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A ten-to-one power gain is more than I'm used to seeing from just one push-pull pair of transistors on 2 meters. Found a review on eham.net that said more like six-to-one for this model. Much closer to what I'm used to seeing from bipolar transistors.

Detaching C1 should serve only to disable the keying circuit. Leaving it connected should boost the input-side SWR only a very little. It is meant only to steal a tiny bit of the RF-drive power to activate the relay, not enough to increase the mismatch.

Just as an educated guess it sounds like a failed capacitor. Not easy to check in the circuit. I would start by comparing the temperature of the two RF power transistors. If one of them runs hotter than the other, look for a bad cap feeding into (or out of) the transistor that's running cooler.

This kind of amplifier circuit is not well isolated between input and output. Any mismatch trouble in the output will disrupt the input impedance.

73

<blockquote data-quote="nomadradio" data-source="post: 757412" data-attributes="member: 22">A ten-to-one power gain is more than I&#039;m used to seeing from just one push-pull pair of transistors on 2 meters. Found a review on eham.net that said more like six-to-one for this model. Much closer to what I&#039;m used to seeing from bipolar transistors.Detaching C1 should serve only to disable the keying circuit. Leaving it connected should boost the input-side SWR only a very little. It is meant only to steal a tiny bit of the RF-drive power to activate the relay, not enough to increase the mismatch. Just as an educated guess it sounds like a failed capacitor. Not easy to check in the circuit. I would start by comparing the temperature of the two RF power transistors. If one of them runs hotter than the other, look for a bad cap feeding into (or out of) the transistor that&#039;s running cooler. This kind of amplifier circuit is not well isolated between input and output. Any mismatch trouble in the output will disrupt the input impedance. 73</blockquote>

[QUOTE="nomadradio, post: 757412, member: 22"] A ten-to-one power gain is more than I'm used to seeing from just one push-pull pair of transistors on 2 meters. Found a review on eham.net that said more like six-to-one for this model. Much closer to what I'm used to seeing from bipolar transistors. Detaching C1 should serve only to disable the keying circuit. Leaving it connected should boost the input-side SWR only a very little. It is meant only to steal a tiny bit of the RF-drive power to activate the relay, not enough to increase the mismatch. Just as an educated guess it sounds like a failed capacitor. Not easy to check in the circuit. I would start by comparing the temperature of the two RF power transistors. If one of them runs hotter than the other, look for a bad cap feeding into (or out of) the transistor that's running cooler. This kind of amplifier circuit is not well isolated between input and output. Any mismatch trouble in the output will disrupt the input impedance. 73 [/QUOTE]

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