Good day all
I have lately been giving my Mark IIIs a break by running my ST-70 again. I have noticed that my ST-70 power transformer runs hotter than those in my Mark III amps - not much, but noticeably so. The ST-70 is on a top shelf same as was my Mark III amps "looking at the ceiling" as Bob puts it (sounds like Making Whoopee but never mind!).
I have fairly sensitive hands, brought on by 20+ years of software development - I can not touch my ST-70 power transformer for any extended period, it is too hot.
So... I went "researching" on this subject on the World-Wide Web and came up with the following (from various sources):
1. Many tube amplifier power transformers tend to run hot - some were actually DESIGNED to run for extended periods at temperatures around 100 deg. Celsius (that's 212 Fahrenheit for you ex-Colonials south of the Canadian border
)
2. The heat is not caused by "bad transformer design" as some people out there on the WWW think, but is merely an unavoidable consequence of a transformer having to deliver several B+ voltages of 300 - 450 volts, and at the same time also driving high-current tube heaters
3. Some famous classic amplifiers, for instance the Marantz 5 or one of the earlier McIntosh amps (can't quite remember which) ran just as hot as the average ST-70 or Mark III power transformer
4. Some amplifier power transformers don't take too kindly at being cooled down (forced-air cooling etc) as it is contrary to the design engineer's parameters - obviously it won't damage it but core temperature was taken into account when the transformer was designed, so a cooled-down transformer is probably not running exactly at its design specs... (for the non-engineers, electrical conductors will change resistance in relation to temperature - carbon-based conductors decreasing with rising temperature, but most metallics including copper will increase)
Do anyone care to comment about these observations? I'm afraid it is so many years since I left engineering school that I have forgotten the maths involved in calculation Q and efficiency in transformers (been in software far too long, actually), not that I really care
- the above does seem logical / plausible to me.
-- JunkyJan, BC Canada
I have lately been giving my Mark IIIs a break by running my ST-70 again. I have noticed that my ST-70 power transformer runs hotter than those in my Mark III amps - not much, but noticeably so. The ST-70 is on a top shelf same as was my Mark III amps "looking at the ceiling" as Bob puts it (sounds like Making Whoopee but never mind!).
I have fairly sensitive hands, brought on by 20+ years of software development - I can not touch my ST-70 power transformer for any extended period, it is too hot.
So... I went "researching" on this subject on the World-Wide Web and came up with the following (from various sources):
1. Many tube amplifier power transformers tend to run hot - some were actually DESIGNED to run for extended periods at temperatures around 100 deg. Celsius (that's 212 Fahrenheit for you ex-Colonials south of the Canadian border
)2. The heat is not caused by "bad transformer design" as some people out there on the WWW think, but is merely an unavoidable consequence of a transformer having to deliver several B+ voltages of 300 - 450 volts, and at the same time also driving high-current tube heaters
3. Some famous classic amplifiers, for instance the Marantz 5 or one of the earlier McIntosh amps (can't quite remember which) ran just as hot as the average ST-70 or Mark III power transformer
4. Some amplifier power transformers don't take too kindly at being cooled down (forced-air cooling etc) as it is contrary to the design engineer's parameters - obviously it won't damage it but core temperature was taken into account when the transformer was designed, so a cooled-down transformer is probably not running exactly at its design specs... (for the non-engineers, electrical conductors will change resistance in relation to temperature - carbon-based conductors decreasing with rising temperature, but most metallics including copper will increase)
Do anyone care to comment about these observations? I'm afraid it is so many years since I left engineering school that I have forgotten the maths involved in calculation Q and efficiency in transformers (been in software far too long, actually), not that I really care
- the above does seem logical / plausible to me.-- JunkyJan, BC Canada
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