Acrosound Stereo 120
Steven L. Bender
Circa 1957 KT-66 / EL-34 Ultra-Linear based power amp. I've been using one
for about twelve years, and I've had to replace several caps, resistors,
rusted bias pots, but working without a schematic or anything has been
HELL!
I'd appreciate ANY INFO that anyone has on this Dave Hafler ( Pre-Dynaco )
amp.
Steven L. Bender
<< slbender@ mcimail.com >>
<< slbe...@nyc.pipeline.com >>
Paul J. Stamler
: The Acrosound Stereo 120 is a dual amp on one chassis using a common power
: transformer, sort of like Stu Hegemans' 1961 Harmon Kardon Citation II, but
: it pre-dates that unit by about four or five years earlier, circa 1957.
: I'm pretty sure of that date; it was, I believe designed by Dave Hafler
: prior to his starting Dynaco in the early 1960's. It uses thin bulb KT-77
: or EL-34 tubes in the output and is an UltraLinear Design, using an extra
: output winding for the feedback loop, which I think some other amps like
: the HK - Citation II don't do. I think there was a few nice Marantz units
: ( 8B ?? ) which had a similar design, with that extra winding, etc. Can
: anyone update me / correct me on that ???
A few corrections: These amps weren't designed by Dave Hafler, but by
Herbert Keroes, his former partner in Acrosound. Together they developed
the Ultralinear circuit in the early 1950s, and wrote an article for
either Audio or Radio & TV News describing it. They then had a falling
out, and Hafler went off to start Dynaco, around 1954-55. Keroes
continued with Acrosound, putting out the Ultralinear II ca. 1958; he had
an article in the Sept. '58 issue of Audio describing the circuit. It
used a very good output transformer, with less ultrasonic resonance than
typical transformers of the time, like Hafler's Dynacos. He also used an
excellent phase splitter, the long-tailed pair. The whole amplifier was
marvellously designed--except that he ran his output tubes, EL-34s, at
144mA for the pair, and they glowed dull red when properly biased, and
died very quickly. He got 60W from a pair of EL-34s that way--for a
while. Still, it was a very nice amplifier; I have a few in my basement,
awaiting reconstruction.
The Audio article in 1958 included an explanation of his variable
damping/hybrid feedback arrangement, which allowed some interesting
effects including the complete elimination of back-EMF from the feedback
circuit, at the cost of a fairly low damping factor when this circuit was
switched on. (The damping factor was about 15-20 with the hybrid circuit
switched off, typical for tube amps of the time.) It also included a
schematic, unfortunately without parts values, but it still could be
useful for figuring out what's what. More usefully, Sams published a
Photofact sheet for the Ultralinear II. I have one, but I'm afraid it
would take a few months to locate it, since I've moved several times
since acquiring it. I can tell you that all the bias adjustment and
balance pots are 5K, the bias resistors are 4.7 ohms, the input plate
resistors are 100K and 82K for the top and bottom units, and I seem to
remember the driver plate resistors are 47K, and its common cathode
resistor is 18K, several watts. The common cathode resistor for the input
long-tailed pair is, I think, 100K.
The reason I am going on at such length about the Ul-II is that, as far
as I can tell, the Stereo 120 was a stereo version of the Ul-II. I
suspect it appeared later than you think; I've never seen one, and the
only reference I've been able to find to it was an ad in Audio in 1962,
where I seem to recall they said it was new. I could be wrong, though.
With modern parts, adequate power supply capacitance, and decent output
tubes, this is a damned good-sounding amplifier. You can substitute 6L6
tubes in the outputs, for lower power but very clean and musical sound.
You can also, Acrosound claimed, substitute KT-88s, but when I tried that
they sounded very mushy and flabby in the bass, and wooly everywhere
else. You might experiment with bias settings: the high bias did produce
good performance, but short tube life. Set bias on each output tube for
0.34V across the cathode resistor.
Good luck, and let me know what else you come up with.
Peace.
Paul
Steven L. Bender
Hi fellow Audiophilles, Sorry if this is sort of a duplicate post, when my
mail reader opened the prior one I had posted, it was blank....
First - I'm interested in the ACROSOUND STEREO 120 Tube Amp. Does anyone
have any information, schematics, technical data, etc, beyond what is
stated below about it ???
The Acrosound Stereo 120 is a dual amp on one chassis using a common power
transformer, sort of like Stu Hegemans' 1961 Harmon Kardon Citation II, but
it pre-dates that unit by about four or five years earlier, circa 1957.
I'm pretty sure of that date; it was, I believe designed by Dave Hafler
prior to his starting Dynaco in the early 1960's. It uses thin bulb KT-77
or EL-34 tubes in the output and is an UltraLinear Design, using an extra
output winding for the feedback loop, which I think some other amps like
the HK - Citation II don't do. I think there was a few nice Marantz units
( 8B ?? ) which had a similar design, with that extra winding, etc. Can
anyone update me / correct me on that ???
about a netwide show of hands ??? Anyone ever owned one, seen one, used
it, etc ???
Thanx, and Happy new Year to all!!!
Steven L. Bender
<< slbe...@mcimail.com >>
<< slbe...@nyc.pipeline.com >>
Mark van Roojen
> : transformer, sort of like Stu Hegemans' 1961 Harmon Kardon Citation II, but
> : it pre-dates that unit by about four or five years earlier, circa 1957.
> A few corrections: These amps weren't designed by Dave Hafler, but by
> Herbert Keroes, his former partner in Acrosound. Hafler went off to start Dynaco, around 1954-55. Keroes
> continued with Acrosound, putting out the Ultralinear II ca. 1958; he had
> an article in the Sept. '58 issue of Audio describing the circuit. It
> used a very good output transformer, with less ultrasonic resonance than
> typical transformers...
> ...marvellously designed--except that he ran his output tubes, EL-34s, at
> 144mA for the pair, and they glowed dull red when properly biased, and
> died very quickly. He got 60W from a pair of EL-34s that way--for a
> while. Sams published a
> Photofact sheet for the Ultralinear II. I have one, but I'm afraid it
> would take a few months to locate it, since I've moved several times
> since acquiring it.
> The reason I am going on at such length about the Ul-II is that, as far
> as I can tell, the Stereo 120 was a stereo version of the Ul-II. I
> suspect it appeared later than you think; I've never seen one, and the
> only reference I've been able to find to it was an ad in Audio in 1962,
> where I seem to recall they said it was new. I could be wrong, though.
More details. I concur that the date was pretty late, just before Acro
went public, did not do well, and went under after which Keroes committed
suicide. I believe that this occured in round abouts 1962. (Probably Mikey
knows best.) Audio reviewed the Stereo 120 and noted that it was an excellent
amp which could easily have been rated at 70 wpc. Soon thereafter Acro
contracted with Radio Shack to produce the HK210 which was rated at 140
watts (70 pc) and looked (aside from the paint) remarkably like a stereo
120. Not too much later Acro went under so the association was short lived.
The ULII did preceed this amp on the marketplace by a little bit. I'm guessing
that the stereo amp was only avilable for a short time, judging from their
relative rarity relative to the ULIIs.
I have one of the original HK210s constructed in the factory (though I had
to rebuild it a bit). It uses KT77s which might help some with the glowing
plates. It does say that it can also be used with either EL34s, or KT88s and
6550s, but I have never tried that.
I haven't actually used it much, trying it out once on a couple of Apogee
stages which were just too power hungry to do very well with this amp on loud
passages. It is a nice amp.
Hope this is of some use.
Mark
MagneQuest
clarified many of the main points brought out about the history of Acro
and Dyna and their respective principals. Thought I might throw in just a
few tidbits that I know.
It was circa 1954-55 when David Hafler started Dynaco. A few years ago I
did some research at the state capital in the bureau of corporations
archives. Without digging out my records this time frame is about right
for the genesis of the Dyna Co. Originally operating out of a small
commericial building in the 5600 block of Master Street out in West Phila.
Dyna next moved to a location in Powelton Village (a west phila
neighborhood)...they actually where at two locations one on 41rst street
and the other (relying on memory here folks) on Powelton Ave. Of these
first three buildings two of them are still standing...the one on Powelton
Ave being leveled for hospital construction. Then it was off to 3060
Jefferson Str which is north of the art museum area....not a great
neighborhood. Then off to the suburbs in NJ till Tyco divested.
Of the Dyna transformer archives that I have I believe the earliest
tranney design is from 1954. From indivduals with whom I talked to about
the histories of the two companies and their principals the prevailing
sense or recollection was that the split up of the two parties from the
Acro company was based largely on a difference of opinion on whether or
not it was smart to offer kits. Story has it that Acro was suffering a
bit financially and David thought that kits would be a good way to
increase revenues and profits with Herbert believing that such would not
be profitable.
While the newly formed Dyna company met with a great degree of success
almost from the start Acrosound did not fare so well. Acrosound filed
for bankruptcy in a Phila federal court in 1963. However Herb reopened
the transformer shop with a new company name called Quaker City
transformers. Herb's stepson gave me a ream or so of stationary with the
Quaker City logo and stuff on it. In late 1970 Herb went to work for
Acopian (a power supply company) and helped set up manufacturing
capabilities in a new plant in Melbourne, Fl. Early in 1971 Herb
tragically took his own life while visiting with his family in Elkins
Park, Pa.
David Hafler whom still resides in Philadelphia was instrumental in
helping me get started. When I first bought the Peerless archives and
went out and hustled up some sales I kept thinking that the winding
portion was a no brainer. I remember my first "shop space" at 13th &
Walnut on the seventh floor of a run down office building....hustled a 800
lb winder up seven flights of stairs with a buddy of mine in pieces (the
winder not my friend <G>)....went in a day or so later to wind some coils
and at the end of the day still had not got down one solid layer without a
slew of crossovers....despondent I thought I was doomed and I can remember
thinking "at least I have the money to give back to everyone". When I got
home I called David Hafler and asked him if he might know anyone whom
could help me out of this jam. David suggested that I contact Paul
Kleinschmidt whom was a winder at Acrosound many years ago and whom was
currently retired. After digging around a bit I got a phone number for
Paul and called him.
Paul started working at Acro about 1952. Paul had polio when he was a kid
and when he finished high school he was looking for a job when a community
newspaper had an ad for winders for Acro. Paul went and applied for the
job but was first rebuffed by Herb whom felt that the tasks where better
suited for women. Paul tried to explain that he was looking for a "sit
down" job due to his polio. In retreat Paul thanked Mr. Keroes for the
interview and was at the front door when Herb called him back and said he
would give him a chance. Paul did well and stayed in the tranney business
for 40 plus years and is one of the most highly regar
MagneQuest
The first company registered was Acro Electronic Products Co. and is in
file #2915 at the Bureau of Corporations in harrisburg, Pa. My short
notes doesn't have a date for this filing.
File #2915 shows that the previous company was changed to Acro Products
Mfg. Co. on 2-21-61.
File # 0294285 is for Quaker City Transformer Co. and was filed on
6-21-63.
The original filing with the state for Dyna Co is in file #101283...sorry
don't have the date noted in my scratchings.
CBC Industries Inc. whom acquired many of the assets of the Acro company
through bankruptcy proceedings was located in Kensington . To my
knowledge and based on conversations with one of the prinicpals of CBC
this company never did produce any new products with the Acro name but
simply liquidated inventories that they acquired.
To this day the engineering archives of Herb Keroes have never been
located in their entirety (or even significant portions thereof). I did a
lot of legwork on this and contacted many business associates and family
members and etc. The only complete blueprint ever recovered was for the
Acro TO 350 transformer and then through a very circuitous and
surrepititous route. Paul has extensive knowledge of the construction
details and building practices of the tranneys... and can recite many of
the intracies of the designs. A family member gifted me some
miscellaneous books, articles under construction for magazines, and papers
that Herb had with him from his last trip to his home in Pa. Paul has
told me that Herb was never one for tidy paperwork (I guess I follow in
his path on that number) and that when he first worked for Herb...Herb
would write down the winding instructions on scrap pieces of paper from
memory and give them to the winder.
Much of the genuiousness of Herb's transformer designs is covered by his
patent. The two numbers that I have handy are patent #'s 2 710 312 and 2
680 218. The earlier is probably the tranney patent and the latter the
jointly held "UL" patent with David Hafler.
Mike
Herb Keroes died on Nov 10 1971 and is buried in the Mount Sharon cemetary
in Springfield, Pa.
MagneQuest
(MagneQuest) writes:
Great software from AOL...huh? Sorry the post got cutoff...see if I can
reconstruct the balance of the post.
> Paul did well and stayed in the tranney business
>for 40 plus years and is one of the most highly regar
>
...is one of the most highly regarded "tranney winders" in the Phila
region.
Acrosound was headquartered, in it's heyday, in a section of Phila called
Manayunk at 369 Shurs Lane. Several years ago the building was for sale
in a "shell" like condition for $65,000. It was bought by a yuppie whom
made a spectacular home out of the building. The building was perhaps
3,000 sq ft and built into the side of a hill....Mr. Hafler told me that
they had continual problems with shallow springs flooding the first floor
and David was shocked when I told him the asking price since he remembered
that the building had been constructed for $8500. This building has like
two feet thick field stone walls...neat building...wish I called have
pulled off buying it.
Paul told me that he can remember Acro shipping out 500 TO 300's a week to
Heath.
They had bought a bunch of those home type in wall ovens and that is what
they used to heat up the tranneys in preparation for the wax impregnation.
Herb was very skilled at adapting implements and tools of relatively low
cost to get the job done. Paul still has the first winder that Herb
built...it was constructed using a Lincoln 3 speed transmission and was
driven by a variable brush shifting AC sewing machine motor. For the TO
300's Herb designed a purpose built multiple coil winder wherein they
could wind 30 coils per stick at one time.
Dyna's tranneys where also built in Manayunk by a company called
Tresco...which stood for Transformer Electrical Specialties Co. In the
mid-seventies it was sold to a the management team and the name changed to
G&G Tresco. And about 1980 or so Technitrol bought the company and
operated it until late 1994 doing mostly mil-spec work. In 1994
Technitrol closed up the transformer operations and yours truly acquired
the lion's share of the production equipment...including 3 Universal 108
multiple coil winders that were rebuilt in 1982 at a cost of $15,000 each
and that had not ever, ever been put into service after the expensive
overhauls. Paul remembers production of the A470 output trans being so
brisk that Tresco was running three shifts a day for coil winders for this
job alone. A profecient employee on a 108 could wind up to 100 coils a
day. And a rough rule of thumb is that you need six to seven employees
per full time winder to do all of the ancillary operations necessary to
finish the transformers.
The Tresco facility was many, many multiples the size of Acro in terms of
production space. David was a very astute business man and was very, very
loyal and utterly above board with his suppliers from what I have learned.
For instance he used the same sheet metal house (at B & Allegheny aves in
the Kensington sections) for over thirty some years even employing them
for the sheet metal work for the Hafler Co. offerings. This company was
called Dalco. They had a 100,000 sq ft facility on several floors and
this building sold in the early nineties for 30 cents a square foot...and
this after the owner had put in 60,000 dollars of new windows in the
building with the prior decade.
If Lynn Olson is tuned in...he can tell you about my infamous unauthorized
tours of Phila's industrial landscape. So many cool buildings that
employed hundreds of thousands of workers now sitting idle, vacant, or
vastly underutilized. And graffitti everywhere. But in the heyday these
buildings and businesses where mighty economic locomotives and audio and
hi-fi played a significant role in Phila's economy.
Ooops...better end here before I get cut off again. Someone let me know
if I am boring the readership to tears or not.
Mikey
David N. Barnett
>Ooops...better end here before I get cut off again. Someone let me know
>if I am boring the readership to tears or not.
Boring? Never! This stuff is gold. More, please!
--dnb
Michael P. Gangemi
Dittoes!,
Mike
--
Mike Gangemi "Life sounds better in a vacuum..."
TUBESTUFF
Palmdale, CA
fax: (805) 285-0737
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