Burning through Pilot Light Bulbs

[Robin]

Have you tried a different power tube? Does the static stop if you touch or move the tube slightly in the socket?

[Don Frantz]

I finished a Two Stroke a couple months ago and had the same pilot light problem. Burned out two, got one from Radio Shack and it worked. Maybe there’s a bad batch?

[Andy]

Yeah, it appears that there were some of the 3V pilot lamps in the box of 6.3V lamps. Sorry about that guys. I’ll be checking that going forward.

[Mitch]

Hi Again,

I had a little bit more time today to try and troubleshoot this static issue. I’m 99% sure it isn’t speaker related, since I got the same static sound when I played the amp through an external 1×12 cabinet. To check the grounding of the output jacks, I connected an alligator clip between the soldered ground connection on one of the output jacks and the ground terminal strip attached to the power transformer – this had no effect on the static sound.

It also doesn’t seem to be a bad power tube, since I got the exact same noise when I switched the power tube to the EL34 that came with the kit.

Today when the static was happening, wiggling the power tube and poking at the power tube socket pins did NOT have any effect on the static. However, poking at the solder connections on the eyelet board did – at first – seem to have an effect, although I could never isolate a particular connection. It seemed like poking at any solder connection on the board would cause the problem to stop. After a few minutes of this, however, the eyelet board poking stopped having any effect on the static.

I made a recording of the static, but I still haven’t had any luck getting attachments to work. I don’t know if hearing the sound would be of any help, but I could email an MP3 file of the offending noise to anyone who has a minute to listen to it – or if there is someone else who could attach the file to a post here on the board, I could email it to that person.

Again, thanks to everyone here for your time and assistance!

Mitch

[Robin]

If torquing the board causes the noise, that would indicate a marginal solder joint or a loose connection. It’s possible that one of the components has a faulty lead too, so push on the caps and resistors.

[Mitch]

Thanks Robin,

I think maybe I’m going to have to just go over each of the solder joints again, since I can’t seem to isolate the problem to one of them in particular.

I’ll report back after I have a chance to do that.

Mitch

[beelzebum]

You stated earlier that when you mute the strings, the static stops. Are these still the symptoms? If so, this sounds more like an induced noise into the input on your preamp tube. By touching the strings of your guitar it ends up eliminating the noise by grounding you to the amps ground. Poking around with the chopstick, depending on where you poke, might just be a coincidence. Or you have a loose spot on the preamp tube also.

[Mitch]

Hi Beelzebum,

Yes – if I touch the guitar strings, the noise stops.

If I don’t touch the guitar strings, the noise eventually fades out – sometimes within a couple of seconds, but sometimes it will persist for much longer (on the order of 20 seconds or more – by that point, I’ve usually touched something on the guitar or amp that stops the sound).

By induced noise, do you mean that the noise is coming from the guitar? I’ve tried different guitars, single coils, humbuckers, etc. – and they all make the noise. When the same guitars are plugged into my other amps, they don’t produce this static noise.

I’m still trying to figure out a way to get a recording of the noise posted here – but in the meantime the best way that I can describe it is still “static.” It doesn’t sound like distortion, it sounds like radio static.

Thanks again for everyone’s continued input – I very much appreciate the suggestions and advice.

Mitch

[Andy]

Send me the mp3 at andy at tubeampnetwork dot com and I will see if I can’t get it posted.

[Andy]

Here is an MP3 file of the static that Mitch is experiencing.

[attachment=101]static.mp3[/attachment]

[Robin]

Definitely not the way a Two Stoke is suppose to sound. I’ve never heard one do that before. If you’re sure it’s not a bad tube or the speaker, I would suspect another component. Double check that you have the feedback loop wired correctly (from the OT).

[Mitch]

Thanks Andy for posting the MP3 file!

Thanks Robin for the suggestion. Just to be sure I’m pointed in the right direction, the feedback loop you are talking about is the 68Kohm resistor between the speaker output jack and pin 8 of the preamp tube, correct?

Mitch

[Mitch]

OK – I double checked the 68Kohm resistor in the feedback loop, and it measures at 1.5Kohms on my multimeter. The stripes say that it should be 68Kohms, and I’m 90% sure that it measured correctly when I checked all the parts before soldering up the eyelet board. It must have become damaged somehow during assembly.

I’ll buy some new 68Kohm resistors tomorrow and see what happens if I replace it.

As always, thanks for all the help!
Mitch

[beelzebum]

The 68k feedback resistor must be measured out of circuit. if you look at the schematic, one end ties to the top of the 1.5k cathode resistor, which itself is tied to ground. On the other end, Of the 68k, it is tied to the output transformer, which is also tied to ground. The output transformer will show almost no resistance when measured with the meter. So if you read it in the circuit, it would only show you the 1.5k next to it. I would guess that the 68k resistor is fine, you can double check if you want, but you must at least remove one of the leads.

[Robin]

I was not suggesting that the feedback loop component values are incorrect, only that perhaps there might be a problem with the component itself, like a broken lead (even internally). You can usually prove that by poking the component itself and see if it makes the symptom better or worse. You are sure it’s not the speaker?

[Author]

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