re: dentron amplifier(s)
:My friend has lent me an old Dentron GLA-1000 amp. (Yea, I know, it
:isn't what I would call much of an amp either but it is in like new
:condition and he bought it cheep about 3 years ago and hasn't used it
:since. Sort of a waste.)
Lent it to you not working, He's a friend eh..?
:One of the little pieces of information that came with the manual
:was an article out of Ham Radio magazine with regard to installing load
:sharing resistors in the cathodes to prevent the catastrophic failure of
:all of the tubes in the event that one went short. Seems reasonable so
:far.
Aside from the "fuse" action, some 10 ohm resistors in the cathode lead
of each tube improves linearity quite a bit. It's a great idea and I'd
love to
see a copy of that article. Please consider sending me a copy of it or at
at least tell me what year and month of the mag. The resistor addtion
will
also force the tubes to share the current better.
:The other note in the article is that the amp was designed for a
:tube called a D-50 but 6LQ6 was a suitable substitute but, BUT, that
:they would not work on 10 meters due to the inter electrode capacity
:differences...OK so far...
OK, ... but not really true, the 6LQ6/6JE6 tube plug right in, the bias
might have to be reset, but most case, it probably won't be too much
different. The Svetlana EL-509 is a candidate for the Dentron, there is
an article on their web site and a technical bulletin.
What the Svetlana conversion project fails to do is complete the job...
The cathode current should be cut off in standby by a simple mod using
the original relay. The 509 is a current production tube of similar size
and operation. The Svetlana tube seems to be a winner for a retrofit.
:My question is how do I make 6LQ6's work in this amp? I know that
:other sweep tube amps exist that either use 4ea 6LQ6 or similar tubes so
:how come this one won't? (BTW it doesn't seem to work on 10 either and
:I have checked to see if the mod was done to connect the tank circuit
:up.)
Drop in a quad tube set into a working chassis, circuit and go. There's
no mystery. If you can obtain GE brand tubes, they seem to handle
the extremely high anode voltage. You probably need to finish the 10
meter input circuit if you have a "B" version.
:My Second question.
:There is reference to an update kit to put the input tuning network
:in this amp as was done later in the "B" model. Obviously since Dentron
:no longer exists, does anyone have a spare kit around or can provide the
:component specs for the input tuning network on each of the 5 bands it
:covers. I am assuming that we are talking about a pair of caps and a
:tunable coil form of some type (Pi net) for each band.
Two or three ideas...
1) You can contact Amp Supply or similar for something they sell. 2)
Carl, KM1H back east has amplifier input boards (his current "health"
status is unknown now) for sale. 3) You can make up an input box or the
best idea is to buy a cheap antenna tuner and run it in front of the
amplifier using some nice meter like the Autek auto watt/swr meter unit
to get the presets. The parts are cheap and the values are in the
manual.
:If you happen to have the 5 coil forms available for a reasonable
:price, please let me know what you want for them as I haven't seen any
:out here at the swap meets in a LONG time. I'm not afraid of the work,
:just need the parts.
Contact Amidon for some toroids, the original coils in my Dentron GLA's
are made around toroid forms. They have a great data sheet and the price
is right. Small t-50-2 forms if memory serves.
: If there are any other improvements that can be made to this little
:amp that you are aware of and would care to pass along, they would be
:greatly appreciated. I am doing these improvements to say thanks to my
:friend for letting me use the amp for a while.
Cut off/reduce the cathode current in standby mode, clean up the cheezy
pc board on top of the plate choke used for the tube anode connections
(make it smaller or get rid of it). Add a 10 ohm resistor in each cathode
lead. Make the bias adjustable. Add or incorporate tuned input (buy a
cheap small antenna tuner if you have to). Look at the filter caps with
a suspicious eye. Add a HV glitch resistor. Add 10 meters and warc bands
and build better parasitic suppressors using data/parts available from
the ag6k web page.
: My observations of this amp gives me some ideas. Here are some
:conclusions I have drawn so far...
:The power transformer seems heavy enough to perhaps be used in a
:voltage multiplier to incorporate some other more suitable type of
:transmitting tube, say either a single 4CX400 or a 4CX800 maybe.
Yes, it has been done. but the duty cycle must be low. ie ssb The
transform runs very warm.
:The tank components seem heavy enough to accommodate perhaps up to
:800 watts or a bit more in a less than contest use amp...
pretty much SSB operation only...
:With the high cost of sweep tubes ($30 or more each) and the cost of
:a single 4CX400 by Svetlana at $130 and the 4CX800 at $190 plus $22 for
:the socket these look like a possible alternative. Am I on to something
:here or have I missed a better mod/rebuild? Perhaps a pair of 4CX250B's
:with the G3SEK tetrode board?
The Dentron GLA 1000 is a cost effective building block when you don't
use the original Dentron circuit or you improve it quite a bit.
:Looking forward to your thoughts on the subject...
:Mike Baker KØQZ/7
:Peoria, Arizona.
cheers mike
skipp@pilot.ucdavis.edu
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