From bruce@ashbysolutions.com Sat Jun 12 13:19:04 2004
Subject:Re: Tube (and Amp) Terminology

Hi James,

> - The Leslie uses two pentode tubes operating in Class AB, while
the Speakeasy uses a triode tube running in Class A.

I thought they were beam tetrodes?

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From the Amperex data sheet:

"The ECC82 (12AU7) is a miniature, low-gain, medium-mu twin triode, each section of which has an individual cathode connection."

And from the GE data sheet:

"The 6550A is a beam-power pentode primarily designed for use in audio-frequency power amplifier applications."

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> - The Leslie power amp uses a soft rectifier circuit that was
actually considered a design limitation in its day; the Speakeasy
uses a firmer power supply design.

There's a silicon bridge rectifier which is pretty firm, although
there is the 8ohm 5watt resistor to limit inrush. You can't mean
the OC3 voltage regulator as it only affects biasing and not the
plate voltage which is supplied direct from the end of the smoothing
inductor. What would you say is the design limitation?

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Yes, I meant to say the "regulator" circuit, not the rectifier. The 0C3, like any tube regulator, will vary a bit over the operating range, adding a bit of "sag" to the whole process. It's not a huge item, but it does add to the total picture. It will also age and vary in performance more than an equivalent solid-state device.

Regards,

-BW
--
Bruce Wahler
Ashby Solutions™ http://music.ashbysolutions.com
978.386.7389 voice/fax
bruce@ashbysolutions.com