Dentron GLA-1000 (plain), B & C Amplifiers


The Dentron GLA-1000 Plain (80-15/10 meters, no tuned input), the GLA-1000-B (80-15 meters, tuned input) and the GLA-1000-C (160-15 meter) Sweep tube Amplifiers make a nice desktop amplifiers when some circuit updates are installed.
I enjoy working on RF Amplifiers. The Dentron GLA-1000 is a Sweep (or Beam Power) Tube Amplifier I've always liked to use as a cost effective parts source. The amplifier chassis with proper circuit improvements can become a long term reliable amplifier. Some of the original circuit short falls are pretty gross and easily corrected. Cathode current is not reduced or "cut-off" in receive mode. There is no failure mode "glitch protection," nor are many of the "current state of the art" updates present which would probably improve the circuit preformance. It's just a relative measure of time before the Amplifier fails for any number of reasons or "circuit short cuts." Why wait for the often expensive smoke, read the text and references I provide and you will hopefully learn how to "roll your own" updates into your Amplifiers. The results are well worth the time and expense.

There are quite a few previous GLA-1K articles published (see the other "Ham Radio Mag text in the other Dentron Download) providing some suggested improvements. So far all of the ones I've seen have failed to include the very simple standby mode "tube cutoff" circuit and much needed glitch (failure) protection. Pity too, as there's already a set of unused relay contacts in the amplifier available for the cathode current cut-off update.
This zip file package is a 1st draft workup of my Dentron GLA-1000 Sweep Tube Amplifier improvements which work on similar chassis layouts like the Amp Supply LK-1000 and various ARRL Handbook Circuits. There's a great picture file of my simple current cutoff circuit, the original circuit diagram, a digram with some improvements noted and the 1st draft of my modification/update text. How about some picture gifs in the future for fun..? It just takes time...

Please let me know if you find a mistake, or you have something to add to the text. Enjoy and by all means drop me an Email if you have specific questions.

Below is the same description page text you will see for the other down load.

The Dentron GLA 1000 "Plain" B and C Amplifiers were sold as low cost Amateur Radio "sweep tube" RF Linears. The dentron1.zip file is a package of information to repair, modify (includes the original Dentron Factory 10 meter kit installation instructions), update and maintain your Amplifier. This page and the download files will increase in size as I hope to add more information. The "plain" or "first version" GLA-1000 did not include a tuned input circuit (cathode path) and the zener bias diode was a poor choice in value. The later B version included a much needed tuned input and the stud zener bias voltage changed to 24V. The last and very rare GLA-1000C traded the 10 meter band position for 160 meter operation in Compliance with new FCC rules.

There is a "Tech Sheet" available on the Svetlana Tube Company web page which describes conversion of a Dentron GLA 1000 B to their current production EL-509 tube(s). A cost effective alternative to NOS D-50 or 6LQ6/6JE6 replacement tubes. This is a great conversion reference souce, but IMO the modification "update" is not very complete.

The tube cathode current should be cut off or reduced when the unit is in the standby (receive) mode. This is not a problem as the original tr relay has an extra set of unused contacts which are ideal for the task. I have written the "cathode current cut off" modification text into an article, which you may down load free from the Sonic Web Server Amateur Radio Page. Feel free to Email me should you have questions about the package. Please use the included cathode lead cutoff circuit paperwork "text" I've set up as a basic idea guide for your retrofit. A more formal writeup will come as time allows. A scanned image of the original gla amplifier circuit diagram, and my suggestions are included. Both the gif and pdf file formats are supported.

The download page also provides a copy of an old Ham Radio Mag (rip) article for reference only and the Dentron factory blurb sheet for the ten meter mod as often listed should be L7 (input toroid coil) - 5 turns 18 guage enam wire on T50-6 Amidon core - C35 (input section, towards tranceiver) - 150 pF 500V capacitor, C36 (input section, towards cathodes) - 36 pF 500V capacitor.
These values were offered by other sources and are not confirmed by me. The Ham Radio Magazine text has technical problems, don't use it as a reference for your amplifier repairs or retrofit.

Far Circuits now offers up a batch of PC boards for the Svetlana EL-509 retrofit, but more work needs to be done. No one has come up with the proper tuned input part values for use with the much different drive impedance of the Svetlana Tubes. It's not hard, but no one has done the home work yet. I'll include some soluctions into my text when I have time to work out the proper input circuit part values.

enjoy
skipp


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