F-50 Tubes glowing blue..??? also fuzzy background noise

[dubber84]

Hey everyone, sorry for the noobish question here. I have an F-50, and the 2 6l6's in the back had a couple little blue spots reflecting on the glass of the tubes. I replaced the stock 6l6's after this with a pair of my cousin's JJ 6l6's, and experienced the same problem. There is also a fuzzy background noise as well. I'm not turning my amp back on till i get another set of mesa 6L6's, but in the meantime does anyone know what's going on? thanks-

 

[fdesalvo]

Not sure about the noise, but the blue glow is a normal and beautiful condition of a functioning vacuum tube!

 

[Brewski]

Is the fuzzy noise sort of a soft metallic ringing or tambourine sort of sound? If so, try tightening the aluminum metal retainer bar that goes across the back of the amp. I had that sound with my F-50 and found that mine was slightly loose and I'd get that tambourine sound from it vibrating.

 

[vulture2600]

usually when a tube glows blue or purplish it means its leaking and oxygen is being burned.

 

[Red Barchetta]

AAAAAAAHHHHHHHHHHHH!!!!!! NO fdesalvo!!!!! Bad toad...bad!!!!


The blue glow is NOT normal....it means there has been oxygen introduced into the tube and thats BAD BAD BAD.



As far as the noise, it could just be that one of the tubes has gone microphonic.


RB

 

[Lespaulstandard]

from my experience, ALL tubes will glow blue.. it is from the electrons hitting the glass. Blue glow on the glass from holes in the plate structure is OK. Blue glow everywhere = BAD.

 

[fdesalvo]

Hahah, no blue glow = no electrons!!! Hahaha, yes, thee is an excessive amount to be considered.

 

[cnumb44]

Here's something I found:

From "Sylvania Engineering Data Service", vol. 1, pg 23 (1960?):

BLUE GLOWS

Blue Glows are not tube detriments per se. They are, however, suspects in the eyes of many receiving tube users for lack of a full understanding of their origins. There are several types of Blue Glow which can be described as follows:

FLUORESCENCE-this type of glow is usually violet in color and most noticeable around the inside surface of the glass bulb. It is most pronounced on power tubes and is the product of electron bombardment of the glass taking place within the tube. It generally has no adverse affect upon receiver performance, and in fact, tubes displaying this phenomenon are particularily good with respect to gas content.

MERCURY VAPOR HAZE-is a blue-violet glow associated with those tube types which rely upon mercury vapor for proper operation. In such cases, the blue glow should be evident indicating proper operation.

GAS-produces a blue haze, generally confined to the vicinity of the mount structure. The proper function of gas types such as thyratrons, voltage regulator and voltage reference tubes, requires the presence of this glow as an indication of proper tube operation. Some voltage regulators use neon instead of argon and as a result exhibit a pink-orange glow. It is, however, a distinct detriment in vacuum receiving types, where the presence of gas in large amounts can cause malfunction of the equipment.

 

[dubber84]

thanks for the help...

replaced the 6l6's with a new mesa set, problem was solved for a bit but then i got some crackling => hum and it sounds like the fuse blew. So I'll have to order a new fuse from mesa...i guess i should order a 12ax7 as well, maybe it was my preamp tube that went bad (but i took it out and it looked fine...though i guess it could still be a bad tube)

 

[dubber84]

ok i replaced the fuse with a new 2 amp 250v and...it blew after about 5 seconds.

Is this likely a problem with the tubes? i guess i'll have to take it in to get looked at

 

[Red Barchetta]

I've had fuse blow problems with other amps on 4 or 5 different occasions, and in 3 of them, the tech traced the problem back to a shorted out tube. (1 power and 2 preamp)


RB

 

[dubber84]

ok so i took the amp back to guitar center to talk to the guy about the problem, and they actually gave me a new amp on the spot. now this was probably stupid, but i didn't try it out there (because they had just gotten it in, brand spankin' new pretty much).

i get back home, let it warm up and flip the standby switch and the same damned fuzzy sound greets me. this is NOT normal, the f-50 i originally reported problems with was fine for a couple months before acting up. It doesn't matter if the guitar is plugged in or not. It doesn't matter if the effects loop is at 10 or 90 or if there's even any cables plugged in to the effects loop. It is most definitely something with the amp...i switched the 6l6's around and swapped the v1 and v2 12ax7's and still the same problem. Also got a temporary volume drop again. I'm about to jump off a friggin cliff. :evil:


btw the fuzzy sound sounds like static...almost like the sound you get from an fm radio when it's not getting a station and it is erratic.

 

[MesieBooga]

I've had bad power tubes when that static sound happens. Did you try tapping a pencil eraser on the power tubes?

 

[Dersu Uzala]

BTW read on for the only accurate way to confirm gas leakage (into the tube):

To prevent any remaining gases from remaining in a free state in a vacuum tube, modern tubes are constructed with "getters", which are usually small, circular troughs filled with metals that oxidize quickly, with barium being the most common. Once the tube envelope is evacuated and sealed, the getter is heated to a high temperature (usually by means of RF induction heating) causing the material to evaporate, absorbing/reacting with any residual gases and usually leaving a silver-colored metallic deposit on the inside of the envelope of the tube. If a tube develops a crack in the envelope, this deposit turns a white color when it reacts with atmospheric oxygen. Large transmitting and specialized tubes often use more exotic getters.

 

[Surfcaster]

My limited experience with Mesa's (my F50 and a friend's Nomad 45) is that there is often a white noise type sound emanating from the speaker, when it's fully powered with the standby in the on position...even when there's nothing plugged in. It's not loud, but it's there. To be honest, I don't notice on my amp anymore (maybe I need to check again) but I remember noticing it when I first got it and when I borrowed the Nomad 45 (before I bought my F50). Unless it's obnoxious I probably wouldn't worry about it.