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Jim, I've only tested them so far on 40m, but since the receiver noise figure is set by the 12BZ6, I don't expect any significant impact by changing the first mixer. I swapped between the 6HS6 and the 6J5P while listening to very weak SSB signals from the east coast at the band noise level this afternoon and was not able to detect a difference in readability of those signals. Any significant increase in receiver noise would show up best on the 10m band, but again it should be slight.

I noticed no obvious difference in how the AGC performed using the Russian tubes. They seemed to work fine. If there are specific tests you'd like performed, I will try to conduct them.

Dave