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

The Dentron GLA 1000 "Plain" B and C Amplifiers were sold as low cost Amateur Radio "sweep tube" RF Linears. The 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.


We/I get a lot of Email from visitors who drop into these file down load description pages via a web search "engine" (like Google). Vistors are not able to locate the file download icon for that specific description page. There is a simple way to find the file download icons on the main sonic web page...

First and best: Use the menu icon just below to the main sonic page.

Second: Back space out the page your now looking at in your browser location line. As an example, using the description page. Remove the last portion of the web location with the keyboard back space key to read then press your Enter Key to reload the main sonic page "just in front" which would probably has the inforamation you're looking for. This works on most of the current browsers at most web sites.

Third: You can always contact me using the Email Icon below. I'll try to get a back to you asap with a practical answer.

Copyright 1998 through 2004