static right channel

[debassige]

Finished my crack last night.  Did a continuity test and everything was fine, did not do a voltage test (I know, shame on me) but i will tomorrow.  Now I am a newbie (not electronically inclined at all) and this is my first kit of any kind so bear with me and my terms and lack of knowledge.

I have static (loud) in the right channel (along with a voltage test i will also be re-flowing all joints).  The static is there with no input (nothing hooked up at all and the volume does not affect it.  I pulled both tubes, no static, I inserted the larger tube, static but not as loud, both tubes and well, we have static.  Also it seems that one of the LED's is a little dimmer (or not, maybe it's just me.) 

My manual is at work along with my tools so tomorrow I will check and recheck everything and do a voltage check and re-flow all joints but is there anything in particular I might look at to begin with?

 

[Grainger49]

Without both tubes you have no amplification so you will not hear anything.  There is voltage there but there could be no output.  The standard way to test just the Crack would be to short the input hot (input RCA jack center) to the input ground (input RCA jack outer). This tells you what the Crack noise is without injecting any open input noise.  You can put an alligator clip jumper across each input.  If you don't have any of these they sell them at Radio Shack and you should have a half dozen if you are a kit builder.  And you are now.

But good troubleshooting.  Putting in the large, output, tube and getting noise says that the noise is present in the output stage.  It is possibly the tube.  I find it funny that adding the input tube amplifies the noise.

Reflowing the solder joints is a good idea, I certainly wold have told you to do that first.

Post back when you try this.

 

[debassige]

Re-flowing was my first thought and will be the first thing I'll try tomorrow.  I am literally hundreds of miles from anywhere in the middle of a desert so access to spare parts and tools is somewhat limited although I'm sure i can scrounge up some jumpers.

What will shorting out the inputs do?

just rechecked things again.  The static was not present in the output stage (just big tube plugged in) but a soon as the small tube (input stage) is added the static is present.  With just the small tube in there is nothing but if the big tube is the output stage that would make sense so the problem seems to be with the input stage, I'm guessing? but will troubleshoot tomorrow and see what happens (I was sure there was static with just the big tube installed earlier, maybe not?)

Thanks

Despite the problems I am having this was a very easy kit to build and the directions were spot on, once I've diagnosed the amp and have used it for a while i will probably pick up either another Bottlehead amp or upgrade the Crack.  I am going to reread the directions to get a better understanding of the circuit, kind of rushed things the first time.

 

[Grainger49]

Shorting the inputs keeps them from picking up RFI or EMI.  It eliminates any hum that an open input can cause.  It doesn't always cause hum but sometimes does.

And now you have found that the static is in the input stage.  It could be the tube.  I'll bet there are no replacement tubes in the middle of the desert hundreds of miles from anywhere.  So you can't tie that down. 

With just the input tube in there is an open circuit at the output.  But your troubleshooting has tied the problem to the input stage.  It doesn't have to be the tube.  It could be that the tube socket has a little corrosion on it.  It is new but no one knows how many years ago it was made.  So try putting the tube in and pulling it about 6 times.  This cleans both the tube pins and the socket.  I get that "scratchy noise" (what it was often called in the 70s) every so often and this cures it for me.  It could be the volume control.  Running it up and down (with the Crack off) a dozen times might help. 

Doc's new instructions are incredible!  I have built kits since 1964.  Nothing compares!

 

[ironbut]

The first thing is to do your voltage checks. I wouldn't be surprised it that checks out though since many meters kinda average out transient voltage irregularities if they're fast.
After that, do as Grainger suggested and plug and unplug the tubes a few times to clean the pins and sockets.
Also, after the unit has been powered down for an hour or so, go through and lightly wiggle all the wires and components to be sure that all the solder joints are holding on tight. One or two may just look good. (pay particular attention to the spots where a single wire is routed "through" one connection and ends on another like the ground on the headphone jack, both should be soldered).
Even if none seem loose, reflow the solder on all the joints.

Going into a little more detail about what the noise sounds like would be nice.
You said it was a static sound. Is it snappy, hissy, poppy sounding?
Noisy tubes have a poppy, bubbly sound to them. Sometimes this kind of noise will go away with tube burn in.
Also, you said the noise was loud. Is it loud like screaming guitars loud or more like the level of brushwork on a snare in the background?

 

[jrebman]

I'm guessing you'll find something amiss around the 9-pin tube socket, and as you mentioned that one of the LEDs was dimmer than the other, that's probably where I'd look for a cold solder joint first.

If you've got a bad tube and can't find one in the middle of the desert, I have some spare 12au7s and I could send you one.  No gurantees of how great a tube it is, but it is tested and will work.

Good luck, though I think this should be an easy fix.

-- Jim

 

[debassige]

Good news, static is gone!!!  I re-flowed every joint and the static is gone, I am one happy camper

Thanks to everyone for their help.

I don't have what might be considered an appropriate set of phones currently to test the amp to it's full potential, currently all my headphones (3 pairs) are below 64 ohms but in about 2 weeks I'll return to civilization where I have a few to choose from and I'll bring a few pair back with me (including a pair of T1's), however listening to it through a cheap pair of panasonics, I'm impressed and I do have a pair of 701's with me that, although not the best match for the amp, really sound nice (forgive my lack of audio terminology).

Running the amp straight through my laptop their is a noticeable amount of background noise but running it straight from an MP3 player it is dead silent (which leads me to believe the computer is the culprit) would a DAC solve this problem?

Thanks again for everyone's help and should I ever run across a thread like mine I certainly will have some input, RE-FLOW!!!

 

[JC]

Good for you!

I can tell you that my PC sound card is very noisy, and I am hoping that taking the digits out to a DAC solves the problem; otherwise, the whole notion of computer-based sound is going to lose its appeal very quickly.

 

[Grainger49]

Sounds like you are in business now.  Move the PC as far away from your Crack as possible.  The computer generates noise that tubes can pick up.  Luckily the noise diminishes with the square of th distance you move away.  A normal length connector at full length should help. 

But that won't help the noise generated by the sound card that JC mentions.