[Hallicrafters] SX28 2nd AVC.

[hallicraftersx28 at aol.com]

Think you've got V7 confused with V8.V7(6B8) is the S-meter amp. tube plus 2nd detector behind the front panel. V8 (also 6B8) is the AVC amp. tube.
Both of the control grids of V5(6L7) and V8 are connected to IF transformer T1.

Probably ended up opening a GOOD transformer ,now you gonna have 'fun' putting it back !
Nick






-----Original Message-----
From: Brian Goldsmith <brian.goldsmith at echo1.com.au>
To: hallicrafters at mailman.qth.net
Sent: Fri, Aug 27, 2010 3:49 pm
Subject: [Hallicrafters] SX28 2nd AVC.


Greetings to all.
he SX28 has two AVC systems,I have some problems with the second which is
entred around V5,6SL7 and V7,6B8.According to all of the various schematic
iagrams I have,grid(s) 1 of V5 and V7 are fed with an AVC voltage derived
rom V7s detector diode(s).A glance at the schematic will show there should
e 100k of resistance between the top cap connectors of V5 and V7.In my set
here is an open circuit.I carefully sketched out all the existing
onnections around the first IF transformer T1 and removed it from the
et.When I opened the transformer I was surprised to find a different setup
o that shown in all the schematics I have.When traced out,grid 1 of the
7,6B8 has been removed from the 2nd AVC line and connected to the 6SA7
node via a 270pF capacitor with a 500k resistor to ground from the grid.The
emainder of the transformer connections are as the schematics.The
ransformer and associated wiring etc. appear to be completely original.The
il manual calls up a type 50B082B 1st IF transformer,the transformer in my
et is marked 50 082B.Serial number of the set is H159134.
an anyone shed any light on this difference and why it should be so?
Brian G. 
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