Topband: Heater Choke Value

[Thomas Hoeppe]

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 at suddenlink.net>
To: <topband at 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
> _________________
> Topband Reflector
>