Maybe being in Thailand, where 230vac is supplied with TWO wires, makes me
ask.... what is 4-wire 240vac service?
Charles Harpole k4vud@hotmail.com
> From: w9ac@arrl.net
> To: at6c@bellsouth.net; Amps@contesting.com
> Date: Sun, 3 Apr 2011 10:35:01 -0400
> Subject: Re: [Amps] Alpha vs Henry
>
> George,
>
> If 160m is of interest to you, may want to re-evaluate Henry amps, including
> the 5K.
>
> Concerning mods for the 77Dx/Sx: few mods have been published and either
> version of the 77 is fine as it is. I own a 77Dx and have avoided a
> conversion to the Sx for several reasons:
>
> 1) Added cost of an 8877 during replacement;
> 2) Slightly added difficulty in isolating trouble with a pair of tubes. A
> minor issue;
> 3) The added class of power really requires changing the RF output connector
> to a DIN type;
> 4) Fuse holders should be upgraded;
> 5) Relatively poor Ep regulation of the Sx version unless an outboard
> Hypersil transformer is used. Some folks have reported better regulation
> with a direct- replacement Dahl type although it's a snug fit;
> 6) The Dx already has way more reserve than needed for most operating modes
> in American-licensed service.
>
> Added together, I just can't justify the change. However, I did make the
> following changes to my 77Dx:
>
> 1) Isolated neutral from chassis ground. As it stands, these Alpha amps are
> not UL compliant. Although not compliant with the NEC, the NEC is factually
> a premise wiring standard -- not a product wiring standard. The mod is
> super-easy since it involves only cutting a jumper on the Cinch-Jones power
> plug. However, 4-wire service and 4-wire power cord is required. If you
> have not already added 4-wire 240V service, consider it if you plan on using
> older Alpha and Henry amps;
>
> 2) Elevated the filament return off the chassis. I detest the chassis being
> used for high-current filament returns -- even more of a concern with the Sx
> as 20A of current flows in the chassis. It's a personal bias of mine; many
> Alpha amps have run for decades without issues;
>
> 3) Added a filament choke. A side benefit is that there's just enough of an
> IR drop through the choke as a result of my 250VAC mains to ensure that the
> filaments run at 5.0V. Before adding the choke, my filament voltage ran
> above Eimac's specification and I was replacing tubes way too often because
> of filament issues. High filament voltage combined with many intermittent
> on/off cycles leads to these failures. Also, after inclusion of the choke,
> I did not tie the filament to the cathode (e.g., AL-1500) although that
> could be done if I were convinced of the necessity. I've seen arguments
> both ways (primarily fault related) from respected amp designers as well as
> former Eimac engineers. It stays unconnected for now;
>
> 4) Added gas discharge tubes to the filament and cathode terminals, and
> added bypass caps to the filaments connections.
>
> Just my $0.02, and I'm sure others will disagree with me on some of these
> changes. Good thing I'm not writing article for QST!
>
> Paul, W9AC
>
> ----- Original Message -----
> From: "George Steube" <at6c@bellsouth.net>
> To: <Amps@contesting.com>
> Sent: Sunday, April 03, 2011 7:58 AM
> Subject: [Amps] Alpha vs Henry
>
>
> > Looking at purchasing an Alpha SX/DX or Henry 5K for my amp collection.
> > Any
> > advice/comments on these amps would be appreciated. My biggest concern
> > with
> > the Henry would be future tube replacement. Any recommend mods for
> > either
> > amp? Thanks.
> > George
> > W2GS
> >
> >
>
>
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