Crackling/frying bacon noise - deluxe reverb ri

[Twosteps]

Don't wanna sound like an idiot that keep asking questions and doing nothing here but while transforming the bjr project is kinda 50/50 my friend's drri has this problem occurred the other day. It sounds like you're burning a bacon in a very hot pan or hard rain if that make sense.

The tubes are ok, trannies are ok(I think) the noise would come up as soon as the standby switch is on - even with all the pots off. It's a U.S one so it uses a step down transformer from 230v with no ground.

Has anybody experienced this? It feels like a long shot asking for a diagnosis online and I don't have to fix this but I'm just curious.

Any suggestions would be appreciated

[John]

The first thing to try is replace the plate load resistors. I've not had experience with that myself yet, but it's a common problem in older amps, and many times those resistors need replacing. Use metal film or carbon film, 1 watt is better than 1/2 watt.


You understand, this is just what I've read many, many times. :)

[jojokeo]

Since it's a re-issue model it has a circuit board and small carbon films in already? I don't have any photos handy of one I worked on about 8 months ago but I think this is the case. If not and they are CC then check and replace as John suggests but it's a high probability there are one or more bad soldering contacts on those cheap Chinese boards. The wave soldered contacts heat up and cool down over and over expanding & contracting where eventually you'll start seeing the tell-tale little rings around the terminal leads in various places. Touch 'em up, it'll never hurt and prevent something from happening in the future.

[Twosteps]

Yes, I've read about the plate load resistors somewhere but since this is a reissue one I've kinda ruled it out. It has those tiny carbon film and all other cheap parts. It just look bad all together you know  all the solder joints have something like rosin flakes all over the place but I assumed that those are the solder flux that came off over time?

I might take the board out and do the touch up - a bit of a hassle but no spending money.

This noise is happening on both channel with all the pots off. It just happen right away after I switch on the standby switch. Anymore thoughts? Thanks guys!

[Willabe]

........ but since this is a reissue one I've kinda ruled it out. It has those tiny carbon film and all other cheap parts.

I would say no, you shouldn't just 'because it's a reissue amp'. Don't rule out the MF (metal film) resistors (R's) here's why;

It has those tiny carbon film

So, what wattage are they and what quality are they? I'd bet they aren't up to the job in their position in that amps circuit. 

[Twosteps]

Right, I'll try replacing all the plate load resistors and also touch up the joints. Ee'll see how it turns out.

[jojokeo]

check and clean tube sockets also and try a few different tubes or move a few around just in case to eliminate that too.

[Platefire]

Yeah, that was my first thought---try a known good preamp tube in all the positions one at a time to see if it stops. So while you are changing out preamp tubes to test, you could clean the sockets at the same time. Also, turn your cell phone off---it can cause a rukus! Platefire

[p2pAmps]

From the amp degug page
http://www.geofex.com/ampdbug/ampdebug.htm

noisy tubes
Noisy plate resistors. The carbon composition resistors used on the plates of preamp tubes often go very noisy, especially in older Fenders. If swapping tubes does not fix the trouble, locate the circuit that seems noisiest by tube swapping, and then replace the plate resistors in that circuit with equal-value metal film or metal oxide resistors. You can use carbon comp if you can find them, but the problem is likely to recur.
Noisy resistors in the B+ decoupling string, often around 10K in value
Unusual: An ultrasonic oscillation can cause an intense insect-like hissing that sounds very much unlike normal hiss.

Rare: leaky coupling capacitors or faulty controls
Rare: a slight ongoing arc on the output tube socket(s)
Rare: a bad solder joint somewhere in the signal chain
Rare: internal arcing or noise in almost any part in the preamp section"
Rare: internal arcing or noise in almost any part in the preamp section"

[Toxophilite]

Is there a frying bacon smell?? mmmmm
Check for bacon on the power tubes!

[keithv]

I had an identical problem, but with a JTM45.  Checked the tubes, checked the trannies, checked the plate resistors.  None of those were the problem.  The amp worked fine...it just had this awful white noise (definitely not 60 cycle hum) all the time.  Turns out to be the exact same problem this guy had here:

http://www.marshallforum.com/workbench/45881-jtm45-suddenly-has-static-sound-2.html

Ended up being the 250pF cap that connects to the treble knob, which should be the same for the AB763, except you have two channels so you'd have to track down which one is the culprit.  Should be easy enough....just pull the preamp tubes and see which one is causing the problem.  Might be the same problem for you.

[Twosteps]

Got round to do some touching up today. The problem still there, also definitely not the tubes - I can swap any tubes and the problem still there. Most joints are actaully ok and I don't think it's the plate resistors(well, I might be wrong but they're firm and the joints are clean). It can't be the bright cap cause I've removed one on vibrato ch. Dunno anybody got suggestions? 

Ps. I opened the cap can and there's something on the positive end of the caps(see pic). Is this normal?

[sluckey]

You can't look at the plate resistors and tell if they are noisy. Just replace them (probably ain't gonna be fun on that PCB). Filter caps are also high on the suspect list.

Since the noise is present on both channels even with the pots on zero, I'd start with the PI circuit and filter cap/s associated with the PI. First, pull all the little tubes except V6 (PI, should be closest to the big tubes) Is it still frying?

[Twosteps]

Yeah, admittedly, it was plain laziness that I didn't replace them. Since it occur on both channels with all the pots off I just assumed that the chance of the plate resistors went bad at the same time is slim.

I did pull v1-5 off and the noise disappear. So this means the problem lies in the pre section in front of the PI? Do I just put the tube back one at a time v5-1 to narrow down the area that has problem?

Thanks again for your help 

[sluckey]

I would now suspect a problem that's common to both channels. Like filter caps.

[Twosteps]

Well, like in the picture that I attached, it does seem like something had leaked out of the caps and dried there - on the positive ends. They all had it, I just picked some out. I suspected it might show that there's something wrong but my friend said it could happen and maybe not be the problem. Is there a way to check? Or I might just replace them all since it's pretty to do.

[sluckey]

Replacing them is the best way to check them.

[Twosteps]

Cheers! 

[Twosteps]

Ah well, it's not the filter caps. This giving me headache now. Never cared about fixing amps but this one make me feel like I don't wanna give up, you know..

Here's the situation

- The worst guy is v4 - half reverb recovery and half third gain stage of vibrato ch. if I put in this tube there'll be a very loud crackling noise.

- Without v4 (other tubes in) I can still hear the noise but at a lot less volume

- With just v1 and v6 there's still the noise at lesser volume

- With just v1 and v6 and I disconnected the whole vibrato ch./reverb/vibrato circuit the noise was still there at even lesser volume

- With just v6 - dead quiet.

If this is the series "House" it's the scene now that everybody gathers in a room with Dr. House sitting on the table next to a whiteboard listing out the symptoms finding for things that they have in common.... 

Anybody got a clue????

[punkykatt]

http://el34world.com/Hoffman/tools.htm
Build yourself Doug`s listening device in the link above.  You will be able to find(hear) where the crackling /hiss enters the circuit.
 Punky

[shooter]

It sounds like you're burning a bacon

definitely get a listening amp,
 while you're waiting I've found "that sound" most often is bad connections in a HV path.  I'm not sure your skill set but if you know how to work on HV live, AND stay alive!!!,
use chopsticks to move things around, "drum" on things with a chopstick, flex the pcb with chopsticks, wiggle tubes, connectors, cables, jacks.  my last 2 bacon frying problems were bad sockets fwiw.

[Twosteps]

Never knew such thing as a listening amp exist ;) seems like a must have tool really. I'm gonna build one soon. Thanks Punky.

@shooter, dumb question but how did you find out which socket was bad?

By the way, the noise I'm getting is really loud and would pop up as soon as I turn the standby switch on. I have to turn it off right away let alone go on and knocking things. I'll recheck the connections again but last time I did they were all fine unless I accidentally skipped some joints. 

[shooter]

how did you find out which socket was bad

I don't believe your problem is a socket, but it's possible.  I found the 1st one easy enough, every time I bumped the chassis it would go a crackly, I turned off the lights, wiggled tubes and found this cool blue arcing between 2 pins - carbon tracked.  I have the advantage of a scope, so on the 2nd one I was monitoring the plate and cathode and everytime is jiggled the tube the scope would go all crackly and DC volts would jump all over.

With the listing amp you can just start with V1 in and listen - good? add the next tube, repeat.
but even before that you can pull all the tubes and measure - monitor the B+ nodes with a meter.  Tap - thump, poke and prod, if it stays solid, move on to the signal path with the listening amp