Question for you vacuum tube guys: One's got the blues

Automatic Washer - The world's coolest Washing Machines, Dryers and Dishwashers

Help Support :

C

Cybrvanr

Well-known member
Joined
Jan 23, 2005
Messages
1,287
A Hammond Organ is a great instrument to play the blues on, but what does it mean when the mica piece on the end glows blue? It's most prominent when the organ is first powered up, and after 15 minutes or so, it goes away. The organ sounds the same as it ever has. Removing the tube and checking it on a tube tester reveals that it's emission is good and strong, and has no shorts.

What you're looking at is an amplifier in a 1936 vintage Hammond Organ. The leftmost tube is a 5Z3, the power supply tube, then there's 4 2A3 tubes (3 visible in the photo) that are the amplifier finals that supply close to 100 watts to a set of 2 15 inch Jensen eletromagnetic speakers. That's one of the 2A3's there that is glowing blue. This amplifier places close to 1000 volts on the plates of those things!!!
 
Blue tubes

Well... I have seen that before in tube amps. If fact my Seeburg juke has one tube that has a blue tinge to it,and the amp was rebuilt. I do not know what effect it has on the tubes or amp,if any. I would not worry about it. However I think you need to post some pictures of this classic Hammond organ.... I'll tell you what... If you post some nice pictures of the Hammond,I will post pictures of my restored 1912 Chickering player piano. :)

Rick
 
This type of blue glow is usually not a problem. A pale blue haze could mean trouble (soft vacuum), but not a nice blue glow. Cameras have been known to emphasize the glow in pictures.

I assume this organ has been overhauled at some time. If it has all the original capacitors, it's just a matter of time before you let the smoke out of the power transformer. If it has no fuse in the B+ (high voltage) line, one should be added.

Ken D.
 
That's Good Advice Ken!

Cybrvanr, they call a blue glow around the outside of the tube envelope a "gassy tube". Like Ken says, it just has a soft vacuum, not really a worry. If you swap tubes and the blue glow follows the tube, that's what you've got.

The blue glow to worry about is when you see blue at the core of the tube, between the plate and cathode. This indicates excessive current and will lead to tube and component failure. Cherry red plates are also an indicator of this.

But in this case I think you're just fine!
Cory
 
Flourescence in the tubes

Looks like the tube is actually OK. I have seen this in 5U4 and other types of power tubes in my power amps I used to use(McIntosh MC60)Its a flourescence from electrons striking the mica or the glass envelope of the tube. Also see this effect in some of the transmitter tubes I use in our transmitters.They are running 15Kv at about 13A each.they too have glass envelopes.As long as your plates aren't glowing and the inside of the tube isn't blue or sort of "rainbow" colors(gassy).Oh-have you tried the tube in another position or another peice of equipment that uses the same tube to see if it glows the same way?From the looks of the pix-doesn't look harmful.
 
2A3

I have also seen these tubes used a "pass tubes" in series voltage regulators in some equipment-and have seen a similar glow-esp when a lot of current is drawn from the power supply.The 2A3 is an excellent power amp tube and "glass pass transistor" for power supply regulators.High end Hi-Fi folks love these tubes-similar ones were used in very old theater amps.
 

Latest posts

Back
Top