Which tube does my amp use? 845 or 211 - diyAudio
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Old 7th November 2010, 06:00 PM   #1
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Default Which tube does my amp use? 845 or 211

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Last edited by HP8903B; 19th February 2014 at 02:57 AM.
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Old 7th November 2010, 06:16 PM   #2
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Who makes the amp? If the amp uses fixed bias you could measure the voltage at the grid contact.
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Old 7th November 2010, 06:26 PM   #3
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I don't know who makes the amp. I attached some pictures.
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File Type: jpg Tango 845 Amp.jpg (34.6 KB, 493 views)
File Type: jpg Tango 845 Amp (bottom).jpg (64.2 KB, 468 views)
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Old 7th November 2010, 06:38 PM   #4
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I think that you need to send this amplifier to me
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Old 7th November 2010, 07:02 PM   #5
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To measure the grid voltage, do I put the RED probe on the Pin 1 (Grid) and the BLACK probe on the Pin 2 (Filament)? Do I do this with the tube installed? If so, which tube should I installed? I do notice that the 211 and 845 have very different DC grid voltage, 211 is -61V and 845 is -145V at 1000V plate voltage.

What do I do if it has adjustable bias?

Man
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Old 7th November 2010, 07:16 PM   #6
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You better know EXACTLY what you are doing to poke around in an amp with a B+ of 1kV!
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Old 7th November 2010, 07:19 PM   #7
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Thank you for the EXCELLENT advice.

That is why I am here seeking for specific instructions.
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Old 7th November 2010, 07:54 PM   #8
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To measure the bias voltage, the black probe should be connected to pin 1 (grid). The red probe should be connected to chassis ground.
Do this without the tubes installed.
What are the other tubes in the amplifier?
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Old 7th November 2010, 08:01 PM   #9
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Put the black probe on the chassis ground and measure the grid voltage without the tubes. Don't try measuring the plate voltage. Most digital meters top out at 1KV and unloaded the supply will read much higher. Judging by the pics the amp looks homemade but well built. If the bias has enough range then you could run either tube depending on the transformer impedance.
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Old 7th November 2010, 08:24 PM   #10
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Thank you very much for the information.

So does that mean the two factors that determine which tube to use are the grid DC Voltage and output transformer impedance?

I am pretty sure the output transformer impedance is 7k. If it is 7k, is it for 845 or 211?
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