Mark IV valves glowing blue???

[wrxmania]

Hi All,

I have a Mark IV Hardwood (shortbody) with 2 x EL34 JJ's (Blue) in the outer sockets and NOS JAN Phillips (Small Bottle) 6L6's in the inner sockets. The sound from this combo is great. I have all Mesa pre-amp valves.

However, recently I notice that as soon as I power up the Phillips valves (switch from class A to simulclass mode) the Phillips valves (now with power) glow blue at base and the tops - they don't make any noise when I tap them etc, the amp is not noisier. Is there anything wrong with this (I am running tweed power BTW, not full power)?

Should valves glow blue under normal load settings? They are hotter to touch than the EL34's but I understand small bottle valves do get hotter.

Can't find any advice about this so some tips would be appreciated.

Brian

 

[wrxmania]

PHEW!!!

Nothing to worry about - it is actually perfectly normal and in some respects can actually be a good sign.

Check this useful link:

http://members.aol.com/larrysb/blue_glow.html

Brian

 

[Boogiebabies]

Yes, in most cases the blue glow is cobalt deposits in the plate material.
I do not get why the 6L6's would be hotter than the EL34's. It is usually the other way around as the EL34 sockets are biased much hotter than the 6L6's. You may want to put a bias meter on the 6L6's to be sure you did not get a pair that naturally draws high plate current. You dont want them pulling - 74ma of current or they will burn out quicker or just pop. In a MK IV you should have 460 volts at the plates. 75% of MPD would be 48ma on a 30 watt 6L6. Anywhere below this will give you good tone and more tube life. A Boogie can even sound good at -27ma.

 

[wrxmania]

Cheers for that,

Just after I bought the tubes (and the amp) about 6 weeks ago I had the amp checked out thoroughly by the Mesa Engineer here in the UK, as he is local to me and I know him directly.

He was completely bowled over by the Phillips valves (said the Mesa's were not good that were in it - new amp :O). He said the sine wave was "beautiful" and the best he had ever seen - his description was they were "perfect". He went straight home as I was leaving to order himself a set for a custom tube pre-amp/power he had designed and was planning to market. So I am 100% confident they are drawing exactly the right current and exactly what they should. Also, the JJ EL34's I have in the amp are blue glass so I would not notice if they were also glowing blue.

The amp sounds really great so I have no concerns about the sound. Hope the tubes last as they are great.

Brian

 

[Dasein]

Can you post some photos of the back with the glowing tubes? That would be cool.

 

[RussB]

Here's a shot of a quad of 7581A's...in this pic they're in a '69 Twin Reverb, but they now live and breath in a MKIII.

These tubes have a very pronounced blue glow to them, and you gotta dig how it pulses with the music 8)

 

[wrxmania]

Yep - that looks very familiar just not so red. I will need to watch my mobile disco at the back of the amp soon

Brian

 

[axwielding1]

I still have my original 415 sylvannias, and they have a blue glow as well. They test excellent, and sound frigging awesome. I kinda like the blue glow.
ax. :twisted: