>I do not have the exact wording at this computer of prior statements, but I
>do recall that Rich stated that the G2DAF failed two actuals tests. The
>first was with an 813 tube and the second was with a 4CX250B tube. Since I
>had no standard for the 813, I discounted it.
The 813 is designed for Class C, grid driven service with relatively low
screen potential. I have never seen 813 data for grid driven linear
service with elevated, regulated screen potential. My guess is that the
results are unsatisfactory.
>
>However, I was reminded that the G2DAF had failed two tests. Therefore, I
>wanted to examine the 813 tests. My assumption (which I think was
>reasonable) was that the 813 when grid driven with a constant screen voltage
>was significantly inferior
Without data, who can say?
>As farto the 813 when configured as a G2DAF amplifier
>(grid driven with variable screen voltage derived from the driver).
>However, it appears now that the test was in fact with a 813 configured as a
>G2DAF amplifier compared to the 813 operating in grounded grid.
>
>What sort of a comparison is this? Rich's statement that "The 813 is not
>linear in grid driven service" would mean that a G2DAF test with an 813
>would be faulty by the very rules stated by Rich. Thus that test is
>meaningless. It is like comparing apples to road graders.
? Hardly. The man who owned the 813 amp. decided to convert it from
DAF to G-G because he found out that grid-driven linear service was
apparently not possible for the 813.
>
>Suppose we take a 4CX1500 (which has superb 3rd order imd in grid driven
>service) and operate it in a G2DAF circuit
The DAF circuit normally runs fairly high grid current. The 4cx1500B has
a 1w grid.
>and compare that to a 4CX1000 in
>grid driven service with regulated screen. Any bets on which amplifier
>would win? I would not bet my pension on that one without a lot of
>empirical tests and also a close reading of the rules.
>
? A 4cx1500B is pretty hard to beat if it has a shunt screen regulator.
.
>And, what are the desired standards for 3rd order distortion anyway?
IMO, 30db down or better is fairly ok. Transceivers are usually a bit
better. . .
>
>Thiswould perhaps be a good discussion topic. -30 db 3rd order distortion
>products do cause splatter. Is that the minimum level of distortion for a
>ham to transmit with. For years I listened to W7FY (now deceased) who ran a
>4CX1500 in grid driven service.
? The "B" version or the "A" version?.
>His station was significantly cleaner than
>other signals and a real pleasure to tune off of. Using his signal as a
>standard, other signals were noticbly inferior. Unfortunately, a lot of
>transceivers still use -30 db as the standard. Some of the newer
>transceivers use high voltage output transistors and have significantly
>cleaned up the drivers - which means now we should concentrate on the
>amplifiers and get good strong signals instead of bad strong signals.
>
>I listen on the dx window and hear a lot of signals that could be better. I
>believe the newer Alpha (and other amplifiers) have contributed a great deal
>to cleaning up the bands because of two factors: first is the use of superb
>triodes (3CX800A7), and secondly with the use of peak reading led measuring
>devices to replace the analog meter.
>The second factor may be more
>important than the first. Using my older Alpha with analog meters, I find
>that my scope indicates full power when the meter only registers about 10%
>of key down reading.
Either way, the amplifier still has to be tuned for max. out with max
drive. Either metering system can be used to detect max out.
>There are a few souls who yell into the mike when
>excited and trying to work dx and peg the meter (I have been in the shack of
>a couple), and with the analog indicators, hams can make the meters pin
>without quite as disasterous consequences.
CB operator syndrome is apparently contagious, Colin.
- Rich..., 805.386.3734, www.vcnet.com/measures.
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|