Building again - authentic 18W this time!

[shakti]

More good news: I tossed in another 68k for the trem channel while still waiting for a Piher, just so I could test both channels thoroughly. The buzz from the normal channel is still there with tone on 0, but I guess this is a grounding issue which is well known with that channel. Need to fool around with the grounding a little to make that go away, but it's not a big issue as it's not there with a guitar plugged in or the tone turned up above 0.

The crackling noise was still there though, for both channels, so it must have been something in the PI or the power amp...but as I was playing and testing, it seemed to get less and less noticeable, until it was completely gone! I have played the amp for close to 30 mins now with no more issues except the normal channel buzz. The trem channel sounds killer too, and the tremolo itself works flawlessly - no noise, no bad throbbing sound! I don't know what was causing the problem - perhaps some of the ceramic caps just needed "bedding in"? They have been sitting unused for God knows how long, and may have been stored under humid conditions, perhaps some humidity that needed to evaporate?

Need to test it some more and try different tubes, for now I just threw in some spare and well used Ruby EL84s, probably relabeled JJs. The amp has a very lively feel, the volume comes on very fast and it really feels extremely "in your fingers", and just compresses more and more from volume 3 and up. I am probably just used to playing very loud amps as it does feel like it doesn't have a ton of power, but I guess that's what you get when you're used to playing Hiwatts through 4x12s... The distortion is very sizzling and slightly buzzy, but again, that's something that's supposedly the nature of the beast with these 18-watters and some of the EL84 character when driven hard. I have actually forgotten to check the anode voltage on the EL84s, but I think it's fairly high as all the voltages coming off the PT were on the high side. I am using 125R for the cathode resistor. Some originals had 100R, but many people are using 150R to go a little easier on the EL84s.

I do suspect that the ceramic caps are adding to the slightly buzzy nature, perhaps I will try to swap in mustards in key positions, but again it's kind of cool and how these amps were originally made.

Hope to put up more photos and maybe a short video soon.

[neikeel]

More good news: I

I do suspect that the ceramic caps are adding to the slightly buzzy nature, perhaps I will try to swap in mustards in key positions, but again it's kind of cool and how these amps were originally made.

Hope to put up more photos and maybe a short video soon.

Excellent. I think the ceramics do add some 'grain' to the tone. In mine you will see I mainly used Mustards on the normal channel which is much smoother.

I actually tend to use the trem channel with the trem turned off with tone turned up to max and the volume usually on 1-2 for rehearsals and 4-6 for smaller gigs as you get crispness and guitar response without flubbing ut. If you turn it up to 10 completely it gets a great 'brown sound'.

[shakti]

The normal channel is still a touch smoother sounding than the trem channel even with all ceramic caps. It also feels a little bit more powerful and louder than the trem channel, but not by much.

I am still getting some intermittent gremlins though...the occasional crackling noise and another noise from the normal channel which is probably tube related. I am going to give it some more time to bed in before I start hacking away though. I actually haven't soldered the HV end of the PI caps as I thought I'd do some quick swapping there to compare with mustards. They do sit very tightly in the turrets though, so I didn't think that could cause the crackling noise, but I suppose it's possible after all. That position (junction between the PI caps and the 100k PI plate resistors) I guess is susceptible to noise, but I don't know for sure. That's where the 47pF fizz cap usually goes, but this amp doesn't have one.

[shakti]

With everything soldered in place, I am still getting some occasional crackling distortion. It does seem to be vibration related, at least it happens much more easily on certain notes and with the volume turned up at least a little. I've tried tube swaps (albeit not the PI tube). Seems to happen on both channels. WIth the volumes turned up high, I can induce some crackling by tapping hard on the volume and tone controls. When the crackling isn't there, the amp does sound great if perhaps a touch brittle. It really has a beuatifull organic feel to it, very "vintage" if you will. Sounds killer with a Strat, and I don't find it lacking in treble or openness at all. The alnicos probably help with that, and possibly the ceramic caps too.

I'll get a cap tester and check the ceramic caps, give them some more time to burn in to see if the issues goes away or not. Any other suggestions to where that loud vibrating crackling distortion might be coming from?

[DG45]

Not an expert at all but have you tried poking around with a chopstick or plastic rod at the solder joints, passives and tubes to see if you can induce the crackling. Maybe a carbon comp. resistor going south? I think you said that you didn't swap the PI tube. That would be worth a try as well I would think.

[shakti]

I did try with a chopstick and couldn't detect any particular spot that was sensitive. I could of course have a suspect solder joint somewhere, but on inspection they all seem fine. I'll try to swap the PI tube though.

[shakti]

I promised some videos, here they are...crappy playing, just done off the cuff to demonstrate the tone and the two issues I have.

First video, Les Paul into the normal channel on 6-7. AS you can hear it sounds fine until I hit certain notes and then I get a very loud crackle.



Second video, micing a little closer as this one is a more faint noise. You can hear a harsh high frequency buzz riding on top of the note then dying away. This is plugged into the normal channel with guitar volume rolled back. In the second half of the clip I plug into the trem channel and do the same thing...no noise there. I'll admit this could be tube related, but it's hard to tell as this noise is also intermittent.



Last video, this time with a Strat plugged into the trem channel. I think this amp sounds killer with a Strat - very open and chimey but with dirt very easily available when you dig in. Kind of a cross between a Vox and a Marshall. The tremolo is very hypnotic sounding.

[shakti]

Just to clear up any confusion;

- the crackling noise appears on both channels. I had it in the beginning, then it seemed to go away, and then it has returned, but is intermittent. I have tried swapping the phase inverter tube and the output tubes (the only tubes common to both channels) but that doesn't make it go away. I can elicit some of this crackling when the amp is turned up loud by tapping on the control panel, but I could not elicit it with a chopstick on the tubes or the tube sockets or wires to the sockets.

- the harsh high frequency buzz in video #2 is only audible on the normal channel. It is intermittent. You'll have to turn the video up loud to be able to hear it. I can elicit something that sounds similar to this buzz also by tapping on the control panel when the normal channel is turned up loud. The normal channel does not have input grid resistors per the original schematic, and I am not using shielded wire on the input grids, but neither did the originals.

[neikeel]

Fixed yet?

[shakti]

Unfortunately, no. I've been splitting my time between this and sorting out the 68/69 SL issue (see other thread), so haven't been able to put much time in. I'm not really sure what I'm looking at here...the faint squeel/oscillation following the notes on the normal channel could possibly be a lead dress thing, and perhaps shielded wire on the inputs will sort that out. But the crackling is eluding me so far. I've read about ceramic caps becoming microphonic, but I really don't know if that's a possibility with this sort of noise. It might be a simple thing, but I haven't found it yet. Any suggestions?

What do you think of the sound? I dig it, but it seemed brighter/crisper than I expected. The alnicos probably play a part in that. The recording adds some harshness.

[shakti]

Played the amp a good 20-30 minutes earlier today, and had no crackling noises. I don't know whether to be happy or frustrated about that, but I suppose the former is the most appropriate response. We'll see if it turns up again.

The other issue (harsh but very faint buzz riding along on the notes on the normal channel) goes away if I touch V1 with a rag, so that too seems to be vibration-related, and may be the tube itself, or in worst case is the tube socket (which has a hairline crack in the shield base). That one should be easy enough to get rid of.

[neikeel]

I have experienced that sort of intermittent (almost resonant frequency) type of crackle a few times. It has been an intermittent joint failure each time. On on it was a dry joint on V2a grid of a JTM100, another time the wire in the spring mechanism of the fuse holder of my 68 JMP50 - there ws corrosion where the flexible wire is inside. The problems would come and go, I went through all the visible things, pulling out perfectly good things like filter caps etc.

It may be worth checking all the joints under your board and re-sweating them?

[shakti]

Yep, I'll do that if the problem returns. If you listen closely in the video, you will hear that the note continues just about unchanged, there's just a lot of crackle on top of it. That could probably tell us something...I'm just not sure what!

[RockinRocket]

I had that crackling on a JMP 50 build. Ended up being a cold solder joint on the 100k V2. Id check the trems 220k across the plates.

[shakti]

Thanks for the tip! The issue seems to have resolved itself. I reseated the chassis to minimize vibrations, and tightened the rectifier tube a little. It was missing a tube retainer, and I have a suspicion it may have been vibrating in the socket enough to cause the noise. It has been gone for a looong while now, but if it reappears I'll go over all the solder joints again.