[TenTec] Centurion is on the Fritz

[Bob McGraw - K4TAX]

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 at Mindspring.Com>
To: "Discussion of Ten-Tec Equipment" <tentec at 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 at k8jhr.com>
> To: "Discussion of Ten-Tec Equipment" <tentec at 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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>
>
>
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