[JMS] Lambda 28 Woes

Tue Aug 30 13:53:51 EDT 2005

What I like the most about this list is the great information available.

Don, I did NOT have the bridge wired correctly. I had the positive and 
negative sides of the bridge output wired backwards. I switched the wires
and VOILA!!  ALL is correct now!

Okay.. now to get to work on the HV sensing circuit!

Thanks so much!

getting close here..

W5SUM

---------- Original Message -----------
From: "Don Buska" <D.Buska at Advantest.com>
To: "The James Millen Society Members Email Reflector" 
<james_millen_society at mailman.qth.net>
Sent: Tue, 30 Aug 2005 10:19:39 -0700
Subject: RE: [JMS] Lambda 28 Woes

> 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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------- End of Original Message -------