Fizzle Noise

[passfan]

Rawnster had this exact problem and it turned out to be a loose leg on his (inexpensive) Bourns volume pot. He changed it to a PEC pot and the problem went away. It seems the rivet that secures the lug onto the carbon trace can sometimes either be loose or get loose. I think you have danced all around this. Change the pot and let us know. ...Are you using the Bourns version?

No, worse... the cheap alpha's. I've contemplated going to the pec's. I'll have to wait. It makes sense though, with a 12ax7 for v1 I get all kinds of underlying crackle just off standby, depending on the tube it's so bad I don't even wait to see if it feeds back I just shut it down.

[passfan]

A new set of PEC pots should be in by early next week. Should have them installed by next weekend and I'll post results.

[Structo]

Just be aware that the PEC pots are stainless steel and you cannot solder to the back of the can.

[Colossal]

Well , not only have I not been able to find it, I've managed to make matters worse... I changed all my Russian coupling caps out to orange drops and I've lost my tone. What was a beautifully warm sounding amplifier is trebley as all getup.

Passfan,

Out of curiosity, what brand and series of Orange Drop did you use?

Thanks.

[passfan]

Well , not only have I not been able to find it, I've managed to make matters worse... I changed all my Russian coupling caps out to orange drops and I've lost my tone. What was a beautifully warm sounding amplifier is trebley as all getup.

Passfan,

Out of curiosity, what brand and series of Orange Drop did you use?

Thanks.

They were the 715P's that AES sells, nothing special. I was also using a .0033 for C8 and changed back to a .0022 with the orange drops, plus I tried Glenn's choice of 220pf for C12 as well. It got so trebley it was uncontrollable but, was it that or my pot problem ? I should know soon.

[passfan]

Just be aware that the PEC pots are stainless steel and you cannot solder to the back of the can.

I noticed that. It appears that people are using a ring terminal around the shaft between the pot and the chassis and tying that to the buss , is this correct?

[M Fowler]

Some are using those ring terminals and others will raise the pot leg above the pot body and run the buss wire through that terminal and other pot terminals that are grounded continuing to the input jack and then to the floor of the chassis to ground.

Like a Dumble style amp.

[JamesHealey]

Well , not only have I not been able to find it, I've managed to make matters worse... I changed all my Russian coupling caps out to orange drops and I've lost my tone. What was a beautifully warm sounding amplifier is trebley as all getup.

Passfan,

Out of curiosity, what brand and series of Orange Drop did you use?

Thanks.

They were the 715P's that AES sells, nothing special. I was also using a .0033 for C8 and changed back to a .0022 with the orange drops, plus I tried Glenn's choice of 220pf for C12 as well. It got so trebley it was uncontrollable but, was it that or my pot problem ? I should know soon.

715P explains that problem then, you can't use these in a wreck build they're far too bright u need polyester ODs.

[passfan]

Got my pots in and installed. Pulled all cards and installed a different type of jumper wire. Got a couple of tung sol reissues to go with my ge 12ay7. Absolutely no microphonics whatsoever (Even from the wire off the center wiper of the volume pot). Tone stack works as it should and this thing sounds great until about 1/2 volume, then I have something crackling somewhere intermitantly. I have a slight buzz as well although I used a bigger power tranny and dropped 50 volts with a zener, it might be noisy. My B+ is 436. I had an "oh shit" with the new power tranny. The heater winding is 12 volts center tapped and I forgot. My heaters had 12 volts on them for maybe a minute or two counting offs and ons. The tubes are still working or so it seems. I'm going to go back to 5881's instead of el34's and see what she does. I think I'm really liking the Rocket more now that I can AB the two. I like the breakup better, although the Rocket gets quieter than the Express

[passfan]

Well it would appear that my output tubes were damaged. The breaking up at 1/2 volume was eliminated by swapping them out to another pair of output tubes which worked fine , no breakup. After checking their bias, the current on one is off from the other by 6 ma's when before they were dead matched. At lower volume they sound fine but when you open them up they crackle. The amp runs and sounds great now from just an hours worth of playing. The PEC pots seemed to cure my ills and the zener worked fine. My B+ is around 436 and all other voltages are so close I'd almost call them spot on..., not quite. Biased my 6L6GC's at 50 ma's and they bite pretty well. I've learned my lesson, no more cheap pots in high gain amps.

[passfan]

Well it would appear that my output tubes were damaged. The breaking up at 1/2 volume was eliminated by swapping them out to another pair of output tubes which worked fine , no breakup. After checking their bias, the current on one is off from the other by 6 ma's when before they were dead matched. At lower volume they sound fine but when you open them up they crackle. The amp runs and sounds great now from just an hours worth of playing. The PEC pots seemed to cure my ills and the zener worked fine. My B+ is around 436 and all other voltages are so close I'd almost call them spot on..., not quite. Biased my 6L6GC's at 50 ma's and they bite pretty well. I've learned my lesson, no more cheap pots in high gain amps.

One final update here and then I'll let it go. I noticed in the layout file that pin 1 of the output socket is grounded, but when I wired the circuit I went by the schematic (old habits) so I didn't ground it. My initial startup was with a pair of 6L6GC's which don't have a pin 1 so I never noticed it. When I finally recieved my EL34's from AES I had this fizzle problem which then wound up being a pot problem and hence this thread. Well the EL34's I thought that were damdged by my heater mishap were misbehaving at higher volumes because of the ungrounded control grid. They sounded fine at lower volumes but crackled above half. Since I went back and grounded pin 1 they work fine. I guess the ungrounded grid interacted with things inside the tube at higher voltages.