[AMRadio] GG 813 Linear in GE Ham News


Jim candela jcandela at prodigy.net
Thu Sep 29 07:47:54 EDT 2005


Gary,

    Yes your correct. That said a 813 has conservative Pd rating of 125
watts whereas tubes like the 572 which appear similar in plate area are
rated for 160 watts Pd. The rule of thumb is for AM use is that the max
carrier output is 1/2 the Pd of the tube(s) + feedthrough power (G-G
circuit), so for two  813's we have (125 + 125)/2 + 25 (guess) = 150. This
assumes an efficiency that is about 33% carrier alone, and 66% at 100% sine
wave modulation. I bet we can get closer to 200 watts out for ICAS service
and still have headroom for 100% modulation from a pair of 813's. Those
tubes better be forced air cooled, and you better be talking without pause
since the tubes will cool down with modulation (efficiency doubles at 100%
sine wave modulation).

	This rule of thumb doesn't seem to apply to my Central electronics 600L
linear which has a one 813 grid driven in AB2 mode. This amplifier can put
out 100 watts carrier and modulate it fully to + 100%. This implies the tube
is dumping 200 watts (no modulation) for 100 watts output. There is color in
the tube for sure, but 200 watts? I don't think so. Maybe those broadband
couplers in the patented 600L somehow boost the efficiency. I have never
figured out why the 600L can do that.

Jim
WD5JKO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of Gary Schafer
Sent: Wednesday, September 28, 2005 9:24 PM
To: Discussion of AM Radio
Subject: Re: [AMRadio] GG 813 Linear in GE Ham News


A pair of 813s in GG are only good for 150 watts carrier out on AM.

73
Gary  K4FMX

doxemf at aol.com wrote:
> Hello All,
>
> The thread on final circuits has been great to follow especially with the
mention of 813's.
> It is still a very cost effective tube and in good supply NOS since the
audio crowd has yet to make much use of them.
>   I have a copy of GE Ham News from Nov-Dec 1959 that features a "Kilowatt
Grounded-Grid Linear Amplifier" to quote the cover.
>   It uses a pair of 813s GG with a standard Pi Net output configuration 5
band switched 80 -10 mtrs.
> Looks real easy to build and with the exception of the B&W filament choke
FC-15, I have most of the needed parts or
> can find them. The construction article is well documented and pictured.
>   Is anyone is familiar with this amplifier or better yet knows of one
being built? If 160 meters would be easy to extend to with more L & C where
needed then it would work well for anyone with a good drive source.
> For those that do not have the Ham News Issue I can scan a copy and e-mail
it.
>
> Thanks for any info,
> Bill  KB3DKS/1
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