[AMRadio] New Transmitter


Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Mon Nov 27 13:31:40 EST 2006


I don't know if you would get as much power out
of the 572b's as the 813's.
The 813 loves 2000 volts at 200ma each, and they will run
all day that way, you can push them to well above that.

572b's are triodes, and in my 811/812/572b rig, the 572b's 
gave very little power over the 812a's, lots more plate current
could be had, but not much more power output.
I suspect I needed to bump the voltage way up to run
them where they want to be and get more power out.

The 813 lends itself to pie net output, the 572b
needs to be push pull since it's a triode.
There are ways around that but it might be tricky.
A real push pull link coupled triode RF deck works really
well, tunes up nice, and is very stable, at least if its
built well and neutralized.
A joy to operate.

The 813 pie net is also very stable and easy tuning.
My pair runs a vacuum cap and a roller inductor ganged,
so I have plate tune and load, for continuous coverage
from 1.5 to 30 Mc. I normally run it at 2000 volts at
400 ma, around 600 watts of carrier, pep can be over 2500
watts if I run the audio up.

The 811/812/572b push pull rig ran 1500 volts, about
340 ma of cathode current (-70 ma grid drive) is 270
ma of plate current for 300 watts out.
No color on the plates.

With the 572b's, I likely would need to take the volts up
to 2000 or more to get good power out.

The 812a modulated by 811a's is a good setup, you can run it 
at 1500 volts both modulator and rf, and with bias on the mod
tubes up to 1700 or more volts.

The powerhouse rig would be the 813's modulated by 813's
in AB1 (regulated screen volts). I bet that would be clean.

Brett
N2DTS

  

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Mike Sawyer
> Sent: Monday, November 27, 2006 10:46 AM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] New Transmitter
> 
> Jack,
>     Did you mean 572's or 872's? 572's are triodes and 872's 
> are mercury 
> rectifiers. I suspect you meant 572's. The 572 are ok but I'm 
> here to tell 
> you that the 813 is a damn near indestructible tube! I have 
> seen plenty of 
> 572's that have crapped out from abuse of some sort or 
> another. But I have 
> yet to see an 813 that has crapped out. Take it from me, they 
> are a very 
> hearty tube and you can get them cheaper than the 572's.
> Mod-U-Lator,
> Mike(y)
> W3SLK
> ----- Original Message ----- 
> From: "Jack Schmidling" <jack at schmidling.com>
> To: "Discussion of AM Radio in the Amateur Service" 
> <amradio at mailman.qth.net>
> Sent: Monday, November 27, 2006 10:35 AM
> Subject: Re: [AMRadio] New Transmitter
> 
> 
> Jim Wilhite wrote:
> > In my 1964 handbook there is a One-Band Kilowarr Amplifier 
> that uses a
> > pair of 813s.  It is grid input and would be easy to 
> modulate using 811s
> > or 572Bs.
> 
> That brings up something that is confusing to me.  I have 
> been reviewing
> specs to get familiar with the more popular tubes out there 
> as they were
> just numbers to drool over back when I was homebrewing.  I never got
> beyond 807's.
> 
> Anyway, I looked into 872's because that is what is in my 
> SB200 and was
> surprised to find that the plate dissipation is considerably 
> higher than
> an 813.
> 
> So, why would one not modulate 872's with 813's?
> 
> I guess I should forget about the higher voltages.  Too many senior
> moments these days.
> 
> js
> 
> p.s.  The D104 works great with the new Mouser cartridge.
> 
> -- 
> PHOTO OF THE WEEK: http://schmidling.com/pow.htm
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> http://schmidling.com
> 
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