Dull Hum Amp Sound Question - Page 3

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Re: Dull Hum Amp Sound Question
On 4/13/2019 7:54 AM, ABLE1 wrote:
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OK, as a follow up on this Amp challenge the following is
new information.

 > Found Date of Install >>1991<< that makes it 28 years old.
 > Amp is a University Sound Model# 1110  100 Watt Amp
 > Temporarily installed a Ground Lift Adapter at power plug.  No Change
 > Removed output leads and connected a single speaker         No Change

At this point I think it is safe to say that the Amp and/or Caps in the  
Amp are defective.  It matters not, since a new replacement is the  
obvious next course of action.  On either end on the heatsink there are
a couple of transistors 2N5881.  The Caps are not visible, so it would  
need to be disassembled.  I will do so after I remove and before I place  
in the nearest dumpster at the recycle center.

That is unless someone wants to pay for shipping and you can play with  
it.  Otherwise it had a good life.

Side Note:
It is a shame that 'some' have found it necessary to get nasty in the  
postings.  All I can say is what was the point??  I know for 'some'
anything said about the negative action will fall on blind eyes.  It is  
my opinion that the Usenet is or was designed to give the users a way to  
help others.  It is very sad when all goes into the toilet.

Thanks to all of those that assisted with good help and insight.
All is appreciated.

I will now go back to lurking and picking up little tidbits of info.

Have a good rest of your week.

Les


Re: Dull Hum Amp Sound Question
ABLE1 wrote:

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** So a wall mount amplifier, made in the USA in the 80s and 90s.  

Uses transformer drive as well as output for 70V lines. Single supply rail with one, 10,00uF 50V electro. See manual with schems:  

http://pdf.textfiles.com/manuals/STARINMANUALS/Bosch%20-%20EV/Archive/University%20Sound/1110,%201160.pdf

FYI: There is a bad drawing error in the power stage for the 1110 model concerning the output transformer primary connections.  

In any case, an genuine antique in the world of line voltage PA amps and long overdue for retirement.  

Rest of Mr ABLE's meandering drivel snipped.  



....  Phil  


Re: Dull Hum Amp Sound Question
On 4/15/2019 5:16 PM, snipped-for-privacy@gmail.com wrote:
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  Nice job Phil, helping is good.
    Mikek

PS, please correct the typo, others don't know as much as you, and might
not know how to interpret that value.


Re: Dull Hum Amp Sound Question
On Monday, April 15, 2019 at 5:35:19 PM UTC-4, ABLE1 wrote:
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Just my two cents.  Sounds like you're in the alarm system business and thi
s
is a customer with a business that has a four story building that uses a
paging system.  IMO, since this system isn't your forte, why get yourself
involved in screwing around with it?  Probably better they get the right te
ch
and if they are a business, they should be able to afford one.  I'd be conc
erned
that something will go wrong and I'd get blamed, lose a customer, etc.  
Like Clint Eastwood said, a man has to know his limits.

Re: Dull Hum Amp Sound Question
On 4/15/2019 7:30 PM, snipped-for-privacy@optonline.net wrote:
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Hi Trader,

Your 2 cents are almost correct.

However, this is a Non-Profit and I am on the verge of making
a new Amp a donation.

I have been doing a wide variety of work for them for over
20 years.  15 years at an old location and now about 5 years
a this new location.

The donation will be well received.

Very good customer and they like me!!!

Les


Re: Dull Hum Amp Sound Question
On Monday, April 15, 2019 at 5:35:19 PM UTC-4, ABLE1 wrote:
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I am pretty frugal and at one time would have taken it and replaced  the  c
ap.  Since it is 28 years old , the  big electrolytic cap is almost sure to
 be bad  or at least bad soon. But I have no use for it.  You might list it
 an Ebay before putting it in a dumpster.   Back in the sixties the mean ti
me to failure on hi-rel transistors was estimated at 1500 years.  So most o
f it would  still be good.  I once replaced about a dozen caps in an Hi-Fi  
receiver.  

                                Dan  


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Re: Dull Hum Amp Sound Question
snipped-for-privacy@krl.org wrote:

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** MTBF figures need careful interpretation.

1500 years equates to one unprovoked failure in 1500 units, per year,
within the expected life of the device and assuming normal use conditions.
  

A 28 year old, wall mounted PA amp that has seen 24/7 operation will be suf
fering severe deterioration in almost every component as well as the PCB it
self. Even soldered connections are no longer trustworthy and push on types
 only functional by sheer luck while on borrowed time.

FYI:  

TO3 BJT devices using Aluminium packages were rated at 5000 thermal cycles  
before failure. This is why Motorola and most others changed to steel paks  
sometime in the 1980s.

A paging amp in constant use would be a sitting duck for this sort of failu
re.



....  Phil  


  

Re: Dull Hum Amp Sound Question
On Monday, April 15, 2019 at 8:58:10 PM UTC-4, snipped-for-privacy@gmail.com wrote:
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.  

If you had a 1500  lot sample and had  one failure per year, in 1500  years
 all 1500 units would have failed.


On the other  hand if you had a 1500 lot sample   and a  1500 year mean tim
e              to  failure, in 1500 years , half of the sample would  have  
  failed.  At least that is how I understand it.

                Dan

  

                                Dan


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uffering severe derioration in almost every component as well as the PCB it
self. Even soldered connections are no longer trustworthy and push on types
 only functional by sheer luck while on borrowed time.
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s before failure. This is why Motorola and most others changed to steel pak
s sometime in the 1980s.
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lure.


Re: Dull Hum Amp Sound Question
On Tuesday, 16 April 2019 13:58:48 UTC+1, snipped-for-privacy@krl.org  wrote:
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In your first explanation the failure rate falls from initial 1/yr since the number in service falls over time.


NT

Re: Dull Hum Amp Sound Question
snipped-for-privacy@krl.org wrote:


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** Try reading what I wrote.  
  
MTBF numbers are not predictions of huge life spans, that is the dumb the mistake naive folk always make.  


....  Phil  

Re: Dull Hum Amp Sound Question >>UPDATE<<
On 4/13/2019 7:54 AM, ABLE1 wrote:
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For those that are interested.

Replaced the Amp today with a New Bogen TPU100B Amp.
Swap took about 30 minutes mainly due to the location.
Would have liked to reposition but was not possible due
to the limited space.  The Amp works great and all is good.

I opened up the old University Sound Amp and there was only
one Cap.  50V 10000uf  1.125" Dia. x 2" Long
There were no signs of any leakage.

There is another smaller alum. can that had no markings.
The end wire leads had a silicon sealant filling the end.
Not sure what it is or was.

For me there is really no good reason to repair this Amp.

Therefore it is going to trash.

Thanks again to all the input even though I posted in the
wrong group.

Happy Easter.

Les

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