[TenTec] Any issues with Corsair II --> SB-200 amp?

Sat Dec 18 03:04:21 EST 2004

Hey, you guys are in general, technically correct, but in this case
completely WRONG!

Perhaps you should take a look at the SB-200's schematic and reconsider.

The 120v mains enters the SB-200 with both sides floating above ground and
are fed to the input (primary side) of T1.  The 3rd wire (safety ground) of
the mains connects directly to the chassis.  T1 has 3 windings on its
secondary:
 - Filament
 - HV
 - Bias (120v)

One of the two wires of the (secondary) bias winding is tied directly to
chassis ground.  The other wire feeds the cathode of a half-wave rectifier
and its -130v output provides the tubes' bias and also keys the T/R relay.
It happens to be negative because the tube's bias needs to be negative.

It is perfectly OK and perfectly safe to key this -130v with the Corsair's
internal relay. In fact a second, external keying relay isn't going to add
any safety at all because if somehow the AC would short-circuit in the
transformer (T1) and get into the SB-200's relay keying circuit, it would be
all over the chassis and all over the coax and thus all over the Corsair
anyway, despite the external relay which has been suggested.

All you have done with your suggestion is to add excessive (and destructive)
delay into the keying circuitry.

AGAIN, IT IS PERFECTLY ACCEPTABLE TO KEY THE SB-200 DIRECTLY WITH THE
CORSAIR, USING THE CORSAIR'S BUILT-IN EXTERNAL T/R KEYING RELAY!

(Please heed my warning about QSK-Delay in my previous post)

73
Rick

-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Duane - N9DG
Sent: Friday, December 17, 2004 5:38 PM
To: tentec at contesting.com
Subject: Re: [TenTec] Any issues with Corsair II --> SB-200 amp?

I would not directly key a 125V circuit either. In
fact the Corsair II manual specifially advises against
it. The EXT T/R section of the manual it says in part:

"One side of this switch is also at ground potential
and therefore should NOT be used to switch the 115/230
volt line"

I always use another relay as a matter of course
regardless of voltage level because it is a way to
assure DC isolation of the keying cicuit and helps to
avoid ground loops.

Duane
N9DG

--- denton <denton at oregontrail.net> wrote:

> The Corsair II...and I have one..does have a relay
> to key an amp..
> However I would use a second relay between the rig
> and the amp just to be 
> sure...
> ----- Original Message ----- 
> From: "NJ0IP" <Rick at DJ0IP.de>
> To: <tentec at contesting.com>
> Sent: Friday, December 17, 2004 5:19 PM
> Subject: RE: [TenTec] Any issues with Corsair II -->
> SB-200 amp?
> 
> 
> > The SB-200 does indeed have tuned inputs (only for
> 80/40/20/15/10 meter
> > bands) and will work just fine with the Corsair II
> (from an RF standpoint)
> > on these 5 bands.  The SB-200's T/R relay keys
> with -130v @0.051A., so 
> > that
> > prohibits keying it with an open collector
> circuit.  I can't remember if 
> > the
> > Corsair II also had a relay for keying external
> amps.  I think it does. 
> > If
> > it does, then enable it and it will key the -120v
> just fine.
> >
> >
> >
> > I'm sure someone here can tell us if the Corsair
> II has a keying relay for
> > the amp.  It will also be described in the user's
> manual if its in the 
> > rig.
> >
> >
> >
> > If the Corsair does not have a relay for keying
> the external Amp, you can
> > obtain a "Soft Key" kit from Rich Measures 
> (http://www.somis.org/) - I
> > think it only costs a couple of dollars.  You have
> to make a slight
> > modification to the SB-200's relay to enable it to
> key with +130v instead 
> > of
> > - 130v, but that's very simple to do.  After
> installing this simple kit, 
> > you
> > can key the amp with open collector circuitry.
> >
> >
> >
> > If you run a lot of CW, one problem you will
> probably run into over time 
> > is
> > arcing and possible burning of relay contacts on
> the SB-200's T/R relay.
> > This will happen regardless of whether you are
> keying with the softkey or
> > with the Corsair's relay (assuming it has one).
> >
> >
> >
> > The combination switches to TR to transmit fast
> enough because the Corsair
> > adds enough delay to allow for this.  The problem
> is, you really need to 
> > add
> > some delay before the Amp's T/R relay switches
> back to RX.  Otherwise you
> > will often incur the state where the relay has
> begun switching back to RX
> > when the TX signal comes again.  It is unable to
> change directions fast
> > enough to settle in the TX position before RF is
> applied, and it arcs. 
> > Not
> > bad the first 20 or 50 times it happens, but
> eventually it burns the relay
> > contacts enough that you incur errors.  This is
> typically a failure of the
> > relay to switch the antenna back to the
> transceiver in RX mode.  Easy to
> > recognize because you don't hear anything (or else
> it is very weak). In 
> > this
> > case, you have to clean the relay contacts with a
> burnishing tool.  This 
> > is
> > easy to do, but requires pulling the cabinet off
> of the amp.  How often 
> > this
> > is required will depend on your amount of use of
> the amp.  I found I was
> > cleaning mine every 2 or 3 months.  I finally
> built my own device to allow
> > me to adjust the relay delay and was able to
> eliminate this problem.  By 
> > the
> > way, my device also keys the -130v so you don't
> need the softkey.
> >
> >
> >
> > Rich also sells a kit for replacing the open-frame
> relay with a vacuum
> > relay, but that costs a bit more. Once you have
> installed this mod, you 
> > can
> > run full QSK with the SB-200 and the Corsair II.
> >
> >
> >
> > I also have to ask what you mean by "interface".
> >
> > There are probably all kinds of boxes available on
> the market which I am
> > unaware of.
> >
> >
> >
> > Gud luk and have fun with it.
> >
> >
> >
> > 73
> >
> > Rick

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