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How can the interstage drive either 300Bs or 2A3s without any modifications?

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This is not a challenge. I just want to know what it is about the 2 tubes that they can use the exact same power supply, driver and transformers and be prefect subs. The 300B puts out 8W, the 2A3 4W. Are they really so identical...operating points and all?
"What did the Romans ever do for us?"

Follow Ups:

RE: How can the interstage drive either 300Bs or 2A3s without any modifications? - Acoustic-Dimension 03:17:17 05/16/10 (0)
They don�t use the �same� power supply. There are different voltage taps on the powertransformer. This way the 300B is supplied with a higher B+ then the 2A3.

The voltage on the interstage transformer and driver tube is lower then the high tension on the 2A3 output tube, so with a different voltage dropping resistor ( 300B versus 2A3) in the power supply, it is made sure that the tension on the driver tube is correct.

With a driver tube and interstage that is designed to drive a 300b tube (to be able to provide the needed voltage swing), driving a 2A3 tube is no problem as the 2A3 requires less voltage swing.

P.S. a 300B (in it�s normal A1 operation point) does not need a driving current. That�s the difference between tubes and transistors, tubes require no current, only voltage.
But the 300b requires a very large voltage swing. Not many drivers can supply this (without distortion). When you change the anode load from a resistor to an interstage, the interstage will give you about 40% more voltage swing at the same distortion, or for the same voltage swing about 40% less distotion, and the the distortion also has a much nicer distibution of the harmonics.

An interstage does not care which tube it has to drive, the only important thing is making sure that you select the right driver tube. The driver tube must be able to supply the needed voltage swing and (very important) have the right internal resistance. It can�t be too low or too high. A driver tube with a to low or to high internal resistance will turn the interstage into a �tone controle�

Best regards, Peter
RE: How can the interstage drive either 300Bs or 2A3s without any modifications? - GTCharlie 01:34:05 05/01/10 (5)
not the same at all. different driving current and voltages, different operating points (plate voltage and current)
- Yes, but...the advertising doesn't exactly say that. Nt - Frihed89 23:26:31 05/02/10 (4)
  Nt
  "What did the Romans ever do for us?"
  - Si would like to know truthfully how the interstage kits for the parallel 2A3 and 300B differ - Frihed89 23:27:47 05/02/10 (3)
    Which I think is a fair question.
    "What did the Romans ever do for us?"
    - RE: Si would like to know truthfully how the interstage kits for the parallel 2A3 and 300B differ - GTCharlie 03:13:29 05/04/10 (2)
      Hi. The 2A3 and the 300B have different driver needs --- the 300B requires massive current. An interstage transformer carries voltage and current. just make sure these are not exceeded.
      - RE: Si would like to know truthfully how the interstage kits for the parallel 2A3 and 300B differ - RC Daniel 20:56:14 01/02/11 (1)
        
        In Reply to: RE: Si would like to know truthfully how the interstage kits for the parallel 2A3 and 300B differ posted by GTCharlie on May 04, 2010 at 03:13:29
        
        Hi GT
        I am very late to this thread, but it may get looked at...
        IIRC, the 2A3 has the (slightly) higher Miller capacitance, thereby necessitating greater current drive. The 300B has greater voltage drive/swing requirements to push it to full power, but is roughly the same as the 2A3 re gain/out put for a given input voltage and operating point & load. So, for a given output, the 2A3 appears to be slightly more difficult to drive; the 300B is capable of greater power, but requires an increased amount of voltage swing.
        Also, IIRC, a DHT starts to draw grid current as it approaches full output; therefore in a common system, the 2A3 will be making greater demands of the driver earlier than a 300B.
        So, the 300B may be more difficult to drive to FULL POWER - all things considered - but may be easier to drive than a 2A3 in some systems (eg. where a 2A3 is being asked to produce next-to-maximum RMS output).
        It has been some time since I have actively thought about this stuff - I could be totally off-track.
        [Edit:
        Just realised how old this thread is; I do not expect a reply or follow-up to my post]
        Cheers
        
        Edits: 01/03/11
        
        Thanks - Frihed89 08:41:32 02/18/11 (0)
        
        In Reply to: RE: Si would like to know truthfully how the interstage kits for the parallel 2A3 and 300B differ posted by RC Daniel on January 02, 2011 at 20:56:14
        
        I am learning. I have seen several 300B circuits turned into 2A3 circuits to take into account these factors, but while it's easy to get information from DIYers, it's harder to get out of mfrs, often.
        "What did the Romans ever do for us?"

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