I diverted an electric piano from the skip the other day.
The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?

Thanks

misterroy explained on 14/10/2012 :
I diverted an electric piano from the skip the other day.
The blown transistor is one of balanced pair in the pre-amp, it is split in
two. Does a balanced pair just mean that the gain of both the BC238
transistors needs to be the same or is there more to it?

Thanks

It usually means that all of the parameters of two transistors are
checked and matched as closely as possible, one to another.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Sunday, October 14, 2012 9:54:44 PM UTC+1, Harry Bloomfield wrote:
misterroy explained on 14/10/2012 :

I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in

two. Does a balanced pair just mean that the gain of both the BC238

transistors needs to be the same or is there more to it?



Thanks



It usually means that all of the parameters of two transistors are

checked and matched as closely as possible, one to another.



--

Regards,

Harry (M1BYT) (L)

http://www.ukradioamateur.co.uk

thanks, its the USA for the replacements then.

misterroy wrote:
I diverted an electric piano from the skip the other day.
The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?

Odd to have a balanced pair in the pre-amp.

Or to shove so much juice down it to split it in half.
Your best bet is to buy two (or more) new ones from the same batch and
select the two that seem to be closes on any way you have of measuring them.

Trouble is you want similar DC AND AC gain.
Having said that its a purist thing. You probably won't notice more than
a shade of extra hum buried in the noise.

What is far more worrying is how on earth a preamp transistor drew
enough current to split...

Thanks


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

misterroy wrote:
On Sunday, October 14, 2012 9:54:44 PM UTC+1, Harry Bloomfield wrote:
misterroy explained on 14/10/2012 :

I diverted an electric piano from the skip the other day.
The blown transistor is one of balanced pair in the pre-amp, it is split in
two. Does a balanced pair just mean that the gain of both the BC238
transistors needs to be the same or is there more to it?
Thanks


It usually means that all of the parameters of two transistors are

checked and matched as closely as possible, one to another.



--

Regards,

Harry (M1BYT) (L)

http://www.ukradioamateur.co.uk

thanks, its the USA for the replacements then.
Are u sure? its a EU designated device..
http://www.ebay.co.uk/itm/BC328-X10-/370415996905


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

The Natural Philosopher wrote:
misterroy wrote:
I diverted an electric piano from the skip the other day. The blown
transistor is one of balanced pair in the pre-amp, it is split in two.
Does a balanced pair just mean that the gain of both the BC238
transistors needs to be the same or is there more to it?

Odd to have a balanced pair in the pre-amp.

Or to shove so much juice down it to split it in half.
Your best bet is to buy two (or more) new ones from the same batch and
select the two that seem to be closes on any way you have of measuring
them.

Trouble is you want similar DC AND AC gain.
Having said that its a purist thing. You probably won't notice more than
a shade of extra hum buried in the noise.

What is far more worrying is how on earth a preamp transistor drew
enough current to split...

Thanks


I had a thought: does this piano have an integral POWER amp? because
that can indeed draw enough current if much of the output stage goes
bang to kill the drivers. And it is conventional to have a balanced pair
of PNPS as the first stage to drive the phase splitter.

If that is the case, you are advised to remove ALL the transistors one
by one and check that they still have diode junctions and not dead shorts.

Replace any that have popped and any obviously burnt resistor and if the
whole thing has a DC fuse remove it and put a meter in there. Should
draw no more than 20-40mA

--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?



Thanks


Balanced pair doesn't mean the same gain. Tranny gain varies widely, and every circuit has to deal with that, normally by using nfb and bias stabilisation.

If a preamp tr has split in 2, the fault isn't due to tr failure, its due to something else allowing that much current to flow. If its a power amp tr, as sounds much more likely, its not as simple as assuming the tr is what caused the fault. But if you can't trouble shoot, its always worth putting a similarish tr in there to see if it works, it might.

BC238 is a general purpose tranny, lots of gen purp trs would substitute for it ok. Data:
https://www.google.com/url?q=http://...2PZzwYv16dWBoA


NT

wrote in message
...
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split
in two. Does a balanced pair just mean that the gain of both the BC238
transistors needs to be the same or is there more to it?



Thanks


Balanced pair doesn't mean the same gain. Tranny gain varies widely, and
every circuit has to deal with that, normally by using nfb and bias
stabilisation.

If a preamp tr has split in 2, the fault isn't due to tr failure, its due to
something else allowing that much current to flow. If its a power amp tr, as
sounds much more likely, its not as simple as assuming the tr is what caused
the fault. But if you can't trouble shoot, its always worth putting a
similarish tr in there to see if it works, it might.

BC238 is a general purpose tranny, lots of gen purp trs would substitute for
it ok. Data:
https://www.google.com/url?q=http://...2PZzwYv16dWBoA


IME, if you have a tr blow (in a DC coupled amp), change the lot of them
else you'll be changing tr's until the cows come home.

On Sunday, 14 October 2012 21:52:39 UTC+1, misterroy wrote:

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?

Just replace both transistors with two more from the same modern manufacturer. The old obsession with matched pairs made sense when (especially for germanium) transistors were made by a "craft" process of diffusion and where their parameters varied according to their times in the oven. With modern structures and manufacturing controls, there's just not that much difference to begin with.

If you still really need a matched pair these days, then you'll also want to have them fabricated as part of an array, so that they're thermally coupled too.

In message , The Natural Philosopher
writes
misterroy wrote:
On Sunday, October 14, 2012 9:54:44 PM UTC+1, Harry Bloomfield wrote:
misterroy explained on 14/10/2012 :

I diverted an electric piano from the skip the other day. The
blown transistor is one of balanced pair in the pre-amp, it is split
in two. Does a balanced pair just mean that the gain of both the
BC238 transistors needs to be the same or is there more to it?
Thanks


It usually means that all of the parameters of two transistors are
checked and matched as closely as possible, one to another.



--
Regards,

Harry (M1BYT) (L)

http://www.ukradioamateur.co.uk
thanks, its the USA for the replacements then.
Are u sure? its a EU designated device..
http://www.ebay.co.uk/itm/BC328-X10-/370415996905



Except that he was after BC 238 not BC 328

--
geoff

Harry Bloomfield wrote:
misterroy explained on 14/10/2012 :
I diverted an electric piano from the skip the other day. The blown
transistor is one of balanced pair in the pre-amp, it is split in two.
Does a balanced pair just mean that the gain of both the BC238
transistors needs to be the same or is there more to it?

Thanks

It usually means that all of the parameters of two transistors are
checked and matched as closely as possible, one to another.

For an initial try-out, buy transistors with the same suffix. BC 238 a,
b & c each have reasonably close gain balance. They shouldn't be more
than a pound or so each, even from your local friendly retail supplier.
If the unit doesn't work, you've not wasted much, and if it does, then
you can buy matched pairs or just buy a batch and match your own.

The worry is about why the original transistor split, and whether the
same thing will happen to a replacement. All the other components in the
circuit need to be checked thoroughly.

--
Tciao for Now!

John.

Andy Dingley wrote:
On Sunday, 14 October 2012 21:52:39 UTC+1, misterroy wrote:

The blown transistor is one of balanced pair in the pre-amp, it is
split in two. Does a balanced pair just mean that the gain of both
the BC238 transistors needs to be the same or is there more to it?

Just replace both transistors with two more from the same modern
manufacturer. The old obsession with matched pairs made sense when
(especially for germanium) transistors were made by a "craft" process
of diffusion and where their parameters varied according to their
times in the oven. With modern structures and manufacturing
controls, there's just not that much difference to begin with.

If you still really need a matched pair these days, then you'll also
want to have them fabricated as part of an array, so that they're
thermally coupled too.

If its a power amp phase splitter better matching will give you two
things: less DC offset on the loudpseaker if its DC coupled and better
common mode rejection of power supply ripple.

--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

geoff wrote:
In message , The Natural Philosopher
writes
misterroy wrote:
On Sunday, October 14, 2012 9:54:44 PM UTC+1, Harry Bloomfield wrote:
misterroy explained on 14/10/2012 :

I diverted an electric piano from the skip the other day. The
blown transistor is one of balanced pair in the pre-amp, it is
split in two. Does a balanced pair just mean that the gain of both
the BC238 transistors needs to be the same or is there more to it?
Thanks


It usually means that all of the parameters of two transistors are
checked and matched as closely as possible, one to another.



--
Regards,

Harry (M1BYT) (L)

http://www.ukradioamateur.co.uk
thanks, its the USA for the replacements then.
Are u sure? its a EU designated device..
http://www.ebay.co.uk/itm/BC328-X10-/370415996905



Except that he was after BC 238 not BC 328

Damn that ythrew me

http://www.ebay.co.uk/sch/i.html?_nkw=bc238
bags of the buggers. Its an NPN too.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?



Thanks

What a goof I have been. I only noticed that the blown bc238 is not part of a matched pair when I looked for the schematic on-line. (There was a paper copy stapled inside the keyboard)
The image is here http://www.clavinet.de/schematics/clavinete7.jpg

The supply is supposed to be 9v, probably 12 volts supplied. I don't have the power supply that was used.
Thank you all for your help. I might still need a matched pair of BC550C

On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?



Thanks

Having looked at the circuit board I dont feel quite as stupid as I did. Beside the battery cables there is a BC108, then beside the on/off switch there is the split BC238, and close to the split one there is a BC550c. Thhttp://www.clavinet.de/schematics/clavinete7.jpge two close together have the same d style case. The BC108 must be an earlier repair.
Off to order a pack of BC550cs.
ta

misterroy wrote:
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?



Thanks

What a goof I have been. I only noticed that the blown bc238 is not part of a matched pair when I looked for the schematic on-line. (There was a paper copy stapled inside the keyboard)
The image is here http://www.clavinet.de/schematics/clavinete7.jpg

The supply is supposed to be 9v, probably 12 volts supplied. I don't have the power supply that was used.
Thank you all for your help. I might still need a matched pair of BC550C

The BC 238 has blown because something is drawing excessive current, or
the input voltage has risen too high. Probably, the 100 microfarad
smoothing capacitor has failed short circuit, as all other current paths
are limited to a total of less than 2 milliamps by resistors. There may
be a short on the circuit board, which you could spot by using a
magnifying glass. Also, check the zener and the 1.8 K resistor in the
circuitry round the BC 238.

The BC 550 transistors do not need to be matched, as their gain is set
by the feedback loops round them.

--
Tciao for Now!

John.

More to the point one really needs to know a bit more about this
amplification stage. Are you saying there are two amps feeding different
paths, or what. What purpose does it serve exactly? are you absolutely sure
that you do not have two different transistors, one pnp and one npn used for
some odd purpose like phase splitting or some such?

Brian

--
From the Sofa of Brian Gaff Reply address is active
"misterroy" wrote in message
...
I diverted an electric piano from the skip the other day.
The blown transistor is one of balanced pair in the pre-amp, it is split
in two. Does a balanced pair just mean that the gain of both the BC238
transistors needs to be the same or is there more to it?

Thanks

I'd be tempted to stick a couple of equivelents in and see what happens. Its
not going to blow it up after all.

Brian

--
From the Sofa of Brian Gaff Reply address is active
"misterroy" wrote in message
...
On Sunday, October 14, 2012 9:54:44 PM UTC+1, Harry Bloomfield wrote:
misterroy explained on 14/10/2012 :

I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is
split in

two. Does a balanced pair just mean that the gain of both the BC238

transistors needs to be the same or is there more to it?



Thanks



It usually means that all of the parameters of two transistors are

checked and matched as closely as possible, one to another.



--

Regards,

Harry (M1BYT) (L)

http://www.ukradioamateur.co.uk

thanks, its the USA for the replacements then.

Brian Gaff wrote:
More to the point one really needs to know a bit more about this
amplification stage. Are you saying there are two amps feeding different
paths, or what. What purpose does it serve exactly? are you absolutely sure
that you do not have two different transistors, one pnp and one npn used for
some odd purpose like phase splitting or some such?

In the circuit that the OP has now posted a link to, the BC 238 is part
of an emitter follower type voltage regulator, and the BC 550s form a
pre amp and tone control circuit. Standard, very basic open collector
type circuit, typical of the period. Matched transistors are not
required, as the gains are set by feedback to be much lower than the hfe
of the transistors and the BC 238 could be replaced by any small signal
NPN transistor with reasonable gain. The only critical parts in the
circuit are the feedback capacitors, resistors and inductors.

--
Tciao for Now!

John.

On 15/10/2012 09:30, John Williamson wrote:
misterroy wrote:

What a goof I have been. I only noticed that the blown bc238 is not
part of a matched pair when I looked for the schematic on-line. (There
was a paper copy stapled inside the keyboard) The image is here
http://www.clavinet.de/schematics/clavinete7.jpg
The supply is supposed to be 9v, probably 12 volts supplied. I don't
have the power supply that was used.
Thank you all for your help. I might still need a matched pair of BC550C

The BC 238 has blown because something is drawing excessive current, or
the input voltage has risen too high. Probably, the 100 microfarad
smoothing capacitor has failed short circuit, as all other current paths

Agreed.

Seems to be the only possibility unless a short has occurred on the
copper side of the board. STray wire come loose or washer rolling around
- that kind of thing.

Replacing the 100uF capacitor and BC238 with almost any NPN transistor
ought to fix it. PSU noise might be improved slightly by putting a
modest capacitor in parallel across the zener diode too.

are limited to a total of less than 2 milliamps by resistors. There may
be a short on the circuit board, which you could spot by using a
magnifying glass. Also, check the zener and the 1.8 K resistor in the
circuitry round the BC 238.

The BC 550 transistors do not need to be matched, as their gain is set
by the feedback loops round them.

--
Regards,
Martin Brown

In article ,
misterroy scribeth thus
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in
two. Does a balanced pair just mean that the gain of both the BC238 transistors
needs to be the same or is there more to it?



Thanks

Having looked at the circuit board I dont feel quite as stupid as I did. Beside
the battery cables there is a BC108, then beside the on/off switch there is the
split BC238,

If thats split .. physically split that is then whatever have you
supplied this with?.

Not mains by any chance?..

If that really is split then change the cap next to it, the Zener diode
will have suffered. I expect and I reckon the other ones will be OK.

Do a simple ohm meter check on them if you know how to and those
transistors are nothing that special, most any NPN will do there and
they do not have to be matched at all.

Also check the 1.8 K to see if it still is at that value..

and close to the split one there is a BC550c. Thhttp://www.clavinet
.de/schematics/clavinete7.jpge two close together have the same d style case.
The BC108 must be an earlier repair.
Off to order a pack of BC550cs.
ta

--
Tony Sayer

On Monday, October 15, 2012 7:46:06 AM UTC+1, misterroy wrote:
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:

I diverted an electric piano from the skip the other day.



The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?







Thanks



What a goof I have been. I only noticed that the blown bc238 is not part of a matched pair when I looked for the schematic on-line. (There was a paper copy stapled inside the keyboard)

The image is here http://www.clavinet.de/schematics/clavinete7.jpg



The supply is supposed to be 9v, probably 12 volts supplied. I don't have the power supply that was used.

Thank you all for your help. I might still need a matched pair of BC550C

Its acting a s a 7.6v regulator, and there's absolutely no protection against surges into the 100uF cap. I'd replace it with a 7806 with 2 diodes in its ground lead. 78s are self protecting.


NT

On 15/10/2012 12:13, wrote:
On Monday, October 15, 2012 7:46:06 AM UTC+1, misterroy wrote:
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:

I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?

Thanks



What a goof I have been. I only noticed that the blown bc238 is not part of a matched pair when I looked for the schematic on-line. (There was a paper copy stapled inside the keyboard)

The image is here http://www.clavinet.de/schematics/clavinete7.jpg

The supply is supposed to be 9v, probably 12 volts supplied. I don't have the power supply that was used.

Thank you all for your help. I might still need a matched pair of BC550C

Its acting a s a 7.6v regulator, and there's absolutely no protection against surges into the 100uF cap.

Actually it is current limited to beta*(Vin-8.2)/1800 taking gain beta
as 300 and Vin as 12v that gives about 650mA worst case peak current (or
160mA off a 9v supply). But it won't occur for long enough to stress the
transistor unless the capacitor is a dead short to ground.

The original circuit is OK, but might benefit from a small capacitor in
parallel with the zener to filter out noise at source.

I'd replace it with a 7806 with 2 diodes in its ground lead. 78s are self protecting.

There is a 7808 but it won't like a 9v battery. You need about 2v of
headroom over the regulated output voltage.

And 78xx series are also inclined to oscillate wildly at RF if you don't
put the appropriate decoupling capacitors close to the device.

--
Regards,
Martin Brown

On Monday, October 15, 2012 12:37:56 PM UTC+1, Martin Brown wrote:
On 15/10/2012 12:13, meow2222 wrote:

On Monday, October 15, 2012 7:46:06 AM UTC+1, misterroy wrote:

On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:

Its acting a s a 7.6v regulator, and there's absolutely no protection against surges into the 100uF cap.



Actually it is current limited to beta*(Vin-8.2)/1800 taking gain beta

as 300 and Vin as 12v that gives about 650mA worst case peak current (or

160mA off a 9v supply).

fair enough - but the 328 is specced as having beta 120 - 800, and an unregulated 12v psu would deliver about 19v, so its all a bit iffy


But it won't occur for long enough to stress the

transistor unless the capacitor is a dead short to ground.



The original circuit is OK, but might benefit from a small capacitor in

parallel with the zener to filter out noise at source.



I'd replace it with a 7806 with 2 diodes in its ground lead. 78s are self protecting.



There is a 7808 but it won't like a 9v battery. You need about 2v of

headroom over the regulated output voltage.



And 78xx series are also inclined to oscillate wildly at RF if you don't

put the appropriate decoupling capacitors close to the device.

A 12v psu would be fine with a 7806 plus 2 diodes. It'd give much better psrr too.


NT

misterroy wrote:
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?



Thanks

What a goof I have been. I only noticed that the blown bc238 is not part of a matched pair when I looked for the schematic on-line. (There was a paper copy stapled inside the keyboard)
The image is here http://www.clavinet.de/schematics/clavinete7.jpg

The supply is supposed to be 9v, probably 12 volts supplied. I don't have the power supply that was used.
Thank you all for your help. I might still need a matched pair of BC550C

Ah. Its been connected to a much bigger battery probably.

Very simple and very poor circuit design all round.

That first BC550 has almost no temperature of component tolerance
stability at all.

The second one does although its limited to 5:1 gain

I would be very include to fit a 7809 type regulator in place of that
transistor and short the zener out and cut the resistor out as well. .

http://www.ebay.co.uk/itm/2-PACK-MC7...-/120744838184

At least that wont explode if overdriven.

If you do decide to replace the transistor any bloody NPN silicon ****
will do. Even a Sinclair branded transistor would work in that position.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

John Williamson wrote:
misterroy wrote:
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.
The blown transistor is one of balanced pair in the pre-amp, it is
split in two. Does a balanced pair just mean that the gain of both
the BC238 transistors needs to be the same or is there more to it?



Thanks

What a goof I have been. I only noticed that the blown bc238 is not
part of a matched pair when I looked for the schematic on-line. (There
was a paper copy stapled inside the keyboard) The image is here
http://www.clavinet.de/schematics/clavinete7.jpg
The supply is supposed to be 9v, probably 12 volts supplied. I don't
have the power supply that was used.
Thank you all for your help. I might still need a matched pair of BC550C

The BC 238 has blown because something is drawing excessive current, or
the input voltage has risen too high. Probably, the 100 microfarad
smoothing capacitor has failed short circuit, as all other current paths
are limited to a total of less than 2 milliamps by resistors. There may
be a short on the circuit board, which you could spot by using a
magnifying glass. Also, check the zener and the 1.8 K resistor in the
circuitry round the BC 238.

The BC 550 transistors do not need to be matched, as their gain is set
by the feedback loops round them.

Except in the first transistors case with has no feedback at all to
speak of.



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in two. Does a balanced pair just mean that the gain of both the BC238 transistors needs to be the same or is there more to it?



Thanks

I think the voltage regulator in my head needs a heatsink.
I am slowly working my way through the posts and with wikipedia holding my hand I am getting there. There may be other questions, but I am enjoying where the original question is taking me.
Thank you all.

On 15/10/2012 10:31 p.m., tony sayer wrote:
In article ,
misterroy scribeth thus
On Sunday, October 14, 2012 9:52:39 PM UTC+1, misterroy wrote:
I diverted an electric piano from the skip the other day.

The blown transistor is one of balanced pair in the pre-amp, it is split in
two. Does a balanced pair just mean that the gain of both the BC238 transistors
needs to be the same or is there more to it?



Thanks

Having looked at the circuit board I dont feel quite as stupid as I did. Beside
the battery cables there is a BC108, then beside the on/off switch there is the
split BC238,

If thats split .. physically split that is then whatever have you
supplied this with?.

Not mains by any chance?..

"I diverted an electric piano from the skip the other day."

On Tue, 16 Oct 2012 19:48:45 +1300, Gib Bogle
wrote:

"I diverted an electric piano from the skip the other day."

"Ten thousand holes in Blackburn, Lancashire"

On Tue, 16 Oct 2012 16:23:08 +0100, Grimly Curmudgeon wrote:

On Tue, 16 Oct 2012 19:48:45 +1300, Gib Bogle
wrote:

"I diverted an electric piano from the skip the other day."

"Ten thousand holes in Blackburn, Lancashire"

Four thousand?



--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

*lightning protection* - a w_tom conductor

In message , Bob Eager
writes
On Tue, 16 Oct 2012 16:23:08 +0100, Grimly Curmudgeon wrote:

On Tue, 16 Oct 2012 19:48:45 +1300, Gib Bogle
wrote:

"I diverted an electric piano from the skip the other day."

"Ten thousand holes in Blackburn, Lancashire"

Four thousand?

That was 35 years ago ...

(CBA to look up the precise year)

--
geoff