JBL SA660 amp, 1969

[N Cook]

Last time it was used (long ago) it went bang and the owner stored it, so
treading carefully.
Nothing obviously gone bang and cold basic testing the electrolytics and
large Rs seem ok.
Not got to the power devices area yet.
It was correctly altered for use in the UK but ominously a farmyard smell
seems
strongest around the mains transformer, primary seems ok - anyone familiar
with JBL.
I have the schematic


I've now removed the side dished covers to the transformer.
The smell is negligible inside it and nothing charred or smoke stained
inside that I can see, but the two 110V coils measure 4.4ohm and 3.5 ohm .
The failure occured a week after converting the 2 parallel for the USA to
both in series for UK which is another reason for suspecting the
transformer.
But the mains fuse (correctly rated for UK) is still ok.
I'll have to carefully power up via a variac I think

[Randy or Sherry Guttery]

Post by N Cook
Last time it was used (long ago) it went bang and the owner stored it, so
treading carefully.
Nothing obviously gone bang and cold basic testing the electrolytics and
large Rs seem ok.
Not got to the power devices area yet.
It was correctly altered for use in the UK but ominously a farmyard smell
seems
strongest around the mains transformer, primary seems ok - anyone familiar
with JBL.
I have the schematic

I'm way more familiar with JBL speakers than their active products -
though IIRC I went through an amp like yours in the late 70's. Again -
IIRC - it's circuit was fairly routine for the times, nothing exotic.

Since you have a schematic - and suspect a problem in the power supply,
I suggest you disconnect any line filter caps (primary or secondary);
and isolate the loads (rectifiers, etc.) from the secondary. Run up the
power transformer with your variac - either meter the current - or if
you don't have an AC ammeter - put an incandescent light bulb in series
with the primaries - a 60 or so watt bulb should do nicely with no
load(s). If the transformer pulls very little current (almost no amps /
bulb remains dim) run the transformer for an hour - checking the
temperature every so often. This should establish no shorts or other
problems in the transformer.

Then just start moving down circuit - connect the rectifiers, disconnect
the filter caps - repeat the above test - though if there is a problem
in the rectifiers - it will likely show up almost immediately.

In something this old - you should consider replacing the filter caps -
just as a matter of routine. Same with any paper coupling caps - they
tend to leak when this old (nearly 40 years).


Let us know how it goes - I'd love to have a JBL amp pushing my speakers
- even if just for the gee-whiz of having the speaker and amp logos match.

good hunting..!

[John Stone]

Post by Randy or Sherry Guttery
Since you have a schematic - and suspect a problem in the power supply,
I suggest you disconnect any line filter caps (primary or secondary);
and isolate the loads (rectifiers, etc.) from the secondary. Run up the
power transformer with your variac - either meter the current - or if
you don't have an AC ammeter - put an incandescent light bulb in series
with the primaries - a 60 or so watt bulb should do nicely with no
load(s). If the transformer pulls very little current (almost no amps /
bulb remains dim) run the transformer for an hour - checking the
temperature every so often. This should establish no shorts or other
problems in the transformer.
Then just start moving down circuit - connect the rectifiers, disconnect
the filter caps - repeat the above test - though if there is a problem
in the rectifiers - it will likely show up almost immediately.
In something this old - you should consider replacing the filter caps -
just as a matter of routine. Same with any paper coupling caps - they
tend to leak when this old (nearly 40 years).
Let us know how it goes - I'd love to have a JBL amp pushing my speakers
- even if just for the gee-whiz of having the speaker and amp logos match.

Randy,
I owned a power amp only version of this amp, called the SE460. Here's a pic
of a lower power version.

Loading Image...

Here's some pics of an amplifier similar to what the OP is talking about:

Loading Image...

Loading Image...

I can only say to the poor guy working on this thing: good luck. This
amplifier used a very novel circuit for the day called the "T" circuit.
Essentially it was a triple complementary set of pre-driver, driver, and
output transistors all configured as emitter followers. Each preceding stage
required higher voltage, than the one following it, so essentially there
were 6 separate power supplies for the output stage. Capacitors were a big
issue on these. JBL had special caps that were very compact for their
values, and I recall them being very expensive even back in the 70's. The
whole thing is a real rat's nest to work on and very tightly packed, and I
remember how much I hated digging into them when I was a bench tech. But, I
can say that when it worked, it was one of the best sounding solid state
amps of its day. They had 4 models, a 40watt and 60 watt integrated, and a
40 and 60 watt power amp. The power amp had space for a small circuit board
that they would sell you, for eq of specific JBL models. I have no idea if
they ever actually supplied the eq. modules. I wouldn't go near one of these
things today.

[Buck Frobisher]

Eveready must have had to give them something for the name. "Energizer?
Naw, people will never remember that, it sound dumb!"

[Randy or Sherry Guttery]

Post by John Stone
Randy,
I owned a power amp only version of this amp, called the SE460. Here's a pic
of a lower power version.
http://www.audioheritage.org/images/jbl/photos/wolf-photos/se400-front.jpg
http://www.audioheritage.org/images/jbl/photos/wolf-photos/sa600-color.jpg
http://www.audioheritage.org/images/jbl/photos/wolf-photos/sa600-bottom.jpg

You're right - the 600 series is different than the unit I worked on -
which I think was a 400 series - and was designed to install right in
the speaker cabinet (like the Paragon, etc.)- so was likely a 401, 402 -
408, etc.

Post by John Stone
I can only say to the poor guy working on this thing: good luck. This
amplifier used a very novel circuit for the day called the "T" circuit.

I think all of the JBL power amps used the "T" circuit -

Post by John Stone
Capacitors were a big
issue on these. JBL had special caps that were very compact for their
values, and I recall them being very expensive even back in the 70's.

With today's modern caps - it shouldn't be too hard to find proper
values that fit; though depending on the layout of the SA (vs. SE) that
is something to be considered.

Post by John Stone
The
whole thing is a real rat's nest to work on and very tightly packed, and I
remember how much I hated digging into them when I was a bench tech. But, I
can say that when it worked, it was one of the best sounding solid state
amps of its day. They had 4 models, a 40watt and 60 watt integrated, and a
40 and 60 watt power amp. The power amp had space for a small circuit board
that they would sell you, for eq of specific JBL models. I have no idea if
they ever actually supplied the eq. modules. I wouldn't go near one of these
things today.

Send them my way - they'd look great siting on my Sovereigns (even if it
is the twin Sansui AU-999s driving them)!

Seriously - they are JBL - carry that badge - and as you noted - were
designed with the D130 / LE15 series boxes in mind (Harkness, Paragon,
Hartsfield / Olympus, Sovereigns, and Paragon D4400 ).


BTW the SA660 can be seen here:
<Loading Image...>

Guess it's time to think about getting rid of my 90% complete Harkness
cabinets... As old as I'm getting, with as little spare time as I have -
I'm beginning to doubt I'll every finish them. Maybe it's time to pass
them along...

best regards...

[N Cook]

On 2/26/07 8:17 AM, in article

Post by Randy or Sherry Guttery
Since you have a schematic - and suspect a problem in the power supply,
I suggest you disconnect any line filter caps (primary or secondary);
and isolate the loads (rectifiers, etc.) from the secondary. Run up the
power transformer with your variac - either meter the current - or if
you don't have an AC ammeter - put an incandescent light bulb in series
with the primaries - a 60 or so watt bulb should do nicely with no
load(s). If the transformer pulls very little current (almost no amps /
bulb remains dim) run the transformer for an hour - checking the
temperature every so often. This should establish no shorts or other
problems in the transformer.
Then just start moving down circuit - connect the rectifiers, disconnect
the filter caps - repeat the above test - though if there is a problem
in the rectifiers - it will likely show up almost immediately.
In something this old - you should consider replacing the filter caps -
just as a matter of routine. Same with any paper coupling caps - they
tend to leak when this old (nearly 40 years).
Let us know how it goes - I'd love to have a JBL amp pushing my speakers
- even if just for the gee-whiz of having the speaker and amp logos

match.

Randy,
I owned a power amp only version of this amp, called the SE460. Here's a

pic

of a lower power version.
http://www.audioheritage.org/images/jbl/photos/wolf-photos/se400-front.jpg
http://www.audioheritage.org/images/jbl/photos/wolf-photos/sa600-color.jpg

http://www.audioheritage.org/images/jbl/photos/wolf-photos/sa600-bottom.jpg

I can only say to the poor guy working on this thing: good luck. This
amplifier used a very novel circuit for the day called the "T" circuit.
Essentially it was a triple complementary set of pre-driver, driver, and
output transistors all configured as emitter followers. Each preceding

stage

required higher voltage, than the one following it, so essentially there
were 6 separate power supplies for the output stage. Capacitors were a big
issue on these. JBL had special caps that were very compact for their
values, and I recall them being very expensive even back in the 70's. The
whole thing is a real rat's nest to work on and very tightly packed, and I
remember how much I hated digging into them when I was a bench tech. But,

I

can say that when it worked, it was one of the best sounding solid state
amps of its day. They had 4 models, a 40watt and 60 watt integrated, and a
40 and 60 watt power amp. The power amp had space for a small circuit

board

that they would sell you, for eq of specific JBL models. I have no idea if
they ever actually supplied the eq. modules. I wouldn't go near one of

these

things today.

Yes the "T" circuit requires a series of 5 diodes to set the central biasing
for the cascade.
Its a bit on hold at the moment because the owner says the same problem of
going bang occured when it was in the States, repaired there, but he
retained the replaced bits which suggests other than mains transformer.
Waiting for him to get back to me to describe these bits.
On retesting the primaries , excluding fuse and switch paths they were 3.3R
and 3.7R which is not too removed from proper sorts of values.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

[N Cook]

I've now some history on this amp now.
When it was "repaired" in the states the two 10 ohm resistors were replaced
in the Zobel shunt on each output as severely burnt.
This would suggest ultrasonic oscillation but there are no amendments to the
amp, just the 2 Rs replaced.
The reported pops were probably the two 2 terminal thermal? circuit breakers
in line with each speaker going open circuit, resetting themselves later.
Glass bulb devices , anyone any idea what sort or rating these are, not
specified in the schematics, just listed as JBL part number 13176.
I've now powered up to 150V , wired as 240V mains and all is settled with
75V on each primary and +-31V on the first power rails rather than +-51V ,
full mains . Proportionate voltages on each of the other 4 power rails per
each channel on this "T" amp. Cold testing of all major components showed
nothing untoward except the smell apparently strongest at the transformer
The smell may be from where it was stored and nothing wrong with the
transformer.
First , before winding the mains up more, is to determine where best to put
some hf oscillation suppression.

The two 10R replacements are fine this time but the charring on the
originals and smoke damage on the adjascent large wire wounds mean the
oscillation was on both channels. There is certainly a lack of any
non-electrolytic caps on any of the power rails so add some in there for a
start, any other ideas. ?
Anyone know aof a JBL owners group ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

[N Cook]

I've now some history on this amp now.
When it was "repaired" in the states the two 10 ohm resistors were replaced
in the Zobel shunt on each output as severely burnt.
This would suggest ultrasonic oscillation but there are no amendments to the
amp, just the 2 Rs replaced.
The reported pops were probably the two 2 terminal thermal? circuit breakers
in line with each speaker going open circuit, resetting themselves later.
Glass bulb devices , anyone any idea what sort or rating these are, not
specified in the schematics, just listed as JBL part number 13176.
I've now powered up to 150V , wired as 240V mains and all is settled with
75V on each primary and +-31V on the first power rails rather than +-51V ,
full mains . Proportionate voltages on each of the other 4 power rails per
each channel on this "T" amp. Cold testing of all major components showed
nothing untoward except the smell apparently strongest at the transformer
The smell may be from where it was stored and nothing wrong with the
transformer.
First , before winding the mains up more, is to determine where best to put
some hf oscillation suppression.

The two 10R replacements are fine this time but the charring on the
originals and smoke damage on the adjascent large wire wounds mean the
oscillation was on both channels. There is certainly a lack of any
non-electrolytic caps on any of the power rails so add some in there for a
start, any other ideas. ?
Anyone know aof a JBL owners group ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

[Steven]

Post by N Cook
I've now some history on this amp now.
When it was "repaired" in the states the two 10 ohm resistors were replaced
in the Zobel shunt on each output as severely burnt.
This would suggest ultrasonic oscillation but there are no amendments to the
amp, just the 2 Rs replaced.
The reported pops were probably the two 2 terminal thermal? circuit breakers
in line with each speaker going open circuit, resetting themselves later.
Glass bulb devices , anyone any idea what sort or rating these are, not
specified in the schematics, just listed as JBL part number 13176.
I've now powered up to 150V , wired as 240V mains and all is settled with
75V on each primary and +-31V on the first power rails rather than +-51V ,
full mains . Proportionate voltages on each of the other 4 power rails per
each channel on this "T" amp. Cold testing of all major components showed
nothing untoward except the smell apparently strongest at the transformer
The smell may be from where it was stored and nothing wrong with the
transformer.
First , before winding the mains up more, is to determine where best to put
some hf oscillation suppression.
The two 10R replacements are fine this time but the charring on the
originals and smoke damage on the adjascent large wire wounds mean the
oscillation was on both channels. There is certainly a lack of any
non-electrolytic caps on any of the power rails so add some in there for a
start, any other ideas. ?
Anyone know aof a JBL owners group ?
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/

www.lansingheritage.org or www.audioheritage.org as I remember get you
into the Lansing Heritage site and forums. You will find they are JBL
#1 and Altecs are cool too, but in the neighborhood of Lansing Street
Ti rules...