A really nice tube amp!

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E:B:LC:US:1


TIA,

Jon

"Jon Yaeger" wrote in message
...
A really nice tube amp!


http://cgi.ebay.com/ws/eBayISAPI.dll...PageName= ADM
E:B:LC:US:1


TIA,

Jon, So how do you know the filters don't leak or have excessive ESR? A
variac keeps it from going up in smoke, but it doesn't repair bad caps.

How do you know that all of the paper caps don't leak? Aren't those the
black beauties/bumblebees that are notorious for leakage?

I have never seen one of those old black plastic caps that didn't leak
current and/or oil. I had hundreds of new ones and threw them all away,
leaky garbage. But, that
was before I knew that suckers would pay $30 each for them on ebay.

"This amp will bring a lot enjoyment to the buyer with a minimum of fuss."

If those are the original caps, I wouldn't bet on it. Mark

in article , truegridtz at
wrote on 6/12/05 2:29 AM:


"Jon Yaeger" wrote in message
...
A really nice tube amp!


http://cgi.ebay.com/ws/eBayISAPI.dll...PageName= ADM
E:B:LC:US:1


TIA,

Jon, So how do you know the filters don't leak or have excessive ESR? A
variac keeps it from going up in smoke, but it doesn't repair bad caps.

*** I check the caps with a capacitor tester. I reformed the electrolytics
over a long time interval. They run cool.

How do you know that all of the paper caps don't leak? Aren't those the
black beauties/bumblebees that are notorious for leakage?

*** Yes, they are black beauties and Sprague caps. I checked the voltages
across the caps and looked for leakage. I also touched them to check for
heat. In my experience, leaky caps often get hot.

*** I haven't had much bad experience with the bumblebees. If I suspect a
bad cap, I'll take it out of circuit, put a 1K resistor in series with it,
and connect it to a HV power supply and measure the voltage across the 1K
resistor to determine leakage. I did not do this with this amp, because I
didn't think it was necessary.

I have never seen one of those old black plastic caps that didn't leak
current and/or oil. I had hundreds of new ones and threw them all away,
leaky garbage. But, that
was before I knew that suckers would pay $30 each for them on ebay.

*** I do have a bag of bumblebees and I I'll test your theory and report
the results here.

"This amp will bring a lot enjoyment to the buyer with a minimum of fuss."

If those are the original caps, I wouldn't bet on it. Mark

*** Yes, caps do fail in McIntoshes from time to time. However, I think
even you would be surprised at the number of similar amps out there that
have most if not all of their original capacitor compliment. Are they just
hobbling along with their leakage and other infirmities? I don't know . . .
.. my sample isn't large enough. But they are still playing music . . . .

Jon

"Jon Yaeger" wrote in message
...
in article , truegridtz at
wrote on 6/12/05 2:29 AM:


"Jon Yaeger" wrote in message
...
A really nice tube amp!



http://cgi.ebay.com/ws/eBayISAPI.dll...PageName= ADM
E:B:LC:US:1


TIA,

Jon, So how do you know the filters don't leak or have excessive ESR?
A
variac keeps it from going up in smoke, but it doesn't repair bad caps.

*** I check the caps with a capacitor tester. I reformed the
electrolytics
over a long time interval. They run cool.

You mean a meter that tell you the capacitance?

How do you know that all of the paper caps don't leak? Aren't those the
black beauties/bumblebees that are notorious for leakage?

*** Yes, they are black beauties and Sprague caps. I checked the
voltages
across the caps and looked for leakage. I also touched them to check for
heat. In my experience, leaky caps often get hot.

The paper beeswax caps have an unusual ability to keep on working long after
they should be in the garbage can. Even though they don't get hot they will
still leak current and mess up tube bias. The leakage also varies a lot
with age and other circumstances. The inside of them is often such a gooey
mess that it seems inconceivable they they could ever really short out.

*** I haven't had much bad experience with the bumblebees. If I suspect
a
bad cap, I'll take it out of circuit, put a 1K resistor in series with it,
and connect it to a HV power supply and measure the voltage across the 1K
resistor to determine leakage. I did not do this with this amp, because I
didn't think it was necessary.

Doesn't sound very accurate. If a non-electrolytic shows any leakage at all
then it is bad. The leakage will be just a few uA so I doubt that the 1K
resistor method would pick it up. The leakage often rises slowly with time,
after the amp has been on for awhile.

I have never seen one of those old black plastic caps that didn't leak
current and/or oil. I had hundreds of new ones and threw them all away,
leaky garbage. But, that
was before I knew that suckers would pay $30 each for them on ebay.

*** I do have a bag of bumblebees and I I'll test your theory and report
the results here.

The impregnant used in most old paper caps rots and it doesn't appear to be
necessarily
related to atmospheric contamination. I had many hermetically sealed paper
caps that went bad.

You need a hi-volt power supply and a DVM in series to check for leakage.
Check them at maximum voltage. Leakage in a deteriorated cap will most
probably change with age, voltage, and temperature so the transformers and
tube may suffer an early death due to improper grid bias.

"This amp will bring a lot enjoyment to the buyer with a minimum of
fuss."

If those are the original caps, I wouldn't bet on it. Mark

*** Yes, caps do fail in McIntoshes from time to time. However, I think
even you would be surprised at the number of similar amps out there that
have most if not all of their original capacitor compliment. Are they
just
hobbling along

Hobbling along is ridiculous. An amp of such quality and reputation should
be running out in front. There is no need for any fuss. Replacing all the
caps makes the best sense. The electrolytics may not get hot, but they are
grenades with loose
pins. Why risk a transformer?

Yes, the collectors want the original parts left in it.
The paper caps, despite accusations of "audiophool", do have a very pleasing
sound and it is understandable that people want them left in there for that
reason.


The old electrolytics usually have at least one bad element and all of them
are too old to be called reliable. High ESR can create a hot spot. It
doesn't get the whole cap hot, but there is localized heat that will
eventually breach the winding. It is sort of like hardening of the arteries
in electrolytics. You need an ESR meter to check it, unless you hook up a
homebrew checker with signal gen, scope, and appropriate cables. The recipe
is on the web, easy to find. As I recall, they can be checked for ESR while
still in the circuit.

Many old electrolytics don't leak and work
fine, but the ESR is many times what it should be. This directly transfers
to heat generation inside the cap. It may cause them to eventually explode
and
stink the house up. Takes a long time to wipe all of the slime out of the
amp. The amp will stink for months, like dead fish.

with their leakage and other infirmities? I don't know . . .
. my sample isn't large enough. But they are still playing music . . . .

In my repair world leaving those old caps in there is like leaving an old
line cord on it: just asking for trouble.

If you ever want to replace the paper caps with affordable paper caps that
also have the unique and pleasing paper sound then use ARCO/EM radials.
They look like chocolate brown orange drops. They were made in the 70s.
The impregnant is mylar instead of beeswax so they don't leak or go bad.
(the impregnant fills the holes in the paper dielectric)
They are excellent caps and I have never seen one leak. I don't know how
many of them are still around, though.

As for the old electrolytics, I have some old 60s TEK scopes that have the
original caps. They all work fine, but I know they are degrading the
performance of the scopes.

Macs sure are pretty. Mark

Jon

in article , truegridtz at
wrote on 6/12/05 3:48 PM:


"Jon Yaeger" wrote

*** I check the caps with a capacitor tester. I reformed the
electrolytics
over a long time interval. They run cool.

You mean a meter that tell you the capacitance?

**** Yes, and an ESR meter. Here's a rule of thumb: If a capacitor tests
bad, it is. If it tests good, it may still be bad . . . . ;-)

How do you know that all of the paper caps don't leak? Aren't those the
black beauties/bumblebees that are notorious for leakage?

The paper beeswax caps have an unusual ability to keep on working long after
they should be in the garbage can. Even though they don't get hot they will
still leak current and mess up tube bias. The leakage also varies a lot
with age and other circumstances. The inside of them is often such a gooey
mess that it seems inconceivable they they could ever really short out.

**** As I mentioned previously, I use the DVM / HV leakage test method that
you abscribe to. But only out of circuit.

*** I haven't had much bad experience with the bumblebees. If I suspect
a
bad cap, I'll take it out of circuit, put a 1K resistor in series with it,
and connect it to a HV power supply and measure the voltage across the 1K
resistor to determine leakage. I did not do this with this amp, because I
didn't think it was necessary.

Doesn't sound very accurate. If a non-electrolytic shows any leakage at all
then it is bad. The leakage will be just a few uA so I doubt that the 1K
resistor method would pick it up. The leakage often rises slowly with time,
after the amp has been on for awhile.

**** I test only non-electrolytics with the HV / DVM method. I use the
cap meter / ESR test on electrolytics, and sometimes a scope to check for
hum on PS electros. Probably a better route would be to find and buy one of
those Heath testers with a magic eye. I think the HV / DVM method on
coupling caps is accurate enough.

I have never seen one of those old black plastic caps that didn't leak
current and/or oil. I had hundreds of new ones and threw them all away,
leaky garbage. But, that
was before I knew that suckers would pay $30 each for them on ebay.

**** I routinely test caps I replace, even ones that do not show any other
signs of problems, just to learn which ones go bad. I have learned, for
example, to replace EVERY coupling cap on Japanese gear. I routinely
replace driver coupling caps to protect output tubes. The McIntosh in
question uses Sprague 0.22 @ 600V for this purpose, not bumblebees. The
Spragues have held up in my tests.

**** When replacing caps, I usually substitute Orange Drops or the
reasonably-priced polypropylene caps from Mouser & DigiKey. But a lot of
people feel that these caps are detrimental to the sound of vintage gear,
and prefer the OEM parts. I use premium RelCaps and other brands in my new
builds but not on the refurbs. So with US made products, I replace those
items that test bad, and almost always the output coupling caps. If you
disagree with my strategy, well, no one is forcing you to bid on my stuff.
You are entitled to your opinion. OTOH, you could buy something and mod it
until your heart is content . . . .

**** My choices seem to hold up. No one has yet to inform me that they
have experienced cap failure on gear they obtained from me. Not that it
couldn't or doesn't happen, it just hasn't, to my knowledge.

*** I do have a bag of bumblebees and I I'll test your theory and report
the results here.

The impregnant used in most old paper caps rots and it doesn't appear to be
necessarily
related to atmospheric contamination. I had many hermetically sealed paper
caps that went bad.

You need a hi-volt power supply and a DVM in series to check for leakage.
Check them at maximum voltage. Leakage in a deteriorated cap will most
probably change with age, voltage, and temperature so the transformers and
tube may suffer an early death due to improper grid bias.

**** We are on the same page here, as previously noted.

Hobbling along is ridiculous. An amp of such quality and reputation should
be running out in front. There is no need for any fuss. Replacing all the
caps makes the best sense. The electrolytics may not get hot, but they are
grenades with loose pins. Why risk a transformer?

Yes, the collectors want the original parts left in it.
The paper caps, despite accusations of "audiophool", do have a very pleasing
sound and it is understandable that people want them left in there for that
reason.

**** You've articulated the dilemma well.

The old electrolytics usually have at least one bad element and all of them
are too old to be called reliable. High ESR can create a hot spot. It
doesn't get the whole cap hot, but there is localized heat that will
eventually breach the winding. It is sort of like hardening of the arteries
in electrolytics. You need an ESR meter to check it, unless you hook up a
homebrew checker with signal gen, scope, and appropriate cables. The recipe
is on the web, easy to find. As I recall, they can be checked for ESR while
still in the circuit.

**** My ESR meter does a pretty good job in circuit, but I don't always
trust it 100% unless I remove and test it.

Many old electrolytics don't leak and work
fine, but the ESR is many times what it should be. This directly transfers
to heat generation inside the cap. It may cause them to eventually explode
and
stink the house up. Takes a long time to wipe all of the slime out of the
amp. The amp will stink for months, like dead fish.

**** Agreed. I've been pretty lucky with US gear. Maybe it is just that
.. . . . Dumb luck.

with their leakage and other infirmities? I don't know . . .
. my sample isn't large enough. But they are still playing music . . . .

In my repair world leaving those old caps in there is like leaving an old
line cord on it: just asking for trouble.

If you ever want to replace the paper caps with affordable paper caps that
also have the unique and pleasing paper sound then use ARCO/EM radials.
They look like chocolate brown orange drops. They were made in the 70s.
The impregnant is mylar instead of beeswax so they don't leak or go bad.
(the impregnant fills the holes in the paper dielectric)
They are excellent caps and I have never seen one leak. I don't know how
many of them are still around, though.

As for the old electrolytics, I have some old 60s TEK scopes that have the
original caps. They all work fine, but I know they are degrading the
performance of the scopes.

Macs sure are pretty. Mark

**** Thanks for the good advice. You are absolutely correct that all caps
should be replaced for high rel service. But by the same token, so should
out of spec resistors and similar suspect parts. As you know, current
production HV cans are hard to come by, so I'm sometimes pressured to leave
in what seems to work fine. I once restored a Scott 222C amplifier that had
a 3 section can with a positively charged contained. I ended up removing
all of the goo and junk and installing 3 discrete caps. Yuck.

**** I took a "100% rel" approach to a Dynaco ST-70 I restored and modified
on my site (www.yaegeraudio.com). There is a reason that I am listing it
for $995, and even so, I figure I'm making about $10/hr. If I sell it at
that price.

Jon, It is getting so long that I will make this one shorter.

Do you find paper beeswax caps that have no leakage at maximum voltage?

Sounds like we are pretty much in agreement about rebuilding. On second
thought the 1K resistor may give a good reading on the leakage. I'll have
to do a little arithmentic to see what the input to the meter would be.

I have heard of people who check only for catastrophic leakage,
and not for a small current. I thought that you may have only been checking
for catastrophic failures.

Repacking those cans is very expensive labor, and people don't like the
axials strapped all over the place. I have often wondered who turns their
amp over to look at the caps? I guess it is a collector's ego type thing.
WOW, look at those beauties.

The more work you do on an amp the less money you will probably make. Then
again, if it quits in a short period and the customer wants you to pay the
return shipping for a repair then there goes the profit.

Sounds like you have reached a reasonable compromise between labor, customer
desire, and reliability. I would do it a bit differently, but I can see
where you are coming from. You sell a working unit that has no obvious
defects at present. This is probably the most practical approach to making
a sufficient profit.

I searched for the RelCaps that you mentioned and ended up at Percy Audio.
I though they may have been paper. The only paper caps that I found are
Jupiters for $15 each, way too much.

I can't buy a Mac right now, no more shelf space. Since I am into
quadraphonic I would need two of them. I was mainly curious about how you
dealt with the cap issues. There are so many people who think that they are
restoring audio equipment and they are only screwing with it. I recall that
you said that you replace the hi-volt blocking caps. This is what is most
important.

I do think that not checking the electrolytics for leakage is a mistake. I
reform every cap and find many NOS caps that don't go down to an acceptable
leakage. They may be technically useable, but I reject them. The same
thing goes for old can caps. They still work, but the leakage never settles
down. IOW they will not completely reform. This indicates a weak point in
the dielectric film that will pass excessive current and may heat up and
cause the cap to fail. The ESR is OK and there is no ripple, but they are
technically not healthy caps.

What intrigues me is how so many people get away with letting things go. In
my world everything that I gamble on usually comes loose so I don't gamble
on anything. My motto is "I never want to see it again." Many people don't
replace selenium rectifiers. Not in my world.

I see so many strange and unpredictable situations. For example, a few
years ago I put belts on a cassette deck and cleaned the pots etc. I used
it for years, but the left channel kept getting weak and muddy. I cleaned
the play/rec switch until it had to be spotless. It turned out that the
factory had left the flux between the input terminals on the board. I
scraped the flux off and the left channel came to life.

Surely it didn't do this straight out of the factory. I guess over time the
metallic molecules migrate in the flux and align into a semi-conductive
path. Who knows.

I also see a lot of bad solder joints. Sometimes the plating on the
terminal is loose. The solder joint is good, but it is affixed to the
plating. It is rare, but it does happen.

Do go through your bag-o-beeswax and post the leakages. Mark

in article , truegridtz at
wrote on 6/12/05 7:38 PM:

Jon, It is getting so long that I will make this one shorter.

Do you find paper beeswax caps that have no leakage at maximum voltage?

*** I need to find a few minutes to set up the test. May be a couple of
days yet. But I'll post something. I'll have to be sure I can identify the
voltage ratings on these guys, and wear some safety goggles . . . ;-)

Sounds like we are pretty much in agreement about rebuilding. On second
thought the 1K resistor may give a good reading on the leakage. I'll have
to do a little arithmentic to see what the input to the meter would be.

I have heard of people who check only for catastrophic leakage,
and not for a small current. I thought that you may have only been checking
for catastrophic failures.

Repacking those cans is very expensive labor, and people don't like the
axials strapped all over the place. I have often wondered who turns their
amp over to look at the caps? I guess it is a collector's ego type thing.
WOW, look at those beauties.

The more work you do on an amp the less money you will probably make. Then
again, if it quits in a short period and the customer wants you to pay the
return shipping for a repair then there goes the profit.

*** Right. But you never know. I recently sold a beautiful, totally
remade Citation II with a tested compliment of 6550s. I took out the tubes
and packed them separately for shipment across the country. The amp had
been run for awhile with these tubes. The customer reported that the plates
were red and the tubes went bad. He also smoked a cathode resistor. I'm
convinced he had no clue how to bias them. Nonetheless, I sent him a brand
new quad of matched 6550s for free. My unexpressed thought was if he burned
these up then too bad!

Sounds like you have reached a reasonable compromise between labor, customer
desire, and reliability. I would do it a bit differently, but I can see
where you are coming from. You sell a working unit that has no obvious
defects at present. This is probably the most practical approach to making
a sufficient profit.

*** Yes, it is a balance. There is also that non-renewable resource
called TIME, which is definitely a factor. I don't sell anything in bad
faith, but I think there is some understanding with most vintage clients
that unless you redo it thoroughly there is a chance of future component
failure. When you figure all of the time that goes into restoring stuff the
profit is often modest, if there at all (or maybe it is, but you make
$5/hr!).

I searched for the RelCaps that you mentioned and ended up at Percy Audio.
I though they may have been paper. The only paper caps that I found are
Jupiters for $15 each, way too much.

*** I've got MultiCaps, Aeons, and PPEs from France. None cheap.

I can't buy a Mac right now, no more shelf space. Since I am into
quadraphonic I would need two of them. I was mainly curious about how you
dealt with the cap issues. There are so many people who think that they are
restoring audio equipment and they are only screwing with it. I recall that
you said that you replace the hi-volt blocking caps. This is what is most
important.

*** Agreed. Bad caps here can cost you a set of tubes and a tranny. Do
you have a quadraphonic tube set up?

I do think that not checking the electrolytics for leakage is a mistake. I
reform every cap and find many NOS caps that don't go down to an acceptable
leakage. They may be technically useable, but I reject them. The same
thing goes for old can caps. They still work, but the leakage never settles
down. IOW they will not completely reform. This indicates a weak point in
the dielectric film that will pass excessive current and may heat up and
cause the cap to fail. The ESR is OK and there is no ripple, but they are
technically not healthy caps.

*** These problems you describe have gone under my radar, because if I
reform a cap and it doesn't get warm and it tests at rated capacity I'll
usually leave it alone. I'll have to do some of my own checking. In the
meantime, do you have any favorite sources for NNS (new new stock) multi
cans? I think Ned sells them . . .

What intrigues me is how so many people get away with letting things go. In
my world everything that I gamble on usually comes loose so I don't gamble
on anything. My motto is "I never want to see it again." Many people don't
replace selenium rectifiers. Not in my world.

*** When I service computer stuff, it's another standard. I REALLY don't
want to work on something I've fixed inside of the warranty period, and I
take the steps necessary. Thus my repair recall rate is very low. For
example, I fixed a $100 computer logic board for a machine shop controller
that would have cost $70K to replace. I replaced every SMT electro on it,
and coated the regions around the caps with conformal coating so that even
if they did leak, no further circuit erosion would occur. I did likewise
with a replacement PCB to use as a spare. This client was VERY happy.

*** It's amazing how much people get for junk right out of an attic, eh?

I see so many strange and unpredictable situations. For example, a few
years ago I put belts on a cassette deck and cleaned the pots etc. I used
it for years, but the left channel kept getting weak and muddy. I cleaned
the play/rec switch until it had to be spotless. It turned out that the
factory had left the flux between the input terminals on the board. I
scraped the flux off and the left channel came to life.

Surely it didn't do this straight out of the factory. I guess over time the
metallic molecules migrate in the flux and align into a semi-conductive
path. Who knows.

*** Flux removal is critical with SMT repair. Time after time I've seen
residual flux cause problems in high-impedance circuits. I'm cautious about
using the flux-free solders - I don't really like how they act compared to
the rosin core. The water-soluable compounds are very reactive and you have
to wash it ALL off. Impractical or impossible when repairing, as opposed to
new fab. Rosin flux is sticky stuff. I wonder if it is contaminants such
as dirt (vs. metal migration) to blame.

I also see a lot of bad solder joints. Sometimes the plating on the
terminal is loose. The solder joint is good, but it is affixed to the
plating. It is rare, but it does happen.

*** Use liquid flux ;-)

Do go through your bag-o-beeswax and post the leakages. Mark

*** Will do.

"Jon Yaeger" wrote in message
...
in article , truegridtz at
wrote on 6/12/05 7:38 PM:

Jon, It is getting so long that I will make this one shorter.

Do you find paper beeswax caps that have no leakage at maximum voltage?

*** I need to find a few minutes to set up the test. May be a couple of
days yet. But I'll post something. I'll have to be sure I can identify
the
voltage ratings on these guys, and wear some safety goggles . . . ;-)

Kevlar vest might be nice,too,

I'll keep an eye out for your results. I found some "CP" type military
paper caps, hermetically sealed. I'm going to see if I can get any leakage
out of them.

I recall that Sprague changed their part numbering somewhere around the late
50s. I have both listings somewhere around here if you get a weird part
number. The bumblebees should use the common color code.

Sounds like we are pretty much in agreement about rebuilding. On second
thought the 1K resistor may give a good reading on the leakage. I'll
have
to do a little arithmentic to see what the input to the meter would be.

The 1K resistor method should be accurate. I get string heater caps
100uf/160V down to about 10uA after reforming. This would show up on the
1K as 10mV.

snip

The more work you do on an amp the less money you will probably make.
Then
again, if it quits in a short period and the customer wants you to pay
the
return shipping for a repair then there goes the profit.

*** Right. But you never know. I recently sold a beautiful, totally
remade Citation II with a tested compliment of 6550s. I took out the tubes
and packed them separately for shipment across the country. The amp had
been run for awhile with these tubes. The customer reported that the
plates
were red and the tubes went bad. He also smoked a cathode resistor. I'm
convinced he had no clue how to bias them.

Why should the customer be involved in the repair process? Weren't they
biased (I have never seen the amp) properly when he recieved the amp? Seems
like he should have just plugged in the tubes and turned it on. Evidently
there is a knob and he screwed with it.


Nonetheless, I sent him a brand
new quad of matched 6550s for free. My unexpressed thought was if he
burned
these up then too bad!

Ouch. Sounds a bit too nice, but the one thing that is to avoided is an
irate customer. The time spent worrying with the situation is far more
expensive than a new set of tubes. Hopefully it only happens on rare
occasions.

Sounds like you have reached a reasonable compromise between labor,
customer
desire, and reliability. I would do it a bit differently, but I can see
where you are coming from. You sell a working unit that has no obvious
defects at present. This is probably the most practical approach to
making
a sufficient profit.

*** Yes, it is a balance. There is also that non-renewable resource
called TIME, which is definitely a factor.

I feel that it is the most important factor. If you get behind and have to
work too hard then you get tired and then everything goes wrong.

I don't sell anything in bad
faith, but I think there is some understanding with most vintage clients
that unless you redo it thoroughly there is a chance of future component
failure. When you figure all of the time that goes into restoring stuff
the
profit is often modest, if there at all (or maybe it is, but you make
$5/hr!).

5/hr, that's where I usually end up , all things considered. I overhaul old
record changers most of the time. They are so screwed up with the rotten
rubber, dried grease, abuse, rotten wires, corroded terminals, and no direct
replacement cartridge so I have to make an adapter plate. Just adjusting
them takes hours sometimes. Test playing them takes hours. The older ones
from the 40s have no provision for tracking force adjustment. That can take
a lot of precious time. Removal and installation can eat up the hours, too.

I searched for the RelCaps that you mentioned and ended up at Percy
Audio.
I though they may have been paper. The only paper caps that I found are
Jupiters for $15 each, way too much.

*** I've got MultiCaps, Aeons, and PPEs from France. None cheap.

I'll check 'em out on the web.

I can't buy a Mac right now, no more shelf space. Since I am into
quadraphonic I would need two of them. I was mainly curious about how
you
dealt with the cap issues. There are so many people who think that they
are
restoring audio equipment and they are only screwing with it. I recall
that
you said that you replace the hi-volt blocking caps. This is what is
most
important.

*** Agreed. Bad caps here can cost you a set of tubes and a tranny. Do
you have a quadraphonic tube set up?

No, solid state. It is an amp (built it myself) that is "overcompensated".
I increased the capacitance of the compensation cap until the amp starts
rolling off at about 17K. It takes a lot of the solid state type annoyance
out of the sound. I also have a passive equalizer which helps tremendously,
and also have a large collection of different stylii so I can find one that
works best on a record. Playing a record with a microline stylus is usually
a mistake. A concial brings out a lot more of the quad phase info (matrix).
This is a quad decoder that I built that has much better accuracy than the
commercial ones, makes a big difference. So, I'm not suffering with an
annoying solid state system. I can make it behave, but I do want some tube
amps with nice big OTs, expensive. When I finally realize that I will never
find the time to build them I'll see what you have to offer. I don't like
amps with the little ringy OTs.


..

I have some mono tube amps here. Heath W-2, RCA photophone, and another
large RCA with four 6L6s.and one of those OD3 type regulators that are used
in the better amps. Trouble is, I only have one of each and only the Heath
is overhauled and I don't like the sound of it. I used RN65D metal films.
Evidently tubes don't like metal films. I am going to find another W-2 and
use carbon. If it sounds better then I will convert the first one to
carbon.

What I really want at present is the right schematic for a tube buffer
between the equalizer and the preamp. The 50C5 spec sheet shows 10-20%
harmonic distortion so that sounds like a mistake

The problem is the load for anything but a beam power tube. These input
impedances are about 20K and tubes don't like that.........don't need any
gain, just a buffer.

I do think that not checking the electrolytics for leakage is a mistake.
I
reform every cap and find many NOS caps that don't go down to an
acceptable
leakage. They may be technically useable, but I reject them. The same
thing goes for old can caps. They still work, but the leakage never
settles
down. IOW they will not completely reform. This indicates a weak point
in
the dielectric film that will pass excessive current and may heat up and
cause the cap to fail. The ESR is OK and there is no ripple, but they
are
technically not healthy caps.

*** These problems you describe have gone under my radar, because if I
reform a cap and it doesn't get warm and it tests at rated capacity I'll
usually leave it alone.

It is probably a safe bet if it hasn't been sitting for years. What bothers
me is when equipment (caps only needed a gentle reforming) has been sitting
for years and someone plugs it in and it doesn't work so they pass it off on
someone else to get it out of the way. Those few moments of initially
energizing the caps is when a hole can be burned into the dielectric. It is
like a hole in a dyke. It will continue to erode. A cap that has been
continually used for 40 years that doesn't overheat is probably OK. When an
electrolytic sits for over 3 years the oxide falls away from the foil and
ther layer gets very thin, so the cap doesn't hold rated voltage until
reforming of the oxide layer.

I'll have to do some of my own checking. In the
meantime, do you have any favorite sources for NNS (new new stock) multi
cans? I think Ned sells them . . .

Well, AES sells them. They have 9 types of multi element for 30-35$ each.
I'm not sure if Bill Turner (rec. antiques.phono+radio) sells them or not, I
think he does. His URL is "dialcover." I'll look around and let you know.
I am always researching parts on the web. I'm hoping to get a parts website
open this year, inventory is the problem. Got all the FTP problems solved
and Mozilla has a built-in HTML editor. Got a digital camera for little
pictures of parts.



What intrigues me is how so many people get away with letting things go.
In
my world everything that I gamble on usually comes loose so I don't
gamble
on anything. My motto is "I never want to see it again." Many people
don't
replace selenium rectifiers. Not in my world.

*** When I service computer stuff, it's another standard. I REALLY don't
want to work on something I've fixed inside of the warranty period, and I
take the steps necessary. Thus my repair recall rate is very low.

This is surely why you have survived in this business.

For
example, I fixed a $100 computer logic board for a machine shop controller
that would have cost $70K to replace. I replaced every SMT electro on
it,
and coated the regions around the caps with conformal coating so that even
if they did leak, no further circuit erosion would occur. I did likewise
with a replacement PCB to use as a spare. This client was VERY happy.

No doubt. Unless you are really quick with a soldering iron that sound like
one of those $5/hr jobs. Sounds like wet tantalums. That sulfuric acid
really eats things up. SMT is surface mount? Surface mount wet tantalums?
Wet tantalums are a strange category of capacitors, if that is what you were
dealing with. I had hundreds of them, axials NOS, but I threw them away
because they have a tendency to leak. I recall that the only way to get low
ESR with very low volume is to use the wet tantalums.


*** It's amazing how much people get for junk right out of an attic, eh?

Yes, as opposed to putting their money into something that will really work.
They don't realize what it takes to make it reliable again. Many think that
they can "get er goin" if they just mess with it enough. A lot of people
try to do this with an old car. In my automotive days it was very common to
see someone buy a worn out collectible car and first sink money into a bra
(hides the wrecked front end) and tape deck (gettin' ready to cruise that
cherried out custom machine) and then it would sit until the dream burned
down. They would search for some magician that could jiggle somethin' under
the hood and get it to run again. After a few ripoffs they would sell it
off.

There is also the issue of fraudulent and/or incompetent repairs in vintage
audio. Many of those who deal with vintage equipment cheat people and give
a more expensive piece of junk back to them. They just fix something and
charge $50/hr, but they don't fix everything. Thus it is understandable
that many, including myself, are snakebit when it comes to paying someone to
overhaul something. They don't understand that a TV shop is paying rent,
lights, insurance, and they have to cheat people or they will go down.
Working on something that is only a few years old is not at all like
overhauling old vintage gear. It sounds to me like you really try to do
things right, but many don't. I always try to remember that people are
looking at me through eyes formed in the past.



snip.


*** Flux removal is critical with SMT repair. Time after time I've seen
residual flux cause problems in high-impedance circuits. I'm cautious
about
using the flux-free solders - I don't really like how they act compared to
the rosin core.

Flux-free sounds like a headache.

The water-soluable compounds are very reactive and you have
to wash it ALL off. Impractical or impossible when repairing, as opposed
to
new fab.\

Yes, they dip the boards at the factory and they want to rinse them quick.
The solder bath probably has a critical temperature to some it flow right,
impossible with an iron.

Rosin flux is sticky stuff. I wonder if it is contaminants such
as dirt (vs. metal migration) to blame.

I would like to know. Mabey it has capacitance. It surely doesn't show up
as a conductor with a DVM. I was reading about MOVs (varistors) the other
day. They are a mixture of compounds that form a huge array of
series-parallel semiconductor junctions. The first transistor was some sort
of simple PN junction, a "catwhisker" metal junction of some sort.
Evidently there are all sorts of molecular combinations that form junctions,
and these junctions have capacitance. There aren't enough of them to form a
conductive path, but they have capacitance. The mobile electrons may
generate flux fields that join into a most pernicious situation.

I also see a lot of bad solder joints. Sometimes the plating on the
terminal is loose. The solder joint is good, but it is affixed to the
plating. It is rare, but it does happen.

*** Use liquid flux ;-)

I'll give it a try. I have some sitting here, good stuff, Keen-O-Flux.

Do go through your bag-o-beeswax and post the leakages. Mark

*** Will do.

I'll watch for the results. There was a radio-restorer on one of these
newsgroups a few years ago that usually leaves the original beeswax
paper-shell caps in his radios. He lives around the Dakotas somewhere.
There weather up there doesn't wreck the caps. They are still the pretty
colors that they were in the 50s.