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Lectrolab R400 Output Transformer?

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  • Lectrolab R400 Output Transformer?

    I'm working on a Lectrolab R400 guitar amp, and I decided to run some checks on the output transformer.

    This is a single 6V6 amp, and the amp has what appears to be the original 8 Ohm Quam speaker. However, tests on the output transformer show that the primary OPT impedance is around 16k Ohms @ 1kHz with an 8 Ohm resistors on the secondary. It appears, as far as I can tell, to be the original output transformer. The OPT has an additional output tap, but that one measures even higher, like 35k into 8 Ohms.

    These amps aren't very well-documented. Were they the type of budget amp where the builders just sort of threw together whatever surplus parts they could get whether or not it was technically right?

  • #2
    Unless I had compelling reason to think this was not designed, I would assume the transformer was appropriate to the task.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      I'm sure it works, but isn't 5k-8K more typical as a load impedance for a 6V6?

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      • #4
        That other tap would give you around 16K into 4 ohms, so I'd think it's a 4 ohm tap if the 8ohm tap is also 16K.
        Champs run 8K OT's with single ended 6V6, but the desired impedance does depend on circuit conditions such as voltages, and priorities such as distortion versus output power etc.
        And you are sure it is stock OT ?
        Originally posted by Enzo
        I have a sign in my shop that says, "Never think up reasons not to check something."


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        • #5
          Originally posted by g1 View Post
          And you are sure it is stock OT ?
          It's hard to be sure of anything on these. It took some research just to identify the amp as it had no brand or model number markings on it whatsoever.

          The OT has a slightly unusual mounting flange that matches the screw holes on the chassis, and there are no other empty holes in the chassis where another OT might have been mounted. That leads me to believe it's probably stock.

          With some of these inexpensive amps, I sometimes get the feeling that they were just throwing them together and getting them out the door.

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