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Thunderbird Club

#98,823
PillO said:
I did a bunch of that stuff many years ago in high school. Much of the knowledge is lost t the sands of time. Absolutely correct. Interesting that many/most people think that running a tube amp without a load poses a danger to the tubes. In fact it is the output transformer, which is one of the more expensive components (more so than the power tubes).
Click to expand...
yeah, Miles' post reads confusing and this happens often when this is discussed..
a "high" load is actually a "light" (approaching an open) load.
a "low" load is actually a "heavy" (approaching a short) load.
Part of the confusion IMHO stems from the fact that loads began to get categorized this way when low Z (SS) circuitry became prominent and folks would refer to loads from an Amperage (not Voltage) perspective.
It always surprised me that tube amp manufacturers did not make provision for a short at the output jack when no speaker was hooked up, one (the short) that would be placed in series with the speaker when it was hooked up...could have saved users loads of grief..
 
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#98,824
PillO said:
I did a bunch of that stuff many years ago in high school. Much of the knowledge is lost t the sands of time. Absolutely correct. Interesting that many/most people think that running a tube amp without a load poses a danger to the tubes. In fact it is the output transformer, which is one of the more expensive components (more so than the power tubes).
Click to expand...
I never knew why or what the issue was with unloaded tube amps. Only that power without a load is a bad idea. Which was never a problem, because I only own tube combos that always have a load attached and solid state bass heads that do not seem to be bothered by much of anything, including heavy dewfall.
 
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#98,825
Gaolee said:
I never knew why or what the issue was with unloaded tube amps. Only that power without a load is a bad idea. Which was never a problem, because I only own tube combos that always have a load attached and solid state bass heads that do not seem to be bothered by much of anything, including heavy dewfall.
Click to expand...
because the output transformer transforms the high Z of the tubes to the low Z of the speaker, when unloaded the voltages on the primary (tube) side of said transformer will reach VERY high voltage levels that will breakdown the insulation rating of the windings causing them to short.
 
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#98,826
I should mention that playing a wedding on a plywood stage in a field when heavy fog and dew rolls in is a good mouth zapping time, but the 360 did not seem to notice at all. Go figure. So much for delicate old equipment. I would admit that I have not had to do anything except plug in and power up since I got it. But that would be tempting fate, so I won't.
 
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#98,827
Chucky Stiletti said:
because the output transformer transforms the high Z of the tubes to the low Z of the speaker, when unloaded the voltages on the primary (tube) side of said transformer will reach VERY high voltage levels that will breakdown the insulation rating of the windings causing them to short.
Click to expand...
Kinda like having two kids on kne side of the see-saw instead of one on each side. Or maybe two big kids on one side and a little one on the other. Sproing! That is my simple minded mechanical way approaching the way that happens.
 
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#98,828
Chucky Stiletti said:
yeah, Miles' post reads confusing and this happens often when this is discussed..
a "high" load is actually a "light" (approaching an open) load.
a "low" load is actually a "heavy" (approaching a short) load.
Part of the confusion IMHO stems from the fact that loads began to get categorized this way when low Z (SS) circuitry became prominent and folks would refer to loads from an Amperage (not Voltage) perspective.
It always surprised me that tube amp manufacturers did not make provision for a short at the output jack when no speaker was hooked up, one (the short) that would be placed in series with the speaker when it was hooked up...could have saved users loads of grief..
Click to expand...

And here only 70 years after the development of the transistor, designers are starting to think about running tube amps without load (Ampeg PF-20T and 50T). Only takes a few decades for the designers to work out how to save users from easy errrors...
 
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#98,830
Gaolee said:
I should mention that playing a wedding on a plywood stage in a field when heavy fog and dew rolls in is a good mouth zapping time, but the 360 did not seem to notice at all. Go figure. So much for delicate old equipment. I would admit that I have not had to do anything except plug in and power up since I got it. But that would be tempting fate, so I won't.
Click to expand...
I like a good mouth zapping. But we may not be talking about the same thing.
 
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#98,831
Gaolee said:
Kinda like having two kids on kne side of the see-saw instead of one on each side. Or maybe two big kids on one side and a little one on the other. Sproing! That is my simple minded mechanical way approaching the way that happens.
Click to expand...
you'd be surprised how many electronic problems are taught/solved using mechanical analogues..
 
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#98,832
TOP 50th Anniversary tour in Monterey tonight.....can't wait...GO ROCCO!!!
ent2-tower-power_2018-09-11_18-08-51.jpg
 
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#98,836
Gaolee said:
I never knew why or what the issue was with unloaded tube amps. Only that power without a load is a bad idea. Which was never a problem, because I only own tube combos that always have a load attached and solid state bass heads that do not seem to be bothered by much of anything, including heavy dewfall.
Click to expand...
My PF350 is fine with no load - but heavy dewfall? I can't even leave it in the trunk for an afternoon at 2 degrees Celsius. (36 in American)
 
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