If there is a problem in seeing any power out (at all), then it is not just
a T/R problem.
At a minimum, he should be seeing the 50w of drive power that is applied to
the amp because that would pass straight through to the output.
If one of the tubes are blown, he should be seeing a couple hundred watts
out but find it won't load properly.
If both tubes are blown, he would see no power out.
It's hard to believe both tubes would blow at the same time.
More likely is an internal fuse either in the filament side or in the HV
side.
This could be caused by one of the tubes shorting.
If he sees no output at all from the amp, then I would unscrew the coax to
the input and hang it directly on a watt meter and dummy load. Make sure
the transceiver is putting power out at that point.
It's hard to troubleshoot when all of the info is spread out over several
emails.
In order to hone in on the problem, if I were doing it I would work through
the following check list RECORDING my results for each step:
..1). Remove all cables from the amplifier
..2). Then connect the amplifier to a dummy load with a "measured good"
short coax (measure with coax between the dummy and his RigExpert analyzer,
then scan 30 MHz wide, f=16 MHz). If the SWR curve is flat across the
spectrum, the coax is good.
..3). Switch the amp on and check if the tubes are both lighting up to
normal brilliance.
..4. Switch the meter to read plate voltage and record the amount of HV it
shows. Should be about 3400v.
..5). Connect a short cable with RCA phono plugs on both ends to the jack
which is used for keying the amp with a single cable. If the amp has a menu
to select which type of keying, place it in the single cable mode.
..6). Switch the amp from standby to operate and touch the center pin of
the other end of this short cable to chassis ground. The amp should key.
If there is a standby/operate light, it should light up for "Operate". Each
time you touch the cable to ground, you should hear the relays switching.
..7). While still touching the cable to the chassis, check and record Grid
Current (Ig). Should be about 100mA.
..7). While still touching the cable to the chassis, check and record Plate
Voltage. Should be about 3400v.
STOP and evaluate the results.
If any of these steps failed to give the expected results, then there is no
need to apply RF power to the amp.
It's not going to work.
If this is not all OK, then I suggest sending the amp to Ten-Tec.
James has a lot of experience in working with low voltage circuits,
especially audio circuits, but he has no formal training or lab experience
for working with VERY high voltage. One mistake could blow up lots more in
the amp, or as Mike pointed out, COULD BE FATAL.
If all of the above tested OK (which I doubt), then check the output power
of the transceiver directly at the end of the coax that connects to the amp.
- If that is OK, then set the transceiver to about 10w output, CW, and then
connect the coax back to the amplifier.
- With the short cable (2x RCA Phono) still connected to the Amp Key Jack
on the amplifier and while monitoring "Plate Current" (Ip) on the amp,
manually touch the center pin to ground again to place the amp in operate
mode and then key the 10w CW. He should see a significant rise in plate
current.
- If that works, then do it again and quickly adjust the PLATE TUNE and
LOAD for max power out. Should be about 100w. If it is, then the problem
is, the transceiver is not keying the amp. I don't think this is the
problem because he has tried a couple of different transceivers and all had
the same results. Still, we need to check this.
Somewhere in this long procedure, something will stand out and say "HERE I
AM".
That will be the clue to what has happened.
My guess, the amp has overheated during continuous use as NCS.
James had it mounted inside of a shelf with little breathing space.
I warned him a couple of years ago that this was very bad for the amp but it
sure looks good.
If he didn't move it, then this is probably the reason it burned up.
Amplifiers should always be out in the open with plenty of breathing space.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Thursday, October 23, 2014 10:43 PM
To: tentec@contesting.com
Subject: Re: [TenTec] Centurion is on the Fritz
On 10/23/2014 10:54 AM, Richards wrote:
> I have modest DIY sills and test equipment but I am game to try any
> diagnostic test within my skill level. Any ideas?
I don't know that particular amp, but if my Titan were doing it, I would
suspect the failure of the TX/RX relay. The Titan keying logic monitors the
position of the relay and won't TX unless the relay has pulled in.
Another thought -- try CW and see if it works. If it does, it could be a
failure in the audio chain. Something as simple as a broken mic cable.
73, Jim K9YC
_______________________________________________
TenTec mailing list
<mailto:TenTec@contesting.com> TenTec@contesting.com
<http://lists.contesting.com/mailman/listinfo/tentec>
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|