Module preamp tubes don't glow when turned on?

[Anomaly]

Okay might be a dumb question here :lol:
Got my first module the other day, pop it the lower slot on my RM22 fired it up. sounds great! all knobs working.. I sneak into the preamp tubes thru the vacant slot. I don't see any glow on the preamp tubes on the module? is this normal? :?:

 

[KillTone]

Some pre-amp tubes do not glow much and sometimes you have to be at the right angle to see the glow. As long as the module works and sounds good no worries.

 

[Anomaly]

Some pre-amp tubes do not glow much and sometimes you have to be at the right angle to see the glow. As long as the module works and sounds good no worries.

I couldn't see any glow at all? I'm looking from the top vacant bay and I have the preamp module at the bottom on my RM22. but anyways, so this means changing preamp tubes won't change anything at all tone-wise :?:

 

[JKMV12]

if you look at the tube, the rod-like thing in the center of the each 'plate' is the cathode which has some heater element inside. That is the only thing that should give off a considerable amount of glow. If you see the plates on the outside glow then you have a problem b/c that is red plating. This means that the plate has started to dissipate too much power for too long. This maximum value is typically 1W for 12AX7 tubes. Though normal working conditions for a preamp tube are usually set far below the conditions necessary for red plating to occur. It is very unlikely. It is more common with power tubes b/c sometimes they are designed to work closer to the maximum dissipation values (i would assume not by choice).

Anyway b/c preamp tubes are so small and only a small part of the cathode/heater is visible...you will not notice as much glow as you would in a power tube. You were probably expecting the entire tube to be somewhat illuminated but that shouldn't happen b/c the light emitted by the cathode is mostly concealed by the plates.

next time you turn on your amp...take off the metal cases around the preamp tubes in the back of the amp and you will see exactly what i am talking about.

 

[Jaded Faith]

It's entirely dependent on the tube design and angle you are viewing it at. Glow is far from the best indicator of a functional preamp tube and you shouldn't expect the same glow you would see from your power tubes. If in doubt, just try a another pair of tubes in that module to see if the sound improves. Rotate them through one tube at a time.

As long as you have sound from it they are working and there is 200-300V going through them....just in case you got the urge to stick you finger in through that open slot. :shock:

 

[Anomaly]

I just find it kind of odd, can't see any glow at all like the preamp tubes are not working? but anyways, It doesn't really matter as long as I get the sound and it's working. thought I'd ask if this was normal w/ RM line amps..

 

[JKD]

It is 'normal' but not tied to the RM line of amps.

On some pre-amp tubes the heater filament is mostly hidden by the tube plate structure....seems to be quite common on long-plate tubes but that's by no means all inclusive/exclusive.

Sovtek 12ax7LPS is a good example of this but I have some old RCA tubes that are similar.

You can swap pre-amp tubes for any 12ax7 or compatible (ECC83, 5751, 12at7, 7025 etc.) Some of the tonal changes can be pronounced, as there are gain level differences across the frequency spectrum.

 

[Anomaly]

I change the preamp tubes to JJ & Sovtek and remove the cover. There's the glow .. I don't know maybe those stock EH tubes are busted ? :lol:

 

[VitaminG]

can't be too busted if you said the module sounds great

 

[Jaded Faith]

No, it's all in the inner construction of the tube. Some tube designs make the cathode very hard to see and that means there will be little to no visible glow. Sovtek LPS's are often sold with the following statement on the webpage:

One other note about the construction of these tubes is they have filaments that are almost completely encased in the plate structure. They often don't "light up" when working properly. This is not a problem, it's normal for the LPS."

That's right from www.tubestore.com: http://thetubestore.com/sovtek12ax7lps.html

 

[Nightdare]

When your powertubes don't light up,...

...then you should start to worry :wink: :lol:

 

[JKMV12]

When your powertubes don't light up,...

...then you should start to worry :wink: :lol:

and when you have the other extreme...they glow too much...you should worry too. (red plating)

 

[m0jo]

No, it's all in the inner construction of the tube. Some tube designs make the cathode very hard to see and that means there will be little to no visible glow. Sovtek LPS's are often sold with the following statement on the webpage:

One other note about the construction of these tubes is they have filaments that are almost completely encased in the plate structure. They often don't "light up" when working properly. This is not a problem, it's normal for the LPS."

That's right from www.tubestore.com: http://thetubestore.com/sovtek12ax7lps.html

Yep, The EHX's are related to the LPS, don't know if that's the reason, but they both don't have much visible glow because it is obscured by other parts.

Contrary to popular belief, tubes don't glow that much at all. It's just that small heater element deep in there.
Don't tell this to anyone with an Engl though! :lol: *cough* leds *cough* .. :lol: