[Amps] Building an Amp, Selecting a Tube

[Radio WC6W]

Hi Roger,
   The 4CX1500B is only good for a KW out, so you'd need a pair.  The other three '1500x tubes I previously noted are each good for 2KW solo.   

   You didn't mention any size/weight restriction in your original multi-dimensional query.  I'd suggested the Henry 4K Ultra as it will do 2KW out all day and has the physical space to facilitate your desired band additions.

   If size and weight are added to the specs, I'd surmize that an 8877 with a switching power supply may trump all other options.   Eschewing all bands save 6M would save lotsa $$ on coils, caps, switches and perhaps a third of the physical volume.

   At the risk of engendering a zillion questions, here is a link to an autotuning 8877 design (in process) which may prove to be of interest... or not.

http://wc6w.50webs.com/wc6wamps/index.html?fr40.html

   It should be squeezable into a 17" x 17" x 6.5" hi cabinet and will weigh in the vicinity of 40 lbs.   Six meters would remain problematic sans the output network trick that I previously noted.

73 & Good afternoon,
   Marv WC6W

http://wc6w.50webs.com/


--- On Sun, 7/27/08, Roger (K8RI) <sub1 at rogerhalstead.com> wrote:

> From: Roger (K8RI) <sub1 at rogerhalstead.com>
> Subject: Re: [Amps] Building an Amp, Selecting a Tube
> To: wc6w_amps at yahoo.com
> Cc: amps at contesting.com
> Date: Sunday, July 27, 2008, 7:13 PM
> Radio WC6W wrote:
> > Hi Roger,
> >   You wandered in several dimensions with that query.
> >
> >   
> Oh, yah...<:-))
> >   For 2 KW out, I'd recommend going with a single
> tube, unless providence brings something else, with
> sockets, your way. The obvious choice is an 8877.  Somewhat
> rarer, and typically less pricey surplus, are the old
> 4CX1500A, and 5CX1500A/B which are also good for 2 KW out
> but, are filament power hogs.
> >   
> <sigh> about 15 to 20 years ago I cleaned out a bunch
> of stuff as I was 
> so busy and seldom on the air. I had three, new 4CX1500Bs. 
> The A 
> version is the real current hog at 38.5 amps (nominal)
> while the B runs 
> between 9 and 11 amps. Now I wish I had those back. Of
> course the B is 
> the one that takes the expensive socket. 
> >   Covering 160-6 meters is a challenge.
> That's not a necessity. I'm just spoiled with the
> auto band switching 
> between 160 and 6 on the HL-1.5Kfx. I've also
> entertained the idea of 
> just a 6-meter amp.  I was ordering one from Alpha when the
> 1600B became 
> unavailable.
> >   You might consider either switching to a separate
> output network for 6 or... there is an old trick of
> inserting a small (adjustable) coil, which will only
> marginally affect low band operation, between the
> tube's plate and the tune capacitor.  On 6M, the
> tube's output C then becomes the input capacitor of
> output network and the low band plate capacitor becomes the
> load cap with a separate small L coil from this point to the
> 6M output connector.  If the pi section of the low band
> output network is simultaneously set to 160 Meters, it will
> have enough reactance (circa 5K ohms) to be irrelevant.  A
> separate plate choke will be necessary for 6 or... the
> through the coil plate feed trick may be employed.  See:
> http://wc6w.50webs.com/wc6wamps/index.html?fr62.html
> >
> >   Finding the tube may not be the hardest part of your
> quest.  The tank L's, C's and bandswitch seem to be
> somewhat less available nowadays.  And let's not forget
> the matter of some largish power supply parts.
> >   
> If need be I can wind the coils and probably find the
> capacitors, but 
> and adequate band switch could be a problem.
> >   Transistors would be a whole 'nother can of
> worms.  2 KW reliably suggests 16 devices plus a bunch of
> splitters and combiners, a bank of output filtering, a 4 KW
> power supply, and if running into anything less than a
> perfect 50 ohms a 2KW rated tuner.  It ends up being lots
> more stuff.
> >
> >   
> Everything except the tuner is built in, but it makes for a
> complex 
> design. Except for the tuner it's quite compact and
> easily lends itself 
> to liquid cooling.  I've actually taken a pair of 160
> watt, 2-meter 
> amps, using splitters and combiners tweaked them into well
> over 300 
> watts out.  (BTW step one is disabling the RF keying
> mechanism in one of 
> the amps and slaving it to the other. Otherwise it can get
> interesting 
> as they take turns keying each other<:-))
> >   Now what was that about buying a commercial amp? 
> :-)    I believe that old Henry 4K Ultras are going in the
> low $3K range; Not all that much when you consider that
> those prices are in inflato-dollars.  You'd only need
> to add a few parts for 6 & 160 to meet your goal.
> >   
> But man are they big and heavy! <:-))
> 
> I just got rid of a 2K4 with heavy duty Peter Dahl plate
> transformer and 
> a spare set of Eimac tubes.
> I might just get another 76A and put a pair of 3CX800s in
> it as a  
> 6-meter monoband amp.  I'd make up a new front panel
> and have a neat, 
> compact, rugged, and relatively inexpensive amp.  The 76As
> are going for 
> bargain prices most of the time at usually less than $1000
> with full 
> output although the prices cover quite a wide range.  If I
> could get a 
> good 3-holer, I'd use it for HF and convert my old
> 2-holer to 6-meters.  
> That would be the least expensive and neatest route with
> the least 
> work.  Once the 8874s gave out I'd convert the three
> holer to a pair of 
> 3CX-800s as well. That should run the legal limit, key down
> for hours.
> > 73 & Good evening,
> >    Marv WC6W
> >
> > http://wc6w.50webs.com/
> >
> >
> > --- On Sat, 7/26/08, Roger (K8RI)
> <sub1 at rogerhalstead.com> wrote:
> >
> >   
> 73 and thanks for the ideas.
> 
> Roger (K8RI)