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 itīs 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