Popping Noise = Clipping ?

[liggs17]

I finished an S-5 electronics stereo kit last night, hooked it up, turned it on, and to my great astonishment, it worked. Coming out of the left channel, however, was a "popping" noise whenever the volume was in the middle (not low or very high). Any ideas? Is this clipping?

And how do I "burn in" new tubes? I keep seeing references to this in various posts, and I understand the theory (I think) but can this be accomplished by simply playing the amplifier, or leaving the amplifier on for a period of time, or do I need separate equipment?

Liggs17

[SHiFTY]

Swap the tubes between channels- it could be a faulty tube, in which case it would appear on the other channel.

Check all your solder joints (discharge the caps first!) and all component values.

As for tube burn in, best done with a few beers and some good music

[Sherman]

I'm with Shifty here. Tube swap is easy to do and should be the first thing you try.

I suspect however that you'll find the answer in a bad solder joint. Further, I would especially check the ground connections. The through-holes for the grounds by the output are especially large, much larger than the supplied wire and getting a good solder joint there can be a little tough (I know from experience ).

[Miles Prower]

Originally posted by liggs17
I finished an S-5 electronics stereo kit last night, hooked it up, turned it on, and to my great astonishment, it worked. Coming out of the left channel, however, was a "popping" noise whenever the volume was in the middle (not low or very high). Any ideas? Is this clipping?

Clipping doesn't sound like that. Where did you get the VTs? Sounds like you have a gassy final that's flashing over. Had the same thing happen a few weeks ago with a gassy 807. You could see the blue glow fill the space between the cathode and anode. Bad news indeed.

And how do I "burn in" new tubes? I keep seeing references to this in various posts, and I understand the theory (I think) but can this be accomplished by simply playing the amplifier, or leaving the amplifier on for a period of time, or do I need separate equipment?

Liggs17

Just play the amp: that'll "burn in" the VTs just fine. If using fixed bias, just be sure to keep an eye on the current. You'll probably have to readjust the bias the first few times you power up. Should stabilize relatively soon.

[liggs17]

Thanks to all for the replies. I will definitely try the easiest solution first, switching the vacuum tubes. They were provided with the kit by S-5 electronics. I have a sneaking suspicion that they are fine and that it is a solder joint that is bad (1st time soldering).

I was warned in this thread and have seen in other threads that I should dishcharge the capacitors before messing around with the wiring. How do I accomplish this? I actually posted a similar question the other week in the "safety" thread, but haven't gotten any feedback. Any suggestions would be appreciated.

Liggs17

[HollowState]

When a tube amplifier is switched off the tubes stay hot long enough to draw down the power supply to a safe level in most cases.

HOWEVER, it is always a good idea to manually discharge the power supply capacitors anyway as a safety precaution. Do this by bridging them one at a time for a few seconds with a low value resistor. 500 ohm/2 to 5 watt is typical. The actual value is not critical.

Use a pair of insulated clip leads with each resistor lead. One going to comon ground (B-) and the other to the capacitor positive. A slender medium lenght screwdriver with a well insulated plastic handle is helpful to reach and touch the capacitor positive.

You may have heard that a capacitor will recharge somewhat through it's internal dielectric absorption. While this is technically true, it's effects here are negligible once manually discharged.

Victor