Hi all,

I've got a rather frustrating problem with a Rivera M60 tube amplifier:
after switching on, it often makes very soft chugging and popping noises,
which most of the time disappear within a few dozen seconds, after which
the amp seems fine. Very occasionally, the chugging turns into louder
popping, with an occasional audible AC mains hum. Sometimes, it just blows
its mains fuse (1.6 amp slow, at 230 volts mains voltage) - but after
replacing it, nothing else seems damaged or blown up.

I've tried replacing all tubes and all HV supply caps, but alas, to no
avail.
I've had contact with Paul Rivera himself over this matter, and at first
he seemed very helpful. Then, for no apparent reason (I was just about to
order a set of supply caps and a schematic diagram), I couldn't contact
anyone from the Rivera company any more. The phone was busy all the time,
and e-mails went unanswered.

My question: does anyone have a schematic diagram of this particular amp?
Without it, it's going to be very hard tracking down the cause of the
problems mentioned - the chugging sound usually lasts only a very short
while, and is very weak as it is, which makes tracking it down on a
double-sided PCB near impossible.

TIA, regards,

Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/

On Sun, 04 Sep 2005 21:43:43 +0200 Richard Rasker
wrote:

I've got a rather frustrating problem with a Rivera M60 tube amplifier:
after switching on, it often makes very soft chugging and popping noises,
which most of the time disappear within a few dozen seconds, after which
the amp seems fine. Very occasionally, the chugging turns into louder
popping, with an occasional audible AC mains hum. Sometimes, it just blows
its mains fuse (1.6 amp slow, at 230 volts mains voltage) - but after
replacing it, nothing else seems damaged or blown up.

I don't know this amp, but a problem like this always makes me want to
check the grid bias supply for the output tubes. A problem with the
diodes or the caps in this circuit can make a lot of noise AND will
destroy things if it gets bad enough.

It shouldn't be too hard to find, even without a schematic. Look up
the output tubes and find the control grid pin. Measure the DC voltage
there as you turn the amp on with no input signal. Trace back from the
tube to a low voltage supply that should put out something like -10 to
-20 VDC, with virtually no AC ripple.

On old amps, I tend to find selenium rectifiers that are no longer
good. On a more modern amp, I'd suspect a bad filter cap in this
supply.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Op Sun, 04 Sep 2005 21:12:57 -0500, schreef Jim Adney:

On Sun, 04 Sep 2005 21:43:43 +0200 Richard Rasker
wrote:

I've got a rather frustrating problem with a Rivera M60 tube amplifier:
after switching on, it often makes very soft chugging and popping noises,
which most of the time disappear within a few dozen seconds, after which
the amp seems fine. Very occasionally, the chugging turns into louder
popping, with an occasional audible AC mains hum. Sometimes, it just blows
its mains fuse (1.6 amp slow, at 230 volts mains voltage) - but after
replacing it, nothing else seems damaged or blown up.

I don't know this amp, but a problem like this always makes me want to
check the grid bias supply for the output tubes. A problem with the
diodes or the caps in this circuit can make a lot of noise AND will
destroy things if it gets bad enough.

It shouldn't be too hard to find, even without a schematic. Look up
the output tubes and find the control grid pin. Measure the DC voltage
there as you turn the amp on with no input signal. Trace back from the
tube to a low voltage supply that should put out something like -10 to
-20 VDC, with virtually no AC ripple.

This voltage for the bias setting is OK; besides, the amp is nice and
quiet when I remove the end stage driver tube (12AX7) - so apparently
the problem is located in or before the driver stage. Removing the preamp
tubes does not change anything. Then again, a faulty driver stage can
hardly cause the mains fuse to blow, so it's a bit of a mystery.

On old amps, I tend to find selenium rectifiers that are no longer
good.

This one's about four years old, so no selenium here.

On a more modern amp, I'd suspect a bad filter cap in this supply.

Yeah, that's what I figured. But it's not one of the main caps, which I
replaced. Ah well, I'll have to keep digging, I guess. It's just that it's
quite a complex amp on a double-sided PCB, which makes it very difficult
to figure everything out, lacking a schematic diagram.

Anyway, thanks for your reply :-)

Regards

Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/

I wouldn't doubt if it's the output tubes. Oscilloscopes made by
Tektronix had a time delay relay of about 1 minute. The dc voltage (B+)
to the tubes was fed throught the relay. The heater voltage was applied
upon placing the power switch on, then one minute later the B+ was
applied via the Time Delay Relay. Maybe you could try this with a
switch for experimentation. I have heard tube amps make noise when
turning on and turning off. My own personal Macintosh MC240 on
occaision makes noise powering up or down. It usually is an indication
of an output (6L6) on it's way out. I change them when they spark
inside or blow a fuse. I can live with a little noise on power on /
off. Take Care, Kevin

"Richard Rasker" bravely wrote to "All" (04 Sep 05 21:43:43)
--- on the heady topic of "Rivera M60 tube amp question"

I'd check the screen grid resistor and its decoupling electrolytic
cap, if used. Sometimes a defective tube socket contact can cause
intermittant pops and noises. Check the coupling caps to the output
tube grids. Check the output tubes' negative bias circuit if used. An
open circuit in that part of the bias circuit will make the tube draw
a lot of current and burn fuses. When I was a kid, my first amp was a
"Riviera" not "Rivera". Tube amps are easy to diagnose but the high DC
voltage bites real hard! Beware working in a live circuit, never work
alone, and make sure the other person is trained in CPR.

A*s*i*m*o*v


RR From: Richard Rasker
RR Xref: core-easynews sci.electronics.repair:341342


RR Hi all,

RR I've got a rather frustrating problem with a Rivera M60 tube
RR amplifier: after switching on, it often makes very soft chugging and
RR popping noises, which most of the time disappear within a few dozen
RR seconds, after which the amp seems fine. Very occasionally, the
RR chugging turns into louder popping, with an occasional audible AC mains
RR hum. Sometimes, it just blows its mains fuse (1.6 amp slow, at 230
RR volts mains voltage) - but after replacing it, nothing else seems
RR damaged or blown up.
RR I've tried replacing all tubes and all HV supply caps, but alas, to no
RR avail.
RR I've had contact with Paul Rivera himself over this matter, and at
RR first he seemed very helpful. Then, for no apparent reason (I was just
RR about to order a set of supply caps and a schematic diagram), I
RR couldn't contact anyone from the Rivera company any more. The phone was
RR busy all the time, and e-mails went unanswered.

RR My question: does anyone have a schematic diagram of this particular
RR amp? Without it, it's going to be very hard tracking down the cause of
RR the problems mentioned - the chugging sound usually lasts only a very
RR short while, and is very weak as it is, which makes tracking it down on
RR a double-sided PCB near impossible.

RR TIA, regards,

RR Richard Rasker

.... Wasted power is current squared times the resistance.