One of my amps has started making a soft crackling noise. The noise sounds like a combination of static and rustling leaves.
The amp in question is a Weber 5F1 Champ clone that I built about 5 years ago. It is modified with a 5F2A tone stack replacing the low level input jack. Speaker is a Weber 8" alnico.
Troubleshooting to date is as follows:
1. Replaced the 12AX7, 6V6GT, and 5Y3 tubes with new ones. No real change in the noise but the original 6V6GT apparently was on the way out as the new tube (JJ 6V6S) sounds louder and better.
2. Checked all mechanical and soldered grounds, all are good.
3. Touched up a few suspicious looking solder joints and replaced the wire to ground from the 12AX7 cathode resistor and bypass cap.
4. Tubes are not microphonic. Tapping on the solder joints between the input jack and the grid input of the 12AX7 with a wooden chop stick creates some noise but I think that is to be expected.
5. Cleaned volume and tone pot with Deoxit.
6. Noise seems to be in the 12AX7 stage as it goes away when the tube is pulled or volume turned down.
7. Tube sockets all cleaned.
8. Noise seems to increase as amp warms up.
All this has resulted in a noticeable decrease in the noise but it is still present. It is not hiss.
Any other suggestions or thoughts?
Amp Noise
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Stevem
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Re: Amp Noise
The noise is the plate load resistors ( pins 1 and 6 ) on the preamp tube .
They are likely 1/2 watt resistors there now and I would up them to 1 watt resistors and you will never have that issue again.
In rare instances I have had a cathode resistor become noisy ( off of pins 2 and 7 ) and even the 68k ( or whatever valve ) resistor off of each input jack go noisy.
I would replace these resistors with metal film types, not Carbon comp types while your in there!
They are likely 1/2 watt resistors there now and I would up them to 1 watt resistors and you will never have that issue again.
In rare instances I have had a cathode resistor become noisy ( off of pins 2 and 7 ) and even the 68k ( or whatever valve ) resistor off of each input jack go noisy.
I would replace these resistors with metal film types, not Carbon comp types while your in there!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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bluesky1958
- Posts: 5
- Joined: Sat Jun 20, 2020 6:12 am
Re: Amp Noise
Thanks. First useful response i have received. I can replace the 3 resistors in the input circuits quicker than more troubleshooting. They are all carbon or metal film already.
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bluesky1958
- Posts: 5
- Joined: Sat Jun 20, 2020 6:12 am
Re: Amp Noise
I decided to replace both plate resistors and the cathode resistor/bypass cap on the 12AX7.That seems to have done the trick. After a total of about an hour playing and just sitting idling there is just a barely audible hiss. I'm satisfied.