[Amps] Henry 2K-2 3-500 mod

[James Durham]

I'm looking for some info from someone who has actually done the mod to put
3-500's in a Henry 2k-2.

My 3-400s finally bit the dust after years of service and its time to think about
putting 3-500s in there.

My understanding was that all that was involved was lowering the sockets to
accomodate the greater height of the 3-500's.  I did this. Now, the glass envelope
of the tubes nearly fill the round holes in the chassis where the air comes through.

So, I'm wondering if part of the mod involved making those holes larger? 

Also, just as a curiosity, my amp is definitely a 2k-2 , however it has the zener
mod for bias and the plate circuit protective fuse.  2k-2's are not supposed to
have those.   I've had this amp for about 8 years, but never really investigated
to see what the deal is with that.  My buddy suggested that maybe it was an
'end of model' production and is sort of a 2k 2 1/2 ?  So, I thought, maybe somebody
already did the mods, but the zener, etc, look to be a factory installation, but, in that
case, why is it not set up for 3-500s already? Also, although the 10volt zener was
in there, I did not have the correct manual until recently (I had a 2k-3 manual) and
I didn' t realize that the zener was not supposed to be there. Amp worked fine.
No reason to investigate. Probably the IMD was higher than it should have been
with 10 volts bias on 3-400's, but I'm mostly a CW dude, so I didn't notice that.

Anyway, any insight appreciated.  I sure would hate to have to dismantle everything
to cut those holes larger.If that's what has to be done, I'd like to hear how others
did it. I guess you could use a nibbler (Ugh!) or patch in a piece of metal, drill a
center hole and use a fly cutter. 

I did the checking of the clearances with my old 3-400's, but they are only slightly
bigger in diameter, so I think that was a valid test.

Thanks,

Jim, W2XO