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Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: silverfox on November 13, 2016, 11:35:10 pm

Title: Hammond Tone Cabinet- Resurrection of Old Thread
Post by: silverfox on November 13, 2016, 11:35:10 pm
       (http://el34world.com/Forum/Themes/default/images/post/xx.gif) Help Ken!! I picked up a Hammond PR-40 This Weeken (http://el34world.com/Forum/index.php?topic=384.msg400#msg400) « on: June 18, 2005, 06:32:40 am »
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Platefire
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Posts: 614
(2/17/04 9:06 am)
 Help Ken!! I picked up a Hammond PR-40 This Weekend
--------------------------------------------------------------------------------
 Hello Ken and other Hammond enthusiast.

I couldn't resist. I found a Hammond PR-40 Tone Cabinet in a flea Market this week end and picked it up for $20.00. I was
impressed with the heavy duty looking 2-15" and 2-12" speakers and...

11/13/2016:
Well I just did the exact same thing the other day- From a Goodwill As Is outlet and the same price $20.00, but someone had pinched all the tubes from it while it was in the Retail store. From reading the text of the ancient thread above, and having searched for schematics etc.. I've determined this isn't worth anything other than the speakers. They do sound good, but I've already got 12's and 15's. The Choke may be usable but it's only 2.5 Henry. The transformers aren't even useful. It did get my curiosity up though. Briefly considered using the power supply as a bench unit but it looks like, one false move and it'll kill ya! I think the best use will be to put a small tube based power amp in it and use it for a home stereo system. I've got a Maggy 20 or so watt power amp that only needs a cap replaced...

Question- What are the taps on the output transformers used for that seem to FB? My guess is: A FB loop as a crude crossover circuit.

silverfox.
Title: Re: Hammond Tone Cabinet- Resurrection of Old Thread
Post by: PRR on November 14, 2016, 12:28:25 am
> What are the taps on the output transformers used for that seem to FB?

FB.

> My guess is: A FB loop as a crude crossover circuit.

Nothing crude about it. No loudspeaker crossover.

Works "same as" OT speaker tap back to driver cathode. Except there is less gain inside the loop (just one stage). Works wonderful well to damp speaker bass resonance; also OT top-end resonance. Also reduce distortion. It is a popular after-hack to modify Dynacos with 16 and 0 to power tube cathodes. Works the same though grounding is awkward. Hammond wound a separate winding for cathode duty, leaving a good place for a common cathode resistor.

Has some of the advantages of UltraLinear, maybe more, though not the reduction in G2 current in severe overdrive. And UL was patented; any patent on this type cathode NFB musta been expired.