Hi Carl,
-
: A friend of mine has a gla1000 ,plain model, which has
: been modified to use el509's.
-
How? just the physical replacement of the original
tubes with the EL-509's..? ... or was the more complete
job done (cathode current cutoff in standby, parasitic and
tuned circuit values reworked with optimum values
required by the new tubes types)..?
-
: He states that 15 and 10 meters has no gain at all.
-
Reduced output is not a desired product of a
conversion.
-
: I have questioned him extensively on it, input filter,
: pi-net changes, etc. per the Svetlana mod. article,
-
I have found problems with the Svetlana Article and
I consider it incomplete (doesn't contain the easy to
add standby cathode current cutoff circuit and has
other shortfalls).
-
I have considered calling a few incomplete Conversion
Articles - Modifications "to the carpet" because I feel
they have serious short comings and/or errors.
-
But I've seen the grief Rich went through over his
QST Text and decided a prolonged argument with
entrenched mule heads is not worth my time. The
Net provides an idea forum to present information
and opinions, so I put what I can into web pages.
-
: but no output except what is feeding thru. (100
watts input).
-
100 watts drive is way to much... 60 to 80 watts max
drive produces mucho betta' linear operation. I run
mine a 40 to 60 watts input and my similar type
amplifier preforms very well.
-
: he states that the lower bands work fine. 500 or so
: watts out with about 65 watts in.
-
Because (percentage wise) the input/output L&C
Values are less out of wack from what should be
their proper design values. The original circuits
provide a measure of "fudge values" which work
better on the lower HF bands.
The suppressors should also be replaced, L-sup
reduced quite a bit adjacent to the classic 100ohm,
3 watt low L-int resistor.
-
: he and I have been over this thing in detail and have
: not found anything beyond , in my opinion, some
: fault in the pi-net, but he has said that it was
: checked both with an mfj analyzer and with a grid
: dipper, and all seems to be tuning normally. does
: anyone here have any thoughts to share on this
: one???? thanks!!! carl / kz5ca
-
Rework the input and output L&C values as
required. Install modern suppressors and the
standby cathode current cutoff as described in
my Dentron GLA-1000 text available on the sonic
server. Replace the plate blocking capacitors with
proper type/value units.
-
The early GLA and other amplifiers lacking any
tuned input hardware can be retrofit with ckt boards
sold by various vendors. I shy away from anything
pre built unless it's already set up for my specific
type and amount of tubes... ie the values required.
-
In a more practical sense, it's not a bad idea to
"lift" the early Alpha 374 broadband input ckt for
this early model Dentron. Credit where due, it's a
nifty circuit approach for this specific type of
roadblock.
-
hope that helps you with Bill's amplifier..
cheers
skipp
nospam4me@juno.com
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