[JMS] Lambda 28 Woes

[Don Buska]

I was reading further Ronnie:  Help me a bit on your bridge connection
description "Okay I modified my Lambda 28 as per Don's article. I am
hooking the 12.6vac transformer up with its secondary going to the
6.5VAC sourch in the Lambda. 
I come out of its PRIMARY and hook that to the bridge. On the positive
end of the bridge I connected the negative side of  a 22uf 350vdc
electrolytic and the positive side of this electrolytic to the negative
side of the bridge, and common ground."

I assume the bridge has two markings with the little "sinewave" symbol
or are simply marked "AC" right?  Those two are connected to the output
of the transfomer (or the primary of the reversed connected filament
transformer you added).  The "-" terminal of the bridge is connected to
the minus side of the 22uF electrolytic and to the resistor R1 (our
-65VDC terminal).  The "+" terminal of the bridge goes to ground (the
positive side of the 22uF electrolytic).  Is that correct? 

Everything still point to the Zeners being forward biased either by
being backward connected or that the rectifier bridge is connected
wrong.

73

Don N9OO

-----Original Message-----
From: james_millen_society-bounces at mailman.qth.net
[mailto:james_millen_society-bounces at mailman.qth.net] On Behalf Of Don
Buska
Sent: Tuesday, August 30, 2005 11:50 AM
To: The James Millen Society Members Email Reflector
Subject: RE: [JMS] Lambda 28 Woes
Importance: High

Hi Ronnie,

Sounds like the zeners are backward or damaged.  If forward biased they
will have the 1.7VDC drop (see Vf value on spec sheet at
http://www.nteinc.com/specs/5100to5199/pdf/nte5111a.pdf).  You descibe
what sounds like a regular forward voltage drop for silicon diodes at
0.7 each.  Where did you get those diodes????  As you indicate the
cathode end should be toward the ground side in this case of a negative
power supply.  Thus the colored band of the zener diodes should be
toward the ground side.  I think the reason your seeing the -49VDC is
your loading down the transformer.  Is the transformer getting hot?
Disconnect the resistor/zener chain anywhere along the chain, since it
is all series connected.  Then what does your DC voltage indicate at the
filter capacitor? All the bias supplies don't draw much current at all. 

73

Don



-----Original Message-----
From: james_millen_society-bounces at mailman.qth.net
[mailto:james_millen_society-bounces at mailman.qth.net] On Behalf Of
ronnie.hull
Sent: Tuesday, August 30, 2005 11:06 AM
To: The James Millen Society Members Email Reflector
Subject: [JMS] Lambda 28 Woes

hep me hep me

Katrinia couldn't keep me down, but I'm having other problems down here
in da swamp!!

Okay I modified my Lambda 28 as per Don's article. I am hooking the
12.6vac transformer up with its secondary going to the 6.5VAC sourch in
the Lambda. 
I come out of its PRIMARY and hook that to the bridge. On the positive
end of the bridge I connected the negative side of  a 22uf 350vdc
electrolytic and the positive side of this electrolytic to the negative
side of the bridge, and common ground.

I'm using a 1800 Ohm resistor that is  hooked to the negative side of
that electrolytic going to the two 22v zeners in series with the cathode
of the last zener going to the same common ground.

My voltages are wayyyyyyyyyyyyyy off

starting at the top where don has -65 volts I have -49 ( and it falls
off rapidly to 25 volts and stops there), at the next point where don
has
-45 volts I have -1.4 and that last point where don has - 22 volts I
have
-0.7 volts. 

What have I done wrong here?

I checked the existing 6.5vac transformer in the Lambda and it is
actually
6.4 vac and it stays steady.

The output of the backwards 12.6 tranny is 44 volts to the bridge. The
output of the bridge is 49 volts.

can anyone help me shed some light on this?

R
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