noisy tube issues

[bsco]

I have a question....for somebody......when testing for noisy tubes, how do some of you more experienced guys deal with that issue??? Please don't say "replace it and see what happens"....I am referring to pre-amp tubes which when sitting idle with volumes turned up and tone controls set at say 12 o'clock, you hear a sort of crackling or sizzling sound from the speaker....and maybe some small gentle pops......and if you gently strike the side of the tube with say a plastic writing pen, depending on where you strike it, you could get loud cracks and pops.....or do I have the volume controls turned up too high.....

Of course....... When the volume control(s), are turned down you don't hear it....I am referring to new tubes here and it seems the brands don't matter much...just a question I am throwing out there......just to get some ideas from people with more experience than me....
Cheers

[The Dude]

Firstly, I would check tube pins and socket pins (clean and re-tension). Make sure that it's not the socket arcing instead of the tube. Aside from that, if the tube itself is bad, what choice do you have? It's a defective part and you replace it just like you would any other part. Saying that, I have found that sometimes you can move tubes to different locations in the same amp and they work fine.

[Tone Meister]

Firstly, I would check tube pins and socket pins (clean and retention). Make sure that it's not the socket arcing instead of the tube. Aside from that, if the tube itself is bad, what choice do you have? It's a defective part and you replace it just like you would any other part. Saying that, I have found that sometimes you can move tubes to different locations in the same amp and they work fine.

What he said ^^^

[g1]

"replace it and see what happens" can be a crap shoot with modern tubes.
You need a reference, or benchmark tube that you know is average, or quiet, or something.
Then you can get an idea if it is the amp or a tube.
I usually have a few new ones on hand and check them in a known good amp, in the most sensitive spot, like V1 or V2 position. Then I put the quiet ones aside and exchange the noisy ones for more unknown new ones that I will have to test .

[bsco]

thanks guys...I found a video on youtube...this guy had a test fixture built and was using a scope to check for noisy tubes.........maybe instead of building a test fixture which consists basically of a class A amp, I could use the current guitar amp (V1 location) instead......run a signal in and then scope the output....this however will mean taking it apart...more time involved........but not a big lot more.....I am going to try that sometime this week to see how it works out............
Cheers

[Enzo]

With the existing amp method, you don;t need to scope it really, just use your ears.



Long ago I worked on currency validators - dollar bill acceptors for change machines, like you see in a laundromat or arcade. In them are hoppers ful of coins, they vend coins out once a dollar bill is accepted in. Each hopper has a control card. I made a test fixture for the cards. An edge connector on top for the card, and a power supply within. Then There were buttons to increment the coin sensor input, and output indicators to show the pulses that would control the solenoids in the vendor part. I added thumbwheel switches to take the place of the programming input - number of coins per bill. It worked really well. I could hit the vend button, watch the motor run light come on, watch the vend pulses, and input coin detections as it counted them out. I could in seconds see if every function was working. I took some nice photos and sent them and a schematic down to the company that made the change machines.

They were impressed. They said they knocked one together and it worked really well. They suggested a couple small refinements. But mostly they told me, "This is pretty cool, but down here, if we want to know if a card is working, we just stick it in a machine and find out."

[J M Fahey]

^^^^^^^^^^^^^^^^^^^^

The way PC cards (or motherboards or hard disks or .... )
Hardly anybody pulls a Digital Analyzer or whatever, a very fast scope,etc. , they simply plug suspect board in a known good motherboard.

That said, noise is much simpler, if you dare to build it I'll draw and post a Noise Meter, to put some numbers into it (TM)

Basically a suitable socket, a couple switches, some parts , an Op Amp and suitable supplies for everybody (+200/250V - 6.3VAC - +/-15V)

[Leo_Gnardo]

I have a question....for somebody......when testing for noisy tubes, how do some of you more experienced guys deal with that issue??? Please don't say "replace it and see what happens"....I am referring to pre-amp tubes which when sitting idle with volumes turned up and tone controls set at say 12 o'clock, you hear a sort of crackling or sizzling sound from the speaker....and maybe some small gentle pops......and if you gently strike the side of the tube with say a plastic writing pen, depending on where you strike it, you could get loud cracks and pops.....or do I have the volume controls turned up too high.....

First of all, logic tells us the tube involved prior to the VC is the noise culprit, and I'm sure you have that idea squared away no problem... Noisy tubes in early stages get their noise multiplied/amplified by subsequent stages. That's why, in some cases you can use those tubes in later stages and the noise is not apparent. After that it IS a matter of try different tubes.

In some amps like Fenders with their black cardboard, noise can be generated by current leakage thru the board. This has flummoxed thousands of musicians and repair people too. Also plate resistors and even cathode resistors can add a lot of hiss and crackle. If you try a bunch of tubes in a socket and similar noises in all, start suspecting these R's and the board they're on besides. Failing interstage and EQ caps can also be at fault.

Volumes turned too high? In my quiet workshop, late at night and perhaps with too much caffeine, little noises don't sound so little. Spent many an hour trying to chase down what amounts to a triviality in the light of day and even more so with a little ambient noise around. And even more more so when used in a band setting. A couple hits on the snare and cymbals, guitar amp noises fade far into the background. If you find yourself chasing your tail, give it some time off and try again later. Might turn out to be over-concentration, we can all do that sometimes I'm sure.

[bsco]

Thanks guys......I do know the fastest way to test for noisy tubes is to replace them....I have had 3 or four amps here now that have had tube problems....funny thing some of the new replacements are worse than the originals.....but I know what you are saying...resistors can also cause it as bad solder joints, etc....I was just wondering if scoping such circuits would indicate if it was a tube issue or a component issue.....thank you everybody for your advice.....I might go ahead and try it anyway just for the experience if nothing else.......and to Enzo....I used to work for a Lottery...and we had tons of bill aceptors and coin mechs, RGB monitors tons of printer's and printer interface boards and main motherboards.....mostly VLC, Merit. IGT, Hi-Tech, Spielo's infamous "Swinging Bells" game......etc.......plus all the machines that sell lottery tickets for the 6/49 money pot.......and god knows what else...point taken my friend.........
Cheers

[bsco]

Leo....speaking of Fender cardboard issues........what is the best way to clean, de-oxize and seal these suckers without having to tear everything apart??? Or is that even possible??I never had to do one yet.....but it might be a good idea to know up front what would be involved should the occasion occur........Thank you very much.....
Cheers

[Enzo]

I use a heat gun. it works for me.

The boards build up a waxy coating - kinda hazy. I start at one end of the board and go along, like I was defrosting my car windshield with a hair dryer. I can see the change in appearance on the board as the contamination cooks off.

[52 Bill]

If you look for it you can probably find a photo of the original Groove Tube factory tour where there's a photo of a guy sitting behind a Fender Super Reverb or Concert amp. He's wearing headphones that are plugged into the speaker out jack and he is tapping on a preamp tube with a small pencil or whatever. This was their test for microphonic tubes.

I find that heat is best thing to dry out the black fiberboard circuit cards. Hot air from a heatgun or a rework station will often do wonders for the wet, noisy board. In fact to tie a couple of threads together here, I once had a Champ that would cause the guitar volume control to make scratchy noises when turned. Measured a small amount of dc on the input jack. Tried changing the preamp tube, no change. Cleaned and heat dried the board in the preamp section, voltage was gone.

[bsco]

Thank you both Enzo and 52 Bill.......You have been very helpful....
Cheers,
Bernie

[bsco]

I did manage to do a scope test on an amp I had apart....just a very short while ago.... I had the channel set to AC at 50mV per division.....with the volumes turned down, the spikes that showed up when gently tapping the tube were pretty much full scale.....even at .2V per division they were still fairly big......I installed another tube at the same location and there was a big difference in the scope display...so, I guess if the circuit is easily accessible as in most Fenders,then it might be worth doing.....if the the chassis has to be pulled say like a Marshall just for this test then it would not be feasable as far as time is concerned.....but if the chassis was pulled due to another reason, then it might be worth the few extra minutes that it will take to preform it....but as most of you have stated, direct substitution is definately the fastest especially when you have a fairly large number of spare tubes to pick from....and you guys are also correct in stating that a noisy V1 orV2 tube can be re-located to another position to also solve the noise problem........I thank everybody for their help.....
Cheers,
Bernie