If I need 67 volts in a portable radio should I use 7 or 8 nine volt batteries.

That would get you going for a few minutes..

:That would get you going for a few minutes..
:

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Connecting 9V batteries, particularly alkalines, will work well.

Maybe a couple of hundred hours of play time
http://data.energizer.com/PDFs/522.pdf
Also: http://antiqueradio.org/bsupply.htm

Rich
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You can use a wide range of 9 volt battery series hookups- the radio will probably work OK at 45 volts (5 9-volters in series) up to 8 in series (72 volts). The B+ is low current (provided you keep the play volume down) but is not particularly fussy about exact voltages. These batteries are expensive so you might want to hook up an adjustable DC source in place of the battery, then see how low you can go with the voltage before the set starts to falter (poor sound quality, low sensitivity) due to low B+ voltage. Then use that info as a guide to pick the quantity of 9-volt batteries that you need to string together.

You could try 7 or 8. If you want close to 67.5, put 7 diodes (which drop 0.6 volts each), in series with 8 batteries which would lead to 67.8V. Make sure you don't exceed the maximum plate voltage of your tube lineup, but I know vacuum tubes are much more tolerant of voltage fluctuation than transistors, and some of the battery radios used a 90V or 120V plate voltage so I think you would probably be OK with 72V myself.

Another idea is to use 9V sized rechargeable batteries that output 8.4V each. This would lead to a 67.2V output: http://www.batteryjunction.com/tenergy-nimh-9v-200-premium.html?gclid=CJjJyq-Qt7gCFQnhQgodM2EAmQ

:You can use a wide range of 9 volt battery series hookups- the radio will probably work OK at 45 volts (5 9-volters in series) up to 8 in series (72 volts). The B+ is low current (provided you keep the play volume down) but is not particularly fussy about exact voltages. These batteries are expensive so you might want to hook up an adjustable DC source in place of the battery, then see how low you can go with the voltage before the set starts to falter (poor sound quality, low sensitivity) due to low B+ voltage. Then use that info as a guide to pick the quantity of 9-volt batteries that you need to string together.
:
:

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Don't bother with diodes... just wasting battery power. Tubes were used at 45, 67, and 90V in those old radios.
Rich
>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<

:You could try 7 or 8. If you want close to 67.5, put 7 diodes (which drop 0.6 volts each), in series with 8 batteries which would lead to 67.8V. Make sure you don't exceed the maximum plate voltage of your tube lineup, but I know vacuum tubes are much more tolerant of voltage fluctuation than transistors, and some of the battery radios used a 90V or 120V plate voltage so I think you would probably be OK with 72V myself.
:
:Another idea is to use 9V sized rechargeable batteries that output 8.4V each. This would lead to a 67.2V output: http://www.batteryjunction.com/tenergy-nimh-9v-200-premium.html?gclid=CJjJyq-Qt7gCFQnhQgodM2EAmQ
:
::You can use a wide range of 9 volt battery series hookups- the radio will probably work OK at 45 volts (5 9-volters in series) up to 8 in series (72 volts). The B+ is low current (provided you keep the play volume down) but is not particularly fussy about exact voltages. These batteries are expensive so you might want to hook up an adjustable DC source in place of the battery, then see how low you can go with the voltage before the set starts to falter (poor sound quality, low sensitivity) due to low B+ voltage. Then use that info as a guide to pick the quantity of 9-volt batteries that you need to string together.
::
::
:
:

:Another idea is to use 9V sized rechargeable batteries that output 8.4V each. This would lead to a 67.2V output: http://www.batteryjunction.com/tenergy-nimh-9v-200-premium.html?gclid=CJjJyq-Qt7gCFQnhQgodM2EAmQ
:

The rechargeable 9V battery approach is interesting but might be a logistical headache: these things self-discharge in a matter of several weeks. You would either need a custom "battery maintainer" or have a couple of single-battery chargers on hand to get them all refreshed in a reasonable amount of time.

:You could try 7 or 8. If you want close to 67.5, put 7 diodes (which drop 0.6 volts each), in series with 8 batteries which would lead to 67.8V. Make sure you don't exceed the maximum plate voltage of your tube lineup, but I know vacuum tubes are much more tolerant of voltage fluctuation than transistors, and some of the battery radios used a 90V or 120V plate voltage so I think you would probably be OK with 72V myself.
:
:Another idea is to use 9V sized rechargeable batteries that output 8.4V each. This would lead to a 67.2V output: http://www.batteryjunction.com/tenergy-nimh-9v-200-premium.html?gclid=CJjJyq-Qt7gCFQnhQgodM2EAmQ
:
::You can use a wide range of 9 volt battery series hookups- the radio will probably work OK at 45 volts (5 9-volters in series) up to 8 in series (72 volts). The B+ is low current (provided you keep the play volume down) but is not particularly fussy about exact voltages. These batteries are expensive so you might want to hook up an adjustable DC source in place of the battery, then see how low you can go with the voltage before the set starts to falter (poor sound quality, low sensitivity) due to low B+ voltage. Then use that info as a guide to pick the quantity of 9-volt batteries that you need to string together.
::
::If you go higher in voltage than normal, Be sure to use a ZENER diode rated at the B+ voltage. They are sometimes called an "avalanche diode".
: Anything OVER the rated voltage gets by-passed to ground. This is another solution to your problem. It may or may not work, but at least it's worth looking at to see your options.
:

>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<
Do not bother with series diodes, zeners, or anything else. Your radio will work with as much as 90V batteries. The old portables used tubes that could handle over 100V. You will get more audio volume with higher battery voltage. Adding diodes or Zeners just wastes battery energy.

Rich
>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<

::You could try 7 or 8. If you want close to 67.5, put 7 diodes (which drop 0.6 volts each), in series with 8 batteries which would lead to 67.8V. Make sure you don't exceed the maximum plate voltage of your tube lineup, but I know vacuum tubes are much more tolerant of voltage fluctuation than transistors, and some of the battery radios used a 90V or 120V plate voltage so I think you would probably be OK with 72V myself.
::
::Another idea is to use 9V sized rechargeable batteries that output 8.4V each. This would lead to a 67.2V output: http://www.batteryjunction.com/tenergy-nimh-9v-200-premium.html?gclid=CJjJyq-Qt7gCFQnhQgodM2EAmQ
::
:::You can use a wide range of 9 volt battery series hookups- the radio will probably work OK at 45 volts (5 9-volters in series) up to 8 in series (72 volts). The B+ is low current (provided you keep the play volume down) but is not particularly fussy about exact voltages. These batteries are expensive so you might want to hook up an adjustable DC source in place of the battery, then see how low you can go with the voltage before the set starts to falter (poor sound quality, low sensitivity) due to low B+ voltage. Then use that info as a guide to pick the quantity of 9-volt batteries that you need to string together.
:::
:::If you go higher in voltage than normal, Be sure to use a ZENER diode rated at the B+ voltage. They are sometimes called an "avalanche diode".
:: Anything OVER the rated voltage gets by-passed to ground. This is another solution to your problem. It may or may not work, but at least it's worth looking at to see your options.
::
:
: