Rivera M60 tube amp question

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 snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

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

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.

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

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

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.