How did you have the keying hooked up, Tom? It looks like
the Centurion uses a scheme similar to the Alpha 78 whereby
you plug your keyer into the amplifier to generate relay
closure, and then the amplifier generates a delayed keying
signal to key the exciter after the relays are fully closed and
settled in the amplifier:
In the Alpha 78, the RF sensing circuit is there to prevent
hot switching either on relay make or break (if RF above a
certain threshold is present, the circuit in the Alpha won't
allow the RF relays to close or open).
Not sure what they are doing in the Centurion. The web
description says they are using a PB mechanical relay
on the output and a reed relay on the input. The reed relay
would support QSK on the input side, but the PB relay
wouldn't be fast enough to QSK the output. They probably
hold the PB relay shut during QSK and then use the reed
relay to bypass the tube input circuit and connect the amp's
RF input directly to the RF output for RX. A reed relay can't
carry the RF output current of the amplifier, but if it can hold
off the RF voltage present at the amplifier output, then this
scheme could work without the addition of any PIN diodes
or vacuum relays (this appears to be what what TT is
claiming). The rub here would be that the output of the
PI-Network would be in parallel with the antenna during
the QSK receive intervals which might be an acceptable
performance tradeoff [on the low bands with my QSK
exciter and non-QSK amplifier, I can hear loud DX
stations bleeding thru the open frame relay in the
amplifier, giving me poor man's QSK :)]
In any case, I vote for the ALC overshoot. I have seen
that here when trying to match really obscene loads
with my antenna tuner. The tuner would arc at full power
so I would try backing off the exciter drive only to find
that the tuner would continue to arc on leading edges
73 de Mike, W4EF...........................
----- Original Message -----
From: "Georgens, Tom" <email@example.com>
Sent: Wednesday, November 10, 2004 9:08 PM
Subject: RE: [Amps] Ten-Tec Centurion
> Thanks to all respondents for the thoughts.
> A few comments.
> 1. The fact that it does not happen with the other amps does work against
> my theory. I should note that the other amps are not the same (AL1200,
> TL922, AL80A). That said, I don't think it disqualifies the theory. The
> AL1200 can probably absorb the spike. The TL922A relay is so slow, the
> spike may pass before the relay closes. No guess on the AL80A.
> 2. The RFsense in the Centurion is in support of QSK. It is not intended
> to work the way I inadvertently used it. It is true that it necessitates
> hot switching of the relay. I do believe that it supports the theory of
> overshoot transient. Oddly, the despite the hot switching, the
> does not fold back. Conversely, the TL922 is so slow that it does cause
> foldback. Even if the RFsense makes the problem go away, this is not how
> wish to operate the amp. I still would want to understand root cause.
> 3. The padder cap transient response suggestion is a good one. However,
> when not arcing, the amp works exactly as expected with the settings where
> the manual suggests they should be. The padder caps are also both used on
> as well.
> 4. I do not think the antenna is much of a factor. It is a halfwave
> inverted V at 90 feet. Admittedly, it is not a pure resistive 50 ohms at
> all frequencies but it should be well within the tuning range of the amp.
> mention it just so that you all know it is nothing exotic or dramatically
> shortened. I believe it to be free of intermittent connections.
> 5. K2VCO's suggestion on the carrier level is something I will try. I
> be causing this myself.
> 6. Could advancing the load control slightly help out?
> 7. I was also going to try and see if the problem still happened with the
> radio autotuner on in case it impacted any potential spike.
> 8. Ten Tec suggested that the variable cap is probably pitted, causing
> arc. I do not think this is the problem as the arc is not always in the
> same place.
> 73, Tom
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:email@example.com]On
> Behalf Of Georgens, Tom
> Sent: Wednesday, November 10, 2004 3:16 PM
> To: 'firstname.lastname@example.org'
> Subject: [Amps] Ten-Tec Centurion
> I have a Centurion at my contest station in Barbados that works flawlessly
> on 10-80 but will arc on 160. It is tuned into a resonant antenna with a
> reasonable SWR.
> On 160, the amp will occasionally arc immediately on key down. If it does
> not arc immediately, it will not arc if the key is held down. Also, when
> does not arc, it tunes smoothly and at the predicted settings. All of the
> arcing is in the Tune cap and is not always in the same place.
> My theory is that there may be power overshoot from the TS850 on the
> edge of the carrier that is causing the arcing. It is hard to see this on
> the wattmeter and my 3 other amps all work fine. Does this seem like a
> reasonable theory and is there any way to compensate for this?
> On my most recent trip, I performed a flawed experiment. For convenience,
> used a different TS850 to drive the amp and the problem occurred only once
> out of dozens of tries. I then moved it to the TS850 where I had
> noted the problem. In this case, I was never able to reproduce the
> I tried mistuning to some degree but no hint of the problem. However,
> taking the whole thing apart, I noticed that I had never connected the amp
> relay cable. The amp was using RF sensing to key the relay.
> As I said my experiment was flawed but I would like to understand what is
> really happening.
> Any suggestions would be greatly appreciated.
> 73, Tom W2SC 8P1A
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