Well my friends I was gifted a the Dentron GLA-1000 amp in working order. I'm not to sure what if any my plans are for this vintage 70s amp. Tubes seem to be pretty good doing about 90% and looks like its been serviced within the last few years, All in all she's pretty clean, No mods that I can see. I'll play with it awhile and see how it sounds on the air. Are there any pointers this OL' Boat Anchor ? 73 kc4ubc
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I was Gifted or worse a Dentron GLA-1000
- Thread starter kc4ubc (bill)
- Start date
Are there anypointers this OL' Boat Anchor ?
Yeah, don't operate it w/o an antenna hooked up to it or you'll let the magic smoke out!
(it's all I could come up with)
S*R
Yeah, don't operate it w/o an antenna hooked up to it or you'll let the magic smoke out!
(it's all I could come up with)
S*R
This amplifier was designed to allow more drive power than four of these tubes would normally accept. This was done by cranking down the power gain factor of the tubes. The normal grounded-grid setup would get you roughly ten or twelve times the drive power you feed into four of these tubes.
But the average ham HF transceiver is closer to 100 Watts PEP or more. The schematic at CB Tricks has a flaw. The control grids of the four tubes are not connected to ground in the normal way like the diagram shows. In reality, the control grid of each tube is connected to the tube's cathode, and NOT to ground. This causes the screen grid in each to now act as if IT were the control grid. Since the screen grid has a lower sensitivity than the control grid, it takes more drive to get the same output power.
About double, more or less. Expect a power gain factor of roughly times six, maybe eight.
It's an odd design. It also lacks a tuned input circuit. The drive power feeds directly to the tubes' cathodes through a blocking capacitor. As a result, the SWR the radio will see when this amplifier is keyed will run two to one or higher.
Some radios don't care, but this also serves to reduce how much drive reaches the tubes.
It could be made a more "barefoot friendly" amplifier by changing where the control grids are connected, and adding a tuned input circuit. But you'll need one for each band you want it to cover.
But hey, if it ain't broke don't fix it.
Unless you're a true "shade tree mechanic". Their motto is "If it ain't broke fix until it is".
73
But the average ham HF transceiver is closer to 100 Watts PEP or more. The schematic at CB Tricks has a flaw. The control grids of the four tubes are not connected to ground in the normal way like the diagram shows. In reality, the control grid of each tube is connected to the tube's cathode, and NOT to ground. This causes the screen grid in each to now act as if IT were the control grid. Since the screen grid has a lower sensitivity than the control grid, it takes more drive to get the same output power.
About double, more or less. Expect a power gain factor of roughly times six, maybe eight.
It's an odd design. It also lacks a tuned input circuit. The drive power feeds directly to the tubes' cathodes through a blocking capacitor. As a result, the SWR the radio will see when this amplifier is keyed will run two to one or higher.
Some radios don't care, but this also serves to reduce how much drive reaches the tubes.
It could be made a more "barefoot friendly" amplifier by changing where the control grids are connected, and adding a tuned input circuit. But you'll need one for each band you want it to cover.
But hey, if it ain't broke don't fix it.
Unless you're a true "shade tree mechanic". Their motto is "If it ain't broke fix until it is".
73
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The tube cathodes are shunted to ground during RX thru R1. TX bias is provided by a zener diode. The changeover relay K1 has three sets of contacts as it switches the input, output, and cathodes making it a 3PDT.
Thank you for providing that info. I was unsure if I had the right amp in mind. I converted one to a GI7b a long time ago and forgot the details.
Ahhh, this thing was built in three versions. The GLA1000, 1000A and 1000B.
The very-first original version may have been built with a 2-pole relay, but I don't think we have a manual on file for that version or I would check.
Haven't seen one like that for years, but the 2-pole relay issue sounds familiar. Would call for adding a relay to shut down the tubes in receive mode.
73
The very-first original version may have been built with a 2-pole relay, but I don't think we have a manual on file for that version or I would check.
Haven't seen one like that for years, but the 2-pole relay issue sounds familiar. Would call for adding a relay to shut down the tubes in receive mode.
73
BJ radionut
Supporting Member and 6m addict
The 1000B and the RARE 1000C versions both had tuned input.
1000/1000A had outboard tuned input as an option...Dentron CM-1
Really not bad for HF SSB when tubes were $10-20 each...! 6MJ6's originally
500w+ on 80/40/20...about 400w on 15/10m if drive kept down to around 60w...
(manual listed 125-watt drive MAX)
Yea could get more output but better have spare tubes handy
Had several over the years, actually fairly stable if snot not drove out of them
All the Best
Gary
1000/1000A had outboard tuned input as an option...Dentron CM-1
Really not bad for HF SSB when tubes were $10-20 each...! 6MJ6's originally
500w+ on 80/40/20...about 400w on 15/10m if drive kept down to around 60w...
(manual listed 125-watt drive MAX)
Yea could get more output but better have spare tubes handy
Had several over the years, actually fairly stable if snot not drove out of them
All the Best
Gary
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