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A 510? No joke?

I thought that one ran out of steam above 10 or 15 MHz.

Did you use the stock thermoplastic shoulder washer to hold it down? If the efficiency is too low, the heat will catch up with it, even if the wattmeter looks good. If it reaches the melting temp of the nylon shoulder washer, it pulls away from the heat sink, and POOF.

The IRF510 is an enhancement-mode device. Seems to me you would need to place some DC voltage onto the gate to get full power gain. Trouble is, you'd have to switch off the bias for receive, like in a SSB radio.

Gotta wonder what the optimum value for the resistor on the (now) gate? Pretty sure the stock resistor to ground on the (stock) base leg of the final is 22 ohms. That might be the best choice for the 510, or you might get more drive from it with a different resistance value.

IRF510s really are cheap and widely sold. Gotta buy a few and try this. Even if it's no good on a SSB radio, this could be a useful answer to the disappearing 1969/2312, even if it's only useful for AM-only models.

73

<blockquote data-quote="nomadradio" data-source="post: 31065" data-attributes="member: 22">A 510? No joke?I thought that one ran out of steam above 10 or 15 MHz. Did you use the stock thermoplastic shoulder washer to hold it down? If the efficiency is too low, the heat will catch up with it, even if the wattmeter looks good. If it reaches the melting temp of the nylon shoulder washer, it pulls away from the heat sink, and POOF. The IRF510 is an enhancement-mode device. Seems to me you would need to place some DC voltage onto the gate to get full power gain. Trouble is, you&#039;d have to switch off the bias for receive, like in a SSB radio. Gotta wonder what the optimum value for the resistor on the (now) gate? Pretty sure the stock resistor to ground on the (stock) base leg of the final is 22 ohms. That might be the best choice for the 510, or you might get more drive from it with a different resistance value. IRF510s really are cheap and widely sold. Gotta buy a few and try this. Even if it&#039;s no good on a SSB radio, this could be a useful answer to the disappearing 1969/2312, even if it&#039;s only useful for AM-only models.73</blockquote>

[QUOTE="nomadradio, post: 31065, member: 22"] A 510? No joke? I thought that one ran out of steam above 10 or 15 MHz. Did you use the stock thermoplastic shoulder washer to hold it down? If the efficiency is too low, the heat will catch up with it, even if the wattmeter looks good. If it reaches the melting temp of the nylon shoulder washer, it pulls away from the heat sink, and POOF. The IRF510 is an enhancement-mode device. Seems to me you would need to place some DC voltage onto the gate to get full power gain. Trouble is, you'd have to switch off the bias for receive, like in a SSB radio. Gotta wonder what the optimum value for the resistor on the (now) gate? Pretty sure the stock resistor to ground on the (stock) base leg of the final is 22 ohms. That might be the best choice for the 510, or you might get more drive from it with a different resistance value. IRF510s really are cheap and widely sold. Gotta buy a few and try this. Even if it's no good on a SSB radio, this could be a useful answer to the disappearing 1969/2312, even if it's only useful for AM-only models. 73 [/QUOTE]

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