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Re: [Amps] 813's

To: "Fuqua, Bill L" <>, "Tom Osborne" <>, <>
Subject: Re: [Amps] 813's
From: "Carl" <>
Date: Wed, 23 Dec 2015 17:23:36 -0500
List-post: <">>
I save my glow bottles for Class C AM use and as modulators. A couple of 304TL's can really light up the room as can HK-354C's, and 250TH's. Some long years ago I ran a pair of VT-127A's (aka 100TS after WW2) on 40 and 20 CW only at close to 1200W out, the white plates never seemed to weaken them but I did use plenty of air.

I also have a pair of 6C21's (pulse 450TL's running way overvoltage on the filaments as short life wasnt important) and havent run them anywhere near their best glow as regular 450TL's.....yet.

Too bad none of those oldies are good linear amp tubes.


----- Original Message ----- From: "Fuqua, Bill L" <> To: "Carl" <>; "Tom Osborne" <>; <>
Sent: Tuesday, December 22, 2015 11:28 PM
Subject: RE: [Amps] 813's

One problem was that most articles stated that a pair of 813's would work operate at 2kW PEP or about 1200 or 1300 Watts PEP output. I can see why they seemed "unclean" since many hams built these amplifiers from magazine articles and pushed the pair of 813's to the 1 kW average plate input power limit on SSB. But four good 813's should do today's legal limit just fine at 2.5 or 3 kV. That would be like running four 4-125A's or even better 6155 and you can watch the plates glow too.
Which brings up a question I have, anyone ever try 4E27A's in grounded grid?

Bill wa4lav

From: Carl []
Sent: Tuesday, December 22, 2015 6:05 PM
To: Fuqua, Bill L; Tom Osborne;
Subject: Re: [Amps] 813's

While the 813 was rated at 125 PD it was a very conservative CCS and over
years of use Id rate them in the 200-225W range for ICAS service. Compare
the size with the Cetron 572B anode and you can see why; Svetlana and
Chinese are only 125W but the new ones may be higher. This is only for the
graphite anode versions; the later sheet metal version used would melt down
as fast as an 811A in a AL-811 series amp.

With a good tube final exciter such as the Kenwood hybrids the IMD is in the
low -30's real dB; that is about -37 ARRL dB's.

With an SS exciter and an untuned input there is no flywheel effect loading
on the exciter so IMD is typically 3-5dB worse.

The best IMD with a tuned input is at around 2700V but it varies little from
2500 to 3000V when output remains the same; 4 full emission tubes will
easily do 1300-1500W with a little help from a fan.


----- Original Message -----
From: "Fuqua, Bill L" <>
To: "Tom Osborne" <>; <>
Sent: Tuesday, December 22, 2015 1:15 PM
Subject: Re: [Amps] 813's

 Graphite is always messy, I have gotten it on hands clothes and it is
hard to wash out.
I think perhaps they should not have earned such a reputation. I believe
the problem stems from the
fact that most 813 amplifiers in the early days had untuned inputs and
that they were pushed
harder than they should have been. Mind you these tubes in triode
connection are about like 572B's.
They have even less plate dissipation than 572B's but I suspect the idea
of pushing them to
2kW PEP plate input was just too much. Also, most used 813's I have gotten
had very little
emission left. That is an indication that they were used beyond the point
where if pushed to
get full gallon output they were probably producing a very dirty signal. I
think if you use
a good pair, with tuned input and don't try to push them too hard they
will be just fine. Treat them
as if they were a pair of 575B's.
Bill wa4lav

From: Amps [] on behalf of Tom Osborne
Sent: Monday, December 21, 2015 1:57 PM
Subject: [Amps] 813's

Why are 813 tubes considered 'dirty'?

I have an old amp in the attic I haven't used for a long time that has a
pair of 813's in it  I have read somewhere that they are a very 'dirty'
tube.  I'd assume that means lots of spurs or something.

Just wonder why that would be.  73
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