5th of July - Still hearing firecrackers in your head?

[VacuumVoodoo]

When this passes and your hearing returns to your normal super acute "I can hear the grass grow" sensitivity -
If you then begin to hear hum in all and every amp you 've ever built....
A DC-OFFSET-HUMDINGER is the remedy you will need.
Get well soon!

[martin manning]

Belt and suspenders! As a bonus, also very good for relieving stress on heater insulation if there is a cathode follower stage. Thanks for posting!

[Leo_Gnardo]

If you then begin to hear hum in all and every amp
A DC-OFFSET-HUMDINGER is the remedy.

On occasion I've done this to a hum-recalcitrant amp. Oh well there goes another "trade secret." Not to worry, I'm not. TAG readers will now be able to render their amps Hubert. As in Hum-free.

[Reeltarded]

lol

When amp dorks attack. Too funny.

[xtian]

That's cool!

Can I assume there is no requirement for V1 to be at the end of the parallel heater string (although mine usually are), and for the humdinger to be placed near it (and that this is just an artifact of the schematic)?

[VacuumVoodoo]

That's cool!
Can I assume there is no requirement for V1 to be at the end of the parallel heater string , and for the humdinger to be placed near it?

Yes, there is. It's drawn the way it should be done. Especially in hi gain amp. There's a method to this madness.
Any hum due to heater imbalance that happens on first gain stage is amplified consecutively through the whole gain chain.
So I make sure my V1 is as quiet as possible.
Also, it might seem natural to use the left triode on pins 1,2&3 as input but the right one on pins 5,6&7 is less susceptible to hum leakage from heater.
More trade secrets in the open.

[Structo]

What is confusing to me is which triode is connected to pins 1,2 and 3.

For example, the GE 12AX7 data sheet shows pins 1,2 and 3 is the second triode, therefore if you connect pins 1,2 and 3 to the input of the amp, then it would be as you stated.

But, I am not sure if all 12AX7's follow this pinout.

[VacuumVoodoo]

Well, I admit it is confusing...
For some reason triode connected to pins 5,6,7 is usually called No.1 and the one on pins 1,2,3 is No.2.
I find more logical to call call them the other way round. When looking at the tube from the bottom -
that's how I see my tubes 98% of time - with pin 1 at 7 o'clock and count pins clockwise, I see pins 1,2,3 on the left side...
Anyway, that hum susceptability thing is not something we need to really worry about,
unless it's a microphone preamp with gain high enough to record sounds of this action on a straw of growing grass.
One can always swap connections to the triodes and check if there's any difference in hum level.

[martin manning]

Also, it might seem natural to use the left triode on pins 1,2&3 as input but the right one on pins 5,6&7 is less susceptible to hum leakage from heater.
More trade secrets in the open.

I'm thinking this is not significant at all. As I recall this is attributed to a Mazda data sheet, but you do not see it mentioned on any others, and in fact GE and Tung-Sol give "Equivalent noise and hum voltage" of 1.8uV as the same for both sections.

[VacuumVoodoo]

It's in Philips data sheet, "Remark" down on page 1.

[Structo]

You see that is what is confusing, there isn't a standard for the nomenclature.
The Mazda data sheet shows the first triode as pins 6, 7 and 8.
And the picture denotes that.

But with the GE 12AX7, it shows the first triode as 1, 2, and 3 but in the notes it says that is the second triode.

Also I have heard that spiral filaments are humbucking but which tubes have that feature?

[martin manning]

It's in Philips data sheet, "Remark" down on page 1.

Ah, thanks. "More favorable with respect to hum." I guess not favorable enough for them to want to quantify the difference, and this might not be true for tubes made by other manufacturers with different internal construction.

[Leo_Gnardo]

Also I have heard that spiral filaments are humbucking but which tubes have that feature?

Sovtek 12AX7 LPS was "supposed to" be the hubert tubert but I got lots of them that forgot the words.

Also the LPS was "contraindicated" for use in cathode follower or any other circuit that raised cathode voltage significantly.

New Sensor won't be getting any more of my hard earned money for this premium priced flop. Directly or indirectly.

Originally 7025 was supposed to be choice for minimum hum applications.