[John B]

anyone know where to find a power transformer for a McIntosh MI-200

[Staring at old audio chassis as a hobby :)]

On Jun 20, 3:27�am, "John B" wrote:
anyone know where to find a power transformer for a McIntosh �MI-200

http://www.mcintoshlabs.com/owners/

Happy Ears!
Al

[Bret L]

On Jun 20, 11:09 am, "Staring at old audio chassis as a hobby "
wrote:
On Jun 20, 3:27 am, "John B" wrote:

anyone know where to find a power transformer for a McIntosh MI-200

http://www.mcintoshlabs.com/owners/

Happy Ears!
Al

Nope.

The transformer will have to be rewound or a new one wound from
scratch, probably cheaper.

The old one can be torn down but if you have a good working set,
carefully removing its power transformer and measuring its no-load
turns ratios and the resistances, as well as measuring the voltages in
set (use a HV probe and gloves, there is lethal voltage here) under
quiescent and full power to dummy load operation, will be useful and
an improvement. You then spec the new xfmr to use the same size lams
and stack of height, and may transfer endbells and hardware over if
it's an endbell type. If it's potted, you will have to depot it. Mc
used tar-regular old roofing tar-as a pottant, be advised. IOW a
mess....

Any competent transformer shop can do the wind, it is not necessary
to pay an overpriced specialist like the guy in Wisconsin as this is a
common old power transformer design. Also, you will probably want to
have the primary turns count asjusted slightly for the modern higher
voltage on today's AC service. When your unit was new common AC was
110 to 117, rarely 120, and now it's often rarely that low.

[John Byrns]

In article
,
Bret L wrote:

The transformer will have to be rewound or a new one wound from
scratch, probably cheaper.

The old one can be torn down but if you have a good working set,
carefully removing its power transformer and measuring its no-load
turns ratios and the resistances, as well as measuring the voltages in
set (use a HV probe and gloves, there is lethal voltage here) under
quiescent and full power to dummy load operation, will be useful and
an improvement. You then spec the new xfmr to use the same size lams
and stack of height, and may transfer endbells and hardware over if
it's an endbell type. If it's potted, you will have to depot it. Mc
used tar-regular old roofing tar-as a pottant, be advised. IOW a
mess....

Any competent transformer shop can do the wind, it is not necessary
to pay an overpriced specialist like the guy in Wisconsin as this is a
common old power transformer design. Also, you will probably want to
have the primary turns count asjusted slightly for the modern higher
voltage on today's AC service. When your unit was new common AC was
110 to 117, rarely 120, and now it's often rarely that low.

Bret are you sure that common AC was 110 to 117 and rarely 120 when the
MI200 was new? Is there any hard evidence that the nominal line voltage
was actually lower when the MI200 was new, than it is today? My memory
is that when the MI200 was new, the nominal AC supply voltage was
exactly the same as today, what was different was that there was a much
greater variance of AC voltage levels that one might encounter. I
remember measuring AC voltages at the outlet ranging from 100 VAC up to
135 VAC in the days when the MI-200 was new, today the tolerance around
the nominal voltage is much tighter. I attribute this to the AC supply
infrastructure having been greatly stiffened over the years. Today
distribution feeders are heavier and more numerous and there are more
distribution substations resulting in shorter distribution lines, all of
this makes for a much stiffer system that doesn't require the substation
voltage regulators to be set as high as they were when the MI200 was
new. It is my experience that the highest AC voltages appeared around
the time the MI200 went out of production due to the way the substation
voltage regulators were set to compensate for the losses in the old
distribution system during periods of peak load. Subsequently voltages
have come down as a result of regulatory changes that resulted from the
energy crisis and the availability of more sophisticated control
systems, as well as the improved distribution system.

In any case the stock MI200 transformer provides several optional input
taps to accommodate differing AC voltages, so that redesign of the
transformer should not be necessary.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Bret L]

Any competent transformer shop can do the wind, it is not necessary
to pay an overpriced specialist like the guy in Wisconsin as this is a
common old power transformer design. Also, you will probably want to
have the primary turns count asjusted slightly for the modern higher
voltage on today's AC service. When your unit was new common AC was
110 to 117, rarely 120, and now it's often rarely that low.

Bret are you sure that common AC was 110 to 117 and rarely 120 when the
MI200 was new? Is there any hard evidence that the nominal line voltage
was actually lower when the MI200 was new, than it is today? My memory
is that when the MI200 was new, the nominal AC supply voltage was
exactly the same as today, what was different was that there was a much
greater variance of AC voltage levels that one might encounter. I
remember measuring AC voltages at the outlet ranging from 100 VAC up to
135 VAC in the days when the MI-200 was new, today the tolerance around
the nominal voltage is much tighter. I attribute this to the AC supply
infrastructure having been greatly stiffened over the years. Today
distribution feeders are heavier and more numerous and there are more
distribution substations resulting in shorter distribution lines, all of
this makes for a much stiffer system that doesn't require the substation
voltage regulators to be set as high as they were when the MI200 was
new. It is my experience that the highest AC voltages appeared around
the time the MI200 went out of production due to the way the substation
voltage regulators were set to compensate for the losses in the old
distribution system during periods of peak load. Subsequently voltages
have come down as a result of regulatory changes that resulted from the
energy crisis and the availability of more sophisticated control
systems, as well as the improved distribution system.

In any case the stock MI200 transformer provides several optional input
taps to accommodate differing AC voltages, so that redesign of the
transformer should not be necessary.

"Redesign" is a little stiff of a word: in a 60 Hz transformer
(actually in a new design one targets 47 Hz so that 50 hz gen sets
when loaded down won't kill anything) it's a simple matter of a few
more or less turns as needed.

Rather than arguing about it I would simply monitor one's own local
power over at least a week as the results will vary. But in general,
mean AC voltages for the 117 volt nominal household plug, either hot
to neutral, have been creeping up in most locales. The reason is that
motors deal with higher rather than lower voltages better. Modern
consumo electronics is all switchmode and does not really care. The
utilities don't want to fade political heat if brownouts take out air
conditioning and refrigerator compressors, fan motors, et al.

Your results may and probably will vary.

You may not need to adjust the design at all, but then again, the
bogey target here is to get the heater and filament voltages right for
your nominal voltages. B+ is a little fungible, on a transmitting tube
amp a fifty volt +/- B+ isn't a big deal if bias is set accordingly.

Looking through photos I downloaded from ebay sellers the MI 200
power transformers are indeed potted in folded/fabricated cans so the
first step is to depot without damaging the cans. I would probably put
it in a pressure cooker (from a yard sale, you bet) with a fill of,
say, WD40 with some MEK and toluene thrown in and press it down-with
N2!!!!-to ten or fifteen psi and let it sit. This will also attack
the insulation of the wire but it's all coming out anyway.

The can should not be dented or pulled apart. If needed, drill some
small clean holes that can be soldered over and sanded when the can is
repainted.

It would be helpful to have a good one to bench test for needed
parms, then all you care about is the wire gauges and any separating
HV barriers on teardown. It's a fair guess the can will allow for
more lams than Mc used, so for best life, a redesign to accomodate
more iron might well be desireable.

Really, think of it as a new build that has to fit the can. There's
no particular reason to reuse the old lams and it MAY be possible to
benefit from a better grade of steel. You are looking at a LOT of
time vs. maybe ten, fifteen bucks worth of lams, and the wire, etc.

[[email protected]]

On Saturday, June 20, 2009 at 1:27:20 AM UTC-7, John B wrote:
anyone know where to find a power transformer for a McIntosh MI-200

on the output transformer figure out if you need an m185, m208 or m223. then put some requests out or have your existing one rewound, if you have one. I ve seen one guy who does this from reading forums but never a singular unit on ebay. use photos in your requests and try to get some contacts in japan, jay d. kent wa.