Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

how the **** did you lose polystyrenes?


I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.


Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.


Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

On 28/09/10 23:32, The Natural Philosopher wrote:

how the **** did you lose polystyrenes?

They copped a bit too much heat from nearby resistors that were busy
converting themselves to smoke. Now they're a very funny shape.

Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.

Thanks for that. Sounds like a good plan if I can't find the specific
magic numbers from Maplin.

Cheers,

Colin.

In article ,
Colin Stamp writes:
On 28/09/10 23:32, The Natural Philosopher wrote:

how the **** did you lose polystyrenes?

They copped a bit too much heat from nearby resistors that were busy
converting themselves to smoke. Now they're a very funny shape.

Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.

Thanks for that. Sounds like a good plan if I can't find the specific
magic numbers from Maplin.

It was normal to swap the fuse for a very low power sacrificial resistor
when setting the quiescent current, so that you can't draw too much
current to damage output stage, and if you try, the resistor alone goes
up in smoke.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:
In article ,
Colin Stamp writes:
On 28/09/10 23:32, The Natural Philosopher wrote:

how the **** did you lose polystyrenes?
They copped a bit too much heat from nearby resistors that were busy
converting themselves to smoke. Now they're a very funny shape.

Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.
Thanks for that. Sounds like a good plan if I can't find the specific
magic numbers from Maplin.

It was normal to swap the fuse for a very low power sacrificial resistor
when setting the quiescent current, so that you can't draw too much
current to damage output stage, and if you try, the resistor alone goes
up in smoke.

Good plan.

On Sep 28, 11:23*pm, Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

If one channels still ok and one toast, not hard to copy what the
other one's doing current-wise.


NT

On 28 Sep, 23:23, Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.


I hope she's going to stump up for a new amp!

--
Halmyre

Hi Colin
I'm pretty sure I have a scan of the original construction article
if you still need it - assuming we're referring to the 50W MOSFET
module that was very much based on the Hitachi Mosfet data sheet. it
may take me a day or so to track it down...

Regards
J^n

jkn wrote:
Hi Colin
I'm pretty sure I have a scan of the original construction article
if you still need it - assuming we're referring to the 50W MOSFET
module that was very much based on the Hitachi Mosfet data sheet. it
may take me a day or so to track it down...

Regards
J^n
If its hitachi mosfets, they like a bit more current- 30-50mA increase
over minimum.

On 29/09/2010 08:47, jkn wrote:
Hi Colin
I'm pretty sure I have a scan of the original construction article
if you still need it - assuming we're referring to the 50W MOSFET
module that was very much based on the Hitachi Mosfet data sheet. it
may take me a day or so to track it down...

I've found a copy of the mag. Seems they reprinted the same project a
number of times it was so popular.

I found it in ...

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.

--
Adrian C

On 29/09/2010 18:32, Adrian C wrote:

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.


http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Maplin-Kit

--
Adrian C

On Sep 29, 7:02*pm, Adrian C wrote:
On 29/09/2010 18:32, Adrian C wrote:



Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.

http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Map...


Good work Adrian. I have that scan as well, but you beat me to it ...

J^n

On 29/09/10 19:02, Adrian C wrote:
On 29/09/2010 18:32, Adrian C wrote:

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.


http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Maplin-Kit



That's perfect. Many thanks for sorting it out. It came just at the
right time too; I changed the output transistors this evening and tried
the set-up procedure. It lives once more! It's only on the bench at the
moment and I didn't have a speaker handy, but it works fine on a scope.
I'm well pleased. I might even forgive the wife )

Thanks again,

Colin.

Adrian C wrote:
On 29/09/2010 18:32, Adrian C wrote:

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.


http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Maplin-Kit


well I am not surprised it blew up. Pretty amateurish design.

On 30/09/2010 01:40, The Natural Philosopher wrote:
Adrian C wrote:

It's not a MOSFET amp.

well I am not surprised it blew up. Pretty amateurish design.

FWIW I've found an old Maplin catalogue from 1985 with the original
project. (The days when the catalogue had projects and data sheets
printed inside that you could actually dream & build from!)

http://www.scribd.com/doc/38419958/50W-HiFi-Power-Amplifier-Maplin

First paragraph of that reads ...

"A superb quality 50W power amplifier. We threw away all our technical
specification handbooks and designed an amp that just sounded musically
perfect. When we'd finished we found that we'd got a pretty impressive
technical spec as well."

--
Adrian C

On 30/09/10 01:40, The Natural Philosopher wrote:

well I am not surprised it blew up. Pretty amateurish design.

It's better than anything I could have done and, to be fair, my pair did
last over 20 years before one of them blew up. Even then it took a good
whack to do it.

I'm wondering if it was a collector-heatsink short on one of the output
transistors that did it, due to a long-forgotten bodge when I built it.

The holes in the heatsink bracket were too small for the insulating
bushes and, rather than drill them out, I cut down the bushes to match
the transistor tab thickness. Looking back, it was a pretty stupid thing
to do as it didn't leave any margin for error. I reckon one of the
transistors shifted a bit upon cranium-to-shelf contact.

Cheers,

Colin.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Colin Stamp
saying something like:

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

Glad to see you got your priorities right. A wife can be replaced.

Remove positive supply fuse.
Put meter across fuse holder on current setting.
Turn preset fully clockwise.
Turn on amp.
Adjust preset for 20mA.

In message ,
writes
Remove positive supply fuse.
Put meter across fuse holder on current setting.
Turn preset fully clockwise.
Turn on amp.
Adjust preset for 20mA.



Is this the main supply fuse or possibly just for one stage where it is
maybe a method of setting a bias current? No mention of an input
signal, so this is presumably quiescent current?
--
Bill

On 02/11/2013 01:55, Bill wrote:
In message ,
writes
Remove positive supply fuse.
Put meter across fuse holder on current setting.
Turn preset fully clockwise.
Turn on amp.
Adjust preset for 20mA.



Is this the main supply fuse or possibly just for one stage where it is
maybe a method of setting a bias current? No mention of an input
signal, so this is presumably quiescent current?

Yep - it's the quiescent current. It seems to be a response to a
question I asked when I found myself repairing one three years ago:-

https://groups.google.com/forum/#!to...-y/PLG6gqY3y7A

Nice thought though )

Cheers,

Colin.

I bought a couple of these Maplin 50 watt amplifiers as both faulty.
I repaired them both and they sound great.

What was wrong then.
Brian

--
From the Sofa of Brian Gaff Reply address is active
wrote in message
...
I bought a couple of these Maplin 50 watt amplifiers as both faulty.
I repaired them both and they sound great.

On 05/06/14 23:19, Brian Gaff wrote:
What was wrong then.
Brian


4 year old thread dug up by Google

https://groups.google.com/forum/#!to...-y/PLG6gqY3y7A


--
Adrian C

That was my next question on the next thread as well. I do sometimes wonder
what google are up to.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Adrian C" wrote in message
...
On 05/06/14 23:19, Brian Gaff wrote:
What was wrong then.
Brian


4 year old thread dug up by Google

https://groups.google.com/forum/#!to...-y/PLG6gqY3y7A


--
Adrian C

On 05/06/2014 23:26, Adrian C wrote:
On 05/06/14 23:19, Brian Gaff wrote:
What was wrong then.
Brian


4 year old thread dug up by Google

https://groups.google.com/forum/#!to...-y/PLG6gqY3y7A


Yep. I remember starting it!

Funnily enough, this is the second time it's been dredged up, and both
by the same person. The last time was Feb 2013...

Cheers,

Colin.

wrote in message
...
I bought a couple of these Maplin 50 watt amplifiers as both faulty.
I repaired them both and they sound great.

so what do you want, a ****in gold star or something?

On Tuesday, September 28, 2010 at 11:23:51 PM UTC+1, Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

"Huge" wrote in message
...
On 2017-12-21,
wrote:
On Tuesday, September 28, 2010 at 11:23:51 PM UTC+1, Colin Stamp
wrote:
Hi all,

A long long time ago, I made an amplifier using two of these
modules.
Since I made it in my yoof, I'm quite attached to it. Recently
though,
my wife bashed her head on the underside of the shelf it was on.
There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I
sprang up
and flew across the room to switch the amp off (which wasn't easy
since
I had to be careful to avoid my wife who was now rolling around on
the
floor, clutching her head) but I was too late and the left channel
was
toast.

I'm a bit mystified as to how the head-bashing could have caused
any
damage but, aside from that, repairs are progressing and new bits
are on
order; I only lost two of the output transistors, some resistors
and a
couple of polystyrene caps. The only problem I'm expecting is how
to set
up the quiescent current, since I can't find the original
instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to
have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

I have cross-posted this to uk.rec.audio. They may well know.



Did you notice the date of the mail? Its over 7 years old!!


--
Woody

harrogate3 at ntlworld dot com

On 22/12/17 03:32, Huge wrote:
On 2017-12-21, Woody wrote:

"Huge" wrote in message
...

[44 lines snipped]


I have cross-posted this to uk.rec.audio. They may well know.



Did you notice the date of the mail? Its over 7 years old!!

Oh, bugger. Thank you for pointing that out. Apologies.

Can we have the ****s who make these zombie postings killed?

In theory, yes, but in practice, ot may prove more difficult.


--
"Nature does not give up the winter because people dislike the cold."

ۥ Confucius

On Tuesday, September 28, 2010 at 11:23:51 PM UTC+1, Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

i notice theres no diagrams which i was looking for will pay if i get it 0863946719 ireland

On 21/12/17 22:16, wrote:

i notice theres no diagrams which i was looking for will pay if i get it 0863946719 ireland


https://www.scribd.com/doc/38418078/...35Q-Maplin-Kit



--
Adrian C

Adrian Caspersz wrote:
On 21/12/17 22:16, wrote:

i notice theres no diagrams which i was looking for will pay if i get it 0863946719 ireland


https://www.scribd.com/doc/38418078/...35Q-Maplin-Kit

If that isn't it, it will be in another issue of 'Electronics - The Maplin
Magazine', you just need to find out which one. Probably someone has back
issues lying around, or a library has some. As I recall, the December issue
of each year had an index of that year's articles, so it shouldn't be
difficult to find.

Theo

On 21/12/17 23:32, Theo wrote:
Adrian Caspersz wrote:
On 21/12/17 22:16, wrote:

i notice theres no diagrams which i was looking for will pay if i get it 0863946719 ireland


https://www.scribd.com/doc/38418078/...35Q-Maplin-Kit

If that isn't it, it will be in another issue of 'Electronics - The Maplin
Magazine', you just need to find out which one. Probably someone has back
issues lying around, or a library has some. As I recall, the December issue
of each year had an index of that year's articles, so it shouldn't be
difficult to find.

http://www.americanradiohistory.com/...lectronics.htm

--
Adrian C

On 21/12/2017 22:41, Adrian Caspersz wrote:
On 21/12/17 22:16, wrote:

i notice theres no diagrams which i was looking for will pay if i get
it 0863946719 ireland


https://www.scribd.com/doc/38418078/...35Q-Maplin-Kit


I built one of those years ago in a fit of enthusiasm... alas at the
time I had not costed what it would take to turn it into a fully
integrated amp! ISTR buying the bits to make a PSU for just running a
single power amp, and they cost more than the amp kit. (still I reused
them making a bench PSU for my O level electronics project!)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Bit confused what happened between 2010 and now.
However, when I had this happen in a Memorex Amp it actually toasted one of
the speakers.

As for the mode of failure, well, you only need a short across the output
after all.
I was always replacing the ICs in the old Sinclair IC12 amps as they had no
protection at all on the outputs. Texas made the chips
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Adrian Caspersz" wrote in message
...
On 21/12/17 22:16, wrote:

i notice theres no diagrams which i was looking for will pay if i get it
0863946719 ireland


https://www.scribd.com/doc/38418078/...35Q-Maplin-Kit



--
Adrian C