Welcome to New Member Bowlanders
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John Mayberry
Jan 1, 2012, 11:00:02 AM1/1/12
to Lecson Audio
Well, it's a new year and I'm sure this will be an adventure like all
years past.
We're starting off the new year with a new member, who recently
reworked an AC1 back into life.
Welcome aboard, and we look forward to reading about your adventures.
John
years past.
We're starting off the new year with a new member, who recently
reworked an AC1 back into life.
Welcome aboard, and we look forward to reading about your adventures.
John
Jack Ward
Jan 1, 2012, 1:52:01 PM1/1/12
to lecson...@googlegroups.com
Yes, welcome to our interesting group. I need to bring my AC1 back to life as one channel has given up.
Jack
Jack
John
--
Spiny
Jan 1, 2012, 5:36:08 PM1/1/12
to Lecson Audio
welcome to the group, Nice to hear of another member fixing the kit.
I've posted a few bits on fixing Lecsons along with a few other
members over the years. If you would like to share any findings on
fixing your AC1 it would help add to the info in the archive.
jack, hope its not too much of a problem. at least the circuits are
not to complex. do check the connections in the base - muting relay/
fuses/ a/b switch and the zorbel resistors
alan
I've posted a few bits on fixing Lecsons along with a few other
members over the years. If you would like to share any findings on
fixing your AC1 it would help add to the info in the archive.
jack, hope its not too much of a problem. at least the circuits are
not to complex. do check the connections in the base - muting relay/
fuses/ a/b switch and the zorbel resistors
alan
Stephen
Jan 2, 2012, 9:51:14 PM1/2/12
to Lecson Audio
Hello to John and others,
I ought to specify that it is actually the power amplifier AP1, which
I have. I have not yet found the AC1. I found this lecson power
amplifier on ebay, not knowing anything about it other than it being
vintage and of a very unique styling. I bought it on a whim, and
subsequently discovered that this group exists which discusses lecson
audio. A brand I was unfamiliar with, even being a regular on the
forum Audiokarma, which is a forum largely dedicated to vintage audio
equipment.
Lothar mentioned to me that the AP1, being an earlier model, does have
some reliability issues in terms of design and construction. For
example, I did find when I first opened it up, the quick disconnect
style connections to the main circuit boards. At least one was
brittle and on the verge of breaking. I came up with a more modern
solution to these. I also needed to replace some of the wiring and
then redo solder connections to components such as fuses, especially
where wires were too stiff or short to stand up to the stress of
disassembly/reassembly some 40 years after manufacture.
I have learned some interesting facts about replacement parts. For
example the screws that hold the top and bottom plates are #6 - 3/4"
flat head phillips self tapping screws with black oxide finish.
Also, the circuit boards are held to the case with 8-32 x 1/2" machine
screws. I needed to pick up a couple of each that were missing.
I ought to specify that it is actually the power amplifier AP1, which
I have. I have not yet found the AC1. I found this lecson power
amplifier on ebay, not knowing anything about it other than it being
vintage and of a very unique styling. I bought it on a whim, and
subsequently discovered that this group exists which discusses lecson
audio. A brand I was unfamiliar with, even being a regular on the
forum Audiokarma, which is a forum largely dedicated to vintage audio
equipment.
Lothar mentioned to me that the AP1, being an earlier model, does have
some reliability issues in terms of design and construction. For
example, I did find when I first opened it up, the quick disconnect
style connections to the main circuit boards. At least one was
brittle and on the verge of breaking. I came up with a more modern
solution to these. I also needed to replace some of the wiring and
then redo solder connections to components such as fuses, especially
where wires were too stiff or short to stand up to the stress of
disassembly/reassembly some 40 years after manufacture.
I have learned some interesting facts about replacement parts. For
example the screws that hold the top and bottom plates are #6 - 3/4"
flat head phillips self tapping screws with black oxide finish.
Also, the circuit boards are held to the case with 8-32 x 1/2" machine
screws. I needed to pick up a couple of each that were missing.
John Mayberry
Jan 3, 2012, 9:59:28 AM1/3/12
to Lecson Audio
Lothar
Jan 6, 2012, 3:39:08 AM1/6/12
to lecson...@googlegroups.com
Hello Stephen,
GOOD you found some things at your AP1 that do need attention! Would be quite boring otherwise, wouldn't it!?? ;))
Hope you can get an AC1 for a reasonable price. After some really silly high prices recently, price level seems to be back to normal again.
Good hunting !
Lothar
GOOD you found some things at your AP1 that do need attention! Would be quite boring otherwise, wouldn't it!?? ;))
Hope you can get an AC1 for a reasonable price. After some really silly high prices recently, price level seems to be back to normal again.
Good hunting !
Lothar
Stephen
Jan 5, 2012, 7:57:35 PM1/5/12
to Lecson Audio
I was attempting to perform the quiescent current adjustment with my
AP1 in the dismantled state as required in the service manual.
However today I noticed a major problem that forced me to stop. The
hum sound from the power supply was starting and stopping
intermittently. Connected to the dim bulb tester with a 15 watt
bulb, I noticed the bulb light up brightly, suggesting some kind of
fault in the power supply circuit. Then when I unplugged it, I
noticed that the plug itself is what had failed. One of the two wires
was broken at the plug, clearly from many years of wear. As I look at
this power cord, I notice that it seems rather flimsy and prone to
this kind of failure. Especially with the passage of years. It is
probably worth making a note of this, and consider replacing the power
cord might be a necessary part of restoring this piece. As of now, I
have removed the faulty cord. I will need to find a suitable
replacement for this cord before proceeding any futher. Here is an
image of the plug. I am exaggerating the break in the picture. The
break was actually subtle enough that you would probably not have
noticed it.
http://data.imagup.com/11/1140476049.JPG
Another unusual feature stands out with this AP1. The two power
supply capacitors are 6800 uF. According to the Lecson manuals,
6800uF capacitors were fitted on the AP2, and 10000uF were installed
in the AP1. I am reading "British made" on these capacitors, so I am
assuming they are the originals that were installed in the factory.
My AP1 serial number 3478 appears to have been made slightly
differently in that respect.
AP1 in the dismantled state as required in the service manual.
However today I noticed a major problem that forced me to stop. The
hum sound from the power supply was starting and stopping
intermittently. Connected to the dim bulb tester with a 15 watt
bulb, I noticed the bulb light up brightly, suggesting some kind of
fault in the power supply circuit. Then when I unplugged it, I
noticed that the plug itself is what had failed. One of the two wires
was broken at the plug, clearly from many years of wear. As I look at
this power cord, I notice that it seems rather flimsy and prone to
this kind of failure. Especially with the passage of years. It is
probably worth making a note of this, and consider replacing the power
cord might be a necessary part of restoring this piece. As of now, I
have removed the faulty cord. I will need to find a suitable
replacement for this cord before proceeding any futher. Here is an
image of the plug. I am exaggerating the break in the picture. The
break was actually subtle enough that you would probably not have
noticed it.
http://data.imagup.com/11/1140476049.JPG
Another unusual feature stands out with this AP1. The two power
supply capacitors are 6800 uF. According to the Lecson manuals,
6800uF capacitors were fitted on the AP2, and 10000uF were installed
in the AP1. I am reading "British made" on these capacitors, so I am
assuming they are the originals that were installed in the factory.
My AP1 serial number 3478 appears to have been made slightly
differently in that respect.
Spiny
Jan 6, 2012, 4:02:57 PM1/6/12
to Lecson Audio
Its a standard US 2pin plug, I suspect it dosn't conform to UK
electrical regs at 230 volts and one of the AP1's0 I have is later and
they obviously had second thoughts about using the US Style plug and
its factory wired with a UK plug with a ground connection. Its
possible safety ground was not to standard, being just via the signal
lead and the AP amps are metal cased - NOT double insulated!
All the AP1's I've taken apart have the 6800uf caps, never seen a
10,000uf in an AP1 and the AP2 either did not exist or is very rare -
the AP1X and AP3 seem to have been the more powerful options. I have
recapped mine. For those going to do this its not a cheap option,
decent PSU caps with a good ripple tolerance are not cheap, "Computer
Grade" is the type needed.
electrical regs at 230 volts and one of the AP1's0 I have is later and
they obviously had second thoughts about using the US Style plug and
its factory wired with a UK plug with a ground connection. Its
possible safety ground was not to standard, being just via the signal
lead and the AP amps are metal cased - NOT double insulated!
All the AP1's I've taken apart have the 6800uf caps, never seen a
10,000uf in an AP1 and the AP2 either did not exist or is very rare -
the AP1X and AP3 seem to have been the more powerful options. I have
recapped mine. For those going to do this its not a cheap option,
decent PSU caps with a good ripple tolerance are not cheap, "Computer
Grade" is the type needed.
Stephen
Jan 6, 2012, 6:02:30 PM1/6/12
to Lecson Audio
I went ahead and replaced the faulty power cord with a newer two prong
polarized cord cut from an extension cord. I wired the "hot" wire to
the fused connection, the neutral wire to the unfused connection.
Thank you for the detailed information Spiny, it is very useful. I
should specify that I have also recapped this AP1. I used NICHICON
Super Through 6800uF 63V Solder Lug capacitors for the supply
capacitors ($20CND each), with a 2.2uF solen metallized poly bypass on
each. I am reading a supply voltage of +/- 45V. A previous owner had
visibly attempted to repair a bad channel and replaced many of the
components on one of the power boards with NTE transistors. That
repair included installing a tiny 1/4 270 Ohm resistor in the output
circuit, where the schematic clearly calls for a 1 watt resistor, also
noted some charring on the 150 Ohm resistor to which it is connected.
I replaced these with high quality Riken precision carbon resistors
with the correct power rating. I used Takman metal film resistors on
the power boards, and replaced the polarized tantalum beads with good
quality electrolytic capacitors. So no expense spared, however I am
running into difficulty again in getting it back to working
condition.
The second part of the idle current adjustment involves soldering the
red supply lead to the solder tab of 2N3442 transistor on the right
channel board. Then measuring the current with test leads at the -ve
fuse holder and the solder tab of BDX18 (complementary of 2N3442).
When I touched this tab I noticed a significant spark, so I
immediately stopped. I had not noticed that type of problem with the
left channel board. Nothing was damaged, however I need to figure out
what might be wrong with the right channel. I double checked to make
sure that there was no continuity between the output transistors and
the heatsink, which might happen if the insulation were damaged.
polarized cord cut from an extension cord. I wired the "hot" wire to
the fused connection, the neutral wire to the unfused connection.
Thank you for the detailed information Spiny, it is very useful. I
should specify that I have also recapped this AP1. I used NICHICON
Super Through 6800uF 63V Solder Lug capacitors for the supply
capacitors ($20CND each), with a 2.2uF solen metallized poly bypass on
each. I am reading a supply voltage of +/- 45V. A previous owner had
visibly attempted to repair a bad channel and replaced many of the
components on one of the power boards with NTE transistors. That
repair included installing a tiny 1/4 270 Ohm resistor in the output
circuit, where the schematic clearly calls for a 1 watt resistor, also
noted some charring on the 150 Ohm resistor to which it is connected.
I replaced these with high quality Riken precision carbon resistors
with the correct power rating. I used Takman metal film resistors on
the power boards, and replaced the polarized tantalum beads with good
quality electrolytic capacitors. So no expense spared, however I am
running into difficulty again in getting it back to working
condition.
The second part of the idle current adjustment involves soldering the
red supply lead to the solder tab of 2N3442 transistor on the right
channel board. Then measuring the current with test leads at the -ve
fuse holder and the solder tab of BDX18 (complementary of 2N3442).
When I touched this tab I noticed a significant spark, so I
immediately stopped. I had not noticed that type of problem with the
left channel board. Nothing was damaged, however I need to figure out
what might be wrong with the right channel. I double checked to make
sure that there was no continuity between the output transistors and
the heatsink, which might happen if the insulation were damaged.
John Mayberry
Jan 6, 2012, 6:12:34 PM1/6/12
to lecson...@googlegroups.com
One of the things that would be great to develop is an "upgrade" kit-
primarily new capacitors for the various components- AC1, AP1, AP2, AP3,
AP3X.
primarily new capacitors for the various components- AC1, AP1, AP2, AP3,
AP3X.
I ordered a kit from a firm in Belgium a few years ago on a Quad 306
amplifier and it made a night and day difference. In a couple of hours it
went from a dog to a decent amplifier.
Anyone up to the challenge?
Thanks,
John
Spiny
Jan 7, 2012, 4:16:21 AM1/7/12
to Lecson Audio
hi
I used a screw terminal type (vishay 15 amp ripple rating / 10000 hour
rated) similar price @25CD+ tax (£14+tax here) for the power supply
caps, for the rest the tants in the signal line were replace with
non-polarised caps othere with Panasonics I think (what ever CPC had
of reasonable quality at the time). any required resistors with metal
film though I recall I only changed one. The transistors are all
available if needed. The big problem is the germanium diodes (the
HG5008's) It seems you can us any non-point contact germanium - I used
some OA95's to good effect. Old germanium diodes scrounged from 1960's
scrap transistor radios will do at a pinch.
TR21 an 23 are the problem transistors the D43C7 and D42C7 are only
available as NOS at sill prices. TIP 41C will substitute for the D42C7
you can use a a TIP42C for the D43C7 but be aware the pinout is
different.
testing
Stick about a 500ohm resistor in the red lead then measure the voltage
across it. If the board has a fault the voltage will collapse at the
transistor end.Helps stop the fireworks....
With a fault check the semiconductors. And if someone else has tried
to fix it Check the orientation of all the transistors and types, The
boards are not silk screened!
It will work again ;)
alan
I used a screw terminal type (vishay 15 amp ripple rating / 10000 hour
rated) similar price @25CD+ tax (£14+tax here) for the power supply
caps, for the rest the tants in the signal line were replace with
non-polarised caps othere with Panasonics I think (what ever CPC had
of reasonable quality at the time). any required resistors with metal
film though I recall I only changed one. The transistors are all
available if needed. The big problem is the germanium diodes (the
HG5008's) It seems you can us any non-point contact germanium - I used
some OA95's to good effect. Old germanium diodes scrounged from 1960's
scrap transistor radios will do at a pinch.
TR21 an 23 are the problem transistors the D43C7 and D42C7 are only
available as NOS at sill prices. TIP 41C will substitute for the D42C7
you can use a a TIP42C for the D43C7 but be aware the pinout is
different.
testing
Stick about a 500ohm resistor in the red lead then measure the voltage
across it. If the board has a fault the voltage will collapse at the
transistor end.Helps stop the fireworks....
With a fault check the semiconductors. And if someone else has tried
to fix it Check the orientation of all the transistors and types, The
boards are not silk screened!
It will work again ;)
alan
Spiny
Jan 7, 2012, 4:25:31 AM1/7/12
to Lecson Audio
the power amps are simple, two expensive caps and a few (8 )others -
not likely to damage the boards when changed - the quality of the
PCB's is not great however.
the AC1 is a different kettle of fish.
As detailed in the past I have recapped mine, the bag of caps is quite
big! the circuit board needs careful handling as it is likely some for
the pads will come adrift.
the early griplet boards actually use thecapacitor legs to join the
two sides in some places I think - this is a doublesided board without
through hole plating.
the later ones (Proper doublesided boards) ought to be easier.
the AC1 bag of caps would be considerably cheaper than the AP1 ;)
spiny
not likely to damage the boards when changed - the quality of the
PCB's is not great however.
the AC1 is a different kettle of fish.
As detailed in the past I have recapped mine, the bag of caps is quite
big! the circuit board needs careful handling as it is likely some for
the pads will come adrift.
the early griplet boards actually use thecapacitor legs to join the
two sides in some places I think - this is a doublesided board without
through hole plating.
the later ones (Proper doublesided boards) ought to be easier.
the AC1 bag of caps would be considerably cheaper than the AP1 ;)
spiny
Stephen
Jan 7, 2012, 1:46:03 PM1/7/12
to Lecson Audio
I could definitely put together a parts list once I get this AP1 back
to life. One thing I am noticing now is that the muting relay is
not clicking when I plug it in. I did hear it click when it
initially arrived.
I use a hakko desoldering gun in order to quickly and effectively
remove a component without damaging the traces. A quick touch and the
joint is vacuumed off. It would definitely come in handy with a board
with more capacitors to remove, such as the AC1 you describe.
I had another look at the right channel board and noticed something
unusual with the replacement transistors I had sourced for BC177B. I
bought some BC177 (different pin configuration). When I ran an hfe
test on this transistor, I only get about 56. On the original BC177
from the "good board", I am reading hfe of around 380. I know that
these values can vary on the same transistor, however I thought it
could be worth looking into.
I think I used a simliar reasoning with replacing parts. I used OA47
for the HG5008.
"With a fault check the semiconductors. And if someone else has
tried
to fix it Check the orientation of all the transistors and types, The
boards are not silk screened! "
Yes, I have replaced all of the semiconductors on the problem board.
I have tried to be very careful to get the orientation right, which
can be tricky since a couple of them do have different lead layouts
and required bending a lead over another with insulation added to the
collector in order to prevent the leads touching. Even so, I may have
made a mistake somewhere because of the lack of silk screened
information to go on. So I generally used the good board and the
schematic as my guide for comparison.
to life. One thing I am noticing now is that the muting relay is
not clicking when I plug it in. I did hear it click when it
initially arrived.
I use a hakko desoldering gun in order to quickly and effectively
remove a component without damaging the traces. A quick touch and the
joint is vacuumed off. It would definitely come in handy with a board
with more capacitors to remove, such as the AC1 you describe.
I had another look at the right channel board and noticed something
unusual with the replacement transistors I had sourced for BC177B. I
bought some BC177 (different pin configuration). When I ran an hfe
test on this transistor, I only get about 56. On the original BC177
from the "good board", I am reading hfe of around 380. I know that
these values can vary on the same transistor, however I thought it
could be worth looking into.
I think I used a simliar reasoning with replacing parts. I used OA47
for the HG5008.
"With a fault check the semiconductors. And if someone else has
tried
to fix it Check the orientation of all the transistors and types, The
boards are not silk screened! "
I have tried to be very careful to get the orientation right, which
can be tricky since a couple of them do have different lead layouts
and required bending a lead over another with insulation added to the
collector in order to prevent the leads touching. Even so, I may have
made a mistake somewhere because of the lack of silk screened
information to go on. So I generally used the good board and the
schematic as my guide for comparison.
Stephen
Jan 7, 2012, 2:43:12 PM1/7/12
to Lecson Audio
Spiny,
A correction to what I wrote above. On the right channel power board
I have replaced all the semiconductors except TR17, TR19 and TR21 and
TR23. The junction test of these appear to check out with each of
them, however they may still have a fault since this was the board
that had previously failed for the previous owner and these output
transistors appear to be the originals.
A correction to what I wrote above. On the right channel power board
I have replaced all the semiconductors except TR17, TR19 and TR21 and
TR23. The junction test of these appear to check out with each of
them, however they may still have a fault since this was the board
that had previously failed for the previous owner and these output
transistors appear to be the originals.
Stephen
Jan 7, 2012, 3:33:15 PM1/7/12
to Lecson Audio
I've gone ahead and ordered replacements from Littlediode for the
potentially dodgy original output transistors TR17,TR19, TR21 and
TR23) using the TIP41C and TIP42C as alternatives , along with some
new transistor insulators. It could help to get things back on track.
potentially dodgy original output transistors TR17,TR19, TR21 and
TR23) using the TIP41C and TIP42C as alternatives , along with some
new transistor insulators. It could help to get things back on track.
Spiny
Jan 7, 2012, 3:44:47 PM1/7/12
to Lecson Audio
hi Stephen
Nice tools ;) I just received a desoldering station (cheap one) for
Christmas, they are good, much easier then a soldersucker and braid.
the BC177 is the low gain variant, they specified a BC177B - medium
hfe, Looking them up I find the 177 should have an Hfe of 125 to 500
and the B 240 to 500
56 suggests this is faulty .
I use the MPSA 06/56 for repairing lecsons - plenty about and cheap,
Its worth matching TR1 and TR5 and TR3 and TR7, I only match for Hfe
and Vbe, I find this good enough. With MPSA0656 between £3 and £5 for
100 its easy to get some good matches - even 20 will give some close
ones.
Watchout for the trimmer it can go bad, I've replaced these in the
past.
Once the thing is not drawing vast currents and you can get some trim
on the pot then remove the safety resistor - I usually trim and do a
low level test with a 100ohm in the power leads and no load connected.
Do Initial checks without a load, then connect up after checking the
zorbel - seen those fried!
Nice tools ;) I just received a desoldering station (cheap one) for
Christmas, they are good, much easier then a soldersucker and braid.
the BC177 is the low gain variant, they specified a BC177B - medium
hfe, Looking them up I find the 177 should have an Hfe of 125 to 500
and the B 240 to 500
56 suggests this is faulty .
I use the MPSA 06/56 for repairing lecsons - plenty about and cheap,
Its worth matching TR1 and TR5 and TR3 and TR7, I only match for Hfe
and Vbe, I find this good enough. With MPSA0656 between £3 and £5 for
100 its easy to get some good matches - even 20 will give some close
ones.
Watchout for the trimmer it can go bad, I've replaced these in the
past.
Once the thing is not drawing vast currents and you can get some trim
on the pot then remove the safety resistor - I usually trim and do a
low level test with a 100ohm in the power leads and no load connected.
Do Initial checks without a load, then connect up after checking the
zorbel - seen those fried!
Spiny
Jan 7, 2012, 3:53:13 PM1/7/12
to Lecson Audio
TR15 and TR17 are the protection circuit - simple overcurrent
detector, This can catch you out, check the value of the resistors is
in the ballpark, in circuit will do.
some people have cut these out as they restrict the power output - not
good when someone shorts the output...
the Output pair TR27 and TR29 can cause mounting problems. The
through bolts to the collectors need some sleeving and as all power
connects this way replace the original washers in case of corrosion,
sleeve the B and E pins as well
detector, This can catch you out, check the value of the resistors is
in the ballpark, in circuit will do.
some people have cut these out as they restrict the power output - not
good when someone shorts the output...
the Output pair TR27 and TR29 can cause mounting problems. The
through bolts to the collectors need some sleeving and as all power
connects this way replace the original washers in case of corrosion,
sleeve the B and E pins as well
Stephen
Jan 7, 2012, 7:18:28 PM1/7/12
to Lecson Audio
Looking at the trimmers with a meter. One ranges from 0 to 1.9K ohms,
and the other 0 to 2.1K Ohms. The schematic says they are 2K2
trimmers.
I removed the wrongly matched BC177 and will wait for the BC177B to
arrive.
> TR15 and TR17 are the protection circuit - simple overcurrent
> detector, This can catch you out, check the value of the resistors is
> in the ballpark, in circuit will do.
Do you mean the resistors connected to the collector of TR17, TR19
(100 ohm)?
and the other 0 to 2.1K Ohms. The schematic says they are 2K2
trimmers.
I removed the wrongly matched BC177 and will wait for the BC177B to
arrive.
> TR15 and TR17 are the protection circuit - simple overcurrent
> detector, This can catch you out, check the value of the resistors is
> in the ballpark, in circuit will do.
(100 ohm)?
Stephen
Jan 7, 2012, 9:28:24 PM1/7/12
to Lecson Audio
Yes, I did check out the MPSA0656 pairs that I used and the two were
off by at least 100 on the hfe scale.
off by at least 100 on the hfe scale.
Stephen
Jan 7, 2012, 10:47:27 PM1/7/12
to Lecson Audio
I just came across an interesting quote from Glenn McDonald (Echowars
on Audiokarma) that applies to my circuit:
"most small signal transistors should have a gain of 100~150 or
better before the circuit will behave as the designer intended. And of
course, this depends on the circuit, but any small transistor with a
gain of 100 or less is gonna get a crosseyed look from me."
on Audiokarma) that applies to my circuit:
"most small signal transistors should have a gain of 100~150 or
better before the circuit will behave as the designer intended. And of
course, this depends on the circuit, but any small transistor with a
gain of 100 or less is gonna get a crosseyed look from me."
Lothar
Jan 8, 2012, 6:30:40 AM1/8/12
to lecson...@googlegroups.com
Hi Alan and Stephen,
read your posts, but as I have misplaced my Chinese dictionary, I did not understand a word of what you said....no technical mind, but I am SURE you are both right! ;)))
Lothar
read your posts, but as I have misplaced my Chinese dictionary, I did not understand a word of what you said....no technical mind, but I am SURE you are both right! ;)))
Lothar
Spiny
Jan 8, 2012, 12:23:27 PM1/8/12
to Lecson Audio
have to agree, Usually low hfe is power transistors not small signal
ones.
alan
ones.
alan
Spiny
Jan 8, 2012, 12:25:22 PM1/8/12
to Lecson Audio
Hi Lothar
can I recommend "The Art of Electronics, by Paul Horowitz and Winfield
Hill" ;)
alan
can I recommend "The Art of Electronics, by Paul Horowitz and Winfield
Hill" ;)
alan
Stephen
Jan 8, 2012, 4:26:05 PM1/8/12
to Lecson Audio
Thanks Alan,
I was just reading on the Lecson page regarding the AC1 and the need
to often go through many transistors to find a properly matched pair
in order to get the distortion down. Probably explains why the
previous owner's repair with generic equivalent transistors didn't
manage to get the distortion out of the right channel. I did find a
seller who was was offering MPSA06/56 in paired sets. I will pick up
20 or so and try to get some good matched pairs installed and then
take the next steps.
I was just reading on the Lecson page regarding the AC1 and the need
to often go through many transistors to find a properly matched pair
in order to get the distortion down. Probably explains why the
previous owner's repair with generic equivalent transistors didn't
manage to get the distortion out of the right channel. I did find a
seller who was was offering MPSA06/56 in paired sets. I will pick up
20 or so and try to get some good matched pairs installed and then
take the next steps.
Spiny
Jan 9, 2012, 1:57:18 PM1/9/12
to Lecson Audio
I have noticed on some transistors blobs of paint - I wonder if the
factory matched them then marked them for production?
alan
factory matched them then marked them for production?
alan
Stephen
Jan 9, 2012, 5:01:13 PM1/9/12
to Lecson Audio
This is a clever observation Alan. I noticed these paint blobs on
only the "good" left channel board, but would not have thought about
commenting on it here. This also helps to confirm to me that it is
original.
I was a bit confused originally because I did not know which board was
for which channel before finding the service manual. I would like to
confirm something that I am not absolutely sure of. The input
screened lead with the blue wire is for the left board? The one with
the red wire being for the right board? This is how it was arranged
whenever I first opened the amplifier. Also, in this case the wiring
to the 7 pin DIN has the left and right signal inputs had been
incorrectly switched at some point by someone (based on continuity
check). I am also assuming that the blue output wire is for the left
board and the purple one if for the right.
only the "good" left channel board, but would not have thought about
commenting on it here. This also helps to confirm to me that it is
original.
I was a bit confused originally because I did not know which board was
for which channel before finding the service manual. I would like to
confirm something that I am not absolutely sure of. The input
screened lead with the blue wire is for the left board? The one with
the red wire being for the right board? This is how it was arranged
whenever I first opened the amplifier. Also, in this case the wiring
to the 7 pin DIN has the left and right signal inputs had been
incorrectly switched at some point by someone (based on continuity
check). I am also assuming that the blue output wire is for the left
board and the purple one if for the right.
Spiny
Jan 9, 2012, 6:45:26 PM1/9/12
to Lecson Audio
I've pulled the top on an AP1 - the right speaker outputs are
connected to the red signal lead channel on this one (its a later one
with the PSU caps fitted to the transformer, the earlier ones have the
caps attached to the top plate, I have one of each)
the paint "May" be factory matching, It seems to be more than 2 amps,
any takers on other ones with markings? Stan may know.
Tip, When refitting the top trim disk use sticky velcro (tm) pads not
the double-sided foam tape the factory used, makes removing the top
easy without struggling. I use a rubber sucker to lift the tops if
needed.
as an aside, would have been nice if the cases were actually round and
the tops fitted, it seems all the amps had the top disks hand finished
to fit the cylinders. Mine only fit in one orientation - that's both
the metal disk and the trim.
alan
connected to the red signal lead channel on this one (its a later one
with the PSU caps fitted to the transformer, the earlier ones have the
caps attached to the top plate, I have one of each)
the paint "May" be factory matching, It seems to be more than 2 amps,
any takers on other ones with markings? Stan may know.
Tip, When refitting the top trim disk use sticky velcro (tm) pads not
the double-sided foam tape the factory used, makes removing the top
easy without struggling. I use a rubber sucker to lift the tops if
needed.
as an aside, would have been nice if the cases were actually round and
the tops fitted, it seems all the amps had the top disks hand finished
to fit the cylinders. Mine only fit in one orientation - that's both
the metal disk and the trim.
alan
Spiny
Jan 9, 2012, 6:51:11 PM1/9/12
to Lecson Audio
missed that bit
the red signal lead goes to the channel with the blue output wire
which is the right speaker terminals (purple output lead to the left
speaker terminals with the blue signal wire)
the 7 pin input is wired pin 1 right , pin 6 left according to the
manual
Look at the signal lead, one of the ones I have and another I've seen
had poor quality screened cable and the copper screen was turning
green with corrosion - replaced!
alan
the red signal lead goes to the channel with the blue output wire
which is the right speaker terminals (purple output lead to the left
speaker terminals with the blue signal wire)
the 7 pin input is wired pin 1 right , pin 6 left according to the
manual
Look at the signal lead, one of the ones I have and another I've seen
had poor quality screened cable and the copper screen was turning
green with corrosion - replaced!
alan
Stephen
Jan 9, 2012, 10:31:26 PM1/9/12
to Lecson Audio
Another reason I ask about the wiring colour is that I noticed in the
service manual, in the place where they describe the idle current
adjustment for the Left power board, they wrote:
"if any difficulty is experienced, disconnect the blue output lead",
which led me to think that it was the blue lead that went with the
left board.
The velcro idea is one that I will add to the list, as well as better
input wires. Might as well make full use of our modern materials. It
makes it taking these apart for service that much less of a chore.
Something else that I thought up was to remove the quick disconnect
spades from the circuit boards and replace them with two Phoenix
Contact 2-position circuit board terminals. I found a version that
exactly matched the pin spacing on the circuit board. Some slight
modification was needed in order to adapt to the tight layout of the
circuit board, such as the first capacitor at the signal input had to
be installed beneath the board. This allows for a straight wire
connection that can be more conveniently connected with screwdriver,
and will stand up better to repeated disassembly.
part used: PHOENIX CONTACT 1733020 GSMKDS 3/2
service manual, in the place where they describe the idle current
adjustment for the Left power board, they wrote:
"if any difficulty is experienced, disconnect the blue output lead",
which led me to think that it was the blue lead that went with the
left board.
The velcro idea is one that I will add to the list, as well as better
input wires. Might as well make full use of our modern materials. It
makes it taking these apart for service that much less of a chore.
Something else that I thought up was to remove the quick disconnect
spades from the circuit boards and replace them with two Phoenix
Contact 2-position circuit board terminals. I found a version that
exactly matched the pin spacing on the circuit board. Some slight
modification was needed in order to adapt to the tight layout of the
circuit board, such as the first capacitor at the signal input had to
be installed beneath the board. This allows for a straight wire
connection that can be more conveniently connected with screwdriver,
and will stand up better to repeated disassembly.
part used: PHOENIX CONTACT 1733020 GSMKDS 3/2
Stephen
Jan 9, 2012, 10:48:06 PM1/9/12
to Lecson Audio
On my board the MPSA06 were given green paint to the top. The MPSA56
with pink paint. I would imagine that this would have made it easier
to assemble, having to identify the right transistor only once then
mark with paint. I also see that these versions have the pin
configuration printed at the bottom "EBC".
with pink paint. I would imagine that this would have made it easier
to assemble, having to identify the right transistor only once then
mark with paint. I also see that these versions have the pin
configuration printed at the bottom "EBC".
Spiny
Jan 10, 2012, 4:40:58 PM1/10/12
to Lecson Audio
terminals on the board would be good I think, just check current
capacity as there are a few amps flowing when you turn the bass up ;)
I seem to have blue and green, I wonder if the colours signified PNP/
NPN and the gain (hfe) band they tested in?
capacity as there are a few amps flowing when you turn the bass up ;)
I seem to have blue and green, I wonder if the colours signified PNP/
NPN and the gain (hfe) band they tested in?
Stephen
Jan 10, 2012, 7:57:53 PM1/10/12
to Lecson Audio
Yes I think they will be able to handle the job, according to the
datasheet the maximum current is 30A.
http://media.digikey.com/pdf/Data%20Sheets/Phoenix%20Contact%20PDFs/1733020.pdf
] I wonder if the colours signified PNP/
> NPN and the gain (hfe) band they tested in?
I had never heard of colour rankings for transistor gain before, but
it is possible. It definitely is a way of sorting the PNP from the
NPN to make assembly more straightforward.
Stephen
Jan 10, 2012, 8:04:16 PM1/10/12
to Lecson Audio
I was wondering if you thought it matters that the supply voltage from
the capacitors on my AP1 is a bit higher than +/- 40V mentioned in the
service manual. I'm geting closer to
+/- 45V.
Spiny
Jan 11, 2012, 1:47:48 PM1/11/12
to Lecson Audio
on the colours I was thinking the tester in the factory marked them
into Hfe groups for the board stuffers, a thankless task, did that in
my youth at another local to Cambridge factory (HH electronics for
those interested).
45 that's @ 10% on no load with a slightly higher than nominal mains
voltage I would think that's spot on. ;). Here the nominal voltage is
supposed to be 230 volts, Today I get 242 when measured that's 5 % up
so a nominal 40v would be 42.5 just due to mains differences and in
transformer regulation that's fine
Alan
into Hfe groups for the board stuffers, a thankless task, did that in
my youth at another local to Cambridge factory (HH electronics for
those interested).
45 that's @ 10% on no load with a slightly higher than nominal mains
voltage I would think that's spot on. ;). Here the nominal voltage is
supposed to be 230 volts, Today I get 242 when measured that's 5 % up
so a nominal 40v would be 42.5 just due to mains differences and in
transformer regulation that's fine
Alan
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