business until after Christmas.  When I get it back I'll follow up with these leads and let you know what I find.

Best.

[bmccowan]

best quotes

I stole it myself, might be a Sherlock Holmes variation


I used it a lot talking with other Field engineers "Once you eliminate all the good parts, only the bad parts remain"

Similar to a quote that has been attributed to several sculptors including Rodin and Michelangelo - "the sculpture is already in the stone, I just remove the parts I don't need."

[wsscott]

I don't have the amp, but I think I found a simple solution to the wiring problem.  All I need to do is to swap the jumper wires connecting the P5 plates to the circuit board on V2 and V3, and the same thing for the P6 cathodes.  I'll have to wait until I get the amp back, but since half of V2 should be on V3 and vice versa, that's the solution.  I probably need to swap the P4 grid wiring to the circuit board too.

If this is correct, it's my not being able to see the forest for the trees.  Fingers crossed.

[Willabe]

I don't have the amp, but I think I found a simple solution to the wiring problem.  All I need to do is to swap the jumper wires connecting the P5 plates to the circuit board on V2 and V3, and the same thing for the P6 cathodes.  I'll have to wait until I get the amp back, but since half of V2 should be on V3 and vice versa, that's the solution.  I probably need to swap the P4 grid wiring to the circuit board too.

What are you talking about?????

And what does P in P4, P5, P6 stand for?

[shooter]

What are you talking about?????

 
yep, i even broke out the Joe schematic, went back to my novel


pics are worth a thousand words, just use paint or some simple pic editor and indicate what you're saying

[Willabe]

Got into the eggnog?   

[wsscott]

If V stands for a Valve, then P stands for a Pin of the Valve.  Easey Peasey.

[Willabe]

If V stands for a Valve, then P stands for a Pin of the Valve.  Easey Peasey.

No not easy, no one uses that. 

[shooter]

"P" is typically "plug" "J" jack so something like J15 >> P15 would be jack 15 to plug 15.  P15-3 would be plug 15 pin 3

[bmccowan]

Besides the Eggnog

but I think I found a simple solution to the wiring problem

From my perspective this project has been harder than needed because its not clear if the approach is to repair as built, or rebuild according to the schematic you are using. Yes, Ampeg has been wildly inconsistent with this circuit, producing various versions. So you could stick with what they built, or rewire the amp according to a verified schematic of one of the circuit versions. Trying to do both at the same time would drive me to the eggnog and probably some dry refreshment too.
As Shooter, and others, me included, have suggested. Use that schematic as a guide to sketch out what you want to do and Shooter and Willabe will put away the novels and eggnog and help get this beast making music again.

[wsscott]

bmccowan-yea the problem I've been having is that I'd want to repair it as built, but I can't tell how it was built because of the problems with the schematic, and at least 2 prior amp techs that I have recently learned had their fingers in the amp modifying it to make it sound better, and the last one gave up leaving the amp inoperable.

So that's the struggle.

[bmccowan]

I see that its a struggle.
I would forget about what the last two "amp techs" did to the amp.
A month ago several of us recommended that instead of trying to repair what was there, you decide on a schematic and follow it.
You decided to do that, using the Joe P schematic - good choice even if it has a couple minor errors.
First step was to go through the amp, with the schematic and document all the differences. The decision to skip that is haunting the project IMO.
Yes, Ampeg did not consistently follow a schematic, even swapping tube positions on the chassis. It was their company and they took liberties, never suspecting that all these years later we wingnuts would be trying to decipher what they did.
You are not far away from having this working.
When you get it back from your buddy, I still suggest you go through the circuit and mark up the differences with the schematic you are using. That will make finishing it much easier for you and others.

[wsscott]

I started that process with Joe's schematic, but there were so many differences, I couldn't write them on the printout of the schematic and still read them.

What's the best way to do what you recommend?  Some of the differences are values of components, and some of the differences are how components are wired.  So printing out the schematic and marking it up is not so easy to then work from.

I wish I could somehow get Joe's schematic into a piece of software, like DIYLC or something, and work from that.

[Willabe]

I wish I could somehow get Joe's schematic into a piece of software, like DIYLC or something, and work from that.

I'm pretty sure you can and Doug shows how to do that in that DIYLC section.

[shooter]

I started this, then you went off sideways n I couldn't keep up, I just used paint from MS. 

[wsscott]

Shooter-thanks for your work.  I use a MAC so Paint isn't an option but I don't know to draw circuits like that in any software.  I've used DIYLC before but I can't get it to work on my MAC running Sequoia 15.1.1.  I'll see if I can figure something out over the holidays.

[bmccowan]

I'm getting a strong feeling of Deja-vu all over again.
On Mac you can use J-schem or ExpressSch (I don't recall which one works with Mac) and work from existing schematics in .sch format.
As with DiY Layout - the instructions for download and use are all here on Doug's site. Its easy to learn, especially if starting from existing schematics.
Attached is a Reverbrocket schematic in .sch and a copy jpg - not drawn by me. Is it accurate? Accurate enough to work with. And you will learn a lot about schematics.

[wsscott]

Thanks.

[wsscott]

Sorry, I hit the Post button to fast.

I appreciate the info on the schematic drawing issue, but I don't want to take up your time fooling with that. I'd much prefer your time/input when I need it on getting the amp working.  I'll get this amp figured out and working eventually. 

Best.

[HotBluePlates]

Or... use the original schematic that was pasted inside the back panel:
https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_r12r_reverb_rocket.pdf


I didn't check every part on the layout I linked before, but the parts I did check matched the original schematic above.

[wsscott]

None pasted or to be found. Not under the foil.

[Willabe]

None pasted or to be found. Not under the foil.

You don't have 1 but, the link HBP's posted IS a copy of the original schematic that was pasted inside the back panel.

[HotBluePlates]

Or... use the original schematic that was pasted inside the back panel:
https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_r12r_reverb_rocket.pdf


I didn't check every part on the layout I linked before, but the parts I did check matched the original schematic above.

None pasted or to be found. Not under the foil.

You don't have 1 but, the link HBP's posted IS a copy of the original schematic that was pasted inside the back panel.

Right.  The linked schematic is slightly different from the one pasted in my amp (below), but only because my amp pre-dates the move to NJ.  All the parts/connections are the same.

[wsscott]

HotBluePlates--In the schematic attached in your post above, it shows a 25/25 electrolytic cap coming off V1 Pin 3 Cathode with the Negative side of the cap going to ground.  Seems correct.  But in the Layout of the schematic shown in Post 43, on the far left side of the layout at Eyelet 2, it shows the Positive side of that cap going to Ground at the Guitar Jack.  I assume that is a "typo", but just thought I'd check with you.

I ask in part because in my amp there's a short, 1.5", black wire connected at one end to a Ground on the Input Jack for the Guitar, and the other end is left FLYING in the air.  So I'm trying to figure out where that should attach, or if it should be removed.

I haven't gotten the amp back yet from my buddy, but I'm trying to keep occupied until it's returned.  I don't know if that could be affecting the low output volume.

[shooter]

other end is left FLYING in the air.

normal
shielded wire is only grounded at one end, otherwise it creates a "ground loop"

[wsscott]

Yes, but this isn't shielded wire.  Its just a short piece of single core wire that's connected at one end on the jack and its not connected to anything on the other end.

[bmccowan]

If I'm understanding this, you did all that troubleshooting while you had a disconnected ground wire?
I think you need to look at that layout and compare it with the schematic you are following. I suspect the layout has an error - it may show that electrolytic cap backwards. I further suspect that eyelet two connects one of the V1 cathodes to your input jack ground. But you need to take a close look at the schematic to make sure. And then I would make sure that you have no more "flying in space" leads before you try to get the amp sounding right.

[wsscott]

I understand your point about the "disconnected ground wire", but since this amp had a couple of wires like this which appeared to be "add-ons" since they're not in the schematic or layout, like this wire which is also of a different gauge than other wires in the amp which appear to be original, it's kind of hard to figure out what its for and if it should be there in the first place.

I'll hopefully know more when the amp comes back. 

[shooter]

one of the "tricks" to making a wire "shielded", without shielded wire, is to take a standard solid strand wire, ground one end and wrap it around the wire to be shielded.

[HotBluePlates]

HotBluePlates--In the schematic attached in your post above, it shows a 25/25 electrolytic cap coming off V1 Pin 3 Cathode with the Negative side of the cap going to ground.  Seems correct.  But in the Layout of the schematic shown in Post 43, on the far left side of the layout at Eyelet 2, it shows the Positive side of that cap going to Ground at the Guitar Jack.  I assume that is a "typo", but just thought I'd check with you.

It's a typo.  Unfortunately, the draftsman is deceased & someone will need to edit then re-upload the layout.

I ask in part because in my amp there's a short, 1.5", black wire connected at one end to a Ground on the Input Jack for the Guitar, and the other end is left FLYING in the air.  So I'm trying to figure out where that should attach, or if it should be removed.

It should be attached as the layout shows, at Eyelet 2, marked "Guitar Jack Ground."
My amp has the Black wire from the jack connected to Eyelet 2, along with a Green wire that runs over to Eyelet 4 to make the Ground connection.

[wsscott]

Progress!!-I got the amp back yesterday, and the first thing I did was to connect Jack 1 ground to Eyelet 2 of the circuit board, getting it a ground for the rest of the preamp.  In addition the 25/25 cathode cap was connected to Eyelet 1 and it should have been on Eyelet 2, so I switched the negative end of the cap to that Eyelet..  Finally, the 1.2K resistor (at Eyelet 1) coming off the cathode and going to the footswitch per the schematic was installed with a 2.2K resistor and I replaced it with a 1.5K.  I also replaced a couple of other old caps.  There are a few original caps left in the amp as well as 1 old small electrolytic.

So I powered it on, and plugged in my guitar.  With all the pots at 0, it's dead quiet.  The footswitch cable was cut off from the circuit board, so nothing is connected there, and there is no reverb tank plugged in.

When I turn up the volume I get strong, clean guitar sound; however there's a lot of hiss and crackling in the background.  I have enough clean sound and volume at 2-3 on the volume pot that I haven't needed to turn it up higher. Tightening up the tube sockets seemed to have cleared up the sensitivity I was having in the beginning with the tubes as one source of the noise, but I was getting minimal output volume even at full volume on the pot

So fixing the ground to the Input Jack was the big fix so far.  The guitar sound is really strong, and clean but for the hiss, etc.  The tone pot also is responsive.

So now I need to figure out what's causing the noise.  There's no hum that I can tell.  And there's no distortion in the output sound.  So any help on this issue is greatly appreciated.

[shooter]

hiss and crackling

Hiss is typically associated with old carbon Resistors, usually at the plates
Crackling is typically associated with loose solder joints, cracked foil on PCBS, sloppy sockets...something is "making n breaking" contact.

[wsscott]

I'm working on the hiss issues and replaced the 25uf cap connection the cathodes of V4 Phase inverter.  That cathode on Pin 3 connects to a 220 ohm resistor, and also a 10K resistor that goes off and connects to the 8 ohm secondary winding of the Output Transformer, according to the schematic.

The Layout referenced above shows that 10K resistor but its shown like this 10K(1K).  What does that mean?

On the circuit board in the amp, the 10K connects from Pin 3 Cathode on the V4 PI tube socket to a circuit board eyelet.  There is nothing else connected at that eyelet.  It seems like either (1) the 8 ohm lead from the secondary should connect there with another wire then connecting from that eyelet to the Output Jack, or (2) I should connect a new lead from that eyelet where the 10K resistor is also connected and then run that new lead to the Output Jack lug where I currently have the 8 ohm secondary winding presently connected.

Is this correct, and which wiring scheme is better?

I can only assume that whoever removed the Output Transformer before my buddy got the amp, also removed that wiring at the eyelet.

[Willabe]

The Layout referenced above shows that 10K resistor but its shown like this 10K(1K).  What does that mean?

Layout referenced where?

You have 192 reply's! You need to keep the layout and schematic in the new post your asking a question about so we don't have to search for them through 4 pages of 192 reply's.         

I'm working on the hiss issues and replaced the 25uf cap connection the cathodes of V4 Phase inverter.  That cathode on Pin 3 connects to a 220 ohm resistor, and also a 10K resistor that goes off and connects to the 8 ohm secondary winding of the Output Transformer, according to the schematic.

On the circuit board in the amp, the 10K connects from Pin 3 Cathode on the V4 PI tube socket to a circuit board eyelet.  There is nothing else connected at that eyelet.  It seems like either (1) the 8 ohm lead from the secondary should connect there with another wire then connecting from that eyelet to the Output Jack, or (2) I should connect a new lead from that eyelet where the 10K resistor is also connected and then run that new lead to the Output Jack lug where I currently have the 8 ohm secondary winding presently connected.

Is this correct, and which wiring scheme is better?

I'm not sure on your wording, but I think if I understand you, their both electrically the same.

Look at the schematic and look at the layout drawing, the 220R gets connected on 1 end to the 8 ohm OT secondary and the other end to V4 Pin 3.

Your making this over complicated.

I can only assume that whoever removed the Output Transformer before my buddy got the amp, also removed that wiring at the eyelet.

Yes, probably. They might have wanted more distortion, so they disconnected the NFB loop.

Just re- connect it.

The link for the layout that HBP posted is in reply #23. And SEL49 posted a dry/wet signal hi-lited schematic back in reply 154.

And from now on they both can be found here in reply # 193.

[wsscott]

I didn't re-post the Layout, referenced at Post 43, because one of the moderators said I should just reference or ID a link and not re-post because posting takes up Server space.

Any comment on why the Layout refers to the resistor as a "10K(1K)"?

[wsscott]

HotBluePlates-How does your amp wire the Output Transformer secondary to connect to the speaker?

My amp doesn't have an Output Jack for a speaker connection, and there's no empty hole in the chassis for a jack, and there's no terminal strip where some wiring could occur.

Right now I just have the Secondary wired directly to a 1/4" jack, and will ultimately stabilize it in the cabinet in some way.

Thanks.

[Willabe]

I didn't re-post the Layout, referenced at Post 43, because one of the moderators said I should just reference or ID a link and not re-post because posting takes up Server space.

Where at 193 reply's! Nobody knows the link is all the way back at reply #43! Except maybe you! 

So, when you ask a new question that the guys need to look at the layout and the schematic, tell them what the reply # is where they can find them.

Any comment on why the Layout refers to the resistor as a "10K(1K)"?

I have no idea why, but I wouldn't worry about it. Just go with the schematic's 10K.

[Willabe]

HotBluePlates-How does your amp wire the Output Transformer secondary to connect to the speaker?

My amp doesn't have an Output Jack for a speaker connection, and there's no empty hole in the chassis for a jack, and there's no terminal strip where some wiring could occur.

Right now I just have the Secondary wired directly to a 1/4" jack, and will ultimately stabilize it in the cabinet in some way.

Look at the picture in reply #11. (And #10)

It sure looks like Ampeg didn't use a 1/4" speaker jack mounted in the chassis. They just ran the OT secondary fly leads directly to the speaker.

[SEL49]

When that amp was new Ampeg connected the OT secondary directly to the speaker using crimp-on quick disconnect terminals. The OT-151A was a special transformer that was used in several of the 15W to 25W combos during that time period. The OT only had a single 8Ω secondary winding, but there were two black leads and two green leads connected as shown in the pic. One green and black lead went directly to the speaker without ever passing through the chassis. The other green and black wires passed through the chassis and connected to the board for NFB. 

[wsscott]

Thanks.  That's how I'm doing it but using a jack instead of the crimping method.