SOLVED! Rivera Amp Whining Noise

[fair.child]

Dear MBP Fellows,

As the subject is shown, I do need help. I won't post here in case I can figure it myself. I post here because I am almost desperate to figure out the problem with this beautiful amp.

Here's the story:
Last Saturday, I've found a good deal on Rivera Duo Twelve R100. However, it did have some issues.
- The Mid EQ control on the first channel didn't work
- No Footswitch

Okay, I've figured that the amp looks quite old and needs some cleaning. So, I closed a deal and decided to buy the amp relatively cheap for a RIVERA. Okay, the story continues. I came home and tried to unhook everything (tubes, reverb tank, etc) from the amp, then examined inside of the amp.

It turns out I was right, it does need some cleaning. I thought it might be a good idea to replace the tubes as well (power and preamp) since I got fresh spares of EL34's and 12AX7's. I cleaned it up using CRC Connector Spray and left it for a night.

Today, I put everything up (EL34, 12AX7, Reverb Tank, Speakers) and started the amp. It seems the amp didn't sound right. However, the Mid EQ Channel 1 works which I was right and quite happy that my assumption was correct. Whenever I turned up the volume, it gets whining noise (high pitch) and very noisy.
I wonder if it's from the tubes. So, as a process of elimination, I did replace the tubes from the original state (12AX7, EL34). Still got the whining noise, though I might think I need a proper biasing.

Tried to pull off the docs everywhere from the internet for how to bias Rivera. Couldn't find the specific way to bias it for R100. I decided to send an e-mail to RIVERA service. Now, it comes the waiting game. Again, I tried couple times (turning on and off, left the amp STANDBY for about 5-7 mins) and the problem is still persistent.

I am quite desperate and getting ready to call a reputable local tech to help me out. However, if y'all have great suggestions, I do really appreciate it.  I'd love to try my best to fix it by myself way so it will help me better along the journey of amp making and learn new things.

Here are some pictures inside of the amp:















upload photo to internet

[gordo]

I'm not sure if it's just shading but there are a couple of resistors around V4 that look a little toasty.  That whole area looks a little nasty and it could just be from heat coming up thru the board.  Check the solder joints on the tube sockets as well.  What did you clean to bring back the mid control?  Reflowing solder joints on boards that face a lot of heat from tubes underneath can work wonders.  Just be sure to drain the power caps before you get in there.  Also tapping spots on the board and moving wires around with a chop stick (or anything non metallic) while the amp is powered up can sometimes lead to to an issue like an intermittent noise.

Depending on your skill level a common mistake is to identify a problem area, turn of the amp and start working on it.  Again, don't forget to drain the caps.

I'd suspect a wire dress or grounding issue before bias.  It's always good to bias an amp anyway but it doesn't usually introduce funny noises when it's idling like that.

[fair.child]

I'm not sure if it's just shading but there are a couple of resistors around V4 that look a little toasty.  That whole area looks a little nasty and it could just be from heat coming up thru the board.  Check the solder joints on the tube sockets as well.  What did you clean to bring back the mid control?  Reflowing solder joints on boards that face a lot of heat from tubes underneath can work wonders.  Just be sure to drain the power caps before you get in there.  Also tapping spots on the board and moving wires around with a chop stick (or anything non metallic) while the amp is powered up can sometimes lead to to an issue like an intermittent noise.

Depending on your skill level a common mistake is to identify a problem area, turn of the amp and start working on it.  Again, don't forget to drain the caps.

I'd suspect a wire dress or grounding issue before bias.  It's always good to bias an amp anyway but it doesn't usually introduce funny noises when it's idling like that.

Drain the caps, you mean the filter caps, don't you? Noted that.

So here are more pictures and what I've done to debug the amp.

V2 and V3 pictures


For draining the caps, I think these four Nichion caps need to be drained.


V4 section in a closer look.



I sprayed the CRC QD Contact Cleaner and turned the mid knob. I did all actually and cleaned the board using the Contact Cleaner.



I poke the parts using the chopstick and plan to reflow the board. I think that is one way that I've not tried yet.

[fair.child]

@Gordo,

Bravo! I got the culprit. Re-flow the V1, V2, V3, and biased the power tubes to 41 MADC for all EL34. The amp is singing now! I am very happy how it sounds. Just put Merman in front and the mojo is working! Definitely this amp will stay!






upload png google

[alanp]

I thought some of those solder joints looked a bit naff! Mind you the whole PCB looks mildly dodgy.

Nice to hear there was a good, simple fix.

[fair.child]

I thought some of those solder joints looked a bit naff! Mind you the whole PCB looks mildly dodgy.

Nice to hear there was a good, simple fix.

Well, I got the same feeling when I first looked it up. I do really want to replace the board if I can have it from RIVERA. It looks like a similar design from Fender Twin Reverb. Also, I noticed there are couple mods installed on this amp however, I am not sure what mod it is.

So far, I have been putting this up for 3.5 hours and still going strong. Channel 2 is crystal sparkly. I owned several amps before (Mesa, Marshall, Vox, Fender, and Panama). So far, I am amazed how crazily good sounding with this amp, plus wife gives a go/thumbs up.

[gordo]

Good for you!!!  It's way more satisfying to fix it yourself than have someone else do it.  I wouldn't worry about the board looking the way it does.  If it works it's a thing of beauty :-)

You can always get in there with some flux remover or isopropyl alcohol and a toothbrush and clean up the flux residue but likely more trouble than it's worth.

I love Rivera amps.  I don't like to carry Rivera amps but only because Paul didn't skimp on specs and tended to build stuff to last.

[thesmokingman]

for future reference, when troubleshooting noise like that it is beneficial to start by removing everything but the power tubes and start adding tubes back to the amp from the phase inverter back towards the input stopping once you've got your noise ... troubleshoot that section of the amp, repair it, and keep adding tubes back until you're done.

[fair.child]

for future reference, when troubleshooting noise like that it is beneficial to start by removing everything but the power tubes and start adding tubes back to the amp from the phase inverter back towards the input stopping once you've got your noise ... troubleshoot that section of the amp, repair it, and keep adding tubes back until you're done.

Which is I did the method you mentioned. That is the reason it took me a while to figure what the culprit was. When I got the amp, the Reverb was noisy and I figured the I/O Stages are flipped, changed the tube V4.  I started moving and changing the preamp sections after that in order to find the microphonic tubes.

I took Gordo advice to re-flow solder joints on V4, V5. I also did remove a lump of solder joints and checked the continuity with DMM. I drained the caps by shorting the polarity.