[Boatanchors] 30S1 bis query

[Gary Schafer]

Hi Jack,

Since you had problems with the bias pot, it may still have problems. Maybe
open on the ground side putting too much bias on the tube? Check the bias
voltage on the line going to the grid. Just remembered that the screen is at
ground on that amp so you need to measure the bias between the cathode and
grid as the cathode is not at ground but negative by the amount of the
screen voltage. I haven't looked at the diagram in a long time so I can't
remember exactly how things are wired. Check the schematic.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Jack Taylor
> Sent: Monday, August 14, 2006 10:34 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] 30S1 bis query
> 
> Hi Glen John and Gary,
> 
> I was wondering about the references to the KWM2A/32S exciters, but the
> 30S1
> manual refers to the amplifier bias voltage as being
> adjusted for a 200 ma reading presumably on the amplifier Ip meter.  To me
> the manual is a little vague in this area and should read
> "With PTT applied set bias control to read 200 ma Ip in SSB mode with no
> drive", if that's what's intended.
> 
> Appreciate the suggestions and my next step will be to measure the screen
> voltage, once I figure out how to safely do so.  Again,
> the manual is vague on what the screen voltage should be.  The block
> diagram
> indicates 200V, but then the block diagram shows
> the bias supply as being 50V, where I'm measuring -66V or less, depending
> upon where the bias control pot is set.
> 
> Incidentally, I did allow the filaments on the 4CX1000A to cook for a
> couple
> of days before applying power.  A few gremlins
> surfaced.  First the plate meter would indicate 600 ma when keyed with no
> drive.  Also at separate times, a contact on the step
> relay froze as did a contact on the transceive relay.  Getting to the
> transceive relay was easy but restoring it was not.  Then an
> intermittent showed up on the PTT line at the RCA plug, which caused some
> confusion.  The 600 ma keyup problem was
> tracked to a dirty wiper on the bias control pot.  Discovered this with
> the
> unit powered down and an ohm meter across the
> output of the bias supply.  Over time, the resistance would sharply vary.
> Cleaned the control which also took care of a 20
> volt sawtooth on the bias supply.
> 
> Still unable to adjust the bias control for a 200 ma resting current
> reading
> in SSB mode.  Replaced the final tube but really not
> much change in symptoms.  In CW mode, the amplifier appears to be OK.
> Just
> screwy in SSB.  That's why I asked the
> question about the bias setting.  Presumably as one goes towards zero bias
> in AB1, the plate current should increase.
> According to the 4CX1000A data sheet for AB1 operation, the bias should
> be -55 volts.
> 
> Perhaps a measurement of the screen voltage will solve the mystery.
> 
> 73 de Jack - N7OO
> 
> 
> 
> ----- Original Message -----
> From: <eldim at att.net>
> To: "Jack Taylor" <jack at n7oo.com>; <boatanchors at mailman.qth.net>
> Sent: Monday, August 14, 2006 5:45 PM
> Subject: Re: [Boatanchors] 30S1 bis query
> 
> 
> > Hello Jack,
> > This refers to the Exciter Plate Current of 200 MA.  i.e.  When running
> a
> KWM-2/2A Transceiver, or 32S Line Transmitter you normally donot run the
> plate over the recomended max plate current of  220MA when Operating
> "barefoot" or without an RF Amplifier.  When connected to a Linear
> Amplifier, it is recommended to reduce the drive to 200ma with the Loading
> Control/Plate Control, with the final dip being the Plate Contol.  In
> running 200 mA RF Drive to the 30L1 or 30S-1 you insure longer life to the
> Amplifier Input Tuned Circuit.  I have seen Input coils that were toasted
> from overdriving them.
> > 73,
> > Glen Galati, KA7BOJ
> > Tacoma, WA
> >
> > -------------- Original message from "Jack Taylor"
> <jack at n7oo.com>: --------------
> >
> >
> > > I'm having a problem understanding what the 30S1 bias voltage should
> > > approximately
> > > read in the SSB and CW positions. The manual says the "voltage
> necessary
> to
> > > set
> > > idling plate current to 200 ma". On mine, the bias can be adjusted
> from
> > > approximately
> > > -38 to -65 volts and I never see anymore than zero plate current with
> no
> > > drive.
> > >
> > > 73 de Jack - N7OO
> > >
> > >
> 
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