I have a Golden Eagle 150 linear amp that appears to be completely"stock" and in good condition, but I have been told that my signal sounds louder, but "crunchy" when I am on the air. Does anyone know what would cause this? Also, what is the variable resistor attached to the choke on the center left in the attached picture used for? Thanks!
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Help with Golden Eagle 150 linear
- Thread starter fastfreddie1269
- Start date
Welcome to the forum.
I assume you are talking about SSB
The reason that some users report that your signal is "crunchy" is in part caused by a amp with no bias.
Many of these little amps were built like that, just a fact of economics.
The variable resistor you are referring to is actually a variable capacitor, used to help tuning on the output transformer , the thing you called a choke.
It's really best to have a amp that has bias for SSB, you can kinda get away with it on Am but audio quality will suffer on SSB.
If you are comfortable soldering adding some negative feedback across the transistors might help a little bit, but it's never going to be as clean as a biased amp.
73
Jeff
I assume you are talking about SSB
The reason that some users report that your signal is "crunchy" is in part caused by a amp with no bias.
Many of these little amps were built like that, just a fact of economics.
The variable resistor you are referring to is actually a variable capacitor, used to help tuning on the output transformer , the thing you called a choke.
It's really best to have a amp that has bias for SSB, you can kinda get away with it on Am but audio quality will suffer on SSB.
If you are comfortable soldering adding some negative feedback across the transistors might help a little bit, but it's never going to be as clean as a biased amp.
73
Jeff
It's an AM-only linear that has a switch marked "SSB" on the front. It's not there because it's useable, it's there because buyers think it should be. This is an old design, built decades ago with a handful of circuit details totally missing. Saved the maker money, and when everybody was using AM nobody would notice until long after they paid for it. If you fancy using a linear on sideband, there's some redesign and upgrade needed to make it sound right on SSB. Newer linears are built both ways, with sideband "bias" as it's called and also without it. Like this one. The front-panel switch serves only to stop relay chatter. The carrier from an AM signal holds the relay active until you release the mike. Sideband has no carrier, so the relay would otherwise clatter open and closed with each syllable. The SSB switch imposes a dropout delay on the relay to stop chattering while you speak. That's all it does.
73
73
Thanks for your responses! I'm mainly using the amp on am. I discovered that one side of the variable capacitor (thanks for the correction!) Was not even soldered to the output transformer (again, thanks for the correction!), would that possibly affect the "crunchy" sound it has on the air? And how do I adjust the variable capacitor on the output transformer for the best match?
The parts come in a kit from RF Parts, NFB2 is for a two transistor amp, I don't know the current cost.
Keep the leads as short as possible.
Adding negative feedback will help with this but it's no substitute for a properly biased amp.
73
Jeff
Bear in mind that you're correcting boo-boos in the original 1970s design. Not a lot of attention was being paid to the amplifier's input impedance back then. You'll want to put a SWR meter and extra coax jumper between the radio and the amplifier's input jack. If the reading is much over 2 to 1 with the amplifier keyed you'll probably want to tweak the input circuit to bring the amplifier's input-side SWR down a bit. And if it's 4 to one, you really should tweak it down a bit.
73
73
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