I built up a pair of 813s based on the single band amps in QST or the
Handbook back in the early 60s. I used a B&W 850A Tank IIRC after my
infamous 6C21.
I drove them with a number of rigs from the Hallicrafters HT32, HT44, to
a Kenwood 820s. All had tube finals. Back in those days we didn't know
much about signal purity and few of us had a means to monitor the signal
other than listening to it. Panadapters were a rare and sought after
item. SWR meters were becoming popular with most of them being home brew.
Amps of that era (prior to the use of sweep tubes), including the 4-400s
and 4-1000s had little or no protective circuitry and most of those
designs were not amendable to being driven with today's solid state rigs.
About the only way we knew we had a problem was if someone told us. I
was on the air a lot, running that pair of five dollar 813s to the limit
of their ratings with no complaints unlike the 6C21. Good, unused NOS
surplus 813s were plentiful at $5 give or take. Few were gassy, unlike
today, some 50 years later.
I only used them for a few years so I have no idea as to their longevity.
What are the IM ratings (3rd, 5th, 7th) of the 813 when run within its
ratings, grid driven and GG?
73
Roger (K8RI)
On 12/21/2015 Monday 1:57 PM, Tom Osborne wrote:
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
Tom W7WHY
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