Carver and Tube Life

John (Roxy54), thank you kindly :-)

Stickman, I wouldn’t want to speculate on the differences that would result between the two amplifiers with respect to soundstage, dimensionality, bass, or pretty much any other sonic attribute. But given that your 305s don’t seem to strain driving the 20.7 I would think that whatever differences the Silver Seven 700s may make would result mainly from circuit differences and parts differences (including the completely different small signal tubes it uses), rather than from the 3 or 4 db difference in maximum power capability in itself.

And likewise with respect to the 30.7, **if** its sensitivity (for which I couldn’t find a spec or measurement) is similar to that of the 20.7, or higher.

Best regards,
-- Al

Hi Stickman,

Thanks for your question. It so happens that I had addressed that exact question in a post dated 11-17-2017 in this thread, although in connection with a different Carver amplifier. What I said was as follows:

Regarding the statement by Mr. Carver about the 50+ year longevity of the power tubes in his amplifier, I would point out that in general there are statistical approaches that are commonly used in deriving published MTBF (mean time between failure) specifications which produce misleading results.

For example, many of the mechanical (non-SSD) hard drives used in computers have published MTBFs of 1,000,000 hours. Or in the case of some Western Digital Gold Drives I recently purchased, 2,000,000 hours. 2,000,000 hours corresponds to 228 years of continuous operation. Does that mean these drives can be expected to last anywhere close to that amount of time? Of course not. What it means (and I’m choosing the following figures for purposes of illustration) is that if say 100 drives are operated simultaneously one of them can be expected to fail after slightly more than 2 years.

Similarly, **if** Mr. Carver’s 50 year figure is based on similar statistical methodology, and given that there are 12 power tubes in a stereo pair of these amplifiers, it would mean that one tube can expected to fail after a bit more than 4 years.

On the other hand, though, if we assume an average of say 1 hour of use of Mr. Carver’s amplifier per day his 50 year figure would correspond to 18,250 hours. I suppose that if the tubes are driven very lightly, and his design includes good soft start provisions, numbers approaching that figure might not be totally unreasonable. For example, I recall reading that the Western Electric version of the 300B power tube, when used under recommended conditions, can last for 40,000 hours. (I’m not sure, though, if that applies to the original 1930s version, or to the relatively recent reissue, or to both).

In any event, personally I would consider Mr. Carver’s claim as simply indicating that the KT120 and KT150 tubes that are offered with the amplifier will last considerably longer than in most other applications.

Best regards,
-- Al