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Default problem with old mac mono block


hi, i have a pair of old mac 50-w2 mono blocks and one got sick tonight.

the first symptom was a rushing noise a few seconds after the amp was
turned on, much like being between channels with a old tube AM radio.

i powered it off and suspecting a tube swapped tubes with the working amp.

problem satyed with the same amp - so not likely a tube.

i then swapped outputs to the speakers - problem stayed with the amp -
so not the speaker.

when i put it all back together and tried again, one of the output
tubes flashed blue and the fuse blew.

when i've had similar problems in the past, it's been a bad tube,
but it doesn't look like that this time.

thoughts?
--
Lance
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Dan Nicotera
 
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If it has a rectifier tube check that or the power supply caps..that's where
I'd start.
Dan
wrote in message
...

hi, i have a pair of old mac 50-w2 mono blocks and one got sick tonight.

the first symptom was a rushing noise a few seconds after the amp was
turned on, much like being between channels with a old tube AM radio.

i powered it off and suspecting a tube swapped tubes with the working amp.

problem satyed with the same amp - so not likely a tube.

i then swapped outputs to the speakers - problem stayed with the amp -
so not the speaker.

when i put it all back together and tried again, one of the output
tubes flashed blue and the fuse blew.

when i've had similar problems in the past, it's been a bad tube,
but it doesn't look like that this time.

thoughts?
--
Lance



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Rich Sherman
 
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Lance:

Typically a PSU cap (Especially vintage FP types) will have a ticking or
spitting sound prior to failing when the capacitor plates short-out and the
electrolyte starts to ooze out of the bottom seal (Whitish_Brown Powder like
stuff).

If you had a whooshing sound and actually had a Tube Fail you must suspect
something like a shorting signal capacitor, a bias problem or a crispy
resistor that shorted out vs.opening-up. Also a shorting wire could also
have caused this.

Open her up and with a good 100 Watt lamp spend about 1/2 hour looking at
the underside of the chassis for telltale signs of carbon deposits, visually
burned components or anything like a shorted wire or funny smells.

Most often a failure that takes out the fuse has it's roots in a DC short
which caused the Power Transformer to exceed its ratings and take out the
fuse.

Thanks heavens for thiose 0.25cent fuses, they have saved many a precious
Mac Transformer.

Buena suerte amigo,

Rich Sherman

wrote in message
...

hi, i have a pair of old mac 50-w2 mono blocks and one got sick tonight.

the first symptom was a rushing noise a few seconds after the amp was
turned on, much like being between channels with a old tube AM radio.

i powered it off and suspecting a tube swapped tubes with the working amp.

problem satyed with the same amp - so not likely a tube.

i then swapped outputs to the speakers - problem stayed with the amp -
so not the speaker.

when i put it all back together and tried again, one of the output
tubes flashed blue and the fuse blew.

when i've had similar problems in the past, it's been a bad tube,
but it doesn't look like that this time.

thoughts?
--
Lance



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Ricky
 
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Lance:

Definetly open the amplifier up and with a good 100 Watt spot-lamp give her
a good look.

If you have never upgraded the Power Supply or Power Tube Bias components
now is a great moment to consider this.

Look for signs of anything that is discolored, charred or smells like it has
'cooked'

Whatever you do to your Mac's consider that the other Monoblock will be next
in line for an inspection as well.

A whooshing sound can be any number of things. In my experience a failing
power supply cap emits a spitting or ticking sound. Whoosh from the speakers
has to be from a DC short of a Signal Cap or some other component that has
failed after so many years of faithful service.

Thanks,

Ricky
wrote in message
...

hi, i have a pair of old mac 50-w2 mono blocks and one got sick tonight.

the first symptom was a rushing noise a few seconds after the amp was
turned on, much like being between channels with a old tube AM radio.

i powered it off and suspecting a tube swapped tubes with the working amp.

problem satyed with the same amp - so not likely a tube.

i then swapped outputs to the speakers - problem stayed with the amp -
so not the speaker.

when i put it all back together and tried again, one of the output
tubes flashed blue and the fuse blew.

when i've had similar problems in the past, it's been a bad tube,
but it doesn't look like that this time.

thoughts?
--
Lance





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Gene McCluney
 
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In article ,
wrote:

hi, i have a pair of old mac 50-w2 mono blocks and one got sick tonight.

the first symptom was a rushing noise a few seconds after the amp was
turned on, much like being between channels with a old tube AM radio.

i powered it off and suspecting a tube swapped tubes with the working amp.

problem satyed with the same amp - so not likely a tube.

i then swapped outputs to the speakers - problem stayed with the amp -
so not the speaker.

when i put it all back together and tried again, one of the output
tubes flashed blue and the fuse blew.

when i've had similar problems in the past, it's been a bad tube,
but it doesn't look like that this time.

thoughts?



I have these myself,and it is quite probably the interstage transformer
has failed. They were notorious for failing. The transformer driving
the output tubes.

This is a problem, as both this transformer and the output transformer
are solidly potted in the bottom of the case. If you remove the top
cover you will find that there are very few components under there.
There are only one or two coupling capacitors in the entire amp, the
whole output stage and driver stage being coupled with the interstage
transformer.

The power supplys are of course in a separate box/chassis coupled to the
amplifier with a multi-wire cable.

Have you tried exchanging power supplys between amps?

The interstage transformer can be rebuilt, but you have to get at it, and
that is quite difficult without destroying the paint job on the chassis
box due to the heating up needed to unpot it.

Gene McCluney
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