Engineer
October 8th 06, 11:15 PM
Hi, Vacuumlanders,
I while back I acquired a Pioneer SM-B200 AM(two)/SW/FM stereo,
tube-type receiver in a dreadful state (had to rebuild broken tuning
drives, replace several dead and missing tubes, etc.. looked like it
had been in a landfill.) Finally got it all working except the FM
(still needs a complete alignment when I get the time.) On the way I
found two of the four audio section coupling caps were leaky (6BM8
triode section plate to O/P pentode section control grid.) I replaced
all four, of course.
Now, a few weeks ago I picked up a much better looking SM-B200A
receiver on eBay ("as is", of course) and justified on the premise that
if you have one already then two is better! I tested the tubes, ran it
up on a variac and found a very low B+ of around 178 VDC (off a
210-0-210 transformer) and a bad 120 Hz hum. There were two obvious
faults:
A) a nearly dead reservoir cap at the rectifier cathode (replaced), and
B) three of the O/P tubes had -15 to -16 VDC fixed bias (OK) and one
had only -5 VDC (not at all OK!) This tube was pulling far too much
current. Reason: a leaky 0.05 MFD coupling cap - I've replaced two of
them to date and will replace the other two a.s.a.p. when I can get the
required "round tuit" tool... <g> Again, FM needs also needs fixing,
has a MPX addition, too... this stuff is sent to try us!
These caps in vintage Pioneer receivers are all of the same general
type. The recent ones I replaced were marked:
"SUZUKI
OIL JCP-D
0.05 uF
WV 400V DC"
(on the grey plastic finish, over aluminum body, one black end.)
The ones I replaced in the first chassis were marked similarly but,
IIRC, the brand was ELNA (same physical size.) This chassis also has
SUZUKI and ELNA brand 0.05 uF and another value caps - all suspect,
IMHO.
In Pioneer tube chasses, these caps are not only used for coupling but
for decoupling, too, all over the place . However, they seem less
dangerous in decoupling service so I have not replaced them (yet!)
It's just crossed my mind that I've had to replace more of this types
"for cause", i.e. failed, than I have the wax covered, paper tubular
caps in real old radios, the one we all replace for insurance, i.e. the
wax ones that are not actually dead yet (but we should still replace
them, of course.)
So, perhaps it is common knowledge, but I conclude that these little
grey, oil filled 0.05's are very bad news! Expunge them!
Cheers,
Roger
I while back I acquired a Pioneer SM-B200 AM(two)/SW/FM stereo,
tube-type receiver in a dreadful state (had to rebuild broken tuning
drives, replace several dead and missing tubes, etc.. looked like it
had been in a landfill.) Finally got it all working except the FM
(still needs a complete alignment when I get the time.) On the way I
found two of the four audio section coupling caps were leaky (6BM8
triode section plate to O/P pentode section control grid.) I replaced
all four, of course.
Now, a few weeks ago I picked up a much better looking SM-B200A
receiver on eBay ("as is", of course) and justified on the premise that
if you have one already then two is better! I tested the tubes, ran it
up on a variac and found a very low B+ of around 178 VDC (off a
210-0-210 transformer) and a bad 120 Hz hum. There were two obvious
faults:
A) a nearly dead reservoir cap at the rectifier cathode (replaced), and
B) three of the O/P tubes had -15 to -16 VDC fixed bias (OK) and one
had only -5 VDC (not at all OK!) This tube was pulling far too much
current. Reason: a leaky 0.05 MFD coupling cap - I've replaced two of
them to date and will replace the other two a.s.a.p. when I can get the
required "round tuit" tool... <g> Again, FM needs also needs fixing,
has a MPX addition, too... this stuff is sent to try us!
These caps in vintage Pioneer receivers are all of the same general
type. The recent ones I replaced were marked:
"SUZUKI
OIL JCP-D
0.05 uF
WV 400V DC"
(on the grey plastic finish, over aluminum body, one black end.)
The ones I replaced in the first chassis were marked similarly but,
IIRC, the brand was ELNA (same physical size.) This chassis also has
SUZUKI and ELNA brand 0.05 uF and another value caps - all suspect,
IMHO.
In Pioneer tube chasses, these caps are not only used for coupling but
for decoupling, too, all over the place . However, they seem less
dangerous in decoupling service so I have not replaced them (yet!)
It's just crossed my mind that I've had to replace more of this types
"for cause", i.e. failed, than I have the wax covered, paper tubular
caps in real old radios, the one we all replace for insurance, i.e. the
wax ones that are not actually dead yet (but we should still replace
them, of course.)
So, perhaps it is common knowledge, but I conclude that these little
grey, oil filled 0.05's are very bad news! Expunge them!
Cheers,
Roger