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 Post subject: 201 Tubes
PostPosted: Jan Sat 27, 2018 4:35 am 
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Location: Plymouth, MI
Are the early 201 tubes (1 amp) the same as 301 tubes, are they interchangable? I read some of the early tubes that had similar numbers were not interchangable despite the 01 designation. What tubes can be use in place of a 201?

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 Post subject: Re: 201 Tubes
PostPosted: Jan Sat 27, 2018 5:01 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 36509
Location: Livermore, CA
Hi Dan

201 is RCA, 301 Cunningham. Both are the same with 5 volt @ 1 amp filaments. The "A" version 201A etc have .25 amp filaments.

Where are you using the 201? What type of socket? Does it depend on the side bayonet pin?
Other tubes can be used in place of 201 if filament voltage and socket match. Type 30 will operate but has a 2 volt @ .06 amp filament and uses a standard 4 pin socket..

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 Post subject: Re: 201 Tubes
PostPosted: Jan Sat 27, 2018 8:26 pm 
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Location: Plymouth, MI
Just acquired an AK Model 1 from a collector and Leigh's print calls for 1 amp tubes and I don't have any because I never needed any. The collector I bought it from just informed me that it runs fine on 01a tubes, which is great because it is nearly impossible to find brass based, tipped 200 and 201 tubes. I was at the Michigan Antique Radio Club show in Farmington Hills this morning and no one had one.

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 Post subject: Re: 201 Tubes
PostPosted: Jan Sat 27, 2018 8:49 pm 
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Location: Maryland 20709, USA
atwaterkent1 wrote:
The collector I bought it from just informed me that it runs fine on 01a tubes...

The 3925 aka model 1 will not run properly with 1/4-amp filament tubes.

The 3-ohm rheostat will not drop 6.3 volts to 5.0 volts with 1/2-amp drain.

Obviously it's possible to change the A supply voltage, but that's not original.

- Leigh

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 Post subject: Re: 201 Tubes
PostPosted: Jan Sat 27, 2018 8:51 pm 
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Location: Livermore, CA
Dan

For AK model 1 you need tubes with side bayonet pins. Although 201A and 200A will operate your filament rheostat will not have proper control. It's only 2 ohms and made for higher current tubes.

Not a problem as long as your filament power supply voltage is adjustable.

http://www.atwaterkent.info/TechData/Dr ... 925sch.pdf

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 Post subject: Re: 201 Tubes
PostPosted: Jan Sat 27, 2018 9:00 pm 
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Power supply is adjustable. I'll let you know how the 01a's work next week when I wire it up and get it running.

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 Post subject: Re: 201 Tubes
PostPosted: Jan Sat 27, 2018 9:20 pm 
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Proper operation of the rheostat is important because that's the volume control.

Here's the modern schematic:
http://atwaterkent.info/TechData/Drawin ... 925sch.pdf

- Leigh

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Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: 201 Tubes
PostPosted: Jan Tue 30, 2018 3:27 am 
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Location: Plymouth, MI
Wired up my new (new to me) AK Model 1 today. I don't know what one sounds like with the 1 amp tubes, but this one sounded really good with 01A's. I plan to put some 1 amps in later and see if I can tell the difference.

Attachment:
AK Model 1.jpg
AK Model 1.jpg [ 228.26 KiB | Viewed 405 times ]

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