A Question for Bob at CF 2011

I found this on MartinLoganOwners.com (.net?) & wanted to pose the question to Bob & see what is the difference between what the OP said was Bob "borrowing" an old Altec-Lansing design & Bob's own DC Restorer Circuit~

"Every vacuum tube amp in the world suffers from shifting DC operating points, and this unfortunately has remained a functional limitation and maddening sore point for amplifier designers ever since the very beginning of vacuum tubes. Consequently I had to invent a DC restorer circuit using a 6AL5 / 5726 tube; it eliminated every last vestige of DC shift, while simultaneously reducing distortion three-fold and vacuum tube idle power by the same amount. As Tim would say, "Nothing new under the sun", just the same, it's never been done before, and it works flawlessly.

Bob"

Sorry Bob,

My Audio Cyclopedia dated 1959 , on page 547, has shown that the Altec Lansing 436B compressor amplifier also used the same "a DC restorer" circuit that you have claimed invented, what a coincidence, used the same 6AL5 tube. Care to clear-out the smoke? Attached is the schematic.

Altec Lansing DC Restorer circuit.jpg (53.27 KiB) Viewed 717 times

I thought bob used a zener between the grid and the cathode. I see nothing like that in this schema.

I thought bob used a zener

I think he does, he also stated that this diode was not around back then.

Over coffee this morning, I had a chance to sit down with Bob and show him this thread, Gary. Here is his response, right from the horse's mouth.

Thank you for your question as it's a good one. It's not a DC restorer circuit, it's a compressor circuit. It's the difference between a Ninja motorcycle and a walking stick. They are completely different.

If we inspect the circuit carefully, we note that the Altec circuit is AC coupled and is configured as a simple compressor circuit over a threshold. Compressor circuits have been with us since the beginning of time and are designed to prevent overload. It's a simple compressor [Well designed and fully balanced] and that's what it is. Most professional audio gear has a compressor somewhere in the signal chain and this Altec is no exception. It has in common with my circuit a 6AL5 vacuum tube, a simple vacuum tube diode. 6AL5s were used by the zillions in every electronic circuit ever built that needed a fast, small signal rectifier including FM tuners, radar transmitters, television receivers and on and on.

I was inspired by an old DC restorer in the video amplifier section of a vintage TV set. A video signal must retain it's DC value. Hope this helps.

Reply posted to the forum, Tom. Thanks to you & Bob~

My question is did he check the tubes on that Miss Holygram in the video?

I don't think she had a tube Bill......she appeared to be a SOLID state model!

sweet and juicy like these nutz.

I'm far too lazy to make any kind of meaningful post, So I will just go ahead and post my 2523rd "sweet and juicy like these nutz." post here.

You're enjoying that a little TOO much, Jesse~

You're enjoying that a little TOO much, Jesse~

Making a point, Gary. Making a point.

Not a question, but I just noticed this comment over on Club Polk in a thread about Bob's 900 watt tube amps he sold on eBay a while back:

"Nothing but respect for one of the industries greatest. Look at that crazy bastard , you just gotta love it.
They are some sexy ass tube amps. Makes me just want to touch them."

I had a good chuckle over that one ~ thought Bob might enjoy it