Hello Mike!
I have built a linear using a GI46 tube (nearly a GI7B, only the cooler is a
bit better). You see it at www.hoeppe.name
I used 1mm wire CuL on a 1/2" ferrite rod. The rule is "as much as
possible". On 160m the inductance will drop significantly, causing that some
of your RF on the input will be grounded. The gain on 160m is a bit lower!
I accept some voltage drop the the choke, and use 14V heater transformers
and adjust it with small power resistors in the primary for 12,6V on the
base. The little resistance in the choke will keep the inrush current lower.
The chokes in the handbooks are for low voltage glass tubes. It is a good
idea to reduce the wire size in your case and get more inductance and some
resistance!
73s de Tom, DJ5RE
----- Original Message -----
From: "Mike(W5UC) & Kathy (K5MWH)" <w5uc@suddenlink.net>
To: <topband@contesting.com>
Sent: Wednesday, January 09, 2013 10:36 PM
Subject: Topband: Heater Choke Value
Hello Fellow Topbanders:
I have just started the process of converting a MLA-2500 amplifier from
it's original 8875 tubes to Gi-7b tubes. Current;y I can run only abut
400 watts on Topband, (not from the MLA=2500, I have no tubes for it)
The conversion requires a RF Choke in the filament lines. I have searched
the Handbook, and looked at several schematics with no luck.
Please, can someone out there advise the value of reactance required for
this effort. Most construction articles recommend #12 wire, which in this
case, appears to be significant over kill, as the heater current is only 4
amps total.
Thanks & 73,
Mike, W5UC
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