Following The Freaking Heater

12AX7/ECC83 Heater Cathode Voltage with a Cathode Follower

SAY WHAT?

In my Marshall DSL15c, I love the tone and responsiveness of the Tung-Sol 12AX7 pre-amp tubes, coupled with the singing quality of the JJ 6V6s power tubes.

Recently, after replacing the pre-amp tubes, a pre-amp tube burned out after a couple of months, and it was in the middle of a gig.  OUCH!  The high pitch squealing was horrible.  

 So, I did some research.  Good old fashioned research, read, read, read, read, and read some more. 

 Eventually, I figured out that the tube was probably the V3 pre-amp tube.  You see, the V3 tube in the pre-amp section of the DSL15C has a cathode follower in the circuit.  As a test, I pulled the V3 tube out and dropped in a JJ ECC83 that I had laying around. I rehearsed with my band for over an hour and there was no squealing or other weird noises.  Conclusion: it was definitely the V3 tube that died.

OKAY, But What Does a Cathode Follower Have to Do With It?


Apparently, it is a known fact in the guitar tech world, that cathode followers in some leading amp manufacturers (like Fender and Marshall) have always been hard on pre-amp tubes connected to cathode followers.  But, in the past, the old (now NOS) tubes were built very strong and could handle the heater cathode voltage with a cathode follower, so it was never much of a problem.

Still with me?
 

With many of today's best tubes the heater cathode voltage is fine when no cathode follower is involved, but they cannot handle the heater cathode voltage with a cathode follower.
 
In a nutshell, none of the Russian made tubes can handle the heater cathode voltage that occurs with a cathode follower and the tubes go out too fast. 

The only pre-amp tubes known to handle heater cathode voltage with a cathode follower are:
  1. NOS (new old stock) - and I will not pay $250+ for one tube
  2. JJ Electronics - only slightly better than Russian made tubes 
  3. Chinese tubes - specifically Ruby 12AX7A-C5 tubes made in China - and the work very well
So, I ordered a Ruby 12AX7A-C5 pre-amp tube and will put it in the V3 of the DSL15C. Hopefully, it will last longer than two months. If not, will go with the Tungsol 12ax7 and will replace V3 once a month.

Enjoy the Music!

Jimmy Haggard

Comments

Post a Comment