Burning through Pilot Light Bulbs

[Mitch]

Hi Beezlebum,

Now that you point out how the circuit is wired, it totally makes sense that I can’t get a proper reading of that resistor value while it it soldered in place – thanks for pointing that out. I was going along measuring resistors on the eyelet board, and they were all measuring at the expected values except for that one – but now I clearly see why the measurement wouldn’t work for that one. I’m learning quite a bit from this process – thanks!

Robin – I’ve had inconsistent results with poking at various components to see if the noise changes/goes away. Most recently, it seems like poking at the eyelet board doesn’t do anything about the noise. A few days ago, it seemed like poking at *anything* on the board would stop the noise.

As far as the speaker question, here is what I’ve tried:

– 8″ speaker alone
– 10″ speaker alone
– both speakers together
– amp plugged in to external 1×12″ 16 ohm egnater cabinet with impedance switch on amp set to 8 ohms.

The static noise is the same in all cases.

Two additional observations:

1. Turning down the tone pot makes the noise much reduced – but I think that this is only because the noise is in the high frequencies, so it is “rolled off” when the tone control is turned down. I disconnected to the tone control from the volume pot, and the noise is still there.

2. The noise is not there when the amp is just turned on from a “cold” state. It becomes audible after about 3 – 5 minutes. If the amp is briefly powered off to switch tubes, the noise is there immediately with the new tube, so it doesn’t seem to be a function of the tube warming up, but some other part of the amp.

Thanks,
Mitch

[beelzebum]

Is there any change when you switch the boost switch? Also where are you grounding the tone and volume pots. If you are grounding them back to the pot cans themselves, then are they even making a good ground? If you can post some pictures, that would be helpful.

[Mitch]

Hi Beezlebum,

The boost switch does not have any effect on the noise. I grounded the volume pot to itself (back of the pot can), and the ground tab on the tone pot is connected to the back of the can by way of the .0047 uF capacitor as shown in the chassis layout diagram. The nuts holding the pots on are screwed down pretty tight, so I think the pots are grounded well. The next time I get a chance to troubleshoot some more, I’ll try to jumper a different ground to the pots, to see if that has any effect.

I uploaded a few photos of the chassis to my profile page under the photo album “TAN 2 Stroke.” At the moment this seems to be the only way I can get pictures online. If there are other photos that would be useful to see, I would be happy to take more pictures and post them to that album.

Thanks!
Mitch

[beelzebum]

I looked at the images you have. I can’t tell from the image, but do you have both resistors installed on your input jack. I couldn’t see the 68k grid stopper between the jack tip and pin 2 of the 12ax7.

[Mitch]

Hi Beelzebum,

I do have a 68Kohm resistor between the jack tip and pin 2 of the 12ax7.

Tonight I put together an “audio probe” as per the instructions on the billmaudio site (thanks Robin for the suggestion!):

http://billmaudio.com/wp/?page_id=1254

I wasn’t able to locate where in the signal path the noise begins, because I have to have the amp turned up too loud for nighttime use in order to consistently generate the static noise. I’m hoping that I’ll be able to locate the problem component with this probe.

Thanks for the continued suggestions,
Mitch

[Mitch]

Hello again,

Thanks to Robin’s help, I think the noise has been located and eliminated. It seems that it was a poor connection in the socket of pin 8 on the power tube. Tightening that socket “clip” seems to have taken care of the strange static. Apparently my previous efforts to tighten up those sockets were not sufficient.

Thanks to all who chimed in with suggestions and advice – I’ve learned a lot more about how the amp works as the result of chasing this noise around!

Mitch

[Andy]

Sweet!

I learn more from something wrong than everything right Congrats on getting it figured out.

[Robin]

I hope that resolved it. Being that it was an intermittent problem and we could not make it happen again after tensioning the socket, it seems likes it’s fixed. Mitch’s built quality was very good with great solder technique. The scratch built cabinet looks great too, I’m looking forward to seeing it covered. Congratulations, Mitch

[Mitch]

I only got to play guitar for about 15 minutes today, but so far – no static noise!

Thanks again to everyone here, and especially to Robin, for spending some of his Sunday troubleshooting the static with me. His work looks (and sounds) even better in person than it does here on the site!

Mitch

[Robin]

Thanks Mitch,

[Mitch]

Hello,

Just a short follow up to an old discussion. The static noise that Robin helped me eliminate eventually returned, and I decided to replace the power and rectifier tube sockets. The socket for the pre-amp tube fits quite snugly, but the power and rectifier tubes seemed somewhat loose in the original sockets.

I replaced the sockets with Belton “fork type” sockets (instead of the sleeve type sockets that came with the kit). The tubes fit much more snugly in these sockets.

Since replacing the sockets, the noise has not returned at all, even though I have been playing the amp almost daily for the last couple of weeks. I wanted to share this info in case anyone else runs across a similar problem in the future.

Again, I would like to thank everyone who offered help in tracking down the problem!

Mitch

[Robin]

I have been having to re-tension a number of brand new octal sockets lately. These have nothing to do with the TAN kit but they make weak contact just the same. Maybe I’ll try another manufacturer too.

[Andy]

We may have to switch over to the Micalex sockets. They seem to have fewer problems these days. I kinda liked to stay with the ceramic for the vintage vibe, but if they cause issues, then we will switch.

[Mitch]

Hi again,

Well, it looks like I wrote my last message a few days too soon. After over 2 weeks of static-free operation, my Two-stroke started up again with the static noise again yesterday.

At one point, the static became so pronounced and sustained, that it continued even after I turned the volume knob to zero (this is not typically the case – usually the noise goes away when I dampen the strings or turn the volume down).

Why would the noise go away after Robin re-tensioned the sleeves in the power tube socket, and then return in a few weeks? And then repeat this pattern by vanishing after I replaced the tube sockets, but then returning again in another 2-3 weeks?

Any ideas about what kind of problem would manifest in that way?

Thanks,
Mitch

[Author]

Posts