Hello there Leon & Crew,
>
>Earlier this year I bought a Dentron GLA-1000B linear. This is my
>first
>linear and I am not very technically inclined - but I like DXing!!
The Dentron GLA-1000x was a "cost effective" desktop amplifier using
common beam power tubes, often referred to as "sweep tubes". This name
was lifted from the use of these tubes in TV horizontal output circuits
where they could often be liberated.
During the CB radio "heyday" sweep tubes were often used in 27MHz
amplifiers which tends to give them a bad name, although the ARRL
Handbook and many QST projects appeared years before the CB radio fad hit
in the 70's. Using a set of four or six parallel tubes was the practice
of the day in grounded grid or super cathode driven.
>
>The output seems to be a bit light only about 200-300 watts. The
>voltage
These amps were meant to be used in SSB service at the "rated power", the
sweep tubes will handle the excessive plate dissipation only in low duty
cycle use. One of Rich's tuning pulsers is a great help here. The output
of the amp should be above 300 watts though, maybe your tubes are soft.
>reads about 900-910 V and the current from 110mA to 600mA max (on the
>panel meter).
Normally the Dentron "BBQ's" the heck out of the tubes with plate voltage
in excess of 1200 or so, yours seems a little low. But, your in Africa
with a different line voltage, that will all have to be taken in to
consideration. It would be practical to measure the filaments voltage
also.
>
IMO the Dentron amplifiers were physically hardy, but the circuit design
leaves a lot to be desired for many reasons... a lack of cathode
current cutoff during receive, poor efficiency above 21MHz, poor cooling
and the greatly exceeded ratings of some components to say the least.
Per my previous post, I mentioned a past QST article/project where I
"reworked" the amplifier making practical changes where needed. As I've
once again obtained two of these amps in original condition along with a
quad set of Svetlana EL-509 sweep tubes, I'm once again on the project of
reworking an amplifier. I have the luxury of the two amplifiers to
compare the results with at the completion of the modifications.
>Do I need to replace the tubes? If so with what? I don't find the
>number
>(D-50-A ??) in current ads. Any idea of the price and supplier?
>
Yes, like many other companies, this was a house number for the common
6LQ6/6JE6 tube which is around but becoming expensive and hard to find.
Svetlana has a similar type in production which is the source of my
article. The base of the Svetlana EL-509 is different, but most
everything else should make it a smart choice for the retrofit...
The D-50 label may have also come from 6LQ6/6Je6 tubes which were
"tested/rated" at the excessive plate voltage found in the GLA-1000x
amplifiers.
Other common sweep tubes were the 6KD6, 6HF5, 6LF6, GE-8950 and others.
All are out of production now if my information is correct.
>Your ideas would be appreciated.
>
Leon,
Yes, measure your line, filaments and HV voltage, only if you can
ensure your own safety. The lower than average HV you mention, means
there might be something different going on.
>73
>de ZS4Y
>Rev Leon M Foot
Last but not least...
I've received some nice input and offers of help from folks on the list
server here, so I'll be getting on to this project as time allows. Feel
free to chime in if you have addition information.
Thanks
Skip May wv6f
nospam4me@juno.com
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