Antonio Vernucci wrote:
ha scritto nel messaggio
...
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
If the 807 in question has two wires going to the same pin it would be
possible to remove the base and replace it with a 6 or 7 pin base (or
even an octal base) from a dead tube and move the suppressor to its own
pin. OR you could just connect the suppressor to one of the other grid
pins since you're going to run the tube in grounded grid anyway. Either
way though it's no longer an 807 and should be marked as such in case
the tube ends up elsewhere.

I wonder if the 6BG6G sweep tube (or even the 6L6G) was also made in the
same way, with the suppressor having its own wire outside of the bulb?
The 6BG6G is almost an 807 in an octal base. The only difference is
that the 807 has extra RF shielding and sometimes ceramic plate supports
lacking in the 6BG6G. Both tubes are derived from the 6L6G.