[Xtrchessreal]

On Wednesday, September 30, 2020 at 11:41:25 AM UTC-6, Big Bad Bob wrote:
On 2020-08-29 01:50, Xtrchessreal wrote:
The question is simple: When it comes to schematics e.g. I see V1A and V1B How do I know which triode this refers to is V1A Pins 123 and V1B 678. Most data sheets indicate pins 123 to triode two and pins 678 to triode 1

In the Philips data sheet for a 12AX7 they even have a remark stating pins 678 or triode 1 is a better triode with regard to hum.

Some schematics actually show the pins for the specific triode but most only show V1A V2B V3B etc. Its obviously most critical in the first pre-amp stage unless there is a reason by the designer to have something a little different.

Can anyone explain this convention or lack there of?

yeah it's a little disturbing they're not being precise.

Only other thing I would do is look at the GE tube manual for how they
draw it, and maybe infer pin numbers and "which triode" from that.

which tube is it, 12AX7 or ?

The GE manual I'm looking at shows "section one" on pins 6,7,8 and
"section two" on pins 1,2,3. So I'm guessing 'V1A' would be section
one, and 'V1B' would be section two. If you look at the actual
equpment, maybe you can trace a pin to a component to verify?

assembly was often "by hand" back then with point-point wiring. The
schematic could be "the other way" and it still got built right. I
would expect they're all consistent within themselves, but when compared
to other gear... who knows?

I found some good source information by a guy named Rob Robinette.
Its is pretty simple. V1A is pins 123 and V1B is pins 678. The Logic is sequential in nature "A" refers to the lower numbers "123" and "B" refers to higher numbers "678" B comes after A alphabetically and 678 comes after 123.

Many data books refer to triode 1 section 1 as pins 678 and triode 2 section 2 as pins 123. Section 1 is so called due to lower hum compared to section 2. It is suggested to use V1B for a first stage preamp to keep the SNR lower in reference to hum providing a cleaner preamp with more head room less chance of early distortion. Typically you find on most schematics for Fender, Marshall, and many others V1B is the first preamp stage and V1A the distortion stage.

There are a few schematics that show the pin numbers for each triode added to the design of the circuit.

I find information on google groups forums to be mostly intentionally wrong, opposite, and generally terrible. Bogged down with misinformation designed to be provocative and misleading. Its a troll mentality I despise. It is especially despicable since the forums were developed with intention to help people discuss the finer points of the subject matter. Now it is only spiteful with intent to harm by misleading people. As such it is no longer functional as a helpful apparatus. If I had the power to do so I would shut it down as a waste of money, time, and thought.