Topband: best headphones for cw

[Paul Christensen]

>"The KPA does have diodes, but I don't know why the KPA diodes seem to make it and others don't. Maybe not stressed as bad switching into an open load, which might be the real culprit that folks don't want to admit to."

The KPA500 has substantially less field operating time compared with the Alpha 86/89/87A series.   After checking this evening, apparently Elecraft doesn't post schematics of their amplifier.  It would be an interesting exercise comparing notes.   If anyone has a set, please send to me by PM.

Late-generation Alpha 87A amps have ~ 150VDC higher Rx bias  voltage to better withstand high VSWR conditions.  In later QSK-5 devices, Ameritron doubled-up on the number of Rx diodes and placed 1M equalizing resistors across them.  That's a reasonable way to restrict PIN diode voltage without spending a lot of money on higher-priced parts -- although Rx loss may be slightly higher.  

Possibly Elecraft mitigates lightning-induced voltages with a spark gap or other similar device, but without a schematic, it's only speculation.   Given a choice between vacuum relays, or dealing with potential PIN diode issues, I'll still take a PIN structure every time.  OTOH, I respect folks who prefer not opening their amps, and so a  T/R relay is best for them.

Guy made several excellent points concerning T/R relay mounting and the need to completely shock-mount the relay, mounting material, and isolate all relay wiring.  Thin silicone HV wire works well; even better if short loops are used to add further isolation.                                        

>"Anyway, back to the original post, I will recommend the Sony MDR-7506. "

Bose QC25 and Sony MDR-NC7 used here.  Both are a NC type.  The Sony headphones work almost as well and at a fraction of the Bose price.  

Paul, W9AC