Akai M-8 repair-single ended pentode-dual monoblocks-bad output coils !
duty-honor-country
and it just never sounded right, and also emitted a slight burning
smell while playing. Inspection revealed one of the large filter caps
were soldered in backwards from the factory ! This caused one power
resistor to overheat and get slightly black, and also damaged the
power supply transformer for that monoblock (bottom unit in case for
right channel).
Changed out those components, after buying another unit to use that
was being parted out. Also recapped the ENTIRE unit at that time.
Sound improved, but still not what it should be. The VU meters would
stop at about 1/2 level on scale, and unit seemed strained and sound
distorted.
Put it away for about 6 months, then decided to give it another try.
Checked audio output coil resistance on a good unit, measured 420 ohms
primary, 3 ohms secondary, for each monoblock (1 coil per channel).
Checked same on problem unit, measured 2500 ohms on one, and 650 ohms
on another !
Removed output coils from parts donor, each one checked 440 ohms
primary side output coil resistance- put those in problem unit- BANG-
unit is fixed.
VU's now will peg at about 3/4 volume level, sound is loud, strong,
and clear. It sounds GREAT.
Question- what would cause the increased resistance in a primary
winding of an audio output coil ? The coil with the 2500 ohm
resistance, was in the monoblock that had the filter cap in
backwards. ??
DeserTBoB
<prs...@yahoo.com> wrote:
>I bought this unit as a spare from Ebay a few years back. Retubed it
>and it just never sounded right, and also emitted a slight burning
>smell while playing.<snip>
Duh.
>Question- what would cause the increased resistance in a primary
>winding of an audio output coil ? The coil with the 2500 ohm
>resistance, was in the monoblock that had the filter cap in
>backwards. ?? <snip>
A jr. high school electronics shop student could answer this.
It's Charlie "sonofawhore66fourdoor" Nudo again, acting meek and
milquetoast after having two more Google Groups accounts banned for
his incessant eBay spamming.
Hey Noodles. Who CARES about those crapball Akais? Go throw your
thrift store computer into Lake Bumler and leave this NG alone!
John Byrns
DeserTBoB <des...@rglobal.net> wrote:
> On Fri, 01 Jun 2007 04:42:41 -0700, duty-honor-country
> <prs...@yahoo.com> wrote:
>
> >I bought this unit as a spare from Ebay a few years back. Retubed it
> >and it just never sounded right, and also emitted a slight burning
> >smell while playing.<snip>
>
> Duh.
>
> >Question- what would cause the increased resistance in a primary
> >winding of an audio output coil ? The coil with the 2500 ohm
> >resistance, was in the monoblock that had the filter cap in
> >backwards. ?? <snip>
>
> A jr. high school electronics shop student could answer this.
Unfortunately I haven't had jr. high school electronics shop, or even
sr. high school electronics shop for that matter, the high school I
attended didn't offer an electronics class of any sort, so I can't
answer this question, could you please share your knowledge and explain
it to us? The bad transformers I have encountered, where the primary
resistance didn't measure correctly, either had open primaries, i.e. the
primary resistance was very high indeed, or the primary resistance was
lower than it should have been due to shorted turns, usually caused by
overheating. I don't understand how the primary resistance of a
transformer could go high without going open, although obviously it
happened in this case? It would be interesting to dissect the bad
transformer to see exactly how it failed.
> Hey Noodles. Who CARES about those crapball Akais?
Obviously you don't care but that doesn't mean nobody cares, while I
would go for something packaged as an amplifier, if an amplifier was
what I was looking for, rather than something like the Akai that is
packaged as a a tape recorder, if one mysteriously appeared on my front
porch I wouldn't throw it in the trash. It does look like an
interesting amplifier that would be worth auditioning.
Regards,
John Byrns
--
Surf my web pages at, http://fmamradios.com/
Randy or Sherry Guttery
> In article <1v8063trqdp2k2e92...@4ax.com>,
> DeserTBoB <des...@rglobal.net> wrote:
>
>
>>On Fri, 01 Jun 2007 04:42:41 -0700, duty-honor-country
>><prs...@yahoo.com> wrote:
>>
>>
>>>I bought this unit as a spare from Ebay a few years back. Retubed it
>>>and it just never sounded right, and also emitted a slight burning
>>>smell while playing.<snip>
>>
>>Duh.
>>
>>
>>>Question- what would cause the increased resistance in a primary
>>>winding of an audio output coil ? The coil with the 2500 ohm
>>>resistance, was in the monoblock that had the filter cap in
>>>backwards. ?? <snip>
>>
>>A jr. high school electronics shop student could answer this.
>
>
> Unfortunately I haven't had jr. high school electronics shop, or even
> sr. high school electronics shop for that matter, the high school I
> attended didn't offer an electronics class of any sort, so I can't
> answer this question,
Gee, John I'd have loved to have had you in my class -- I taught much of
my senior high electronics class. The instructor (Mr. Watson) was an
automotive instructor - and wile he tried hard (and under the
circumstances did a very good job) he just didn't know the subject that
well - and of course by that time I had my FCC 1st. We'd have gotten you
out of the books, and gotten your hands dirty!
> could you please share your knowledge and explain
> it to us? The bad transformers I have encountered, where the primary
> resistance didn't measure correctly, either had open primaries, i.e. the
> primary resistance was very high indeed, or the primary resistance was
> lower than it should have been due to shorted turns, usually caused by
> overheating. I don't understand how the primary resistance of a
> transformer could go high without going open, although obviously it
> happened in this case? It would be interesting to dissect the bad
> transformer to see exactly how it failed.
Considering the usual failure modes (as you've noted) plus the
"backwards" filter cap - I highly suspect that the unit in question had
been mucked with at some point in it's history (i.e. by someone long
after it left the factory). The only way I can think of for a
transformer to fail as described would be for the wire to part leaving a
carbon trail that had some conduction giving the appearance of higher
winding resistance. However - I can't imagine that surviving subsequent
power applications... So yes I agree completely - a post-mortem of the
transformer would be very interesting.
>>Hey Noodles. Who CARES about those crapball Akais?
>
> Obviously you don't care but that doesn't mean nobody cares, while I
> would go for something packaged as an amplifier, if an amplifier was
> what I was looking for, rather than something like the Akai that is
> packaged as a a tape recorder, if one mysteriously appeared on my front
> porch I wouldn't throw it in the trash. It does look like an
> interesting amplifier that would be worth auditioning.
M8s were marketed here as Roberts 770 series - those were the famous
"Cross-field" units - and yes - for a small amp they were quite well
made, and sounded pretty good. I have always been sad my 770X was so
badly damaged, as it was the first "decent" piece of HiFi equipment I had.
best regards...
--
randy guttery
A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com
robert casey
>>>
>>> A jr. high school electronics shop student could answer this.
Some schools had that? In my school, we just did stuff like doing
square roots by hand (some algorithm similar to long division, I've
forgotten it but if I had to I could find it somewhere on the 'net) or
English grammar or such that shows up on the yearly achievement tests.
>>
>>
>>
>> Unfortunately I haven't had jr. high school electronics shop, or even
>> sr. high school electronics shop for that matter, the high school I
>> attended didn't offer an electronics class of any sort, so I can't
>> answer this question,
>
>
> Gee, John I'd have loved to have had you in my class -- I taught much of
> my senior high electronics class. The instructor (Mr. Watson) was an
> automotive instructor - and wile he tried hard (and under the
> circumstances did a very good job) he just didn't know the subject that
> well - and of course by that time I had my FCC 1st. We'd have gotten you
> out of the books, and gotten your hands dirty!
My high school was strictly a college prep place. No shops or anything
else that wouldn't help on college applications. It was supposedly the
top high school in the county, but college was 20 times more difficult
than this high school.
>
>
>
> Considering the usual failure modes (as you've noted) plus the
> "backwards" filter cap - I highly suspect that the unit in question had
> been mucked with at some point in it's history (i.e. by someone long
> after it left the factory). The only way I can think of for a
> transformer to fail as described would be for the wire to part leaving a
> carbon trail that had some conduction giving the appearance of higher
> winding resistance. However - I can't imagine that surviving subsequent
> power applications... So yes I agree completely - a post-mortem of the
> transformer would be very interesting.
That transformer may have been an incorrect replacement, possibly done
by the same guy that botched the cap.
Randy or Sherry Guttery
> Some schools had that? In my school, we just did stuff like doing
> square roots by hand (some algorithm similar to long division, I've
> forgotten it but if I had to I could find it somewhere on the 'net)
> or English grammar or such that shows up on the yearly achievement
> tests. My high school was strictly a college prep place. No shops or
> anything else that wouldn't help on college applications. It was
> supposedly the top high school in the county, but college was 20
> times more difficult than this high school.
Yes, some high schools did indeed - In my case - Bassett High, La
Puente, CA. MOSTLY the shop classes were trades oriented - being in LA
- they assumed many would just get their union card and make a career.
The electronics classroom shared space with the print shop - in fact
more than once we threw type in the old press and made "business cards",
etc. Bassett was just one of many similar high schools in the region
that fed one of three upper educational schools in the region: Rio
Hondo Jr. College: typical community college; Mt. SAC: Mount San
Antonio Jr. College - HUGE two year prep / vocational school - which has
an enrollment of around 40,000 students at any given time (around 24,000
full time credit; 16,000 part time / non credit) on some 420+ acres.
Mt. SAC has many, many engineering courses such as electronics, as well
as animal husbandry; etc. MT. SAC shares it's "back fence with CalPoly,
Pomona - the "other" fairly well known upper ed campus in the area. I
went to Mt. SAC before going into the Navy. Bassett was (and still is)
just an average school - but does a decent job prepping the kids for
most any direction they decide to take after high school. Yes college at
Mt. SAC was definitely a lot more "intense" than high school - but I
think that's pretty common.
> That transformer may have been an incorrect replacement, possibly done
> by the same guy that botched the cap.
Of course that had crossed my mind as well - but surely the OP would
have noticed a kludge substitute - then again - who knows. At any rate
- a thorough examination of the carcass would tell a lot.
maa...@panic.xx.tudelft.nl
> Hey Noodles. Who CARES about those crapball Akais? Go throw your
> thrift store computer into Lake Bumler and leave this NG alone!
Maybe he should hit you on the head until you die with one. That way you
won't bother us anymore and he will get locked up in jail and the key
thrown away.
John Byrns
"electronics shop" sounds a little too sissified to get your hands
really dirty, I would think auto shop would be a better bet for that,
unfortunately the high school I attended didn't have auto shop either.
It did have wood shop and metal shop though, and I liked to take those
classes instead of wasting a period in "study hall". I did manage to
work my way up to teachers pet in wood shop and earn extra brownie
points by building the models for the teachers projects in the junior
high classes. But wood shop mostly generated a lot of dust and didn't
really get your hands truly dirty. The best for that was metal shop
which involved lathes, milling machines, cutting oil and welding.
Welding was the ticket for really making a mess like setting your pants
on fire by having a ball of molten metal drop into your pants cuff.
I don't know if high schools even offer any kind of shop classes today,
I seem to remember reading in the paper a few years ago that the school
district I pay taxes to dropped shop classes a while back. Computer
classes and such seem to be more important today, and probably offer
less chance for liability issues too. I last took a wood shop class in
an adjoining high school district about ten years ago, and they still
had auto and wood shop at that time, I wonder if they still offer those
classes today.
I didn't get my FCC 1st Phone until after I had graduated from high
school and wanted to get a job at a radio station. As I remember it the
electronics part of the test didn't require any great amount of
learning, however a "law shop" would have been a great help in passing
the part of the test relating to the regulations. IIRC there weren't
many questions specifically relating to broadcast regulations in the
test, but there were about two hours worth of detailed questions on
maritime and aeronautical radio regulations in the test, something that
had little use in broadcasting as far as I could tell. A "plumbing
shop" might have been useful, as the Television transmitter was water
cooled, and in those days before 24/7 operation things could freeze up
over night during the Northern winters. I was told that the cold winter
air also bothered the RCA BTE-10B FM exciter at signon, but I only did
signoff shifts during the winter and I never saw this problem at summer
signons when the air was warm. The building was normally heated by the
waste heat from the Television transmitter cooling radiator and I think
these problems went away when they decided to leave the electric heat on
overnight.
Radiosrfun
news:byrnsj-1F8A4A....@newsclstr03.news.prodigy.net...
John,
Maybe you've never heard the term - but "get your hands dirty" meant "hands
on experience" to many. As you well know - you can't learn "everything" from
books. Sissified or not - it is a widely used term - I suppose - based on
where you live.
In my neck of the woods - all the shop classes that I'm aware of -went out
YEARS ago. That is sad........ Because here - not "everyone" gets to go to
"Vo-Tech" - only a select few. AND the "Vo-Tech" schools aren't really
pushing "Electronics" much - anymore.
And for what it is worth - if you dig into a chassis, tv or otherwise that
has had lots of dirt in it or otherwise, it isn't so hard to conceive that
idea to be true.
RRF
Randy or Sherry Guttery
> "electronics shop" sounds a little too sissified to get your hands
> really dirty, I would think auto shop would be a better bet for that...snip...
> The best for that was metal shop
> which involved lathes, milling machines, cutting oil and welding.
Your instincts serve you well. The reason you'd have gotten your hands
dirty in my class - was that the class project for the year was building
an AA5 from scratch - including going over to the metal shop - using the
shear to cut out a chassis, a brake to bend it to shape - then the
various drills, chassis punches, etc. for mounting terminal strips,
tubes, IF cans, etc. and soldering the chassis flaps (the joys of a good
ol' block of Sal Amoniac being "attacked" by an American Beauty!!).
Obviously - once the chassis was "formed" - filling it up was not a very
dirty job. Now - when we wandered over into the press area - and got
into the press ink... ""mess" took on a whole new meaning... <grin!>
robert casey
>
> I don't know if high schools even offer any kind of shop classes today,
> I seem to remember reading in the paper a few years ago that the school
> district I pay taxes to dropped shop classes a while back. Computer
> classes and such seem to be more important today, and probably offer
> less chance for liability issues too. I last took a wood shop class in
> an adjoining high school district about ten years ago, and they still
> had auto and wood shop at that time, I wonder if they still offer those
> classes today.
>
If there was a liability issue involved, you can be sure a school would
dump it unless it was absolutely required (say, by a state education
dept). Wood shop? A kid could cut his hands up on a table saw, and
we'd get our asses sued off. Same thing with metal shop. And "No Child
Left Behind" doesn't care about shop.
duty-honor-country
> In article <1v8063trqdp2k2e92vhuvtj4b2scqmb...@4ax.com>,
>
> - Show quoted text -
John,
Thanks for reply.
Perhaps I could send you the transformer, you can take it apart and
tell me what you find.
agreed- if it was open, it should not play at all- but it played
duty-honor-country
wrote:
> John Byrns wrote:
> > In article <1v8063trqdp2k2e92vhuvtj4b2scqmb...@4ax.com>,
Randy- rest assured, the filter cap that was in backwards, was the
bone-stock Akai part, and the solder on there was original, nothing
had ever been changed on the unit.
duty-honor-country
>
> - Show quoted text -
Robert- the transformer was the bone-stock Akai transformer, had Akai
logo and part number on it, just like the cap was original also. It
had never been resoldered, it had the factory solder joints in place,
you can tell by the color and aging.
duty-honor-country
one thing I'd like to add, after recapping the unit with modern caps,
it has developed more background tape hiss/noise than the original
caps had.
I have heard of that phenomenon before, that often times when a unit
it recapped, the sound gets tighter and clearer, but tape hiss
appears, due to the new caps causing it
Peter Wieck
An consummation devoutly to be wished.
Hamlet, Prince of Denmark
Peter Wieck
Wyncote, PA
duty-honor-country
Peter, as I remember, you were the guy that insisted this was a push-
pull amp a while back. It's not- only to find out it's a single ended
design-ever since then, you've been answering in this manner- are you
that insecure you can't admit when you're wrong ?
DeserTBoB
<prs...@yahoo.com> wrote:
>one thing I'd like to add, after recapping the unit with modern caps,
>it has developed more background tape hiss/noise than the original
>caps had. <snip>
Duh...probably had a wider power bandwidth than 300-3000 Hz of a
common telephone after the screw-ups were undone...and you think
telephones are "high fidelity" as witnessed by your love of crapball
equipment.
>I have heard of that phenomenon before, that often times when a unit
>it recapped, the sound gets tighter and clearer, but tape hiss
>appears, due to the new caps causing it <snip>
This moronic drivel doesn't require any reply. Charlie Nudo, who just
got two more of his Google Groups spamming accounts banned for
spamming, is trying to "make nice" and make friends again.
Don't fall for it.
Scott W. Harvey
>
> "electronics shop" sounds a little too sissified to get your hands
> really dirty, I would think auto shop would be a better bet for that,
> unfortunately the high school I attended didn't have auto shop either.
> It did have wood shop and metal shop though, and I liked to take those
> classes instead of wasting a period in "study hall". I did manage to
> work my way up to teachers pet in wood shop and earn extra brownie
> points by building the models for the teachers projects in the junior
> high classes. But wood shop mostly generated a lot of dust and didn't
> really get your hands truly dirty. The best for that was metal shop
> which involved lathes, milling machines, cutting oil and welding.
> Welding was the ticket for really making a mess like setting your pants
> on fire by having a ball of molten metal drop into your pants cuff.
>
> I don't know if high schools even offer any kind of shop classes today,
> I seem to remember reading in the paper a few years ago that the school
> district I pay taxes to dropped shop classes a while back. Computer
> classes and such seem to be more important today, and probably offer
> less chance for liability issues too. I last took a wood shop class in
> an adjoining high school district about ten years ago, and they still
> had auto and wood shop at that time, I wonder if they still offer those
> classes today.
Hard to believe it's been 5 1/2 years since I wrote this:
http://groups.google.com/group/rec.antiques.radio+phono/msg/52874faca8a8e930?dmode=source
It seems like an education in the trades really isn't respected like it
used to be. People who would be outraged if they discovered that their
doctor or lawyer was an illegal alien think nothing of hiring such a
person to plumb or wire their house to save a few bucks.
-Scott
Steven
> In article <1v8063trqdp2k2e92vhuvtj4b2scqmb...@4ax.com>,
>
>
>
>
>
Damn straight, John, and I have one up from the last bunch of Estano's
basement goodies I got two weeks ago, as well as an X-1800SD, so it's
of GREAT INTEREST to me!
Steven
wrote:
Randy, if you want to try again, I can at least look at the head on
my M-8 for you. If it's worth it for you $10 plus shipping will take
it. It's very clean all there and intact and was stored in a very dry
basement AFAIK for many years. My email is still real...
Best regards, Steven
duty-honor-country
>
> - Show quoted text -
the 1800SD is solid state, not tubes- I have one of those as well
Peter Wieck
>
> - Show quoted text -
And you are the spammer that demands attention...
And, of course, calls a "winding" a "coil".
Makes all sorts of sense.
Peter Wieck
Wyncote, PA
Steven
And I used to have the sister model with autoreverse, so--duh, I knew
that. Why I never bothered to bid on the Pioneer R_-1020L IIRC they
had here 3 years back, I cannot understand now.
Steven
offer is extended to Randy ONLY, first and foremost.
duty-honor-country
> Thanks idiot spammer
1800SD is solid state, Akai M-8 is tubes.
2 totally different designs- so perhaps you should stand in front of
the mirror while posting this ?
sparky
> "John Byrns" <byr...@sbcglobal.net> wrote in message
>
> news:byrnsj-1F8A4A....@newsclstr03.news.prodigy.net...
>
>
>
Especially if the component came from a house where there was lots of
cigarette smoke.
Steven
I wonder when ____ will ever figure that I have a whole damned
houseful and a shed full of 70 years worth of electronic sets and am
not a frikking retard.
DeserTBoB
>the mirror while posting this ? <snip>
Troll bait. Ignore.
Steven
account was closed due to violations.
You are absolutely worthless yourself, not so mention an annoying
blowhard in disfavor among many of the others here, for all I've
gathered in conversations on the side.
duty-honor-country
>
> - Show quoted text -
and what's that amount to ? a hunk of metal you filled with soldered
in tidbits, that you plug into the wall, and it makes noise
"having' doesn't mean shit, anyone can "have" that
understanding, working on, creating, and helping others- that's worth
more than your pathetic "having"
Steven
Nice speech, when does Bob do the replay?