One of my trouble shooting tips was to look and see if the tubes are lit.
There are two fuses on the filament PC board. One other fuse for the bias
circuit is on the QSK board. Both boards are inside and accessible with
covers removed.
I have experienced the pins of the 3-500 series tubes actually de-soldering
within the hollow tube or the pin. The symptom is an open filament. This
is caused by excessive heat either from inadequate cooling or from a loose
pin to socket contact causing excessive heating. With the filament
requiring 14.5 amps at 5.0 volts it doesn't take much contact resistance to
produce a notable amount of heat at the socket and tube pins.
Do exercise all degree of caution and safety when working on any power
amplifier. Voltages in these amplifiers are lethal and one is not to take
anything for granted.
73
Bob, K4TAX
----- Original Message -----
From: "Curt Gamble" <W0ALC@Mindspring.Com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Friday, October 24, 2014 10:22 AM
Subject: Re: [TenTec] Centurion is on the Fritz
To the TenTec net
I recently bought a Centurion amp from my neighbor here in Cedaredge,
CO.this summer. I used it for about a month
when one day in a QSO it quit transmitting. I had the same situation as
the current case being discussed.
I finally gave up and sent it into TenTec as my time is limited being a
caregiver.
Well to make a long story short there was a cold solder joint in the
3-500 filament wiring around the tube socket area.
If I had a presence of mind I would have looked to see if the tubes were
lit.
Having built a home brew amp w/pair of 3-500Z amp 40 years ago (160M to
10) with vacuum relays, Vacuum variable
etc. I felt kind of embarrassed not to have checked the tubes to see if
they were lit.
BTW I love the amp working with the Orion II
73, Curt WØALC
On 10/24/2014 6:55 AM, Bob McGraw - K4TAX wrote:
When you lift the cover, there is a HV shorting bar that should short the
HV to ground. Notice I say SHOULD. Never take anything for granted when
working with any product that uses high voltage. Use a screwdriver with
a well insulated handle to short the Cap on the top of the tubes to
chassis.
If you've spoken with Gary then take his advice.
73
Bob, K4TAX
----- Original Message ----- From: "Richards" <jrichards@k8jhr.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Friday, October 24, 2014 7:29 AM
Subject: Re: [TenTec] Centurion is on the Fritz
Hi Rick -- Thank you for the suggestions.
1) Your diagnostics mirror those I received from Gary at TT and from
another qualified technician/repairman. Unfortunately, the amp failed
multiple diagnostics, and a conversation with Gary Green confirms it
requires a trip to TT HQ for a full debriefing.
2) Contrary to assumption, the amp failed right away. It failed after
just just few quick exchanges with my relay man in Texas, even before the
second check in. DARN !
3) Contrary to assertion, the amp has AMPLE ventilation. I don't want
anyone to get the impression it was boxed in. Perhaps you do not recall
our previous discussion on this, we worked this over pretty well some
time ago. The stand you mention has HUGE cut outs (larger than the
vents in the amp cabinet) and is open on the front and back. I added a
pair of 120 mm fans to move air around it. There is a four inch clearance
on one side, and 10 inch clearance on the other, so there is no chance
the amp overheated because it is enclosed. It has better ventilation than
if something were stacked directly on or next to it. I am sure you just
don't recall how hard I worked to avoid boxing it in as it has been some
time since then.
THANK YOU ALL FOR YOUR QUICK AND HELPFUL SUGGESTIONS - All of which
confirm it is, as Rick correctly states, outside my expertise. I
appreciate all the suggested diagnostics which could be done with a
closed cabinet as I am surely disqualified from doing anything inside,
especially when it is powered on.
MY ONLY REMAINING QUESTION IS... Is there anything inside that can give
me a jolt (like a capacitor that needs to be discharged) while I remove
the tubes for shipping ? I would hate to discover that by surprise.
Thanks again... it all helped to confirm it requires a qualified
technician to fix.
Happy days.
-------------------------- JHR ---------------------------
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