[Boatanchors] RE: GB> 4-400 tube replacing a 3-400z for circuit test

[Ed Sieb]

The 4-400's will work well, but the output may be a bit low, compared to the
3-500's.  The reason is that 4-400's like a higher plate voltage than
3-500's. 4-400's like a voltage around 3500VDC and higher, while 3-500's
like a voltage around 3000 VDC +/- 500V (2500 VDC - 3500VDC). The optimum
voltage for 4-400's is around 3900 VDC or so.

They'll work well, in any case. Just make sure the screens are tied to
ground along with the grids. (Assuming G-G service, of course!) The sockets
may well have the screens already tied to ground; check first.  I ran
4-40''s in my L4B.  Put out about 1000 W or so, full tilt.

Ed, VA3ES
---------------------------------------------------------

Greg Mijal wrote:
Has anyone used 4-400's in a made for 3-400Z's amplifier?
I have a Swan MK 1 amplifier built for two 3-400Z's and
no tubes.
I do have a set of 4-400's.  The necessity of this is to
evaluate the amplifier overall circuit, not necessarily
"Convert" the amp.
Anyone do this one before?