New to me Deluxe Reverb

[proaudioguy]

I recapped this 77 non-pull boost. I used 16µF F&Ts. I moved the standby switch after the first 2 caps. I changed the cathode bypass for V3 to the AB763 (and most other model DR) value. I am using a 5U4GB but I changed the 2.2K dropping resister to 10k as I want the sag. I have not changed the 330Ks to 1meg, and I have not changed the coupling cap to the PI to .001. That part of the circuit is still A1172. Bias is 70% using plate voltage and mreasureing 1Ohm resisters (bias probe) and using th RobRob calculator that takes into account the small excess current through the cathode. When the amp is dimed, and with the guitar plugged straight in, there is a crackling sound. You can hear it in the video. Any ideas?

https://youtu.be/HK2NneHTnzM

[proaudioguy]

Turned it to 7 on the Vol and it still does that.

[xtian]

70% of max. dissipation is a target we used to aim for, but after building for 12 years, I prefer a cooler bias, closer to 50%.

That said, your next move is to figure out if this noise is vibration related, or purely electronic. Do that by plugging into an external speaker cabinet, so the loud volume is not vibrating the amplifier chassis.

[maxkracht]

Lots of things can cause crackles. Could be a tube, dirt, noisy resistor, bad solder joint, loose connection, etc, etc.. Gotta poke around to find out; chopstick is your friend. If you haven't already, I would start with cleaning and tightening pots, jacks, and tube sockets. The wax on those boards can also get fluxy and gross and cause problems. While you're doing that, keep an eye out for anything amiss.

[proaudioguy]

I changed to a 5AR4 and re-biased to 20mA, slightly less than 70% and the tone of the amp is actually a little nicer, but the sound on the video is still there. Additionally, I now have an audible hum that I did not hear before with the 5U4GB. Unplugged the guitar, moved the volume and tones all the way down and the hum was still there. Plugged the guitar back in and it went away instantly.

[proaudioguy]

Lots of things can cause crackles. Could be a tube, dirt, noisy resistor, bad solder joint, loose connection, etc, etc.. Gotta poke around to find out; chopstick is your friend. If you haven't already, I would start with cleaning and tightening pots, jacks, and tube sockets. The wax on those boards can also get fluxy and gross and cause problems. While you're doing that, keep an eye out for anything amiss.

Everything below 6 is fine though, no crackles at all.

Amp is dead quiet, wax isn’t really even dirty. Its the cleanest one I have personally ever seen other than the ones I built.

I was going to change the 330Ks to 1M and the .01 to .001. Do you all concur? That is the only thing keeping it from being wired 100% blackface. I’ll poke it when I’m in it. I measured every resister and they are all in spec. I was hoping this might be something someone had heard and just knew.

[maxkracht]

Everything below 6 is fine though, no crackles at all.

Amp is dead quiet, wax isn’t really even dirty. Its the cleanest one I have personally ever seen other than the ones I built.

So, it either needs to wiggle enough to make noise, get hot enough to make noise, or draw enough current to make noise... everything I mentioned still applies. I'm not suggesting you clean it for aesthetics.

Following xtian's advice should narrow things down. Whether it happens in one or both channels could as well.

[xtian]

Plugged the guitar back in and it went away instantly.

The leaf switch on your input jack(s) is dirty and not closing like it should, thus the hum when no plug is inserted.

[proaudioguy]

Plugged the guitar back in and it went away instantly.

The leaf switch on your input jack(s) is dirty and not closing like it should, thus the hum when no plug is inserted.

I am going to run a file over that. It happened when the guitar was still plugged in though and with the volume all the way down.

It happened again with the hum last night, and plugging and unplugging the guitar made no difference. Turning the amp on and off made no difference. Letting the amp cool, and turning back on, made it quiet again interestingly. Hum comes after its been on a while.

Turning the amp off gives a bit of a pop as the caps discharge I guess. It happens seconds after the switch to OFF. Standby is not engaged.

[maxkracht]

I am going to run a file over that. It happened when the guitar was still plugged in though and with the volume all the way down.

"The" volumes or "A" volume? Careful with your file, unless you have a special file. You want to knock down the dirt/oxide layer, you do not want to scrape through the plating or bend anything. (could already be bent/meatal fatigued instead of just dirty) Somewhere around 1000 grit will work, doesn't take much. If you remove the plating it will get better for a bit then way worse...

It happened again with the hum last night, and plugging and unplugging the guitar made no difference. Turning the amp on and off made no difference. Letting the amp cool, and turning back on, made it quiet again interestingly. Hum comes after its been on a while.

Could be thermal compression/expansion, could be coincidence. Sounds more like a mechanical issue. Dirt, bad solder joint, loose connection, etc. or a tube failure

[proaudioguy]

You are right, its a mechanical issue.

I tracked down that the grid wire on V4B was very microphonic for one thing. I lifted it and the thump was reduced. I replaced the wire, although I only had solid core cloth covered white. I may go ahead and put the old one back because I don’t think there was anything wrong with the wire but that was the first thing I tried.

I was poking around with a plastic butter knife since I have no chopsticks at the moment. When I was around the 3.3M (same wire) there was a lot of static. There was also on another circuit nearby, maybe an inch away. Maybe static build up on the kniife, but while tapping the board the hum that I mentioned before showed up, then went away. I reheated the eyelets, and added a little solder, and as I said replaced the wire but finally decided to try and get rid of some of the wax. I turned the chassis on its side and used the heat shrink gun to warm it up and a lot of it flowed off the board. I used CRC contact cleaner to flush a lot of it away. It did a decent job, but I didn’t have much, so I switched to 99% isopropyl, but its not a spray. I managed to get about a thimble full of wax off. I poked around and it seemed better. The slight pop that was happening when I turn the amp off, with standby not engaged, did NOT happen. I put the amp back together, the ratty crackling distortion when cranked up is gone and some of the little noises are gone. The side affect, which I am not super happy about is the amp got WAY brighter, brittle even. It changed the entire charachter of the amp. I’m concerned maybe the caps got overheated but since the amp sounds like my TWIN REVERB now, it seems more likely there was a lot of capacitance on the board. I will have to investigate removing the bright cap. Voltage with 5ar4 on the power tube plates is 473 now, much higher than before. I put the 5U4GB back in there.

I have heard there is a spray to remove flux. I have no idea where to look for that.

Sorry for the long winded post. I have been lurking here for many many years. I have a few questions now and then. Always learning.

[maxkracht]

Grid wires are always going to be microphonic, but they usually don't give a big scratchy thump unless there are problems. That 3m3 is where the tremolo channel and the reverb mix. The 10pf cap across that resistor is letting highs pass. Perhaps that cap has drifted, or wasn't properly connected, and now you are getting too much bright.

You don't need solvents for wax, just scrape what you can then add a little heat and something to soak it up. I use cotton swabs and paper towels. Careful not to heat caps too much. No need to go nuts, just get the big globs.

Any big electronics supplier, like mouser or digikey, should carry flux remover. I have some mg chemicals stuff that is ok, but I usually use IPA.

[romberg]

Does the crackle go away if you pull out the reverb driver tube?

The fender design hits this tube VERY hard. On my build (which was an AB763) the reverb driver tube started to overdrive around 6 or 7 on the dial. But the important thing was that when it was in overdrive, it polluted the upstream signal of the channel feeding it. I'd get distortion on the channel even if the reverb control was all the way off. Pulling the reverb tubes made the distortion go away.

The ultimate fix for my amp was to put in a voltage divider (permanent dwell control) in front of the reverb driver tube and hit it a bit less hard.


Mike