This MOPA is for those that have problems when tuning an antenna. The 1625/807 tube is probably the most robust RF tube in the range of 20-30W rated dissipation. So, they don't fear high mismatch levels for long time (but you don't have to exagerate anyway).
In this case, the 1625/807 needs significantly more drive power as compared to the 6DQ6 and 6146 tubes. So, operation on higher Shortwaves can only be achieved with some limitation in the PA stage.
As compared to the 12BY7/6DQ6 MOPA, this schematic does not use neutralization in the final amplifier. This is very strange, but the original article shows quite well how to arrange the connections to ground so to avoid self-oscillations. In my view the operation without neutralization still is an hazard and the cost difference as compared to the alternative which uses it, is negligible.
A few words on how to neutralize practically a valve power amplifier, will be published soon on Masteroscillator.info.
Radioman, Sept. 2015
Posted by Radioman | Permanent Link