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LH 500 back-up tube

Medicman95370

Medicman95370

Guest
Dec 29, 2017
26
15
California
#1
Hey ya'll,
I'm starting to play out for the first time ever live. Our cover band has played about five times over the past few months. Wanting to be ready for anything I'm concerned about the tube in my Hartke LH 500.
Do those of you that have tube amps carry extra tubes? Are they easy to change?
Do any of you have recommendations on changing the type of tube or should I just stick with original model? (I play through a GK Neo 410/classic hard rock)
Lastly, what's the best source for amp tubes?
Thanks a bunch!!
 
#2
The LH500 uses a single 12AX7 tube. I think it would be a good idea to have a spare tube. Normally when you roll tubes, you sub in different brands/models of the same tube type. Different names for 12AX7 include 7025, ECC83, ECC803, etc.

If you have specific goals, I have rolled many of the 12AX7 types that are currently in production. However, tubes respond to circuit conditions, so tube performance may vary from one circuit to the next. Some amps respond to tube rolling. This may allow you to make minor adjustments to the way the amp is voiced. Unfortunately some amps do not respond to tube rolling. Basically they sound the same regardless, meaning there is no potential benefit to putting in a different tube.

Some people like to try lower gain tubes. Gain varies between various brands and models of 12AX7s. A distinction should be made between amplification factor and the tubes tendency to compress and distort. Usually when somebody says high gain, they mean both, but some tube with a relatively low amplification factor tend to distort fairly easily in my experience. In my experience current production Tung Sol 12AX7s have a lot of gain but tend to remain punchy and clean instead of compressing and distorting. In contrast, in many circuits I have found JJ ECC83S to be relatively low gain with a tendency for early distortion.

5751s are very similar to 12AX7s but lower gain and I believe they are considered 100% compatible.

12AT7 and 12AU7 are even lower gain than 5751, but have different operating characteristics. Many people sub these tubes in 12AX7 circuits, but ideally the circuit should have a few components changed for optimum operation. Without rebiasing, the circuit may be prone to asymmetrical clipping.
 

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