On both of my 667V's, R3 ties to R2 on a post on the power switch to ground as a way of swamping the input wattage, so you don't overdrive the driver transistor, and the variable resistor. Also, the way the variable is wired doesn't match, either. Doesn't even look like it's wired correctly to properly utilize the variable.
Texas Star has been known to just install "Eh, that's close enough" value components to certain areas of the amp... maybe they just run out of a certain value, and stick something else in that's close... I don't know.
Here's a pic of a largely "un-modified" 667. I moved the big capacitor near the relay so the SSB delay would work at all power levels, and R3 (75 ohms) had to be changed because the amp was overdriven before I got it, and burned out the resistor.
The things circled in red have been changed/modified from original. The (2) 150 ohm resistors in parallel is R3, which goes to the post on the power switch and connects to R2, which is right behind the next switch down. The circles and arrows indicate where there are capacitors that may be needed to tune the stages. They are not present in the new amp, and may have to be installed at these spots to get the stages tuned correctly. The circle in purple is the variable, note that on my 667V, the top lug isn't even being used, and it adjusts from about 50W all the way up to full output as it should. The new amp is not wired this way, and it doesn't seem right, regardless of what they use for a driver, whether it's a 2SC2290 transistor, or a pair of IRF520 MOSFETS. I would think that the variable wouldn't adjust output correctly, but maybe there's some voodoo under the board that I don't know about.
Hope this helps.
~Cheers~
Texas Star has been known to just install "Eh, that's close enough" value components to certain areas of the amp... maybe they just run out of a certain value, and stick something else in that's close... I don't know.
Here's a pic of a largely "un-modified" 667. I moved the big capacitor near the relay so the SSB delay would work at all power levels, and R3 (75 ohms) had to be changed because the amp was overdriven before I got it, and burned out the resistor.
The things circled in red have been changed/modified from original. The (2) 150 ohm resistors in parallel is R3, which goes to the post on the power switch and connects to R2, which is right behind the next switch down. The circles and arrows indicate where there are capacitors that may be needed to tune the stages. They are not present in the new amp, and may have to be installed at these spots to get the stages tuned correctly. The circle in purple is the variable, note that on my 667V, the top lug isn't even being used, and it adjusts from about 50W all the way up to full output as it should. The new amp is not wired this way, and it doesn't seem right, regardless of what they use for a driver, whether it's a 2SC2290 transistor, or a pair of IRF520 MOSFETS. I would think that the variable wouldn't adjust output correctly, but maybe there's some voodoo under the board that I don't know about.
Hope this helps.
~Cheers~
