Tweed Vibrolux 5E11 vs 5F11 Fuse Rating

[The Dude]

Also, line voltage can vary quite substantially.

[Chuck H]

Also, line voltage can vary quite substantially.

Where I am now it's pretty consistent. But in San Jose, Ca. where I lived sixteen years ago the wall voltage would vary between 117 and 129 all the time. I had test points on the power supply for my bench with a cheapy meter permanently attached so I could just flip it on to check the voltage whenever a measurement was dependent on it.

[Tom Phillips]

...in San Jose, Ca. where I lived sixteen years ago the wall voltage would vary between 117 and 129 all the time...

That's pretty extreme. Coincidentally I just tested the line voltage at my bench by running a DVM with a Min/Max function run for four days. The results were

Note that the meter calculates the average as the weighted value of all 1,993,497 samples taken. That's why it differs from a simple calculation done with the min and max numbers.

[x-pro]

within 10%. That's normal.
If it's 20%....
You are "drying your oars".
(Jargon for things being bad)

[Chuck H]

"drying your oars"

Expressions from other cultures usually seem strange (regardless of where to where) but I like this one.

[Chuck H]

That's pretty extreme.

Yes it is. I knew it then too. Infrastructure for a lot of San Jose never took into account the unbelievable population increases that happened (and continue to). These fluctuation usually happened in the summer when tens of thousands of multi unit dwellings would fire up window mount air conditioners at their whimsy and Pacific Gass and Electric would be making adjustments to the requirement. .

[The Dude]

Of course, line voltage can vary from time to time in the same location. But, what I was mostly referring to was line voltage varying from place to place or venue to venue. We have Furman line conditioners with mains voltage readout on much of our gear. I've seen line voltage over 125V in some venues and as low as 110 in others. I imagine even more radical swings are possible depending on load variance.

[K Teacher]

The assertion that all voltages can vary ± 20% troubles me. This can be true for preamp tube's plate and cathode voltages, because the resistors connected to these pins had usually tolerance of ± 20%, thus causing that much voltage variation.

OTH, if you apply the same variation range to the B+ of 305VDC, means the amp is supposed to operate from 366 to 244VDC… I don't buy it, it's too extreme…

For this to happen, the PT secondary winding needs to vary ± 20% or the outlet voltage needs to vary that much also… It doesn't seem plausible to me…

Using The Dude's example, 125 to 110 would be approx. ± 7% voltage variation from mid-point...

[Helmholtz]

[FONT=Arial]
OTH, if you apply the same variation range to the B+ of 305VDC, means the amp is supposed to operate from 366 to 244VDC… I don't buy it, it's too extreme…

Do you have any evidence that the amp won't work up to +/- 20% variation in B+?

[g1]

It's printed right on the Fender schematics for a reason. It means voltages can vary up to that much. I don't think it would be practical for them to figure out the tolerance for every possible voltage, so they give a worst case scenario.

[Tom Phillips]

It's printed right on the Fender schematics for a reason. It means voltages can vary up to that much. I don't think it would be practical for them to figure out the tolerance for every possible voltage, so they give a worst case scenario.

Agree. It's worse case considering all factors including line voltage variation, transformer variation and component variation. I have seen some very large variations and some of the largest were due to power transformer variations.

[pdf64]

The assertion that all voltages can vary ± 20% troubles me. This can be true for preamp tube's plate and cathode voltages, because the resistors connected to these pins had usually tolerance of ± 20%, thus causing that much voltage variation. ...;

I agree, it doesn’t seem credible to me that a serious manufacturer would accept transformers with a 20% tolerance on their secondary winding voltages. Obviously it would pretty much be a problem with the heater circuits.
So yes, my thinking is that degree of acceptable variance can only really apply to downstream voltages, where normal valve variance means current draws through dropper and load resistances will affect resulting voltages.
Also it allows a fair degree of wiggle room if transformer specs are changed, for whatever reason, avoiding a need to amend the schematic.

[Tom Phillips]

... avoiding a need to amend the schematic.

Yea. There's that. However, I think Fender was a lot better at providing pretty accurate schematics than other early guitar amp companies such as Gibson.