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Why doesn’t a 2a3 equal two 45s sonically?

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Joined 2008
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I know the parameters.

You say that like the operating parameters mean less than the name and the story.

You’d think though, two of the same things would sound a whole lot like just one of them. And yet, that’s not the case.

Yeah, you would think that. I did. But eventually I started to realize that the name doesn't ever say everything that can be said about the object being named. Probably best to treat all names like advertising.

What about their joining makes them so different from being a single?

Well, for a start , how about double the inter-electrode capacitances ?
Which leads back to my original question: What have you tried?

I personally know of at least eight different distinct types of 2a3 and I have been told that there are many others. Then there's the supporting circuitry. Which tubes and what circuitry?

It might be as easy as using a different driver to get the sound you want. But if you don't share details about what you are doing you can't expect any meaningful help. Or maybe you just felt like having a conversation? Nothing wrong with that but it does change the orientation.
The proper design of a Parallel SE 45 amplifier should include individual bias for each of the two 45 output tubes.
I like 45 tubes; but I have never built a Parallel SE 45 amp; nor have I heard one.

A 2A3 that has 2 plates, it can not have individual bias to balance the current in the 2 plates.
I happen to like my later production mono-plate 2A3 tubes.
I will not even attempt to purchase the original mono-plate 2A3 tubes that have 24 filament wires.

Lots of other differences, some mentioned in this thread's posts above, some are not mentioned in the thread above.
Sorry, you lost me there: in what sense is anything twice something different?
Well, twice the current capability, twice the idle current, twice the plate dissipation, half the plate impedance, twice the input capacitance, I´m certain I´m forgetting an couple other significant parameters.

In my book (I guess in yours too, being an Engineer :)) , tubes, being flat from DC to WAY above the Audible band do not have a sound of their own BUT elements connected to them do, which changes with driving current and voltage, frequency, source impedance and so on , sound changes often :rolleyes: attributed to tubes themselves.

And I bet parallel 45 vs. single 2A3 can be roughly similar in 1 or 2 parameters, definitely different in others, so the OP question does have some truth behind it.

Given that, the question:
Can you provide a bit more background? Schematics of the 45 and 2A3 amps, speakers, etc.?
makes a lot of sense, while the answer
You mean that once you see the schematics you can make those valves sound alike? :)
sounds sort of cocky/immature.
So I’m reading that parameters are destiny, that geometry begets parameters, begets OP begets sound. A 45 sounds the way it does because of everything it is and no tube can be made to sound like a 45 until it matches a 45 in every way. Yet no one knows which of the parameters is responsible for what. This is because each parameter interacts with the preceding elements and it’s subsequent elements... in a unique way.

So, it is what it is, no figuring anything out, use it or don’t, try it you’ll like it. Build it and they will come.

Ok. Done that... it’s a great tube...

I just needed to know if I’ve missed anything. Just wanted a chat. Many thanks for all your responses.

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Every body knows how different sound the same reference tube but from different manufacturers . The 2A3 RCA is nothing but 2 x45 RCA but the filaments of the 2A3 has higher impedance each to draw 1.25A each instead of 1.5A for the 45. The filament being the cathode, this provokes more internal feedback for the 2A3 that you can hear the difference only if you use grounded cathode.
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