[powerdoc]

Just got this amp off Craigslist for about what a birthday party for a
bunch of kids costs at McDonalds. It apparently blows the topside
fuse on one side. The inside fuses are intact. Should I expect just
a bad o/p tube? Is the schematic available? What type of load should
I put on the outputs to test it or just use an old speaker? It sure
is more complicated than my Jolida! What is the best way to test the
o/p transformers? Can/should other than stock tube be used? Never
had anything this good in tubes before (can you tell?) and I don't
want to screw up but I do want to have some fun with this. I'm
reasonably electrically savvy and I'm just trying not to reinvent the
wheel if someone else has had this malady before. Thanks in advance
to all.

[Patrick Turner]

powerdoc wrote:

Just got this amp off Craigslist for about what a birthday party for a
bunch of kids costs at McDonalds. It apparently blows the topside
fuse on one side. The inside fuses are intact. Should I expect just
a bad o/p tube? Is the schematic available? What type of load should
I put on the outputs to test it or just use an old speaker? It sure
is more complicated than my Jolida! What is the best way to test the
o/p transformers? Can/should other than stock tube be used? Never
had anything this good in tubes before (can you tell?) and I don't
want to screw up but I do want to have some fun with this. I'm
reasonably electrically savvy and I'm just trying not to reinvent the
wheel if someone else has had this malady before. Thanks in advance
to all.

You need good technical ability to sevice CJ amps ( or ARC amps ).
Yes, all are much more complex than much other gear, and have
double sided pcb boards with circuits running each side, so
readin a schematic and knowing where you are anywhere on the board is a
complete PITA
compared say to working on an old Mullard 520 made by someone's dad 40
years ago,
with simple easy to follow point to point wiring on tag strips.


Check the two speakers you have sound the same when separately used, and
measure the impedance.

If that's withing 10% of each other, then the speakers are not causing a
fuse to blow.
Check all the leads for frayed wires touching and that the speaker is
plugged into the
correct amp impedance outlet, or into the 4 ohm if in doubt.

If you are technical, test the amp and measure the cathode current after
turn on.
All output tube should have within 10% of specified bias currents after
1/2 an hour.

There should be resistors in the cathode circuits to measure.

Crook tubes can slowly give increasing cathode current as they warm up
until finally the anode glows red, and the tube saturates with 400mA
instead of say 50mA
and this may cause a fuse to blow.

The electrode dc and signal voltages on each and every tube in the whole
amp
have to be checked and signs of shorted turns in OPTs et all and this
needs the experienced
person with a schematic to follow what might be causing a fuse to blow.

Sometimes if a driver tube malfunction, only one side of the PP output
circuit
is being driven much, and this side can overheat.

Amps can blow fuses, make noise and malfunction in 100 different ways,
both SS and tubes types; especially modern complex types, and
I get a stream of problems across my bench each week
and it isn't possible always to easily say exactly what is wrong,
so no point saying to much here right now.

Patrick Turner.

[tubegarden]

powerdoc wrote:

Just got this amp off Craigslist for about what a birthday party for a
bunch of kids costs at McDonalds. *It apparently blows the topside
fuse on one side. *The inside fuses are intact. *Should I expect just
a bad o/p tube?

No.

*Is the schematic available?

Yes.

*What type of load should I put on the outputs to test it or just use an old speaker?

Speaker is closest to runtime load.

*It sure is more complicated than my Jolida!

That is OK. Several people like the sound.

*What is the best way to test the
o/p transformers?

Listen to mono music on both channels. If not same sound ...

*Can/should *other than stock tube be used? *

If you have the time and desire, it sholud not be missed.

Never had anything this good in tubes before (can you tell?) and I don't
want to screw up but I do want to have some fun with this.

Have fun, but if you want to learn circuit surgery, suggest you start
with cheap, used tube table radio, or tube clock radio,

*I'm reasonably electrically savvy and I'm just trying not to reinvent the
wheel if someone else has had this malady before. *Thanks in advance
to all.

Well, the description "apparently it blows the top fuse on one side"
is all you tell us about the problem, it may be impossible to tell if
we have had the malady before Some in this group think they are the
only malady in the Universe. Your novel introduction of an actual
tchnical malfuntion may cause some confusion. Be patient.

Please describe your tool set.

Happy Ears,
Al

[powerdoc]

If by tool set you mean my electronic experience it's about 45 years
of fooling around with both ss and tube electronics and understanding
that capacitors stay hot for a good while after the set is off. I
have a scope, a couple of AF generators, a Fluke meter, an HP ac vtvm,
a distortion meter, a GR bridge, a tube tester and a transistor
checker. Does C-J publish the schematic or is it available from
another source? So far haven't been able to find it on the web. Since
I just got it on Saturday all I know about the unit is from the prior
owner. I haven't done anything to the unit itself except take off
the bottom and top plates to look for obviously failed caps and
resistors. The rectifier bridge seems ok. I only have one intact
fuse as the 3/4 amp bbs fuse is rather esoteric and this is a bad
weekend to look for one. The Jolida I have did the same thing before
I bought it (except that the CJ has about 6 fuses and the Jolida only
1) and correcting the bias cured it. The rest of the fuses inside
are intact. I only have 2 of the 6550's and they test good. I need
voltage levels for the various pins of the 6550's if anybody has
access to that info. Again, thanks for the help.

[Patrick Turner]

powerdoc wrote:

If by tool set you mean my electronic experience it's about 45 years
of fooling around with both ss and tube electronics and understanding
that capacitors stay hot for a good while after the set is off. I
have a scope, a couple of AF generators, a Fluke meter, an HP ac vtvm,
a distortion meter, a GR bridge, a tube tester and a transistor
checker. Does C-J publish the schematic or is it available from
another source? So far haven't been able to find it on the web. Since
I just got it on Saturday all I know about the unit is from the prior
owner. I haven't done anything to the unit itself except take off
the bottom and top plates to look for obviously failed caps and
resistors. The rectifier bridge seems ok. I only have one intact
fuse as the 3/4 amp bbs fuse is rather esoteric and this is a bad
weekend to look for one. The Jolida I have did the same thing before
I bought it (except that the CJ has about 6 fuses and the Jolida only
1) and correcting the bias cured it. The rest of the fuses inside
are intact. I only have 2 of the 6550's and they test good. I need
voltage levels for the various pins of the 6550's if anybody has
access to that info. Again, thanks for the help.

As the bias current rises, it should all appear to rise at about the
same rate
in each 6550.

Then when its is biased, check the screen currents to each tube;
they all should be within 15% of each other.

If you have the serial number of the amp, CJ probably
will send you a schematic if you contact them.

Good luck with your efforts; it seems you have the tech background
required to find the
problems like I do, eventually.

Patrick Turner.

[powerdoc]

On May 27, 11:24 am, Patrick Turner wrote:
powerdocwrote:

If by tool set you mean my electronic experience it's about 45 years
of fooling around with both ss and tube electronics and understanding
that capacitors stay hot for a good while after the set is off. I
have a scope, a couple of AF generators, a Fluke meter, an HP ac vtvm,
a distortion meter, a GR bridge, a tube tester and a transistor
checker. Does C-J publish the schematic or is it available from
another source? So far haven't been able to find it on the web. Since
I just got it on Saturday all I know about the unit is from the prior
owner. I haven't done anything to the unit itself except take off
the bottom and top plates to look for obviously failed caps and
resistors. The rectifier bridge seems ok. I only have one intact
fuse as the 3/4 amp bbs fuse is rather esoteric and this is a bad
weekend to look for one. The Jolida I have did the same thing before
I bought it (except that the CJ has about 6 fuses and the Jolida only
1) and correcting the bias cured it. The rest of the fuses inside
are intact. I only have 2 of the 6550's and they test good. I need
voltage levels for the various pins of the 6550's if anybody has
access to that info. Again, thanks for the help.

As the bias current rises, it should all appear to rise at about the
same rate
in each 6550.

Then when its is biased, check the screen currents to each tube;
they all should be within 15% of each other.

If you have the serial number of the amp, CJ probably
will send you a schematic if you contact them.

Good luck with your efforts; it seems you have the tech background
required to find the
problems like I do, eventually.

Patrick Turner.

The schematic would really be sweet! I'll try that on Tuesday. The
nice thing about tube stuff is not ruining it every time you touch
something wrong

[west[_4_]]

"powerdoc" wrote in message
oups.com...
On May 27, 11:24 am, Patrick Turner wrote:
powerdocwrote:

If by tool set you mean my electronic experience it's about 45 years
of fooling around with both ss and tube electronics and understanding
that capacitors stay hot for a good while after the set is off. I
have a scope, a couple of AF generators, a Fluke meter, an HP ac vtvm,
a distortion meter, a GR bridge, a tube tester and a transistor
checker. Does C-J publish the schematic or is it available from
another source? So far haven't been able to find it on the web. Since
I just got it on Saturday all I know about the unit is from the prior
owner. I haven't done anything to the unit itself except take off
the bottom and top plates to look for obviously failed caps and
resistors. The rectifier bridge seems ok. I only have one intact
fuse as the 3/4 amp bbs fuse is rather esoteric and this is a bad
weekend to look for one. The Jolida I have did the same thing before
I bought it (except that the CJ has about 6 fuses and the Jolida only
1) and correcting the bias cured it. The rest of the fuses inside
are intact. I only have 2 of the 6550's and they test good. I need
voltage levels for the various pins of the 6550's if anybody has
access to that info. Again, thanks for the help.

As the bias current rises, it should all appear to rise at about the
same rate
in each 6550.

Then when its is biased, check the screen currents to each tube;
they all should be within 15% of each other.

If you have the serial number of the amp, CJ probably
will send you a schematic if you contact them.

Good luck with your efforts; it seems you have the tech background
required to find the
problems like I do, eventually.

Patrick Turner.

The schematic would really be sweet! I'll try that on Tuesday. The
nice thing about tube stuff is not ruining it every time you touch
something wrong

....but you can ruin yourself if you touch something wrong.

west

[Peter Wieck]

On May 26, 11:17 am, powerdoc wrote:
Just got this amp off Craigslist for about what a birthday party for a
bunch of kids costs at McDonalds. It apparently blows the topside
fuse on one side. The inside fuses are intact. Should I expect just
a bad o/p tube? Is the schematic available? What type of load should
I put on the outputs to test it or just use an old speaker? It sure
is more complicated than my Jolida! What is the best way to test the
o/p transformers? Can/should other than stock tube be used? Never
had anything this good in tubes before (can you tell?) and I don't
want to screw up but I do want to have some fun with this. I'm
reasonably electrically savvy and I'm just trying not to reinvent the
wheel if someone else has had this malady before. Thanks in advance
to all.

After all the good (and marginal) advice given (Patrick's is very
good, for instance), and your statement that you have 45 years +/-
experience around electronics, I will spare you advice on safety and
common sense (which isn't).

There are some pretty basic things to do before servicing any tube-
based equipment with an obvious-but-undiagnosed problem such as you
describe. In no particular order, they a

a) Test all the tubes. Do so on a tester that is capable of giving you
as good information as that species of equipment is capable of doing.
This means a good MC tester, preferably one that allows you to measure
plate currents on the 6550s under test, and vary the bias. Also one
capable of holding the tubes at operating voltage and under load for
about 20 minutes or so. This won't tell you much other than the
general condition of the tubes *except* it will also weed out any one
(or more) tube that is markedly different from the others. If you find
such a tube (and that difference may not show up for 5-20 minutes),
you may have a start on the problem. Caveat: Tube testers are crude at
best, but useful under these conditions for screening purposes. Very
good tube testers are only slightely less crude and only slightly more
useful.

b) Do a complete, careful, unpressured eyeball examination of the amp
under very good light and comfortable conditions. I keep a red "dry-
marker" fine felt-tip pen to put a dot or a tick next to something
that looks different or wonky or to remind me to look back later. A
little sketch-pad beside you with a note when you make a mark also
helps. Touch the mark with a Q-tip later and its gone with no
electrical residue. Especially if something looks different from
channel A to B... Shorts, frays, cold-solders, pinched insulation,
darkened components, smoked components, obvious subsitutions...

c) With the unit off and unplugged, do a basic 'resistance check'
comparing Channel A with Channel B. If you come up with any
differences between A and B, that may indicate a place to start. This
should include the output transformers as well, of course.

d) A quick search found sources for manuals and schematics he

http://www.audiocircuit.com/A-HTML/A...ier%201 1#bla

I am sure there are others. And CJ has an excellent reputation for
customer service and attention.

DO NOT, repeat, DO NOT go beyond the very most basic trouble-shooting
and checking the obvious without a schematic. But you knew that
already. All of the stuff above was to give you indications of where
to start. Without a schematic and good information on what voltages
should be where, you are shooting in the dark with a pretty severe
downside if you miss.

In addition: Here is a method to actually test audio transformers:
http://www.radioelectronicschool.net...ansformers.doc

But in your case, you want to check for leakages across windings as
well as the internal resistance of each winding. If anything is
different one-from-another, that also may be a place to start. But
consider that a bad output transformer may be a result, not a cause...
also all the more reason for careful and cautious testing. If both
OPTs test identically at all possible combinations and permutations of
resistances (winding-to-winding, winding to case, primary to
secondary, both sides of a center-tap and so forth) it is unlikely
that they are at fault.

Take good digital photos of everything before you make/break your
first connection or remove your first component.

Good luck with it, and enjoy!

Peter Wieck
Wyncote, PA

[Phread]

"Peter Wieck" wrote in message ups.com...
On May 26, 11:17 am, powerdoc wrote:
Just got this amp off Craigslist for about what a birthday party for a
bunch of kids costs at McDonalds. It apparently blows the topside
fuse on one side. The inside fuses are intact. Should I expect just
a bad o/p tube? Is the schematic available? What type of load should
I put on the outputs to test it or just use an old speaker? It sure
is more complicated than my Jolida! What is the best way to test the
o/p transformers? Can/should other than stock tube be used? Never
had anything this good in tubes before (can you tell?) and I don't
want to screw up but I do want to have some fun with this. I'm
reasonably electrically savvy and I'm just trying not to reinvent the
wheel if someone else has had this malady before. Thanks in advance
to all.

After all the good (and marginal) advice given (Patrick's is very
good, for instance), and your statement that you have 45 years +/-
experience around electronics, I will spare you advice on safety and
common sense (which isn't).

There are some pretty basic things to do before servicing any tube-
based equipment with an obvious-but-undiagnosed problem such as you
describe. In no particular order, they a

a) Test all the tubes. Do so on a tester that is capable of giving you
as good information as that species of equipment is capable of doing.
This means a good MC tester, preferably one that allows you to measure
plate currents on the 6550s under test, and vary the bias. Also one
capable of holding the tubes at operating voltage and under load for
about 20 minutes or so. This won't tell you much other than the
general condition of the tubes *except* it will also weed out any one
(or more) tube that is markedly different from the others. If you find
such a tube (and that difference may not show up for 5-20 minutes),
you may have a start on the problem. Caveat: Tube testers are crude at
best, but useful under these conditions for screening purposes. Very
good tube testers are only slightely less crude and only slightly more
useful.

b) Do a complete, careful, unpressured eyeball examination of the amp
under very good light and comfortable conditions. I keep a red "dry-
marker" fine felt-tip pen to put a dot or a tick next to something
that looks different or wonky or to remind me to look back later. A
little sketch-pad beside you with a note when you make a mark also
helps. Touch the mark with a Q-tip later and its gone with no
electrical residue. Especially if something looks different from
channel A to B... Shorts, frays, cold-solders, pinched insulation,
darkened components, smoked components, obvious subsitutions...

c) With the unit off and unplugged, do a basic 'resistance check'
comparing Channel A with Channel B. If you come up with any
differences between A and B, that may indicate a place to start. This
should include the output transformers as well, of course.

d) A quick search found sources for manuals and schematics he

http://www.audiocircuit.com/A-HTML/A...ier%201 1#bla

Um, that site doesn't actually have a schematic, but if they ever get
one, they'll be happy to sell it to you.

I haven't dealt with CJ in quite a few years, but they used to have the
attitude that they invented the wheel and were not about to give out
schematics lest someone steal their design.

Fred

I am sure there are others. And CJ has an excellent reputation for
customer service and attention.

DO NOT, repeat, DO NOT go beyond the very most basic trouble-shooting
and checking the obvious without a schematic. But you knew that
already. All of the stuff above was to give you indications of where
to start. Without a schematic and good information on what voltages
should be where, you are shooting in the dark with a pretty severe
downside if you miss.

In addition: Here is a method to actually test audio transformers:
http://www.radioelectronicschool.net...ansformers.doc

But in your case, you want to check for leakages across windings as
well as the internal resistance of each winding. If anything is
different one-from-another, that also may be a place to start. But
consider that a bad output transformer may be a result, not a cause...
also all the more reason for careful and cautious testing. If both
OPTs test identically at all possible combinations and permutations of
resistances (winding-to-winding, winding to case, primary to
secondary, both sides of a center-tap and so forth) it is unlikely
that they are at fault.

Take good digital photos of everything before you make/break your
first connection or remove your first component.

Good luck with it, and enjoy!

Peter Wieck
Wyncote, PA

[powerdoc]

Thanks to all for the help. Stage 1 has been completed, I did a
visual, tested the 2 output tubes I have (I'm supposed to get the
second pair today from the original seller) and I found fuses for it
to test it. That BBS 3/4 fuse is a hard bugger to find but I got the
LittleFuse equivalent at a place that just sells fuses locally and
tried a power-on test without the output tubes and it didn't pop the
fuse. It's been a while since I had to do any construction with tubes
and I'm working on the basis that tube diagrams are looking at the
bottom of the tube. I'll test the 2nd pair of tubes then insert
them. Which way of the bias adjustment screw gives the lowest plate
current? I don't have the manual to explain this to me, as this is
what I want to do. I actually like the way my Jolida does bias
adjustment more than the C-J, as it actually depends on looking at the
actual voltage rather than depending on a secondary circuit where an
LED is extinguished. Waiting for a response from C-J about a
schematic. I have an older B&K preamp that I had to actually talk to
the CEO to get a schematic. I'm not sure why the'd be so proprietary
about a 15 year-old design which could be reverse engineered by most
anyone with a pencil and piece of paper. I'm excited!

[Patrick Turner]

powerdoc wrote:

Thanks to all for the help. Stage 1 has been completed, I did a
visual, tested the 2 output tubes I have (I'm supposed to get the
second pair today from the original seller) and I found fuses for it
to test it. That BBS 3/4 fuse is a hard bugger to find but I got the
LittleFuse equivalent at a place that just sells fuses locally and
tried a power-on test without the output tubes and it didn't pop the
fuse. It's been a while since I had to do any construction with tubes
and I'm working on the basis that tube diagrams are looking at the
bottom of the tube. I'll test the 2nd pair of tubes then insert
them. Which way of the bias adjustment screw gives the lowest plate
current? I don't have the manual to explain this to me, as this is
what I want to do. I actually like the way my Jolida does bias
adjustment more than the C-J, as it actually depends on looking at the
actual voltage rather than depending on a secondary circuit where an
LED is extinguished. Waiting for a response from C-J about a
schematic. I have an older B&K preamp that I had to actually talk to
the CEO to get a schematic. I'm not sure why the'd be so proprietary
about a 15 year-old design which could be reverse engineered by most
anyone with a pencil and piece of paper. I'm excited!


Don't get too excited and forget you are wandering around inside a box
full of lethal voltages.

You should be able to make the driver stages all work fine with equal
drive to grid pins of the output stage
without the output tubes in the amp.
But make sure the B+ doesn't go too high while testing without output
tubes.
Sometimes I place a few equal wattage lightbulbs in series from OPT ct
to 0V,
to be equivalent to the dc power supply load when the output tubes are
conducting,
so a row of lamp sockets on a block of wood is a handy dummy load.

25 watts at 117Vac has current = 210 mA, 7 watts = 60mA, etc.
A quad of 25 watt lightbulbs can be the right load for
a +470V supply meant for a quad of output tubes.

Jolidas can exceed electro cap ratings if the mains goes high, and B+
goes high without a load.

The best led set up is where you have a red and yellow led powered by a
pair of signal bjts
in an LTP so that when equal brightness exists bias is right, red only =
too hot,
yellow only = too cool, not enough current, or no current.
I installed such a set up in a pair of Manley Labs Snappers recently.
No voltmeter needed, and the owner knows if something is wrong
immediately,
and there is also active over current protection so a tube conducting
twice the idle current for longer than 5 seconds shuts down the amp
and the OPT are saved.

Jolida OPT are made in China, and ain't too wonderful, and I've seen
them with shorted turns from overheated tubes because of wrong biasing.

Patrick Turner.

[powerdoc]

SUCCESS!!! Bought 2 new 6550's today as the p/o couldn't find the
original ones which weren't NOS Telefunkens or anything really good
anyway, clocked down the bias, and started it up. No blown fuse
light, the bias lights came on one at a time and I let it sit there
for a while just idling with no input then turned the bias pots and
voila! the lights went out and the fuses didn't blow. The next
problem was finding a program source that had a volume control as all
my sources had just 1v. fixed outputs. Had to get the wife's XM to go
and hooked it up and there was sound, from both channels even! A $200
total investment; now I have to figure out if I'll sell it or go back
to an all-separate sound system. Decisions, decisions. Like the old
adage says, ...." there's no such thing as a free puppy."