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You can see a picture of the loaded PA board at this link:
[MEDIA=facebook]1677859872378055[/MEDIA]

The first problem I spot is the use of the brown and yellow dipped silver mica caps, directly across the output combiner. These caps struggle to handle the current across the output transformer of two 2SC2879's, much less being used at the 800 watt plus level, with 8 transistors in front of them. Those caps will get hot and drift far from the original value, if the amp makes the specified power output.

Another problem I see is the lack of RF decoupling from the DC line. Why don't we see any RF chokes feeding the DC into the RF output transformers? Some ferrite seems to be missing here. Without chokes, the electrolytics are prone to exploding from RF. It also makes it very easy for the final RF to work its way back down the DC line and into the driver stage, where it makes oscillations happen. I won't even get mention what happens when that RF gets into the vehicle electrical system or power supply regulators through the DC line...

PS: Notice there is no coax from that output combiner to the small relays in the back. This means the RF output is carried through an unshielded trace on the PC board. Not so good for impedance and awful for contaminating the input stage and bias circuits, with stray RF from the output.

<blockquote data-quote="Shockwave" data-source="post: 739824" data-attributes="member: 10882">You can see a picture of the loaded PA board at this link:[MEDIA=facebook]1677859872378055[/MEDIA]The first problem I spot is the use of the brown and yellow dipped silver mica caps, directly across the output combiner. These caps struggle to handle the current across the output transformer of two 2SC2879&#039;s, much less being used at the 800 watt plus level, with 8 transistors in front of them. Those caps will get hot and drift far from the original value, if the amp makes the specified power output.Another problem I see is the lack of RF decoupling from the DC line. Why don&#039;t we see any RF chokes feeding the DC into the RF output transformers? Some ferrite seems to be missing here. Without chokes, the electrolytics are prone to exploding from RF. It also makes it very easy for the final RF to work its way back down the DC line and into the driver stage, where it makes oscillations happen. I won&#039;t even get mention what happens when that RF gets into the vehicle electrical system or power supply regulators through the DC line...PS: Notice there is no coax from that output combiner to the small relays in the back. This means the RF output is carried through an unshielded trace on the PC board. Not so good for impedance and awful for contaminating the input stage and bias circuits, with stray RF from the output.</blockquote>

[QUOTE="Shockwave, post: 739824, member: 10882"] You can see a picture of the loaded PA board at this link: [MEDIA=facebook]1677859872378055[/MEDIA] The first problem I spot is the use of the brown and yellow dipped silver mica caps, directly across the output combiner. These caps struggle to handle the current across the output transformer of two 2SC2879's, much less being used at the 800 watt plus level, with 8 transistors in front of them. Those caps will get hot and drift far from the original value, if the amp makes the specified power output. Another problem I see is the lack of RF decoupling from the DC line. Why don't we see any RF chokes feeding the DC into the RF output transformers? Some ferrite seems to be missing here. Without chokes, the electrolytics are prone to exploding from RF. It also makes it very easy for the final RF to work its way back down the DC line and into the driver stage, where it makes oscillations happen. I won't even get mention what happens when that RF gets into the vehicle electrical system or power supply regulators through the DC line... PS: Notice there is no coax from that output combiner to the small relays in the back. This means the RF output is carried through an unshielded trace on the PC board. Not so good for impedance and awful for contaminating the input stage and bias circuits, with stray RF from the output. [/QUOTE]

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