Re: Joe, what are your preferred tubes and why??
Joe's gear must really go through the mill both physically and emotionally (how I like to think about amps when being used). And the persuit of the ideal sound comes at the cost of replacing valves on a very regular basis.
For Mr.Bloggs on the other hand these are the words of Mr Jim Marshall.
"The most important thing to remember about valves is that they have an indeterminate lifespan, rather like a lightbulb. There is no real way of saying categorically what sort of life they will have. Generally speaking, if used two or three times per week, a set of EL34 or 5881 output valves will last 18 to 24 months. Pre-amp valves [ECC83/12AX7] as a rule have about double the life of the power valves, so about 3 to 4 years under normal playing conditions. As different makes of valve operate at different bias settings you should always ensure that matched power valves are used, otherwise their life will be drastically reduced.
When the time comes to change the power valves you will definitely know as valves only have two states, working or not working. The most common symptom of valve failure is the blowing of the HT fuse. On some occasions after replacing the fuse the amp will work for a while but will blow the fuse again when it reaches full working temperature. This is the first warning sign that a valve is failing. If both the HT and mains fuses blow, then blow again on replacement, then it is pretty definite that at least one of the valves has short circuited and needs replacing. Although not absolutely essential, I always recommend that the entire set of power valves should be changed together [two in a 50 Watt model and four in a 100 Watt].
Where pre-amp valves are concerned, the most common fault is microphony : a high pitched whistling noise which is apparent all the time, whether anything is plugged into the amp or not. This is often caused by the first pre-amp valve in the chain and can sometimes be cured by simply swapping pre-amp valves around. Other pre-amp valve related problems include; lack of volume, loss of bottom end, thinning of the sound and loss of all top-end frequencies. Again it is best to replace all the pre-amp valves at the same time.
Occasionally older EL34 power valves could go microphonic, where a low frequency oscillation, quite different from pre-amp valve microphony, would start, particularly if you tapped the amp casing. Here again it is the amp telling you it needs a new set of valves."
"Schiffer broke a bottle on Morgan's head"
