Guess what I found the other day when I was cleaning up? I took the cover off and it looked more crusty than I remembered. I took the boards out and cleaned them up with alcohol, brass brush and cotton swabs. More to come...
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Texas Star DX 400 Input SWR
- Thread starter Shadetree Mechanic
- Start date
I took the case, lid and heat sink and washed them in the kitchen sink. Installed a new face plate and button covers too. I had to replace a couple of traces with flat braided copper, redid the power wire and verified the bias.
Like most transistor amps I have had, this one had an SWR problem on the output. The SWR would change depending on the drive level, I could turn radio power all the way down and get a 5:1! Turning the power up helps to squash the oscillating, but it still varies with the modulation. This is what happens when the builder tries to get every last watt. The solution is to double up on the negative feedback resistors, just add them in parallel. It doesn't take any noticable power away. I also removed the swamping resistors from the amplifier input in SSB mode, I can get 400w peaks on my Autek meter now.
Like most transistor amps I have had, this one had an SWR problem on the output. The SWR would change depending on the drive level, I could turn radio power all the way down and get a 5:1! Turning the power up helps to squash the oscillating, but it still varies with the modulation. This is what happens when the builder tries to get every last watt. The solution is to double up on the negative feedback resistors, just add them in parallel. It doesn't take any noticable power away. I also removed the swamping resistors from the amplifier input in SSB mode, I can get 400w peaks on my Autek meter now.
I am going to put this amp into portable service at my mother-in-laws house. I put magnets on the lid and got a HP power supply with magnets also.
Hiding on the side of the fridge, below the chips and cookies...
DX, here I come!
DX, here I come!
- No one is chatting at the moment.
