Which tube does my amp use? 845 or 211

manp111 · 7th November 2010, 06:00 PM

Could someone tell me how I can determine whether my amp uses 845 or 211 tube?

My amp has the 845 or 211 tube socket. The Tango output transformer on this amp is for both 845 and 211.

I read a few threads on this forum and have a little understanding of the difference between the two.

I don't know much about amp design and circuitry. Is there something that I can measure within the amp to determine which tube?

It has the following Tango transformers:
Power: MS-UVD
Output: FW-50-7S (I think it is 7k primary impedance)
Chokes: MC-5-250D

I would like to use 845 tubes.

Manp111

astouffer · 7th November 2010, 06:16 PM

Who makes the amp? If the amp uses fixed bias you could measure the voltage at the grid contact.

manp111 · 7th November 2010, 06:26 PM

I don't know who makes the amp. I attached some pictures.

Original Burnedfingers · 7th November 2010, 06:38 PM

I think that you need to send this amplifier to me

manp111 · 7th November 2010, 07:02 PM

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

Palustris · 7th November 2010, 07:16 PM

You better know EXACTLY what you are doing to poke around in an amp with a B+ of 1kV!

manp111 · 7th November 2010, 07:19 PM

Thank you for the EXCELLENT advice.

That is why I am here seeking for specific instructions.

Frank Berry · 7th November 2010, 07:54 PM

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?

astouffer · 7th November 2010, 08:01 PM

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.

manp111 · 7th November 2010, 08:24 PM

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?

7th November 2010, 06:00 PM	#1
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	Which tube does my amp use? 845 or 211 Could someone tell me how I can determine whether my amp uses 845 or 211 tube? My amp has the 845 or 211 tube socket. The Tango output transformer on this amp is for both 845 and 211. I read a few threads on this forum and have a little understanding of the difference between the two. I don't know much about amp design and circuitry. Is there something that I can measure within the amp to determine which tube? It has the following Tango transformers: Power: MS-UVD Output: FW-50-7S (I think it is 7k primary impedance) Chokes: MC-5-250D I would like to use 845 tubes. Manp111

7th November 2010, 07:54 PM	#8
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	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? __________________ Frank

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7th November 2010, 06:16 PM	#2
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	Who makes the amp? If the amp uses fixed bias you could measure the voltage at the grid contact.

7th November 2010, 06:38 PM	#4
Original Burnedfingers diyAudio Member Join Date: Nov 2002	I think that you need to send this amplifier to me

7th November 2010, 07:02 PM	#5
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	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

7th November 2010, 07:16 PM	#6
Palustris diyAudio Member Join Date: Aug 2006 Location: Cape Cod	You better know EXACTLY what you are doing to poke around in an amp with a B+ of 1kV!

7th November 2010, 07:19 PM	#7
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	Thank you for the EXCELLENT advice. That is why I am here seeking for specific instructions.

7th November 2010, 08:01 PM	#9
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	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.

7th November 2010, 08:24 PM	#10
manp111 diyAudio Member Join Date: Jun 2010 Location: Austin, Texas	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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