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[email protected] jxj1188@gmail.com is offline
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Default Harman Kardon A500

Hi, I recently bought a HK A500 from ebay and would like to know
something about this amp...

1- I noticed that it´s very weak in power, I use it with a pair of JB
L Jubal, I have to listen beyond the midlle (1 or 2 o clock) to hear in
a good volume, is it right?

2-One transformer was changed, the channel B, how can I see if the job
was well done?

3-I noticed that at this channel B when I turn the balance to only this
side, the treble increases, what can be the problem?

4-the ambience function is not working, what it is the funcion of this?
How can I repair?

5-there are two OUTPUT BAL controls near the tubes, one for each
channel, what are their purpose?

Thank you all, sorry for all the questions.

Murillo

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Peter Wieck Peter Wieck is offline
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Default Harman Kardon A500

First, what, if anything, have you done to it since it arrived to your
care? Then:

Note the interpolations:

wrote:
Hi, I recently bought a HK A500 from ebay and would like to know
something about this amp...


OK. A generally solid low-powered, full-featured vintage tube
integrated amp. Not terribly common.

1- I noticed that it´s very weak in power, I use it with a pair of JB
L Jubal, I have to listen beyond the midlle (1 or 2 o clock) to hear in
a good volume, is it right?


25wpc/rms assuming all other things being good, from capacitors to
tubes.

2-One transformer was changed, the channel B, how can I see if the job
was well done?


Does it work correctly? Was it replaced with an OEM type, an
after-market purpose-picked substitute or a parts-box leftover? How
clean is the work?

3-I noticed that at this channel B when I turn the balance to only this
side, the treble increases, what can be the problem?


And the same thing _Does Not_ happen when you go the other way? As
noted before, could be tubes, capacitors, drifted resistors, or the
wrong output transformer, or simply dirt on the controls.

4-the ambience function is not working, what it is the funcion of this?
How can I repair?


Schematics he
http://intra.engr.uark.edu/~lar/fireamps.html

as well as many other places. Could be caps, tubes, dirt or a bad
Packaged Circuit.

5-there are two OUTPUT BAL controls near the tubes, one for each
channel, what are their purpose?


The description lists this unit as having continuous balance from Mono
to Stereo. I suspect these controls are for that purpose. Some sort of
accomodations to exaggerated stereo sources were built into many early
integrated and pre-amps well into the 70s. Most did it with a single
blend (separation) control, however.


Thank you all, sorry for all the questions.


Don't be, this NG is pretty much for such questions despite rumors,
vendettas and diatribes to the contrary.

Now, some CAUTIONS and WARNINGS:

CAUTION: Lethal voltages exist inside most tube equipment. Unless you
know what you are doing and are experienced working around such
voltages, DO NOT mess around inside beyond changing and testing tubes
and cleaning the controls and setting the bias. If you choose to clean
the controls, do so only with the unit COLD and UNPLUGGED.

WARNING: Most vintage equipment such as this (40+ years old) may need
its capacitors replaced, it may have drifted resistors and it may be
out-of-bias. Your unit has adjustable bias controls, you need to find a
manual and/or good source of information as to how it is adjusted and
do so, first thing. It may be written somewhere on the unit, there may
be some means to do it 'by ear', but whatever it is, do it. With
caution, of course.

LAST OBVIOUS WARNING: Do not operate the unit (excepting testing, of
course) with the cover off. Tubes get very hot apart from the voltages.
Small children, careless adults and pets may be injured.

Even though this unit is described as being 'easy' on tubes, it remains
quite old and tubes do wear out. You should test both the output tubes
and the small-signal tubes even if only for emissions. I know of no
direct substitutes for the 7355 but they are available... not cheap.
The small-signal tubes are generally cheap and common.

Good luck with it. Take your time and be careful.

Peter Wieck
Wyncote, PA

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[email protected] jxj1188@gmail.com is offline
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Default Harman Kardon A500

Hi Peter, thank you very much for all explanations. I´ll try to look
at all that you mentioned.

Murillo

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Peter Wieck Peter Wieck is offline
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Default Harman Kardon A500


wrote:
Hi Peter, thank you very much for all explanations. I´ll try to look
at all that you mentioned.

Murillo


You are most welcome. Just take it one step at a time if you are new at
it. That particular unit is pretty uncommon so you may have a little
more difficulty finding detailed information than with more common
stuff. But it will be a nice player when you get it straightened out.

Some other cautions if you are going to learn on this unit:
CLEANING SUGGESTIONS:

a) DO NOT use steel wool, metal files, brass brushes or any other tools
capable of scratching metal anywhere near any electronics. The filings
can cause spectacular damage. I use an electric eraser with a soft
insert for polishing sockets and jacks, but any of several other means
are equally good if not as fast.

b) for cleaning tube sockets, I use either a plastic or wooden
toothpick dipped in a little bit of 100% volatile contact cleaner. Push
the pick into the socket lightly and spin it lightly to remove surface
oxides. Try to avoid those cleaners that leave a residue behind
(sometimes mineral oil, sometimes oleic acid, sometimes much worse).
Synthetic Oil of Wintergreen is 100 volatile over time if you can stand
the concentrated smell. If individual pin sockets are loose, you will
need to tighten them from underneath if you can reach, or with a stiff
long pin from on top, very carefully.

c) For cleaning pots and switches, use a standard contact cleaner for
those purposes... IN MODERATION! A little goes a long way. Exercise the
switches when you are doing this.

d) Let the thing sit for a bit before applying power and after
cleaning, to limit any volatile residue.

e) Be patient.

And again, good luck.

Peter Wieck
Wyncote, PA

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Peter Wieck Peter Wieck is offline
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Default Harman Kardon A500


Brian wrote:

Your amp should be quite loud! It's a very good sounding amp.


Depends on the first, yes on the second.

That amp into an AR3a, for instance will give substantial volume, but
will not be "loud" with a very dynamic source without clipping, it is
just a little thin for very inefficient speakers. However, I suspect
that the OP needs to do some maintenance and perhaps repairs before he
will realize the full potential of this amp.

Peter Wieck
Wyncote, PA

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Arny Krueger Arny Krueger is offline
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Default Harman Kardon A500

wrote in message
oups.com

Hi, I recently bought a HK A500 from ebay and would like
to know something about this amp...


1- I noticed that it´s very weak in power, I use it with
a pair of JB L Jubal, I have to listen beyond the midlle
(1 or 2 o clock) to hear in a good volume, is it right?


Volume control position versus loudness is a poor test of power output.

2-One transformer was changed, the channel B, how can I
see if the job was well done?


If the transformers are visibly different, then it wasn't an exact
replacement.

Note: this was not one of HK's best efforts, even in the days of tubes. The
OPTs rolled off the bass.

3-I noticed that at this channel B when I turn the
balance to only this side, the treble increases, what can
be the problem?


Who can tell? There's a reason why I have test equipment on my bench, and
looking pretty ain't it.

4-the ambience function is not working, what it is the
funcion of this? How can I repair?


The schematic posted here

http://intra.engr.uark.edu/~lar/fireamps.html

Says that there is a separation control, but no ambience control. It's
basically a sliding stereo/mono switch. It's effect might be subtle enough
that you're not hearing it with speakers.

5-there are two OUTPUT BAL controls near the tubes, one
for each channel, what are their purpose?


I seem to recollect that you are supposed to adjust them with a test tone
and a THD analyzer. Got either?


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Chris Hornbeck Chris Hornbeck is offline
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Default Harman Kardon A500

On 29 Oct 2006 16:59:01 -0800, "
wrote:

5-there are two OUTPUT BAL controls near the tubes, one for each
channel, what are their purpose?


Based on the link that Arny posted, these are DC
balance trims. Unfortunately, the circuit provides
no convenient place to measure. There are a couple
of clumsy ways to do it, if you're bound and
determined:

1) You could measure the OPT's primary resistances
(cold, of course), measure voltage drops across them,
calculate plate currents, and adjust the currents to
be equal.

2) You could make a pair of plug/socket combo's
with cathode current sensing resistors built in.

3) You could permanently insert a small resistor in
each cathode lead, between pin 5 and the trimpot,
and measure across them.

The purpose of the controls is to balance standing
primary currents, which minimizes large-signal
distortion in the transformer. So you could also
4) Measure full power distortion at a low frequency,
maybe 40 Hz, and adjust for minimum. This often
proves to be fairly confusing, though, even with
the needed equipment ready to hand.


All good fortune,

Chris Hornbeck
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