Microphonic power tubes?

[Tubetec]

Its common to find one tube in a used set that has worse microphony than the rest , .
Theres no doubt microphonic powertubes have an effect on the sound ,especially when the amp is cranked , thats the only way to satisfactorily test them ,under actual usage .

 

[radardoug]

There is a very simple test for microphonic tubes. Tap them. If they make noise it indicates loose connections in the tube.
If an output tube is microphonic, change it.

 

[jdurango]

There is a very simple test for microphonic tubes. Tap them. If they make noise it indicates loose connections in the tube.
If an output tube is microphonic, change it.

Yeah, as you can see in the video () they are definitely mirophonic (make noise when tapped or even wiggled). To what extent this is a problem, that's what I'm trying to discern. From what I'm gathering, it sounds like it's not ideal, it's not normal, but to what extent it's acceptable or not is really dependant on how much it affects the sound and how picky the player is about tone. I'm pretty damn picky about tone....it's everything. I play pretty much 100% clean, no pedals, no effects, no amp sims or digital crap....so it's all about tone for me.

 

[CJ]

Do you have tube retainers on the sockets?

Matching isn't important unless you are running quads, the output transformer will take care of mismatch on a pair.

For quads I usually put like say two number 8's on one side and say two number 10's on the other side. Set the bias to split the difference.

Not so good to run an 8 and a 10 on one end of the xfmr as the 10 will hog current and age faster, or bias will run away and you will have a meltdown.

I can see agonizing over tube matching and microphonics for audiophile amps but a guitar amp? You have to be joking. At least in this town where every amp I service comes in with every knob dimed. I can't even go to a show anymore because I serviced every amp within a 100 mile radius and I don't want to worry about an amp blowing up while I am there as they will want me to fix it on the spot with duct tape and a coat hanger.

One guy kept bringing his Carvin back. So I went to a show to see why. So what he does is get completely whacked on drugs and alcohol, sets the amp on 11 with stomp box and just let's the amp feed back at 500 kc for ten minutes. After I saw that I built him a p to p jtm 45 on the carvin chassis and he has not been back sense.

VTV drops a weight from a fixed height to quantify microphonics.

If you gig on a regular basis you will replace tubes once a year so just let it go and hope for less noise on he next batch.

I swear the best amps have heard have microphonic preamp tubes and mismatched phase inverter tubes. I think I have done about 1500 amps in the last 10 years.

And remember, once you get past 20 watts on a pair of 6l6 or el 34, where you set the bias makes absolutely no difference in sound as you are swinging the grids well past the point of caring. Now if you like light jazz, warm that bias up a bit.

My favorite amp is a Princeton reverb with bugle boy 60's Holland el84's into a Fisher output into an Allesendro 10 inch.

Old rca and ge sound so magical and last so long compared to today's junk that any extra noise is worth it. Especially with the war in Ukraine making the price of new tubes ridiculous.

Oh, and one more thing before I get off my soapbox: long tail phase inverters suck donkey.
.

 

[abbey road d enfer]

Yeah, as you can see in the video they are definitely mirophonic

I would definitely suspect oxydized socket/pins.

 

[CJ]

You should also replace or retension tube sockets.

Make yourself a dental pick by taking a small screwdriver and grinding it down to a point small enough to get in there.

 

[jdurango]

I"ll look into retensioning and cleaning them, replacing would be a big PITA. Thanks fellas!

 

[musipol]

Based on servicing many tube amps over the years, that amount of microphonics seems quite acceptable. I agree with the other guys that you should play the thing, at volume, and listen for weird noises (low freq osc, etc). If none, I wouldn't sweat it.

 

[drtechno]

When power tubes wear out they get a hiss and become microphonic.

But in the video that is normal for some plate designs. When you spring load mount them this actually goes away. To make it go away, you can do what the audiophile do and put tube dampeners on them, but its only a placebo to the ones that don't know that this is normal.

 

[seanweaverguitar]

If the preamp tubes are microphonic, you can scrape the pins until they're shiny and wrap a few turns of electrical tape around the glass to get them to behave..

Not sure if you'll ever see this but found this via Google even though I'm a member here on GroupDIY.

Sorting out some tubes in a guitar amp, I have a lovely NOS GE in the phase inverter position that is fine, but in V1 is unusably microphonic. I found this out by swapping positions due to a modern production Sovtek that went too microphonic for recording. In the end, I had to rob an unused (and from this forum I understand unlikable; not worth modding) old channel strip I bought cheep years ago and never use anymore (HHB Radius 40). Was able to pull a Sovtek out of that in order to preserve my guitar amp stash in-house. Vintage guitar amps win over unused cheap channel strips with transformerless mic pres. So about microphonics.....

Legitimately asking to learn since I've been doing guitar stuff for so long and a tube degenerate completely. I've never heard of this before. What does scraping the pins do to relieve microphonics? And would Eurotubes dampeners be just as well as electrical tape? Modern tubes whatever, but I really loathe sending old ones to the trash bin.

 

[abbey road d enfer]

There are several causes for tube microphony. Oxidization of pins is one. By removing oxidization, one of these sources is (temporarily) eliminated.
I don't believe that any kind of dampener can quiet down a tube when microphony is due to loose parts.

 

[Wavelength]

Gang,
Oxidation usually presents itself as more of an on/off kind of noise, pops and clicks as the electric contact is conducting or not. This can happen at the pin level of the tube or the socket contact. I really stay away from the spays at the socket and have some really fine wire brushes made to clean sockets. The spray on tube pins does seem to work.

If the tube is truly microphonic then it needs replacing. Microphonics can happen when the grid is either pulling current or if the tension in the grid (or screen) is somehow faulty. If the grid is pulling current there could be another problem and that is if the power supply is low compared to what is should be. Find the tube by using the volume controls. If you turn down the volume to 0 and you hit the chassis lightly and still here it then it's after the tone stack. If not then it's probably one of the first tubes.

REMEMBER, turn off the amp let it cool down remove the tube, replace it then power up again. Let it cool down, rectifier tubes love to fail if everything is still warm especially GZ34/5AR4 and other indirectly heated rectifiers.