1959slp build, crackle issue

[Iommic_Doom]

I just finished a DIY build of a 1959slp reproduction, and have run into a really weird issue I've never seen before in an amp. (then again, i'm not that experienced)

I have it hooked up to a weber mass200 attenuator into a 15" speaker for testing on my bench.

When I really dig in or have the volume turned up, I get weird sounds coming from my tubes. It's a buzz, almost like they are vibrating microphonically. Except.....I can hear it when the power to the speaker is completely turned off by the attenuator. The power tubes themselves are making the noise... they are buzzing like mini-speakers.
When I turn the speaker on, those buzzes in the tubes turn into crackles/buzzy nasty distortion in the signal......very different from the usual microphonic tube rattle sound. I've never heard anything like it before.

Does this mean bad tubes, or did I mess up somewhere? This is my first time using el34's, so i'm not too familiar with their ins and outs. I'm using svetlana (not s.e.d). I also tried a set of JJ's which had the same effect.

It's somehow correlated to the amount of highs being fed. I get more on the treble channel than on normal, more as I turn up the volume, and it also increases dramatically as I increase the presence or treble knobs.

There was a 47pf across pins 1/6 of the phase inverter on some schematics, and omitted in others. I omitted it in my build. My understanding is that cap helps tame oscilattion, which can cause crackles. That may be a possible culprit, what else should I try?

(all voltages on tube pins are within normal range, sockets are new and clean with good contact)

[Dai H.]

if it's the (output) transformer buzzing, I think this is normal. You just don't hear this usually since the sound (which seemed more prominent IIRC with the amp cranked up) would be drowned out by the speakers.

[Reeltarded]

Don't leave off the fizz cap. Put that 47p on there. I use 100p and higher.

[xtian]

There's nothing wrong. Power tubes vibrate in sympathy with the signal, especially at high power, and you'll notice this only if you're using an attenuator or dummy load.

[Iommic_Doom]

Ah...ok, thanks guys. I put in the fizz cap and it tamed some of the nastyness, but some still remains.

If it's normal for the power tubes or output transformer to vibrate in sympathy with the signal at high power, is it also normal for this vibration to be modulated/increased by turning up the presence? Would a short cause this?

I did some more troubleshooting...

I have a short with approx 1ohm resistance from each of the OT taps to ground. Is this normal? The short it directly from the tap to ground, with the lead disconnected from the rest of the circuit.

[Iommic_Doom]

Nevermind that last troubleshoot, i just realized why that's a retarded question...

[passfan]

Well at least that was good for a chuckle. Glad its sorted out , enjoy your new build.

[Reeltarded]

I would like to hear your amp. Do you thinknit sounds like others you have heard?

Go up to 100pF of the fizz cap. You have the classic 5k/1uF presence circuit? What value is the NFB resistor?

Some tubes/transformers 'sing' more than others.. but there could still be something going on in your NFB circuit if it's extra trashy sounding.

[steveneddy]

What does it sound like through the speaker without the load? That sounds like an OT issue to me.

[Structo]

Did you try different power tubes?

Have you ever tried tube dampers?

They are silicon rings that go around tubes.
Cuts down on rattles which is usually filament noise.

http://www.ebay.com/itm/8-VACUUM-TUBE-A ... 51aa13bc49

I use these on my amps power tubes.

Output transformers can also make noise when improper load is applied.

[Reeltarded]

I think we don't know enough to say, yet.

If there is a loose connection in the NFB circuit the amp will smack into a louder edgey treble tilted coughing kind of thing when it is disturbed by tapping on it or vibrations when playing.

Speculation is going to send you on the wrong chase. Probably need pics and maybe a short recording to help much!

[Iommic_Doom]

The amp sounds good when it's not driven. Not much of a difference with gain below 4 with or without an attenuator load on either channel unless I crank the presence to 10. Dial in anything past a slight crunch and it sounds like a really unhappy circuit.

I can't crank it without a load or record it where it is right now, but I will take it to my studio sometime this week and upload some clips so you guys can hear what it sounds like. I'll have to pick up a higher value fizz cap too. I will also post pics and a voltage chart soon.

I wonder if the grounding scheme has something to do with it. There seem to be a dozen different ways to ground this circuit....I just went with my instinct, what seemed most logical based on the schematic and layout (the supplied layout omitted the grounding layout)

The presence circuit is 5KL/.1uf, the NFB resistor is 47k. The NFB is connected to the 8ohm tap, and when I test the amp it's running 4ohms through the webermass into a 4ohm speaker. The speaker jack is grounded to the same ground as V5 pins 1+8. I do not have the 1ohm resistors between the tube pins and ground as done in some versions but not others. (I wonder if that reference to ground could be causing the problem?). The presence pot is grounded to the lug - not the pot body - which is connected in a line to the mid and two volume pots, and the bias and v2 cathode resistor are grounded between them. Those grounds then go to a chassis ground on the other side of the input jacks. That ground is shared by the input jacks and preamp cathode bypass caps.

I have tube dampers, and that's not really the issue. I've worked through ten tubes on this amp. one set was completely mismatched, the other set had a faulty tube that blew immediately and I had to swap out two. kinda scared of putting another set in, afraid the amp might eat them. The amp rattles on it's own when it's isolated from physical vibrations. I know the sound of tube rattle, and this is very different. When the amp is turned up, those rattles translate into the sound coming from the speaker as very harsh distortion.

[Iommic_Doom]

So here are some pics and a voltage chart.

Worth nothing that when I try playing it cranked (through the attenuator) I can hear the power tubes cackling from the heat....despite my bias being set fairly low (think)

Also, in the 15 min I had the amp on while taking the readings for this chart, I could smell that nasty "something's gonna smoke soon" electronics smell. That was before I plugged in.

Feel free to make fun of my shitty flux-spattered soldering. It looks worthy of making fun of. I have not yet worked out the fine details of solder type vs. temperature.

[vibratoking]

...Feel free to make fun of my shitty flux-spattered soldering....

OK. I can't begin to imagine what you did to cause that mess? That is way beyond anything I've ever experienced. You're doing something very wrong...

[Iommic_Doom]

so I just took it to the studio, tried it out with a 4x12 cab with tonkers.

Apparently, the attenuator is the problem. This amp doesnt seem to like it. I've tried the attenuator with a dozen other amps and never had problems. This particular amp, for some reason, hates it. Sounds great without it. With the attentuator, like a ringmoded poop&icepick sandwich being eaten by an old man with emphysema.

With the controls set at non-spinal tap values, it sounded beautiful.
For a few brief minutes, I could have sworn the ghost of Paul Kossoff had possessed me and my les paul.

Then I dimed it with the channels bridged, hit a boost and got the dreaded blue light and blown fuse.

gaahhhhhhh