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Allen 20: Three ways.....

Rex Everything

Rex Everything

are you Shpongled?
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Well...in an effort to get a set of Acrosound output for my Allen 20's I've ended up with three different amp :)

Two have the "Rondo" markings and one is just branded "Allen Organ" (the Rondo's have the same Allen Organ on them as well).

One of the Rondo's is serial number 1192 and has what I think is an Acrosound opt with the markings "M8-943" and "SP-511"

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The one marked only Allen Organ is serial number 2080 and has what I think to be an Acrosound opt with the markings "M8-943G" and "A0-85-0"

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The believed Acrosounds opt's look a bit different on the bottom where the wires come out. The wires appear to be a bit different color and the earlier serial number one has what looks to be a smaller gauge wire (may just be the wrap).

The third, serial number 3259, has a Stancor opt marked "M8943" and "231-4R"

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A close look underneath shows they all have a bit different circuit also. This is no big deal as at least two will be modded to use the same circuit (a Kegger design)

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Does anyone know if the two opt's I believe are Acrosounds really are Acrosounds and if so are they the same or different as they are marked differently.

My plan was to swap the Acrosound opt and the Stancor so both Rondo amps would be matching in opt. What do you all think?
 
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Rex, since Allen used Acrosound transformers on some of their bigger amps, there is every reason to think these could be Acrosound transformers as well. The can and mount tabs are identical to their smaller transformer line (i.e. TO-300, etc.). One thing you could do is measure the impedance of the transformers. The TO-300 is THE original Ultra-Linear output transformer from the developers of that concept, and was designed around 6L6 class tubes. That transformer is a 6600 ohm unit, with screen taps at 43% of the primary winding, and a 4-8-16 ohm secondary. If yours measures the same as these numbers, that is just one more indicator. Finally, Acrosound was known to produce their transformers in "unmarked" cans for use by others as well.

None of this is proof positive, but I'd bet on it.

Dave
 
Rex - please tell me you are going to use them either in a 3-channel 'stereo' setup or as the front channels in a home theater...

-D
 
derekva said:
Rex - please tell me you are going to use them either in a 3-channel 'stereo' setup or as the front channels in a home theater...

-D
Click to expand...

My current plan is to swap the transformer so the two marked Rondo have Acrosounds, mod the circuit and recap the pair and prolly move the spare on down the line.
 
dcgillespie said:
Rex, since Allen used Acrosound transformers on some of their bigger amps, there is every reason to think these could be Acrosound transformers as well. The can and mount tabs are identical to their smaller transformer line (i.e. TO-300, etc.). One thing you could do is measure the impedance of the transformers. The TO-300 is THE original Ultra-Linear output transformer from the developers of that concept, and was designed around 6L6 class tubes. That transformer is a 6600 ohm unit, with screen taps at 43% of the primary winding, and a 4-8-16 ohm secondary. If yours measures the same as these numbers, that is just one more indicator. Finally, Acrosound was known to produce their transformers in "unmarked" cans for use by others as well.

None of this is proof positive, but I'd bet on it.

Dave
Click to expand...

I was thinking along the same lines Dave.

They look like Acrosound TO-300's but having different markings made me question whether they are the same.
 
One thing to look at to tell if there Acro/TO-300 is the primary wiring has 2 "separate"
B+ inputs on it, 1 for each side of the tubes in the push pall pair, probably 2 red wires.
(usually there tied and soldered to the same B+ power supply input, so look close)

Also something like Dave mentioned is measure DC resistance of there primary windings
to see if your pairs match, also wire coloring would be good indicator of matching them.
 
Of Acro and Allen...so hard to determine proof positive. Can shape? I've got a solid state variac with the same can as an Acro TO-300, (Feeder Corporation of America, Chicago Ill.) right down to the same silver hammertone paint. 2 Separate B+'s? I thought that's what I'd see on my Allen 75's (Acro labeled OT's), thinking that they would be the same as my Acrosound TO-330's. Nope. 1 B+ wire on the Allen's.
Here we all are speculating 50yrs. after the fact! I can only imagine that the engineers from both companies would laughing their asses off at all of us for splittin' hairs! lol
I'd be inclined to think that the two you have that look the same, if they measure the same would be the way to go. From both the aesthetic and performance perspective. They could be (and probably are) Acro, but not necessarily to the same build spec as the TO-300 as is the case of Acro TO-330's and Acro labeled Allen 75's OT's? There's my food for thought?
 
Guit --Your points are very well taken. It is quite possible that Acro was simply the manufacturer, and that the actual transformers are not equivalent to their own product line. Where the Allen transformers are known to be of Acrosound origin, that does imply a quality product, but not specifications of what's in the can.

I think the effort here is one of "if it walks like a duck and quacks like a duck......" Therefore, if the turns ratio, DC resistance, wire color coding, B+ connections, and overall look are the same as a TO-300, then...... But you are quite right. Without actually measuring the delivered performance of these transformers when used in place of the genuine article, then we'll never know!

Thanks for sharing that little tidbit about the single B+ wire. For me, that is a huge clue!

Dave
 
Yes, thanks Guitarbanger!

I'll poke around on these a bit later. Have an amp on the bench already torn apart that needs my attention
 
It's likely that Allen sent Acrosound the specs and maybe even a blue print of the trannies they wanted built. :yes: Allen still has great customer service. It is possible if you were to actually call the guy at Allen and query him he'd know or perhaps be able to point to to a person who'd know. :scratch2:
 
Well it was all drivin' me nuts, on the 75's OT it gives specs of 3300 P to P, which is the same as the Acro TO-330 printed spec, at least in their some of their lit. but more often listed as 3800. However on one of my Allens with Acro's it looks more like 3800, on the other it's 3300, flattop 3's on all! lol Go figure? I've got two other Allen 75's, one has a gold colored paint like on the 90's with no markings (early) and the other (silver in color and later than my acro models) has markings of 3300! To be honest, I've never spec'd any of them, but, I can't tell a dime's worth of difference in the sound between the four of them, lol. All 4 are a little bit different from each other in several different aspects. I guess just due to circuit revisions, as they evolved in production and design changes as well as suppliers of parts. That's just the way factories and companies meandered their way through I guess despite that it drives us a little OCD decades later! lol Someday, it might be more than I can stand and I'll make'em all be the same! lol Until then, I guess I'll just keep enjoying them as they are.
 
I believe my 75's both have Saratoga TX's but they have had several changes made to the circuit.

Watch for a thread soon. Allen is gonna own the tube section here soon.... :D
 
Lar, thought about that one too. In trying to find out more about them (the amp part of Allens) I did stumble on a name of a design engineer that worked for Allen fresh out of college in '58 who I never contacted (he's up there in age). He worked there for 3 yrs. and after that was let go. I've thought about contacting him but thought better having done this before in "guitarland". Some of their recollections change with time and don't always correspond with the facts as is evidenced by date code info and other factors. Hell, I can't remember half of what I did this last week, so I ain't about to try and hold their feet to the fire over something they did 50+ years ago, if ya' know what I mean? lol
 
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