Triode Naming Convention

Big Bad Bob wrote:

==================
Phil Allison wrote:
> > Xtrchessreal wrote:
> >
> >>
> >>> ** The 2 triodes of a 12AX7 / ECC83 are identical,
> >>> one doe not "hum" more than the other.
> > ================================================== ===
> >>>
> >>> Internal connection arrangements for grids and heaters vary
> >>> between versions and brands, maybe having a small effect
> >>> on capacitive coupling if high impedances feed he grids.
> >>>
> >>> It is very common to use DC voltage for the heaters to
> >>> eliminate any issues whether grid or cathode related.
> >>>
> >>
> >> Just read the REMARK on the bottom of page one. https://drtube.com/datasheets/ecc83-philips1970.pdf
> >
> >
> > ** My post is *about that exact remark* - explaining it.
> >
> > An *earthed* internal link from pin 9 travels past grid pin 7 in the scenario described. A link carrying 3.13VAC travels past grid pin 2.
> >
> > This might inject up to 1mV into pin 2 if the grid source impedance were *10Mohms*. However, for a MM phono cartridge, the impedance is 1kohm at 50/60Hz and for a guitar PU about 10kokms.
>
> Actually it's more like 100k for a typical guitar amp pre-amp input,
>

** The source impedance is what matters, and is as I stated.

Guitar PUs and phono PUs are both low value resistors at 50/60 Hz.


> The thing about the phono cartridge amp
> is the RIAA curve which I believe is around 40db higher gain at the low
> end of the frequency spectrum as compare to the high end.

** The RIAA curve boost gain by 16 dB or 6.3 times 50/60Hz compared to mid frequencies. It also boost tube noise by the same amount.

There is NO audible supply frequency hum caused by stray C *inside* a 12AX7.

The OP has misconstrued the comment on the data sheet.


..... Phil

On 2020-10-04 20:30, Phil Allison wrote:
>>> This might inject up to 1mV into pin 2 if the grid source impedance were *10Mohms*. However, for a MM phono cartridge, the impedance is 1kohm at 50/60Hz and for a guitar PU about 10kokms.
>>
>> Actually it's more like 100k for a typical guitar amp pre-amp input,
>>
>
> ** The source impedance is what matters, and is as I stated.
>
> Guitar PUs and phono PUs are both low value resistors at 50/60 Hz.

yeah, but a typical amplifier is going to have a 100k-220k in series
with the preamp input for dual jacks. And the volume control on the
guitar is 50k-100k. So you're right in saying that it has low impedence
at the guitar pickup [which has its own issues with inductive coupling
of hum, but that's a different issue] but the amplifier itself typically
has those series resistors so that you can have multiple guitars on the
same amp.

Given that, even if there's only a slight "barely detectable"
difference, if it's known, I'd just make the design leverage the one
with lower hum (alleged or otherwise) be the 1st stage amplifier.

Big Bad Bob wrote:

==================
> Phil Allison wrote:
>
> >>> This might inject up to 1mV into pin 2 if the grid source impedance were *10Mohms*. However, for a MM phono cartridge, the impedance is 1kohm at 50/60Hz and for a guitar PU about 10kokms.
> >>
> >> Actually it's more like 100k for a typical guitar amp pre-amp input,
> >>
> >
> > ** The source impedance is what matters, and is as I stated.
> >
> > Guitar PUs and phono PUs are both low value resistors at 50/60 Hz.
>
> yeah, but a typical amplifier is going to have a 100k-220k in series
> with the preamp input for dual jacks.

** 68k is most common value on guitar amps with dual jacks.

Has no effect on hum or noise coming from the tube.


> So you're right in saying that it has low impedence
> at the guitar pickup [which has its own issues with inductive coupling
> of hum, but that's a different issue]

** No it isn't - cos it totally swamps the issue here.

FFS give up posting wild guesses as fact.


..... Phil

On 2020-10-09 15:20, Phil Allison wrote:
> FFS give up posting wild guesses as fact.

which ones?

It's not like I haven't built a bunch of guitar amps since I was a
teenager, both tubes AND transistors, nor seen a number of schematics,
nor reverse engineered a Fender amp to build a custom amp based on
Fender's circuits because someone wanted me to, nor having played guitar
since the 1960's, nor having re-worked the electronics on guitars a few
times [including putting a 5 pos switch on a Hondo strat copy that had a
3 pos switch for a friend], yotta yotta.

OK - which of the things I said were "wild guesses" ?

keep in mind that the tech manuals said something I'm agreeing with.
YOU are disagreeing with the tech manuals, and after I provide several
examples based on what I've seen (particularly for older amplifiers,
where this would be more relevant), you say that I'm "posting wild
guesses as fact".

So, since I never actually DID that, then you're welcome.

A typical old amplifier:
http://www.thevintagesound.com/ffg/s..._5c3_schem.gif

(in this case 75k - I've seen as high as 220k, but on average, input
resistors on the shared input are around 100k, which if you think about
it, isn't a whole lot different from 75k or even 68k when you average it
all out)

A typical guitar (strat):
https://wholefoodsonabudget.com/wp-c...-center-6b.jpg

https://tinyurl.com/y6dew9vv

shows volume and tone controls are 250k. I have seen as low as 50k, but
typically 100k as I recall.

This one shows 1M volume controls on the guitar:

https://wholefoodsonabudget.com/wp-c...iagram-12s.jpg

I'm sure you'll see LOTS of variability. Some old guitars [I used to
have one] even had ceramic pickups. And you also have pedal output
impedence. So the variability is pretty wide here.

My guess is that a pre-amp would be designed such that any noise
generated by an audio tube's filament would be minimized based on a very
wide range of possible inputs, single guitar, two guitars, ceramic or
dynamic pickups, 50k or 250k or 1M volume controls, etc. etc..

So if I happen to "ballpark" the values, you should be able to see why.

And I still accept what the tube spec sheet says about hum on one of the
triodes being slightly higher.

Big Bad Boob wrote:

=================
Phil Allison wrote:
> > FFS give up posting wild guesses as fact.
>
> which ones?

** All of them.

>
> It's not like I haven't built a bunch of guitar amps since I was a
> teenager, both tubes AND transistors, nor seen a number of schematics,
> nor reverse engineered a Fender amp to build a custom amp based on
> Fender's circuits because someone wanted me to, nor having played guitar
> since the 1960's, nor having re-worked the electronics on guitars a few
> times [including putting a 5 pos switch on a Hondo strat copy that had a
> 3 pos switch for a friend], yotta yotta.

** Fraid you have no learnt much.

>
> OK - which of the things I said were "wild guesses" ?
>

** The whole lot.

> keep in mind that the tech manuals said something I'm agreeing with.
> YOU are disagreeing with the tech manuals,

** Never said any such thing.

>
> A typical old amplifier:
> http://www.thevintagesound.com/ffg/s..._5c3_schem.gif
>
> (in this case 75k - I've seen as high as 220k, but on average, input
> resistors on the shared input are around 100k, which if you think about
> it, isn't a whole lot different from 75k or even 68k when you average it
> all out)

** Average of what? Not amps sold for sure.

Vox, Marshall, Fender, Peavey, Music Mann and countless others ...



> shows volume and tone controls are 250k. I have seen as low as 50k, but
> typically 100k as I recall.

** With a 10 kohm source (at 50/60 Hz) and turned to half value = what?


> My guess ..

** Another wild guess ????

>
> And I still accept what the tube spec sheet says

** You have no ****ing idea what that 50s doc refers to or if it has any relevance to guitar amps or modern examples of 12AX7s.

FYI

I have 50 years experience designing and repairing guitar amps plus LOTS of other types of audio gear - including tube condenser mics.

You came here on a damn silly notion & got an expert who pointed that out.

You get to like or lump it.


...... Phil

On 2020-10-15 19:26, Phil Allison wrote:
> Big Bad Boob wrote:
>
> =================
> Phil Allison wrote:
>>> FFS give up posting wild guesses as fact.
>>
>> which ones?
>
> ** All of them.
>
>>
>> It's not like I haven't built a bunch of guitar amps since I was a
>> teenager, both tubes AND transistors, nor seen a number of schematics,
>> nor reverse engineered a Fender amp to build a custom amp based on
>> Fender's circuits because someone wanted me to, nor having played guitar
>> since the 1960's, nor having re-worked the electronics on guitars a few
>> times [including putting a 5 pos switch on a Hondo strat copy that had a
>> 3 pos switch for a friend], yotta yotta.
>
> ** Fraid you have no learnt much.

whatever. I'm done with you. It stopped being fun, and now you're just
insisting on getting the last word in.

/me thinking of Pee Wee Herman, "I know you are, but what am I?"

Big Bad Bob + TROLL wrote:

=======================
>
> > Phil Allison wrote:
>>
> >>> FFS give up posting wild guesses as fact.
> >>
> >> which ones?
> >
> > ** All of them.
> >
> >> >
> > ** Fraid you have no learnt much.
>
> whatever.

** **** you.

I'm done with you.

** Man, you are done like a dinner.

It stopped being fun,

** Never come her for fun - shihead.


> and now you're just
> insisting on getting the last word in.


** ROTFL - what the HELL do you think this post of yours is?

You need to take along look in a mirror pal.



...... Phil