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

[HotBluePlates]

Georgeous!! Is that how it was when it was brand new, or is that its condition now?  ...

Both.  It's a mint 1962 Reverberocket I got a few years back.

So original it still has all Ampeg-branded Sylvania tubes, and the cardboard box that carried the amp from Ampeg to the music store that sold it.  The store wrote the list price of $189.50 on the side of the box.

[wsscott]

I want to add a 1/4" speaker output jack to the chassis, and the only spot that looks good is between V4 (PI) and V5 (Output) tubes.  Is there any problem with putting it in that location, ie. hum, hiss, noise, etc.?

Also, any thoughts on adding 2 RCA jacks to the chassis for the Reverb IN/OUT, and a RCA or 1/4" jack for the footswitch(s) controlling them?

[bmccowan]

You are making progress!
I do not believe in drilling holes in vintage amp chasses, even if they are a mess and non-original.
If you differ with the above, my next semi-rant is to get it working well first before making any mods. If you mix mods and repairs you will have a harder time chasing down gremlins.

[wsscott]

I agree with you about the mods.  Get it working first.  I don't know what my buddy who owns the amp thinks about cutting holes.  That will be his call.  He's said he wants the speaker jack, and I don't think he'll change his mind for originality purposes.

So given that a "change is gonna come", any thoughts on my original question?

[bmccowan]

That's a typical location for a speaker jack - so should be ok.
But an option to get the functionality without drilling a hole is a cable end female jack:
https://www.parts-express.com/Switchcraft-128-1-4-Mono-Cable-Mount-Jack-Female-with-Screw-Terminals-093-1009?quantity=1&utm_source=google&utm_medium=cpc&utm_campaign=21081298514&utm_content=162693410634&gadid=692832564687&gad_source=1&gclid=Cj0KCQiA3sq6BhD2ARIsAJ8MRwX-r8xbAbbOuUHZ_Wzc0qinnrYn48aTOjdAOxM_5kH31M8FHbUICZoaAvSwEALw_wcB

[wsscott]

Good option. I’ve never seen that type of jack.  Thanks.

[Willabe]

That's a typical location for a speaker jack - so should be ok.

Doesn't look like there's enough room.

[wsscott]

My parts order came in today, which includes the new OT that was missing from the amp!  Can you tell me how to wire in the new OT so that it doesn't get that loud, horrible, squeal when the amp is turned on?  Thanks.

[shooter]

Can you tell me

 


got a silver dollar?


IF.. the original OT had Phase marks, AND they were indicated on the schematic AND your new OT has phase marks, you might have a 75% change of good guess


50 50 90
if there's a 50 50 chance, 90% of the time you choose wrong, so choose, then do the opposite 

[bmccowan]

There is a YouTube for everything. This one describes the approach Shooter describes:
https://www.youtube.com/watch?v=rMz7JBRbmNo

[Willabe]

Can you tell me how to wire in the new OT so that it doesn't get that loud, horrible, squeal when the amp is turned on?

Just leave the OT plate leads long, until you know for sure you have the phasing right.

[shooter]

IIRC swapping speaker wires works while testing
the squeal is good, improves reaction time, tests hearing, tests patience, self control, self loathing....

[wsscott]

Glad to know I’m not missing something.  I thought there might be a way to do it correctly and not just by chance!  So, I guess it’s better to switch the plate leads vs. the speaker leads so that the + & - leads on the speakers match up.

[shooter]

yes at the speaker, but at the OT's output, which is +   

[wsscott]

Does it go out of phase because the wires on the OT primary are reversed from those on the Secondary when the Secondary is wired to the speaker?

For Example:
Assume you have Red at the top of the Primary, then a Yellow center tap, and then a Green lead at the bottom of the Primary winding.

And on the Secondary you have a Black lead at the top, and a Brown lead at the bottom.

How do you wire the secondary to the speaker to avoid squeal?  Black to + and Brown to - terminals?

[wsscott]

Sorry, assume that the Black lead is the COM, and the Brown lead is 8 ohms.

I just checked the OT spec sheet.

So given this info would it be wired Black to - speaker terminal, and Brown to + terminal?

[Willabe]

Yes.

Can you post that spec sheet?

[wsscott]

Here's the spec sheet for the OT.

[shooter]

see he 2 black dots at the top of the OT near the "coil", those are phase marks, if you put a positive wave on the input wire with the black dot, you will be "in phase" at the dot wire output. 


IF your original had those dots, you would wire "dot wire" to "dot wire" with the new OT and it should be "phased" properly.
in the end, it's not worth your brain energy, if it squeals, simply swap either the inputs or outputs, walla, on to the next thing

[wsscott]

Thanks.  I've learned something even if I may never use it, at least I'll know what those dots mean.

[wsscott]

I'm starting to wire up the filter caps. This amp's can cap was replaced with a 40/40/20/20, and only the two 40uf nodes were ever used.  The circuit's schematic is designed for SIX 20uf cap nodes.  So I guess whoever did the work just doubled up or something with the two larger nodes in the can.

I'm wiring it to use all 4 of those nodes, and then adding two 20uf caps.  I'm trying to get the voltage supply to the circuit to have some resemblance to the schematic.

So my question is there anyway I could be overloading the circuit by doing it the way I want to, since the rats nest of wiring doesn't follow any schematic and many of the components are not even in the location shown on the schematic.  I don't know what "re-wiring" was done, and its gives me a headache trying to figure it out.  I don't even know if it was operating before it was cannablized for parts.

Thanks.

[shooter]

wire it per the schematic you're following, a 40Uf cap is an "Improvement" to the 20uF


make SURE you don't "leave behind" a stray wire from days gone by as your rebuild each section.

[AlNewman]

Here's the datasheet for a 5y3.

It doesn't have a maximum rating for capacitance, but the typical value is stated as 10Uf.
Do with that what you will.  That would be the only place in the amp where adding extra filter capacitance could cause damage.

https://frank.pocnet.net/sheets/049/5/5Y3G.pdf

[wsscott]

In this circuit, there's no cap before the rectifier but only after its 5VAC filament supply. So I wouldn't think it would be an issue.

[bmccowan]

In this circuit, there's no cap before the rectifier but only after its 5VAC filament supply. So I wouldn't think it would be an issue.

I'm not sure what you mean by that, but its that first filter cap, the reservoir cap, that is the issue. One can go down lengthy winding rabbit holes on this subject, but from a practice standpoint, many consider 32uf to be the max reservoir cap value for the 5y3, but many, many amps are operating happily with 40uf in that position.

Related - since you do not know what made this amp fail, and you are uncertain of the wiring, you should be careful on testing and startup. Following a known standard procedure will protect your $ and time investment.

[Willabe]

In this circuit, there's no cap before the rectifier but only after its 5VAC filament supply. So I wouldn't think it would be an issue.

There tied together. The 5acv goes to the rectifiers heater/cathode, depending on if the rectifier tube is directly or indirectly heated. (5Y3 is directly heated) So the 5acv rectifier heater also has the full rectifier dcv on it.

So it is an issue. 

https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_reverb_rocket_12r.pdf

[wsscott]

This amp and the schematic show 20uf caps for nodes A, B, C, D, E and F.  The can that's in this amp is 40, 40, 20, 20 and then there will be two additional 20uf caps added. In tracing the B+ wiring, I notice that some of the plates, ie. pins 2 and 5, in some of the tubes might have B+ coming to them from nodes E and F, but on the schematic the B+ is coming from nodes D and F.  And maybe the plate resistor is lower or higher than in the schematic.  Sometimes it's consistent with the schematic.

My question is does it matter which nodes the plates are wired to as long as they're 20uf caps supplying the B+?

[shooter]

does it matter which nodes the plates are wired to

short answer, Yes
longer "reasoning";
You want the most "sensitive" tubes further down the line, that way the PS "compounded" filtering provides the cleanest VDC.

[wsscott]

I wondered if anyone could tell me why this circuit has a 100uf/25V cap on the cathode to V1 going to ground in parallel with a 2.2K resistor?  I think this is part of the tremolo circuit.  It just seems like that's a big cap even though small in Voltage and physical size.

What's wired in the circuit located in this area, but of course it doesn't connect to the cathode, is a 100uf 325V cap that's a monster.  I'm guessing it was being used for one of the filter nodes.  But there's no cap at all coming off of the cathode on V1 like there should be.  Its got the cathode resistor connected but no cap.

[Willabe]

I wondered if anyone could tell me why this circuit has a 100uf/25V cap on the cathode to V1 going to ground in parallel with a 2.2K resistor?  I think this is part of the tremolo circuit.  It just seems like that's a big cap even though small in Voltage and physical size.

It's not part of the trem.

Read this from HBP on the large cap value for killing humm.

https://el34world.com/Forum/index.php?topic=32255.msg356823#msg356823

[wsscott]

Interesting.  250uf is a big one. 

[shooter]

250uf is a big one.

20 Farads is a big one, 10 thousand mikes (10,000uF) is a normal on computer PS's


250uF is the lazy engineers "fix" in tube amps.

[wsscott]

I got the wiring finished, but not without some frustration with the schematic.  There's an error!  Surprise, surprise.

I was getting weird voltage readings on V-4, the PI 6SL7, for the plate voltages.  Pin 5 was reading ok.  But Pin 1, as shown in the schematic, was showing only mv and Pin 2, the grid, was showing high voltages.  It was driving me crazy tracing the circuit to try and figure out what was going on.  Then I looked at V1, also a 6SL7, and noticed that the numbering on the Pins for the 2 tubes was different!

Long story short, Joe Piazza mis-labeled the PIN numbers for the first half of V4 and reversed the numbers for the plate and grid.  The plate should be numbered "2" and the grid "1".

[wsscott]

I've only had the rectifier tube installed and powered on with my Variac and current limiter.  No glowing bulb.  Voltages are high but as expected.

So I'm planning on installing all the tubes this afternoon and firing it up.

Any suggestions on startup procedure for this one?  Any thoughts on what the bias setting should be?

Thanks.

[shooter]

Any thoughts on what the bias setting should be?

looks to be self biased, PA tubes have a shared common cathode resistor
put your meter across that R, set for VDC, use a 2nd meter to monitor VDC at the PA B+ tap
once the heaters are up and the tubes are drawing current, BOTH meters should "stabilize"
IF the B+ keeps going down and the cathode keep creeping up, POWER OFF
IF they do stabilize at something close to "expectations", use those readings, the R value, crank out some math for tube current
NOTE that R is shared!!  so it's the current for BOTH tubes

[wsscott]

Should I start out by just installing the Output Tubes and see how it goes, ie. smoke, sparks, blown fuse?  Or put in all the tubes and let her rip?

[Willabe]

Should I start out by just installing the Output Tubes and see how it goes, ie. smoke, sparks, blown fuse?  Or put in all the tubes and let her rip?

Put all the tubes in, that's what the bulb limiter is for.

If the bulb stays bright, start pulling tubes 1 at a time until the bulb goes back dim. There's your trouble spot/circuit.

[wsscott]

Ok, I put in the tubes and turned it on, and nothing blew up!

Low glow on the light bulb limiter (LBL).  Variac slowly increased to 120VAC.

Here are initial main observations after plugging amp directly into Variac and LBL removed from circuit:

V-7 Rectifier-Pins 2 & 8 read 375 VDC.  Perfect.  Pins 4 & 6 read 53/46 mv respectively!!  When I measured the voltage there with only the Rectifier installed all the pins read about 499 VDC, but of course no load.  So 2 & 8 go to proper voltages with load applied with the other tubes, but 4 & 6 have essentially no voltage.

V-1 is not getting warm, and no glow. It reads Pin2 326VDC, and Pin5 290 VDC.

I assume its not drawing any current for some reason.

V-3 voltages on P2/P5 are 140/19.  So that's squirrely.

And of course there is no guitar output when its plugged into any of the 3 jacks and played.  Just hiss.

So now the sleuthing begins.

Thoughts on these issues?  Thanks.

[shooter]

no glow

filaments, wiring, tube

So that's squirrely.

Tube, tube R's n C's, wiring..

happy hunting, one problem, one solution typically works best

[wsscott]

These are all new tubes, except I am using the old rectifier.  So I will change that and see if it makes a difference.  I feel like that old tube is okay since I am getting proper voltages on Pins 2 & 8, and high voltage on V-1.

I had previously checked the filament wiring on all the sockets and they were good.

I wonder about the 100uf cap on V-1 Pin 6 cathode that's coupled with a 2.2K resistor.  I'm confused on the grounding of the resistor, and what that cap's negative lead is connected to.  I have them wired to the same lead going to chassis ground.

[shooter]

and no glow.

no-glow = no filament voltage or open filament in tube
see if the tube is getting warm, maybe the glow indicator in your eyes is getting on in age 


I'd leave the rec tube if volts are good

[wsscott]

I checked the continuity on V-1's 6VAC filament wires and it has continuity back through all of the tube sockets and to the pilot lamp where the 6VAC secondary connects.

Tomorrow I'll switch the V-1 pre-amp/tremolo tube with the V-4 PI tube and see if that makes a difference.

[Willabe]

.... Pins 4 & 6 read 53/46 mv respectively!! ....   So 2 & 8 go to proper voltages with load applied with the other tubes, but 4 & 6 have essentially no voltage.

Rectifier tube pins 4 & 6 are ACV. PT only puts out ACV.

When I measured the voltage there with only the Rectifier installed all the pins read about 499 VDC, but of course no load.

You don't really need to measure that with only the rectifier tube in. And you don't really want to do that because as you see now you get 499dcv and that is on the B+ filter caps. Are your filter caps rated for 450v or 500v?

V-1 is not getting warm, and no glow. It reads Pin2 326VDC, and Pin5 290 VDC.

Some small bottle tubes it's pretty hard to see the glow from their filaments, others very easy to see the glow. Turn out the lights in the room, then you can see if their lit.

[wsscott]

Good point on the filter caps.  They're 525 volts. Thankfully.

I switched the V1 and V4 tubes, both 6SL7's, and I also checked the voltages at all of the filament socket pins for V1-V4.

V1 and V4 both have a very very tiny glow, much lower than the 6SN7 tubes.  It can hardly be seen even with the lights off.  And the voltages read 6.3VAC on each tube socket.

So the filament wiring and filament voltage supply to the socket is good, and the tubes are good, but the problem persists.

If current is not being drawn properly on those tubes, would that affect the "glow"?  If so, what would be affecting the current draw?

[Willabe]

Good point on the filter caps.  They're 525 volts. Thankfully.

E- caps can take some over voltage for a little while, but your still stressing them.

Your being over cautious if you 1st tested the rebuild of that amp with just the rectifier tube. Not only do you have a bulb limiter but your also using a variac with it.You can do that but many guys would just use the bulb limiter by itself.

With both the limiter and the variac, even with just the bulb limiter, you could have put all the tubes in and fired it up. Bulb stays lit, just turn it off. Then go back and start pulling 1 tube at a time until that bulb stays dim. Pull a power tube, turn the amp on, look at the bulb, stays bright, turn the amp off, with that 1st tube still out pull the next power tube, etc. When the bulb dims back down again, you found the tube/circuit that's the problem. Or, it might be a direct short in your wiring somewhere else. 

If current is not being drawn properly on those tubes, would that affect the "glow"?

No, if the tube is drawing normal current or not, that won't change the filaments glow.

Some tubes are just hard to see the tip/end of the filament because of the way the tube was made. 

If so, what would be affecting the current draw?

Probably mis-wired, or bad tube. Check the dcv's at all pins, you know this by now. What do you get?

[shooter]

Here are initial main observations after plugging amp directly into Variac and LBL removed from circuit:

re-test volts with amp directly into the wall, PA tube cathode VDC and B+ Tap that feeds the PA tubes, if they fall within "normal"
then start at V1 vdc IF outside norm, fix, add AC signal, get it into and out of V1...this is the fun part, enjoy the process, and DON't add bugs as you progress 

[wsscott]

Shooter-I cleaned the tube sockets, then turned it on to test the voltages.

The voltages at all of 6 of the filter cap nodes seem fine.
A 388, B 353, C 304, D 228, E 202, and F 166 VDC.

The rectifier Pins 2 & 8 that feed HT to the circuit read 388 VDC.

The plates (Pin 3) on the power tubes V5 and V6, read 379VDC.

The cathodes (Pin 8) on the power tubes, read 23VDC.  That is also where the 6VAC center tap connects on V6. It is then jumpered to V5's Pin 8.  I've also got a wire going from V6's Pin 8, to the + side of the 50uf bias cap and 250 ohm 10 Watt bias resistor.

Is the cathodes' reading of 23VDC a "normal" reading?  I don't know what is. 

[wsscott]

I had turned off the amp after these tests for about 20 minutes, and just turned it back on.  When I did I noticed that the V3 tube's filament became very bright for a few seconds, and then went back to a normal glow.  All of the tubes are very sensitive to being even lightly touched, and V3 particularly so.

I would like to say that V3 is for the reverb, but the way this thing is wired I think 1/2 of this tube is for either the driver or recovery stage of the reverb, and 1/2 of V2 covers whatever stage V3 doesn't cover.

So I guess removing V3 for the moment doesn't work.

[shooter]

needs double checking;


23VDC / 250 ohms = 92mA /2 = 46mA per tube
379 - 23 = 356vdc * 46mA ~= 16.38W per tube


If the tubes are 6V6 that's pretty hot, 6L6 about right.

[wsscott]

If I changed that resistor to a 750 ohm, or maybe a 1K 10W, that would get the bias down to almost 12 watts or lower. Correct?

Should I make that change? That’s a big difference isn’t it?