Ampeg Reverberocket R-12-R DIY project

Peegoo

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Do you guys think that Weber Copper Cap rectifier might be contributing to voltage readings that vary from the schematic? Maybe an interesting experiment would be to stick a 5Y3 tube in there and repeat the measurements.
 

Lowerleftcoast

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Still confused. I'm taking 6V6 pin 3 as the plate readings, and pin 4 for the screens. Yes, it would be typical to drop ~5V going through the OT. But if point A ("B+", whether taken at rectifier pin 2 or at the positive of the first filter cap) is ~350, why is plate voltage ~320?

What am I missing?

Unless I'm wrong, the 321 V is measured at the 6V6 screens (at "B"), not plates. I'm not smart enough to know why, on the schematic(s) there's a 5V drop from B+ on OT center tap to the plates (resistance-inductance of half the primary winding?) but the "A" voltage is taken where shown on the lower image of @Peegoo's schematic, no?
Yes CW, according to the schematic the resistance of half the OT primary should be the only resistance between pin2 of the rectifier and pin3 of the 6V6.

Since the voltage drop at 6V6 pins3 are lower than expected and since they are very close to B+ *B*, imo, @Peegoo should find out if the OT CT is connected to B+ *B*.

If Peegoo can't see the connections, I would like to see resistance readings between:
Power supply *A* and 6V6 pins3
Power supply *B* and 6V6 pins3
OT Center Tap and 6V6 pins4
 

Lowerleftcoast

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Do you guys think that Weber Copper Cap rectifier might be contributing to voltage readings that vary from the schematic? Maybe an interesting experiment would be to stick a 5Y3 tube in there and repeat the measurements.
Let's work with what we have for now.
 

King Fan

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Since the voltage drop at 6V6 pins3 are lower than expected and since they are very close to B+ *B*, imo, @Peegoo should find out if the OT CT is connected to B+ *B*.

Aha, you think the amp may be built or modded to have what we think of as screen voltage wired to the plates? Clever; that would explain things. (I'm gonna nickname this voltage, Ampeg's B, as "B+2", since "B+B" makes me think of a tasty beverage :)).
 
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King Fan

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Could this ^^^ have anything to do with @Peegoo's "It does run hot though"?
Dunno. I wonder about the effect on tone. If it's wired like that, I guess it's possible it was done on purpose? Some amps around that time ran some way low B+, and on way dinky PTs. I’m looking at you, 5F10 and 6G2.

But would that happen at the factory? We can also think of amps (hello, Gibson) where the schematic had a weak and eventually absent relationship to the actual build. But still….

How about as a mod? Not sure why (brown the sound?). But mods that alter B+ feed (Stokes, anyone?) are a thing.

I'm looking forward to the next chance our hard-working friend @Peegoo gets to check LLC's resistances -- poor guy. Peegoo, I really appreciate your extra effort here. I'm afraid it's very much in the theme of 'no good deed goes unpunished.'
 
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Lowerleftcoast

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"It does run hot though"?
I'm looking forward to the next chance our hard-working friend @Peegoo gets to check LLC's resistances -- poor guy.
Ohms law says the OT is not wired to *B* (B+2) through a 1k dropping resistance. The resistance of each leg of the OT secondary should work out to about 760R for that voltage drop.
Small AWG used for the OT secondary?
Hot OT?
The 1k dropping resistor measures ~300 Ohms? (Assuming it actually is wired to *B*.)
We will have to wait for the measurements.
 

Peegoo

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I'm looking forward to the next chance our hard-working friend @Peegoo gets to check LLC's resistances

I won't have time to poke around in there today but I'll get to it tomorrow. And just so you guys know, I'm not an EE or circuit designer, but I have just enough knowledge to get into plenty of trouble. I've scratch-built a few amps and done lots of repairs oover the years.
 

chas.wahl

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Nobody's impugning you @Peegoo. Quite the contrary; you're doing this whole issue a great service, and it should be done as, when and if you have the personal interest in it. Besides, you've got the amp, and we're all just theorizing. I happen to think this amp design is very interesting, and it gets a lot of love from owners who use one; that's why we're here, I think.

Being in a walk of life that uses consultants, and having been one too, I heard a funny/revelatory definition: a guy who knows a hundred ways to make love, but he doesn't know any girls. Or: the guy who when you ask what time it is, he says "could I see your watch?" We're the consultants, you're the client-owner with rubber on the ground.
 

chas.wahl

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As an amusement for you all (I am not asking anyone to check it) and at the risk of somewhat derailing this very interesting investigation into @Peegoo's Reverberocket, I have taken the Verberwaffe R-12-R clone's circuit board PDF, and marked it up with component numbers, added a couple components that it seemed to be missing, and "corrected" some values to reflect the original Ampeg design. This is my first step toward drawing my own layout using the same Fendery principles, rather than the Voxy "piano keyboard" style. I'm just providing a URL to my DropBox, because I want to be able to modify it without leaving an outdated prior version here when I can no longer edit this post.
Find it here.
I made a couple changes/corrections and updated the file at about 18:11 on 23 June 2022.
 
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Lowerleftcoast

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This is my first step toward drawing my own layout using the same Fendery principles, rather than the Voxy "piano keyboard" style.
I didn't check the whole layout.

Kibitz:
When you draw your own layout, move the 6V6 cathode cap (C37) & resistor (R31) to the left. Place them in between the dropping resistors (R37, R39) and the filter cap (C2).

This will keep the hot resistors together and away from the the caps. It will also place the *B* ground of the cathode next to the C2 filter cap *B* ground.
 

chas.wahl

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Yeah, the Verberwaffe (like the R-12-R) uses a cap can for 3 of them that aren't shown, and I'm just basically ag'in cap cans -- I plan to distribute all the filter caps into the layout at places where the B+ feeds and grounds of the various "modules" of the amp's organization can be gathered, Blencowe-style, at the various filter caps serving them. I'm well aware that the R-12-R has some "leap-frogging" going on in the B+ and one or two "splits", but the idea is to handle all that as elegantly and simply as possible. Thanks for the reminder to get the hot stuff isolated. I'm thinking about using some vertical space (raising the hot boys) to do that.
 

chas.wahl

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Stancor PM-8409 Power Transformer

Arrived yesterday. What I know so far:

010E3256-E52F-45BD-8B68-77F3F526DA02_1_201_a.jpeg
1DF1EF9F-63B2-4D7F-A908-4EBA47DF2976.jpeg
68703850-5EFE-42A1-A525-7CB33178F581.jpeg
1656096206266.png

Definitely seems to be unused. Though the label (with printing on top layer) was delaminating and in tatters in the eBay BIN photo, and came to me moreso, I was able to read the "PM8409" and the HT and rectifier info, plus the left side of the 6.3 V info but lacking the A rating on that. Still, the model number is something, and the photo below from a different eBay auction tells the full story.

Specs on label
Primary 117 V 60 cycle (blk)
Secondaries 350-0-350 V @ 90 mA DC (red), CT (red-yel)
5 V @ 2.0 A (yel)
6.3 V @ 3.0 A (grn), CT (double wire*, grn)
* I don't know with certainty what "double wire" means. Is the 6.3 V winding actually composed of two separate windings joined in the middle with the CT leadout wire?

Stancor PM-8409 Power Transformer.jpg


None of the windings appears to be shorted with others, or to the laminations.
DC resistances of the various windings (ohms)
Primary (blk-blk) 3.9 to 4.0 (multimeter dithering)
HT (org-org) 293.5
HT CT (striped org wire) to each of the ends of winding 150.6 to 142.8, so a bit unbalanced.
Rectifier (yel-yel) 0.4 to 0.2 or 0.1 (dithering)
Heaters (grn-grn) 0.2 to 0.1 (dithering)
Heater CT to each end of winding (striped grn) 0.0 to 0.1 (dithering)
All leadout wires stranded, not particularly high number of strands, with cloth (or cloth-covered rubber?) insulation. Primary and HT secondary 0.030" ø (22 AWG), heaters & rectifiers 0.048–0.050" ø (18 AWG)

Measurements
Mounting dimensions 2" x 2-25/32" -- so about the same fit as the Hammond 290BX sold for Tweed Deluxe use
Hole for bell (laydown) 1-7/8" to 2" x 2-1/2"
From mounting plane (bottom side of nuts) to top 2-1/2" high
Laminations 2-13/16" x 3-7/16" x 1-9/16" thick -- about 3/8" less thick than 290BX
Bottom bell 1" high from laminations
Top bell 7/8" high from laminations
Total height 3-3/8" -- about 5/8" less than 290BX
Weight 1776 g or 3# 14.7 oz.

What is the best way to check no-load voltages? Use wall voltage on the primary (I have done this previously), or is it accurate if I use an AC source at lower voltage and extrapolate?
 
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2L man

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I tape wires to table and feed mains to primary tack soldering a scrab cable. Good crocodile clips are fine too. Then measure exact mains and if there are more mains inputs measure them as well. They should show proportionally correct voltage ratios. Then all output voltages pressing wire ends against table. Then transformer is documented very well. I always measure OTs too because this take only few minutes and because sometimes transformer builders make mistakes.
 

chas.wahl

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OK -- I've taken a Quality Assurance walkthrough on both the Verberwaffe layout that I annotated and modified somewhat (to include missing board components and clarify off-board connections), and also my own schematic derived from the Ampeg 1962 original. I found several errors of mine in the Verberwaffe layout (both component values/numbers and routing), and in my own schematic also found a couple cap values I transcribed wrongly by a factor of 10 (C17 and C18). Here are links to PDFs of both updated files, plus the service manual, just to keep pointers to all the updated info in one place:
Reverberocket 1962 schematic and service manual, with my markup (not changed lately)
My redraw of the schematic, with some modifications, and also the original schem for comparison
The layout done by "Sonny ReVerb" on EL34world.com for his clone nicknamed "Verberwaffe", with my edits

For links to other original source materials, see my post #1 at the beginning of this thread, and also post #30, with a link to Sonny Reverb's cab thread, showing some photos of his chassis.

There's one thing I'm not confident about regarding schematics: getting the lug 1 and lug 3 straight for the potentiometer controls to achieve the desired action when a knob is rotated. Especially where reverb (dimension) and tremolo (speed, intensity) are concerned, which I have no experience with, theoretical or practical. So I do need to research that by looking at other schematics and layouts, before moving on.

Next I'm going to start on my own layout, leaning on Sonny Reverb's, but trying to rationalize to minimize leapfrogging of power and ground bus elements (and associated underboard shenanigans) as much as possible, and to put all six filter caps into the layout where they're most closely associated with the circuit elements they serve. It will be a long board . . .

I like the pre-perforated boards (nice and modular at a good grid spacing of 9.5 mm, plus red available!) sold by Tubesandmore.com, but 10" won't be long enough, plus I've often found myself wanting another hole -- or maybe 2 -- in the short dimension. So I'll plan on buying similar 1/8" (3 mm) material from someone like McMaster-Carr and drilling my own -- haven't decided yet whether I can deal with fiberglass reinforced or if "phenolic" with paper is a lesser health hazard (for me and everyone else) and good enough from a dielectric/moisture absorption point of view. But that's down the road; right now I need to get a layout that I feel achieves the goals I've set.
 

chas.wahl

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I'm starting to work on a layout for this amp.

My plan is to create the most real estate by using a wide (in the short plan "depth" direction) pan type chassis (brownface or blackface), in the bottom of the amp head à la Ken Fischer, with tubes mounted upright. Right now, I'm leaning toward
a) adding a (7th) filter cap between input tube section V1a and the B+ node C that feeds it (direct from the PI power supply, not through intervening dropping resistors
b) adding an (8th!) filter cap in parallel with the reservoir cap (at B+ node A), separating them with a choke in the B+ to isolate the 2nd one from the 5Y3GT rectifier with minimal voltage loss.
Both of these have been suggested by @Lowerleftcoast. I feel that if I can make them work, fit-wise, they're easy enough to leave out in initial build, and add later to see what the improvement sounds like.

Because I want to put all the filter caps into the circuit right next to the stuff they feed, I know that this will lengthen the board considerably -- those caps are all about 18–19 mm wide, and in "standard" configuration between B+ on one long edge of the board and Ground bus on the opposite edge they pretty much hog a swath that wide across the short dimension of the board. Oh -- I plan to use eyelets, not turrets, because of the latter's need for so much heat when soldering.

I'd like to end up with an amp head that's no more than about 20" wide (I have a tweed deluxe combo cabinet to house speakers) and no more than about 8-1/4" wide. Height is more variable. So, a chassis with long dimension no greater than 18-1/4", and short dimension no more than about 8", but less if I want the knob tops to clear the width. Again, height of the chassis would be less constrained.

Ideas that have been floating around in my head, revolving mostly around "go more vertical":
• Mount the PT (plan-wise with centerline on/near centerline of circuit board) on standoffs on the outside of the chassis, so that the bottom bell actually clears the chassis, and wiring is fed into chassis interior through grommets, like a choke or OT. Better for keeping heat away from the rest of the circuit it seems to me, but what electrical/interference effects might ensue (see next)?
• With PT out of the way, let the circuit board extend beneath the PT, and put it on decently tall standoffs too -- this circuit has a lot of "back-and-forth" involving B+ forks (shown on the top of my schematic), Ground connections and mid-board components connected to somewhat distant other mid-board components (shown mainly at the bottom of my schematic). What would be on the board area that's "slung under" the PT would be mainly the first few filter caps -- what problems might that cause? I'm willing to use more expensive, high-hour life, caps for those, but EMF and heat?
• I've thought about using radial-lead filter caps. Found a pointer to one "xtian" contributor at AmpGarage.com, who's really Aaron Lyon in Chico CA, dba "Monkeymatic". His builds are extremely sanitary and compact, and he often uses radial caps that are turned upside down and mounted through holes in the circuit board, to take the smallest footprint, be in close proximity to circuitry depending on them, and allow other components to be threaded between and around them -- very inventive, though I'm sure such large holes would take me some time to execute.
A good example (there are others on his site, in both the "For Sale" and "Amp Builds" sections):
1657120690299.png


I would be happy to entertain other ideas for making a fairly complicated amp fit into a chassis like the one I've described, short of doing the Vox-style (piano keyboard of components arranged on turrets) or going full-on point-to-point.
 
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Lowerleftcoast

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Mount the PT
You can mount a lay down style PT in an upright position. Some manufacturers had kits to do just that. You can fashion your own out of angle iron or L brackets.
Heat rises so heat from the PT is not concern to caps below. The reservoir cap and first filter cap should not be problem under the PT.
I've thought about using radial-lead filter caps. Found a pointer to one "xtian"... ...uses radial caps that are turned upside down and mounted through holes in the circuit board,
No problem with radial caps. It looks like he had enough room to mount them right side up on that build (without the fancy holes). Try to not make things more complicated than you have to. The can lay on their sides as well.

Be creative. The board does not have to have one row of components. This Hoffman board (below) kinda shows how two rows can fit. Maybe not a perfect example but I hope it illustrates some possibilities.

IMG_2185.JPG

Also consider mounting some components off the board P2P style. For example, Rob 5F6A site shows the 5F6A tone stack mounted on the tone pots.

On your schematic you show three snubber caps from anode to ground right after V2b, V3a, an V4a. These caps will perform the same function when they are from anode to B+. IOW, they can simply parallel the plate resistors. Bear in mind the plate resistors get hot so give some space to keep the caps cool.
 




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