Topband: Heater Choke Value

[Charlie Cunningham]

Hi, Mike

Well, I would think that a reactance of perhaps 150-200 ohms at 160 ( if
your conversion includes 160) would be sufficient. That should be
sufficiently large relative to the tubes' input impedances that it shouldn't
have much of an effect on the amp's input impedance. If you try to make the
choke too large, you ay run into problems with stray and unwanted resonances
on the higher bands. I agree that 12 gauge wire sounds a bit heavy at 4 amps
of filament current, but the main reason for the heavier gauge wire, I
expect, is to prevent any significant drop in filament voltage. Most power
tubes are pretty sensitive to that. Check the data sheets on the tubes that
you are using for minimum and maximum filament voltage. 

Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of
Mike(W5UC) & Kathy (K5MWH)
Sent: Wednesday, January 09, 2013 4:37 PM
To: topband at contesting.com
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