DM
What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
Norm
:this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
:
:DM
Dan
::Hi Dan
::
:: What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
::
::Norm
::
:::this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
:::
:::DM
You could use a center tapped winding for filament of 71A or a low value center tapped resistor. Some radios used a low value pot as a hum balance control. You probably did similar things with a 45? 71A is similar to a 45 but with a 5 volt filament.
If you use a 01A as first audio stage shouldn't use AC on the filament. No matter how hard you work at it there will be some hum. Can't really use a small battery either. The filament draws .25 amps.
You can use a #26 tube. It's like an 01A but with 1 1/2 volt 1.05 amp filament. Due to this high current it's slow to cycle with AC and has less hum. Still need a hum balance control.
For an example of an early circuit using these tubes check Atwater Kent Model 40 schematic.
Norm
:Hi Norm, I am trying to get used to this forum style, I apologize for the slop.
:the situation I am in is that I build tube amplifiers for a living and I have taken on a difficult project for me. directly heated cathodes have always been tricky for me, but I have worked the 300B & 45 with success. A new client of mine had asked me to build a unique headphone amp that could double as a low powered power amp. I figured I could go with a O1A in headphone mode and use the 71A with a higher Mu driver tube for an 8 ohm horn out. my problem has always been with running dc fil`s w/ out going fixed bias.
:I thought going dc fil, cathode bias could be acheved by using a 4.5vac ct full wave forward rect & using a bias resistor off the ct. I do not mind going fixed on the O1A w/ a coin bat, but... man, I could realy use some help on the return flow, any ideas?
:thanks for your time norm.
:
:Dan
:
:::Hi Dan
:::
::: What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
:::
:::Norm
:::
::::this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
::::
::::DM
A humbled builder named Dan
:Hi Dan
:
: You could use a center tapped winding for filament of 71A or a low value center tapped resistor. Some radios used a low value pot as a hum balance control. You probably did similar things with a 45? 71A is similar to a 45 but with a 5 volt filament.
:
: If you use a 01A as first audio stage shouldn't use AC on the filament. No matter how hard you work at it there will be some hum. Can't really use a small battery either. The filament draws .25 amps.
:
: You can use a #26 tube. It's like an 01A but with 1 1/2 volt 1.05 amp filament. Due to this high current it's slow to cycle with AC and has less hum. Still need a hum balance control.
:
: For an example of an early circuit using these tubes check Atwater Kent Model 40 schematic.
:
:Norm
:
: :Hi Norm, I am trying to get used to this forum style, I apologize for the slop.
::the situation I am in is that I build tube amplifiers for a living and I have taken on a difficult project for me. directly heated cathodes have always been tricky for me, but I have worked the 300B & 45 with success. A new client of mine had asked me to build a unique headphone amp that could double as a low powered power amp. I figured I could go with a O1A in headphone mode and use the 71A with a higher Mu driver tube for an 8 ohm horn out. my problem has always been with running dc fil`s w/ out going fixed bias.
::I thought going dc fil, cathode bias could be acheved by using a 4.5vac ct full wave forward rect & using a bias resistor off the ct. I do not mind going fixed on the O1A w/ a coin bat, but... man, I could realy use some help on the return flow, any ideas?
::thanks for your time norm.
::
::Dan
::
::::Hi Dan
::::
:::: What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
::::
::::Norm
::::
:::::this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
:::::
:::::DM
If you want to use old tubes and not have hum why not 27 or 227's? These have a cathode so filament is isolated.
Look at schematics for early radios. A lot of early AC radios used 71A for output & 26 or 27's for preamp. RCA Radiola 60 used 27's with 71A output. Schematics can be found here on nostalgiaair.
Norm
:Hi Norm, your right I did do that with the #45 that worked, but the pre`s were #76`s. The amp I have not been able to make work right that humbles me every time I pull it off the shelf, is a se 245 w/ 2) #26`s on the pre(realy 226`s). the 245 is ac fil & fixed bias, the 26`s are dc fil, & I can not get them to work right. I am not worried about my shelf dust collector right now, but about this new project.
:the tough part is the pre`s and the power tubes need to be dc on the filiments. hum is not an option for this guy. I wanted to stay cathode biased on both tubes, but do not know how to do that. the coin battery was for the grid on the O1A if I had to go fixed.
:thank you for you time,
:
:A humbled builder named Dan
:
::Hi Dan
::
:: You could use a center tapped winding for filament of 71A or a low value center tapped resistor. Some radios used a low value pot as a hum balance control. You probably did similar things with a 45? 71A is similar to a 45 but with a 5 volt filament.
::
:: If you use a 01A as first audio stage shouldn't use AC on the filament. No matter how hard you work at it there will be some hum. Can't really use a small battery either. The filament draws .25 amps.
::
:: You can use a #26 tube. It's like an 01A but with 1 1/2 volt 1.05 amp filament. Due to this high current it's slow to cycle with AC and has less hum. Still need a hum balance control.
::
:: For an example of an early circuit using these tubes check Atwater Kent Model 40 schematic.
::
::Norm
::
:: :Hi Norm, I am trying to get used to this forum style, I apologize for the slop.
:::the situation I am in is that I build tube amplifiers for a living and I have taken on a difficult project for me. directly heated cathodes have always been tricky for me, but I have worked the 300B & 45 with success. A new client of mine had asked me to build a unique headphone amp that could double as a low powered power amp. I figured I could go with a O1A in headphone mode and use the 71A with a higher Mu driver tube for an 8 ohm horn out. my problem has always been with running dc fil`s w/ out going fixed bias.
:::I thought going dc fil, cathode bias could be acheved by using a 4.5vac ct full wave forward rect & using a bias resistor off the ct. I do not mind going fixed on the O1A w/ a coin bat, but... man, I could realy use some help on the return flow, any ideas?
:::thanks for your time norm.
:::
:::Dan
:::
:::::Hi Dan
:::::
::::: What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
:::::
:::::Norm
:::::
::::::this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
::::::
::::::DM
Dan
:Hi Dan
:
: If you want to use old tubes and not have hum why not 27 or 227's? These have a cathode so filament is isolated.
:
: Look at schematics for early radios. A lot of early AC radios used 71A for output & 26 or 27's for preamp. RCA Radiola 60 used 27's with 71A output. Schematics can be found here on nostalgiaair.
:
:Norm
:
::Hi Norm, your right I did do that with the #45 that worked, but the pre`s were #76`s. The amp I have not been able to make work right that humbles me every time I pull it off the shelf, is a se 245 w/ 2) #26`s on the pre(realy 226`s). the 245 is ac fil & fixed bias, the 26`s are dc fil, & I can not get them to work right. I am not worried about my shelf dust collector right now, but about this new project.
::the tough part is the pre`s and the power tubes need to be dc on the filiments. hum is not an option for this guy. I wanted to stay cathode biased on both tubes, but do not know how to do that. the coin battery was for the grid on the O1A if I had to go fixed.
::thank you for you time,
::
::A humbled builder named Dan
::
:::Hi Dan
:::
::: You could use a center tapped winding for filament of 71A or a low value center tapped resistor. Some radios used a low value pot as a hum balance control. You probably did similar things with a 45? 71A is similar to a 45 but with a 5 volt filament.
:::
::: If you use a 01A as first audio stage shouldn't use AC on the filament. No matter how hard you work at it there will be some hum. Can't really use a small battery either. The filament draws .25 amps.
:::
::: You can use a #26 tube. It's like an 01A but with 1 1/2 volt 1.05 amp filament. Due to this high current it's slow to cycle with AC and has less hum. Still need a hum balance control.
:::
::: For an example of an early circuit using these tubes check Atwater Kent Model 40 schematic.
:::
:::Norm
:::
::: :Hi Norm, I am trying to get used to this forum style, I apologize for the slop.
::::the situation I am in is that I build tube amplifiers for a living and I have taken on a difficult project for me. directly heated cathodes have always been tricky for me, but I have worked the 300B & 45 with success. A new client of mine had asked me to build a unique headphone amp that could double as a low powered power amp. I figured I could go with a O1A in headphone mode and use the 71A with a higher Mu driver tube for an 8 ohm horn out. my problem has always been with running dc fil`s w/ out going fixed bias.
::::I thought going dc fil, cathode bias could be acheved by using a 4.5vac ct full wave forward rect & using a bias resistor off the ct. I do not mind going fixed on the O1A w/ a coin bat, but... man, I could realy use some help on the return flow, any ideas?
::::thanks for your time norm.
::::
::::Dan
::::
::::::Hi Dan
::::::
:::::: What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
::::::
::::::Norm
::::::
:::::::this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
:::::::
:::::::DM
Getting DC bias for the grid is easy. From the filament center tap use a resistor to ground. This will make the filament positive when measured to ground. Connect your grid resistor to ground. This will cause your grid to be negative when measured to filament.
Norm
:Hi Norm, I could use an indirectly heated cath, but I wanted to challenge myself, and hold up my end of haveing something unique. the pre will be a 12AU7 for the O1A output for phones and a 12AX7 pre for the 71A output to horn speakers. I do not mind going dc filiments because I can filter the begeseous out of the supply. I liked the idea of using #26`s, because I can use the 2.5v aerogell caps. they are small & cheap & come in values like .5 f & 1 f. I have to figure out how to cathode bias a dc filiment tube with directly heated filiments from a power supply. any ideas?
:thank you again,
:
:Dan
:
:
::Hi Dan
::
:: If you want to use old tubes and not have hum why not 27 or 227's? These have a cathode so filament is isolated.
::
:: Look at schematics for early radios. A lot of early AC radios used 71A for output & 26 or 27's for preamp. RCA Radiola 60 used 27's with 71A output. Schematics can be found here on nostalgiaair.
::
::Norm
::
:::Hi Norm, your right I did do that with the #45 that worked, but the pre`s were #76`s. The amp I have not been able to make work right that humbles me every time I pull it off the shelf, is a se 245 w/ 2) #26`s on the pre(realy 226`s). the 245 is ac fil & fixed bias, the 26`s are dc fil, & I can not get them to work right. I am not worried about my shelf dust collector right now, but about this new project.
:::the tough part is the pre`s and the power tubes need to be dc on the filiments. hum is not an option for this guy. I wanted to stay cathode biased on both tubes, but do not know how to do that. the coin battery was for the grid on the O1A if I had to go fixed.
:::thank you for you time,
:::
:::A humbled builder named Dan
:::
::::Hi Dan
::::
:::: You could use a center tapped winding for filament of 71A or a low value center tapped resistor. Some radios used a low value pot as a hum balance control. You probably did similar things with a 45? 71A is similar to a 45 but with a 5 volt filament.
::::
:::: If you use a 01A as first audio stage shouldn't use AC on the filament. No matter how hard you work at it there will be some hum. Can't really use a small battery either. The filament draws .25 amps.
::::
:::: You can use a #26 tube. It's like an 01A but with 1 1/2 volt 1.05 amp filament. Due to this high current it's slow to cycle with AC and has less hum. Still need a hum balance control.
::::
:::: For an example of an early circuit using these tubes check Atwater Kent Model 40 schematic.
::::
::::Norm
::::
:::: :Hi Norm, I am trying to get used to this forum style, I apologize for the slop.
:::::the situation I am in is that I build tube amplifiers for a living and I have taken on a difficult project for me. directly heated cathodes have always been tricky for me, but I have worked the 300B & 45 with success. A new client of mine had asked me to build a unique headphone amp that could double as a low powered power amp. I figured I could go with a O1A in headphone mode and use the 71A with a higher Mu driver tube for an 8 ohm horn out. my problem has always been with running dc fil`s w/ out going fixed bias.
:::::I thought going dc fil, cathode bias could be acheved by using a 4.5vac ct full wave forward rect & using a bias resistor off the ct. I do not mind going fixed on the O1A w/ a coin bat, but... man, I could realy use some help on the return flow, any ideas?
:::::thanks for your time norm.
:::::
:::::Dan
:::::
:::::::Hi Dan
:::::::
::::::: What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
:::::::
:::::::Norm
:::::::
::::::::this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
::::::::
::::::::DM
Dan
:Hi Dan
:
: Getting DC bias for the grid is easy. From the filament center tap use a resistor to ground. This will make the filament positive when measured to ground. Connect your grid resistor to ground. This will cause your grid to be negative when measured to filament.
:
:Norm
:
:
::Hi Norm, I could use an indirectly heated cath, but I wanted to challenge myself, and hold up my end of haveing something unique. the pre will be a 12AU7 for the O1A output for phones and a 12AX7 pre for the 71A output to horn speakers. I do not mind going dc filiments because I can filter the begeseous out of the supply. I liked the idea of using #26`s, because I can use the 2.5v aerogell caps. they are small & cheap & come in values like .5 f & 1 f. I have to figure out how to cathode bias a dc filiment tube with directly heated filiments from a power supply. any ideas?
::thank you again,
::
::Dan
::
::
:::Hi Dan
:::
::: If you want to use old tubes and not have hum why not 27 or 227's? These have a cathode so filament is isolated.
:::
::: Look at schematics for early radios. A lot of early AC radios used 71A for output & 26 or 27's for preamp. RCA Radiola 60 used 27's with 71A output. Schematics can be found here on nostalgiaair.
:::
:::Norm
:::
::::Hi Norm, your right I did do that with the #45 that worked, but the pre`s were #76`s. The amp I have not been able to make work right that humbles me every time I pull it off the shelf, is a se 245 w/ 2) #26`s on the pre(realy 226`s). the 245 is ac fil & fixed bias, the 26`s are dc fil, & I can not get them to work right. I am not worried about my shelf dust collector right now, but about this new project.
::::the tough part is the pre`s and the power tubes need to be dc on the filiments. hum is not an option for this guy. I wanted to stay cathode biased on both tubes, but do not know how to do that. the coin battery was for the grid on the O1A if I had to go fixed.
::::thank you for you time,
::::
::::A humbled builder named Dan
::::
:::::Hi Dan
:::::
::::: You could use a center tapped winding for filament of 71A or a low value center tapped resistor. Some radios used a low value pot as a hum balance control. You probably did similar things with a 45? 71A is similar to a 45 but with a 5 volt filament.
:::::
::::: If you use a 01A as first audio stage shouldn't use AC on the filament. No matter how hard you work at it there will be some hum. Can't really use a small battery either. The filament draws .25 amps.
:::::
::::: You can use a #26 tube. It's like an 01A but with 1 1/2 volt 1.05 amp filament. Due to this high current it's slow to cycle with AC and has less hum. Still need a hum balance control.
:::::
::::: For an example of an early circuit using these tubes check Atwater Kent Model 40 schematic.
:::::
:::::Norm
:::::
::::: :Hi Norm, I am trying to get used to this forum style, I apologize for the slop.
::::::the situation I am in is that I build tube amplifiers for a living and I have taken on a difficult project for me. directly heated cathodes have always been tricky for me, but I have worked the 300B & 45 with success. A new client of mine had asked me to build a unique headphone amp that could double as a low powered power amp. I figured I could go with a O1A in headphone mode and use the 71A with a higher Mu driver tube for an 8 ohm horn out. my problem has always been with running dc fil`s w/ out going fixed bias.
::::::I thought going dc fil, cathode bias could be acheved by using a 4.5vac ct full wave forward rect & using a bias resistor off the ct. I do not mind going fixed on the O1A w/ a coin bat, but... man, I could realy use some help on the return flow, any ideas?
::::::thanks for your time norm.
::::::
::::::Dan
::::::
::::::::Hi Dan
::::::::
:::::::: What information do you need? Both 01A & 71A are triodes using "4D" base wiring. They operate on 5 volt filament. 01A was used in 1920's battery radios. 71A was used as an audio output tube in battery & early AC radios. Both types have a side bayonet pin and can be used is old twist type sockets.
::::::::
::::::::Norm
::::::::
:::::::::this forum was recomended for technical help on these two tubes, I could use some help if someone has worked w/ these tubes & does not mind sharing.
:::::::::
:::::::::DM