Re: [Harp-L] amp tube life

[MARK BURNESS <markwjburness@xxxxxxxxxxxxxx>]

Depends on the amp & type of tubes & how hot they idle.
 
Power tubes - In general, plenty of large, fixed bias, 6L6 stage amps go typically 5 years or more on a pair of 6L6s at regular/moderate bias - even with a heavy gigging schedule. Champs despite running their tubes very hot can go a decade on a 6V6. It's quite unusual to have a harp amp that needs power tubes changing every 12-18months as is recommended with many guitar amps. Obviously if you hear any deterioration, you should replace them however long, or short,  they have been in there. Most guys change tubes out of curiosity & due to alternartive recommendations, rather than because of rapid wear. Occasionally, RI/current production Fenders will have self-disconnecting 1W screen grid resistors (due to heat & expansion in the PCB eyelets) and these will take a tube with them. Rewiring & mounting new sceen grid resistors (4-5W wirewound) on the tube sockets is a smart move in these instances.
 
Cathode biased, push-pull amps, running high idle currents can be harder on tubes, especially modern 6L6GC that do not meet the 30W dissipation that the name implies, 20-23W is a safe enough margin unless you know your brand of tubes are particularly robust. SED winged C sound sweet but seem to struggle with high dissipations, Sovtek 5881WXT & JJ6L6GC are pretty bullet proof but not everyone loves the sound of them.
 
SF/BF Princetons & Deluxes can be hard on NOS tubes, fine wth cool running modern 6V6...again, only if you like the tone (many will prefer NOS idling hot). The Princeton RI is best fitted with Russian or JJ6V6 unless the rectifier is subbed for a lower voltage type (even then, this sometimes does not give enough wiggle room).
 
Nowadays, modern preamp tubes mostly need changing when they go noisy/microphonic. Preamp tubes run very little current & typically do not wear out at anything like the rate of power tubes. 
 
Harp amps are typically not as hard on their tubes as the same amp used for guitar & there is rarely the need to punish the power tubes with very high disipations to get a good, useable tone (though some old PA amps do owe a lot of their character to doing just this).

________________________________
From: Robert Hale <robert@xxxxxxxxxxxxxx>
To: harp-L list <harp-l@xxxxxxxxxx> 
Sent: Friday, 6 January 2012, 20:40
Subject: [Harp-L] amp tube life

AMPLIFIED HARP
For you playing TUBE amps, what do you hear, and how often are you changing
tubes sets?

pre-amps?
power tubes?

When I played pedal steel 6 nights a week, I could hear the response change
in aging tubes. (Fresh strings and fresh tubes sound incredibly good!). I'm
not sure I am hearing the same with amplified harp.

Your ideas and experience are appreciated.

Robert Hale
Learn Harmonica by Webcam
Low Rates, High Success
http://www.youtube.com/DUKEofWAIL <http://www.youtube.com/user/DUKEofWAIL>
http://www.dukeofwail.com