[TenTec] Centurion Amp - early model, looking for advice

[Mike Schatzberg]

Ok. Your tubes are not biased. This is not the way they would have built the amp. Depending on your meters accuracy, zero bias might allow 140 mils max. 

You have no cut off or operating bias. 

I don't have the road map for that amp, but it apparently uses an electronic bias switching with a transistor switch. Either the switch is bad or the bias source is bad.  I think it takes around 100 volts to cut off the 3-500, and only around 6 to 7 volts to run at 60 to 70 mils for two tubes. 

This is not very difficult to trouble shoot, but you need a fix not a mod. 

There are only a few diodes, maybe a zener, and a transistor to replace at most. 

73,

Mike
W2AJI 

Sent from my iPhone

> On May 26, 2016, at 8:15 PM, <kr2q at optimum.net> <kr2q at optimum.net> wrote:
> 
> The idle current does NOT change between standby and operate.  It is over 100 mils
> (just under the "second line" on the meter or almost 2/3rds of .2 amps.)
> 
> Doug KR2Q
> 
> ----- Original Message -----
> From: Mike Schatzberg
> Date: Thursday, May 26, 2016 8:00 pm
> Subject: Re: [TenTec] Centurion Amp - early model, looking for advice
> To: kr2q at optimum.net
> Cc: tentec at contesting.com
> 
>> Firstly, does the idling current change from standby to operate?
>> 
>> If it does not change, and remains the same, you may have no
>> bias at all. The triodes are zero bias tubes and will operate
>> with no bias.
>> 
>> That would explain why the tubes are running so hot.
>> 
>> If the idling current is around 60 to 75 mils, there is bias
>> voltage applied. If over 100 mils, there may be no bias at all.
>> ( pair of 3-500 triodes)
>> 
>> The higher the idling current, the easier it is to drive the
>> triodes.
>> 
>> 73,
>> 
>> Mike
>> W2AJI
>> 
>> 
>> Sent from my iPhone
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