[AMRadio] GG 813 Linear in GE Ham News


Gary Schafer garyschafer at comcast.net
Thu Sep 29 10:45:03 EDT 2005


Hi Jim,

No magic in the 600L. If you run it at 100 watts carrier out then it has 
to be capable of 400 watts PEP output in order to be linear. That would 
be around 660 watts input. Assuming 60% efficiency in AB2 grid driven.

At the 100 watt carrier level the efficiency would be around 30% so 
input power would be about 333 watts. Plate dissipation would be 233 
watts! 813s will tolerate that for awhile. But I don't think the 600L 
will put out 400 watts PEP? At least not while being linear. You may be 
able to see that much out of it at tune up if driven hard but I would 
bet it gets driven closer to class C with that much power out.

73
Gary  K4FMX

Jim candela wrote:
> 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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> 
> 
> 
> 
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