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#1 2011-04-24 09:37:36

VE3HED
New member
Registered: 2011-04-21
Posts: 2

Heathkit SB-104A

I am building a Heathkit SB-104A from a NIB kit.  Three toroids are missing: #1 - 0.13 uH (White & Red Dots) from the ALC / Output Filter Circuit Board -   #2 & #3 - 3.7 uH from the VFO Buffer Circuit Board.  I scavenged some of these from an old junker, but it looks like the toroids and the boards they were on have been exposed to severe heat as the wax has melted and the boards are pretty discolored.    Would heat affect the characterisitcs of the devices?  If heat has altered the characteristics, should I order the T37 or FT37 cores to wind my own?  All 3 are approximately 9.5 mm in diameter.

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#2 2011-04-24 11:08:06

wa2mze
Member
From: South Florida
Registered: 2009-08-22
Posts: 172

Re: Heathkit SB-104A

With those inductances the toroids are most likely powered iron NOT ferrite.  Chose the material based on the frequency range the cols are being used at and use the inductance calculator on this site to determine the number of turns to wind.  If the the coils have two windings or a tapped winding keep the turns / tap ratio the same.

The circuits you mention shouldn't be handling much power so how did the toroids get exposed to extreme heat (was the shack on fire?)

Last edited by wa2mze (2011-04-24 11:09:06)

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#3 2011-04-24 15:00:32

VE3HED
New member
Registered: 2011-04-21
Posts: 2

Re: Heathkit SB-104A

Thanks for the advice. I have no idea how, or if, the junker was subjected to heat - that was an observation on my part based on the look of the parts.  Having no knowedge of such things, I was wondering if high heat would affect the characteristics of the toroids.  Additional information: #1 - there are 5 turns of what appears to be # 22 AWG on a light green or blue core and the DC resistance is 1.34 Ohms, #2 & # 3 - there  are 14 turns of what appears to be # 36 AWG on black or dark gray cores and the DC resistance of one is 1.01 Ohms and the second is 1.03 Ohms.  Thanks again for your assistance.

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