The “shunting” capacitors to which you refer are only used on 160, 80 and 40
meters.
Thus it is unlikely that they are your root cause.
Your description of excess plate current and not enough output sounds more like
a LACK of load capacitance than an excess anyway. Therefore, even if your band
switch was not switching these capacitors out on 20 and higher, you would see
too little plate current and low output rather than excess plate current with
low output.
I would check the condition of the slip contacts on the load tune capacitor.
If you have a capacitance meter available, measure capacitance between the
stator and ground, see if the value varies from full open to full closed.
Gary
W0DVN
> On Nov 10, 2016, at 5:29 PM, rick@dj0ip.de <Rick@DJ0IP.de> wrote:
>
> If not the tubes, then it sounds like the something in the tank circuit is
> wrong.
> When you build an amp from scratch and are searching for the best place for
> the band taps, as you move from turn to turn and then around the coil to find
> the best spot, you see the same scenario you are describing.
>
> It sounds like it is failing to find a resonance.
> Are you dipping the plate current as you tune or are you just tuning for
> maximum output power?
> I don't have the circuit in front of me and it's way too late at night to
> pull it out and look, but perhaps there are some fixed caps normally switched
> by band and one has blown, or the switch is burned or has a bad or no solder.
>
> Also, have you checked the signal level into the tube itself, after passing
> through the input filter?
> If something is bad in there, that would cause this.
>
> Just for a test you can completely bypass those switched filters, disconnect
> them and apply power to the finals just through a capacitor. This should
> give you similar output power on all bands. If not then the problem is
> probably not in the input filters, so you can reconnect them.
>
> At the end of the day, the only way to fix it is to get in there and fix it.
> You have to try things and eventually you will come across the significant
> clue that leads you to the source of the problem.
>
> Gud luk Mike.
>
> BTW, there is a phenomenon I have discovered... I am 10x better at fixing
> other people's radio than I am at fixing my own. I can only imagine that I am
> subconsciously too emotional, too worried, something, and my mind doesn’t
> think as freely as it does when working on other people's radio.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt, Germany)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Mike Bryce
> Sent: Thursday, November 10, 2016 7:35 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Ten Tec Centaur issues
>
> Rick…
>
> thanks for the advice.
>
> It’s not my first rodeo, and quite aware of the voltages lurking inside.
>
> I simply don’t like working on amplifiers.
>
>
> Nothing wrong with the tubes. I put in a new trio of 811s and still have the
> same issue.
>
> power is produced, but on 20 and 15 meters, too much plate current and not
> enough output.
>
> All three 811’s plates turn nice bright red on the higher bands.
>
> I’m suspecting a failed or failing shunt capacitors on the output.
>
> Mike Bryce WB8VGE
>
>
> prosolar@sssnet.com
>
>
>
>> On Nov 10, 2016, at 2:46 AM, rick@dj0ip.de <Rick@DJ0IP.de> wrote:
>>
>> Mike, it is most likely a tube.
>>
>> PLEASE TAKE ALL SAFETY PRECAUTIONS FOR WORKING WITH HIGH VOLTAGE.
>>
>
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