Tube noise issue

[rwinking]

I am having a tube noise issue in a combo amp  I turn the amp on and there is no noise. After it is on and heated up,  I hear this microphonic noise when I hit certain low notes, usually on the neck pickup. At first I thought it was the speaker making the tube sound microphonic but then I realized that it did not do it until after it is warmed up.  Of course the first thing I did was change out the tubes and put a brand new pair of EL84s in. Same thing, same noise.  I also tried bypassing the speaker and used an extension. No noise there. So the speaker is somehow rattling the tube and making it do the microphonic thing. But then, why is it it only does it after heating up for about 15 minutes? And why two different sets of tubes? Can a tube socket do this?

I would love to hear opinions on this. I would love to take it in to a tech but I live in a small town. One guy (an old marine electronics guy) will not work on any amp made after 1970. Another guy is really young and doesn't get tubes at all. The third guy has Alex Jones on the radio and yells about Hillary running a child sex ring out of a pizzeria and Sandy Hook was phony.

rick

 

PS if anyone knows a good tech that would like to relocate to the mountain west, there is a lot of work here!

[y2kc]

None of those choices sound good. Is this with all of your guitars? 

[rwinking]

Yep. Strat or H-150.

Yeah, my choices of tech are not good. The best one is the Alex Jones fan. He truly knows what he is doing but has a tiny little shop and since "covid-19 is fake" you can't wear a mask in his shop. It was hard enough to deal with his Alex Jones ramblings but I am not about to put my health at risk by going into his shop.

CAn tube sockets get dirty and do this? I have not tried spraying the contacts on the tubes yet....

If I have an idea what it is, the kid that doesn't get tubes might be able to help. Otherwise I have to take it up to Missoula Montana. At least Christopher AKA zguitar from this forum lives up there.

[mars_hall]

You mention microphonics then talk about swapping out the output tubes.  Microphonics usually occurs, if it is going to, within first few tubes in the preamp.  Rap them lightly with a pencil eraser and see if the noise occurs.

Sockets can get dirty, but not likely the cause.

 

My two cents

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[Steiner]

12 minutes ago, mars_hall said:

You mention microphonics then talk about swapping out the output tubes.  Microphonics usually occurs, if it is going to, within first few tubes in the preamp.  Rap them lightly with a pencil eraser and see if the noise occurs.

Sockets can get dirty, but not likely the cause.

 

My two cents

.

There's the right answer.

[rwinking]

Ah Ha! I did not swap out the pre amp tubes. I have one of those Orange tube testers so when I get in the studio, I will focus on them. Thanks so much. It sounds like I will be happy once more and I didn't have to deal with crazy people to get there. you guys are the best!

[kbp810]

Tube testers don’t always catch microphonics; as Mars_hall mentioned, with the amp on and warmed up, tap on the tubes with a pencil or stick or something; a microphonic tube will clearly reproduce the tap as sound. Replace that tube/tubes. 

[pressure]

I tap tubes with a chopstick. Chopsticks are very useful Grasshopper.

[DetroitBlues]

When you're finished, for good measure, there are special rings you can install on tubes to prevent them from vibrating.  Might want to get some of those tube tamers for the future.

[rwinking]

Yep. I have a few of those silicon tube rings around. Usually they work really well.

thx

[TalismanRich]

I had the same issue in my Princeton type amp.   It was preamp tubes that were rattling.   I popped out V1 and replaced it, all was quiet again.  

Combo amps always seem to rattle the cages a lot.

[rockabilly69]

sometimes it's the rectifier tube that you hear a rattle from, I know it sounds ridiculous, but it happens!

[bolero]

ah, the infamous rectumfrier tube....rectum, damn near killed him?

 

anytime that has happened to me, it's been a preamp tube

[rockabilly69]

3 hours ago, bolero said:

ah, the infamous rectumfrier tube....rectum, damn near killed him?

ouch

[loudtubeamps]

Electro Harmonix 12 at's are particularly bad for being microphonic right out of the box.

I needed a replacement for the phase inverter for a customer..I went through 8 or 10 that I had in stock before I gave up and put a 40 year old RCA 12 at in as a temporary replacement.

Four years later, the owner is still running that tube and is happy leaving it as is.

 As mentioned, warm the amp up, volume up..guitar plugged in but volume off.

Hold the base of each tube and give them a gentle flick with your finger..the output tubes can be noisy (more of a rattle than chime) just as much as any of the pre amp tubes and again as mentioned, the first tube in the gain stage is prone to being the loudest for microphonic chime.

[rooster]

On 9/8/2020 at 7:48 PM, pressure said:

I tap tubes with a chopstick. Chopsticks are very useful Grasshopper.

Absolutely. Sometimes you get microphonics off of the circuit board (cold solder joints, loose IC sockets, etc.), and chopsticks don't have any especially conductive elements in them (such as the metal ring that holds the eraser on or the graphite that forms the pencil lead on the other side). Watch the Guitologist on his YouTube channel, and he has some good tricks for tracing down noise in amps.

 

rooster.

[Gianluca]

interesting thread ?

[tbonesullivan]

Any updates? Definitely sounds more likely to be a preamp tube issue than a power tube issue. With everything in the combo, there are even other things that can start to resonate as well.

Pretty much any preamp tube, if you tap it hard enough, will produce an audible sound. However microphonic tubes will "ring" when you tap them. It could also be that a particular part of the chassis or circuit board, once warmed up, is resonating, and causing a preamp tube to resonate with it.