12-20 tube in AC-10 set

[Christopher Tubbs]

I have a AC-10 and the power supply uses 2-245 tubes, one 280 tube and a Amperite 12-20 tube.  The 12-20 tube's base is loose.  I believe they can be re-glued, but I was also researching the availability of 12-20 tubes and also if there was a replacement tube for it.

I found a sheet on antiqueradios.com (I can share the link, but wasn't sure I can put a link to another website for some admin or site rules)...the sheet noted that a 126 tube was a replacement.  I found some 126 tubes, but the 126 tubes have a four pin base, but the 12-20 is a two pin base.

Does anyone know if the 126 is a replacement for a 12-20 tube?
Do you cut off two of the four pins on the 126 and make it work?

Is there an adaptor base that the 126 tube plugs into and the adaptor would have two pins on it that would then get plugged in to the two pin socket on the power supply?

Or what's the "fix" or work around for a 12-20 tube?

[David C. Poland]

Dealing with hen's teeth - a scarce vintage tube. I also have the same 4 tube amp - unrestored.

So glad to see Scott document confirming the proper Amperite. tube. AND the "work around" when the tube fails.

Several Scott models had power supplies with a hi lo switch - Lo for 90 to 115 house voltage. Hi for 115 to 130 volts AC. Home voltage from power companies in the 1920's and 1930's varied widely by region, distance from sub stations and even the time of  day. Too widely for a performance radio to function properly because of the impact on tube filaments and high voltage circuits. The Amperite tube is intended to deal with such wide voltage extremes, in place of the customer monitoring house voltage to select the optimal switch position. 

This Amperite tube is a variable resistor sealed in a vacuum tube. The considerable variety of Amperite tubes is because both the current draw as well as the house voltage presented affect the desired voltage drop as well as the longevity of the tube. The primary winding of your power supply has a special power transformer  "expecting" about 80 volts AC. The proper Amperite tube delivers aproximately 80 Volts AC regardless of the house voltage being anywhere between 90 and 130 volts AC.

Have not seen the Amperite tube on any Scott other than the late production AC-10, so, say, late 1930 or early 1931 or until the first chrome Scott (the Scott Allwave 2-Dial model introduced Spring 1931). Your receiver probably has a pretty high serial number, and the amp maybe a somewhat higher serial number. (some of the AC-10 amps were likely diverted to other uses - I had an 3 tube AC10 power supply amp that appeared modified to power a Shield Grid 9 model, on account of the modified wiring of the big voltage divider in the amp.)

if you have a working 12-20 Amperite tube, I would not be too concerned about a loose base. Opinions on adhesives for loose tube bases on Antique Radio Forum seem to be - avoid unyielding cements lest differential expansion stress over heat cycles break the tube glass at the glue joint. So AVOID Crazy Glue.   Maybe,  somewhat thinned Elmers white paper glue ... just saying.

Hope you also have the proper Scott speaker - a D-90 (which is  ROLA 9 inch pedestal  model with Scott badge). 

[Kent King]

I'll add to Dave's comment: the reference that says a 126 is a substitute is totally wrong. A 126 (x26) is an AC triode. As dave noted, the 12-20 is a ballast tube (big resistor). If it works, re-glue it and keep going, you won't find another one. Dave was right - hen's teeth on this one. My AC-10 has one too, loose base, works fine. I hope I never break it.

Kent

[Christopher Tubbs]

Thank you guys!

The power supply is a Type 45 and # 3177

The chassis is type 601 and #1992

Yes, it has the correct D-90 speaker.  It's got the Scott name plate riveted on it and says D-90

It's in an Orleans cabinet. 

What makes this one special is that it has been in my family since it was bought 1931-1932.  Another collector mentioned that it's totally unheard of a single owner Scott set still in existence due to just the number of years that have gone by.  I've got the instruction manual that went with it and there also another piece of Scott paper with it saying IMPORTANT  This is our New 1930 Model using a Shield Grid Tube in the first detector, otherwise connections are the same.   And then there's an additional note on the same piece of paper saying not to use a light socket aerial.

 

[Norman S Braithwaite]

I would not completely discount the type 26 tube yet.  Its filament may provide the correct voltage drop and some limited regulation.  After all, the popular replacement for the high demand and scarce 4H4C ballast tube is a common type 6H6 tube because its filament provides a similar voltage drop as the 4H4C.  If the type 26 tube filament is a decent substitute, rebasing with the original two pin base and connecting only the filament leads would be appropriate.  If posting a link to the 26 tube suggestion is not supported, just type it as text.  I would like to see the context.

Norman

[George]

I used to own an HRO-60 receiver which uses that same ballast tube. A 6V6 substitutes for the 4H4C fine.

http://www.emmittsfixitshop.com/Projects_HRO_4H4C.html

[Kent King]

Christopher -

Could you post a copy of the "New 1930 model" document, I do not believe I've seen that before. And if possible, I'd love to get a scan of the instruction manual.

I have an AW23 in my collection that I purchased from the original purchaser - so it is a 1936 set with only two owners. That is really great that you have a family set this long - and a really good set at that.

I might have been to hasty in my 126 comment - Norman is right, certain tube filaments might provide an acceptable shunt. Actually, Scott's comment about setting it to the "High" line voltage is probably best, our line voltage today is significantly higher than they had back in 1930.

Kent

Christopher Tubbs said:

Thank you guys!

The power supply is a Type 45 and # 3177

The chassis is type 601 and #1992

Yes, it has the correct D-90 speaker.  It's got the Scott name plate riveted on it and says D-90

It's in an Orleans cabinet. 

What makes this one special is that it has been in my family since it was bought 1931-1932.  Another collector mentioned that it's totally unheard of a single owner Scott set still in existence due to just the number of years that have gone by.  I've got the instruction manual that went with it and there also another piece of Scott paper with it saying IMPORTANT  This is our New 1930 Model using a Shield Grid Tube in the first detector, otherwise connections are the same.   And then there's an additional note on the same piece of paper saying not to use a light socket aerial.

 

[David C. Poland]

IF the type 26 tube  were to be a decent electrical substitute, there is a pinout issue. 

The 26 tube side by side filament pins are #1 and #4, which are the 2 fat pins.

The amp's 2 pin socket fails to connect the filament pins. So tube filament is not connected.

Before cutting off pins to fit the 2 pin socket, solder a wire up close to the bakelite tube base from pin 1 to pin 2. Then cut off pins 1 and 3. Pins remaining 4 and 2 should then fit the socket.

Regarding 1920s globe shaped tube numbering:  the last 2 digits are the significant tube number. A leading 3rd number tried to show the manufacturer. Additional preceding alpha letters indicated the base type. This coding got out of control fast as more companies tried to get into the tube making business.

So the early globe shaped type 26 tube base may display:  126. or 326, or 226 or CX 326 ...

I have 01A type globes: by Airline hot branded GX-201A. By Cunningham CX-301A

Or for a type 27:  Arcturus 127, RCA UY-227

[Christopher Tubbs]

Hi Norman!  Here's the link: https://antiqueradios.com/ballast/

If you scroll down to the Table II (specifications) heading, it starts listing the different tubes and the last column says Exchange with 

...and when it goes farther down the list and hits the 126 tube, its Exchange with is a 12-20. 

It's 100% possible that the info is wrong.  I'm not enough of a radio engineer (by any stretch) to know if it's good info or not. 

Norman S Braithwaite said:

I would not completely discount the type 26 tube yet.  Its filament may provide the correct voltage drop and some limited regulation.  After all, the popular replacement for the high demand and scarce 4H4C ballast tube is a common type 6H6 tube because its filament provides a similar voltage drop as the 4H4C.  If the type 26 tube filament is a decent substitute, rebasing with the original two pin base and connecting only the filament leads would be appropriate.  If posting a link to the 26 tube suggestion is not supported, just type it as text.  I would like to see the context.

Norman

[Christopher Tubbs]

Hi Kent,

  Here's the image of "New 1930 model" paper:

Kent King said:

Christopher -

Could you post a copy of the "New 1930 model" document, I do not believe I've seen that before. And if possible, I'd love to get a scan of the instruction manual.

I have an AW23 in my collection that I purchased from the original purchaser - so it is a 1936 set with only two owners. That is really great that you have a family set this long - and a really good set at that.

I might have been to hasty in my 126 comment - Norman is right, certain tube filaments might provide an acceptable shunt. Actually, Scott's comment about setting it to the "High" line voltage is probably best, our line voltage today is significantly higher than they had back in 1930.

Kent

Christopher Tubbs said:

Thank you guys!

The power supply is a Type 45 and # 3177

The chassis is type 601 and #1992

Yes, it has the correct D-90 speaker.  It's got the Scott name plate riveted on it and says D-90

It's in an Orleans cabinet. 

What makes this one special is that it has been in my family since it was bought 1931-1932.  Another collector mentioned that it's totally unheard of a single owner Scott set still in existence due to just the number of years that have gone by.  I've got the instruction manual that went with it and there also another piece of Scott paper with it saying IMPORTANT  This is our New 1930 Model using a Shield Grid Tube in the first detector, otherwise connections are the same.   And then there's an additional note on the same piece of paper saying not to use a light socket aerial.

 

[Norman S Braithwaite]

The 126 on that list is a type 126 ballast, not a type 26 (127, 226, etc) tube.

Norman

Christopher Tubbs said:

Hi Norman!  Here's the link: https://antiqueradios.com/ballast/

If you scroll down to the Table II (specifications) heading, it starts listing the different tubes and the last column says Exchange with 

...and when it goes farther down the list and hits the 126 tube, its Exchange with is a 12-20. 

It's 100% possible that the info is wrong.  I'm not enough of a radio engineer (by any stretch) to know if it's good info or not. 

Norman S Braithwaite said:

I would not completely discount the type 26 tube yet.  Its filament may provide the correct voltage drop and some limited regulation.  After all, the popular replacement for the high demand and scarce 4H4C ballast tube is a common type 6H6 tube because its filament provides a similar voltage drop as the 4H4C.  If the type 26 tube filament is a decent substitute, rebasing with the original two pin base and connecting only the filament leads would be appropriate.  If posting a link to the 26 tube suggestion is not supported, just type it as text.  I would like to see the context.

Norman

[Christopher Tubbs]

Hi Norman.  Forgive my ignorance, but what would a 126 ballast look like if it's not a tube?  Like a "box" with wires coming out of each side?  And is a 126 ballast still available?

Norman S Braithwaite said:

The 126 on that list is a type 126 ballast, not a type 26 (127, 226, etc) tube.

Norman

Christopher Tubbs said:

Hi Norman!  Here's the link: https://antiqueradios.com/ballast/

If you scroll down to the Table II (specifications) heading, it starts listing the different tubes and the last column says Exchange with 

...and when it goes farther down the list and hits the 126 tube, its Exchange with is a 12-20. 

It's 100% possible that the info is wrong.  I'm not enough of a radio engineer (by any stretch) to know if it's good info or not. 

Norman S Braithwaite said:

I would not completely discount the type 26 tube yet.  Its filament may provide the correct voltage drop and some limited regulation.  After all, the popular replacement for the high demand and scarce 4H4C ballast tube is a common type 6H6 tube because its filament provides a similar voltage drop as the 4H4C.  If the type 26 tube filament is a decent substitute, rebasing with the original two pin base and connecting only the filament leads would be appropriate.  If posting a link to the 26 tube suggestion is not supported, just type it as text.  I would like to see the context.

Norman

[Norman S Braithwaite]

Well, I expect that it will look like a 12-20 ballast with the iron wire in a glass envelope but I prefer to call it a ballast to differentiate it from a type 126 tube thus avoiding the present confusion.

Norman