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This amp was built by P&H Electronics in Lafayette Indiana in 1956..It
used four 1625 tubes or 837 tubes in GG...The manual says that the
1625 tubes are modified ..Doesn`t say what sort of modifications they
have..Tube Manual shows same pin-out ,same socket ,same connections
etc..Anyone know what the modifcations might be...They both seem to
operate all OK with about the same power out..I seem to remember an
article some years back about removing the socket from the tube and
changing some pin connections or whatever...any help appreciated..

If I remember it correctly, the modification consisted in separating the
suppressor grid from the cathode, so that the tube can be operated as a triode.

Actually within the socket there are two separate wires for the suppressor grid
and the cathode, both connected to pin 6. The modification consisted in
de-soldering the suppressor grid wire and moving it to a free pin (pin 2 or pin
5).

Such a modification was not possible for the 807 (the 6.3V version of the 1625),
because it only has five pins in total.

73

Tony I0JX