I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?

:I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?

Jim,
Whenever I restore a radio I always add an in-line fuse.....usually around 1/2 amp - 3/4 amp slo-blow. I have taken to using the inline fuse holder that I can usually find space for under the chassis as opposed to drilling a hole in the cabinet or chassis for a panel mount type fuse holder. Your Sams Photofact or Riders Schematic will tell you the current draw of the radio....some of the larger radios would require a higher rated fuse. I am sure there are a bunch of guys out there that could give you more technical advice.....but I figured I'd let you know how I have been doing the fuse thing.
DennisWess

Hi Jim,

I usually mount a pig-tail fuse under the chassis, which saves from drilling holes, which preserves the original look of the chassis. When mounting the fuse I use large diameter spaghetti tubing over the fuse to insulate the metal caps on either end.

To select the fuse value, calculate the nominal current draw of the radio using the power rating from the name plate.

Current = Power / Voltage (I = P / E)
As an example, a radio with a 75 watt rating will have a nominal current draw of 75 / 120 = 0.62 amps.

Remember that this is the nominal current. The fuse must rated higher than this value. I usually put in a fuse about 2 to 4 times the nominal current. Also, a tube radio will draw significantly higher than nominal current when it is first turned on due to the tube filaments. For this reason a slo-blow fuse is a must.

Hope this helps,
Gary

:I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?

:Hi Jim,
:
:I usually mount a pig-tail fuse under the chassis, which saves from drilling holes, which preserves the original look of the chassis. When mounting the fuse I use large diameter spaghetti tubing over the fuse to insulate the metal caps on either end.
:
:To select the fuse value, calculate the nominal current draw of the radio using the power rating from the name plate.
:
:Current = Power / Voltage (I = P / E)
:As an example, a radio with a 75 watt rating will have a nominal current draw of 75 / 120 = 0.62 amps.
:
:Remember that this is the nominal current. The fuse must rated higher than this value. I usually put in a fuse about 2 to 4 times the nominal current. Also, a tube radio will draw significantly higher than nominal current when it is first turned on due to the tube filaments. For this reason a slo-blow fuse is a must.
:
:Hope this helps,
:Gary
:
::I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?

Thanks, I asked about pig tail fuses at the local electronic supply but they had none. I will check on line. thanks

All you have to do to make a pigtail fuse is to solder wires to an ordinary Buss cylinder fuse (glass type). Do not apply the iron long enough to disconnect the insides. Each cap that is being soldered may try to work its way off from air pressure inside the tube. Hold it in place until it cools. Once both wires are soldered on, test with your meter.

Thomas

::Hi Jim,
::
::I usually mount a pig-tail fuse under the chassis, which saves from drilling holes, which preserves the original look of the chassis. When mounting the fuse I use large diameter spaghetti tubing over the fuse to insulate the metal caps on either end.
::
::To select the fuse value, calculate the nominal current draw of the radio using the power rating from the name plate.
::
::Current = Power / Voltage (I = P / E)
::As an example, a radio with a 75 watt rating will have a nominal current draw of 75 / 120 = 0.62 amps.
::
::Remember that this is the nominal current. The fuse must rated higher than this value. I usually put in a fuse about 2 to 4 times the nominal current. Also, a tube radio will draw significantly higher than nominal current when it is first turned on due to the tube filaments. For this reason a slo-blow fuse is a must.
::
::Hope this helps,
::Gary
::
:::I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?
:
:
:Thanks, I asked about pig tail fuses at the local electronic supply but they had none. I will check on line. thanks

Remember, AC-DC sets are already fused to some extent. The 25Z5, 35Z5 and 45Z5 tubes have cathode connection tabs that are designed to fuse at approximately 140ma. The cathode tabs of the miniature 35Z3 will fuse at about 100ma. This characteristic of the rectifier tube was the only reason that the National Board of Fire Underwriters listed the universal sets without requiring fuses. The Board discussed requiring fuses in the late 1930's and again in the 1950s, but extensive tests showed that the inherent current limiting characteristics of the rectifier tubes provided a more than adequate margin of safety.

:::Hi Jim,
::
:::I usually mount a pig-tail fuse under the chassis, which saves from drilling holes, which preserves the original look of the chassis. When mounting the fuse I use large diameter spaghetti tubing over the fuse to insulate the metal caps on either end.
:::
:::To select the fuse value, calculate the nominal current draw of the radio using the power rating from the name plate.
:::
:::Current = Power / Voltage (I = P / E)
:::As an example, a radio with a 75 watt rating will have a nominal current draw of 75 / 120 = 0.62 amps.
:::
:::Remember that this is the nominal current. The fuse must rated higher than this value. I usually put in a fuse about 2 to 4 times the nominal current. Also, a tube radio will draw significantly higher than nominal current when it is first turned on due to the tube filaments. For this reason a slo-blow fuse is a must.
:::
:::Hope this helps,
:::Gary
:::
::::I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?
::
::
::Thanks, I asked about pig tail fuses at the local electronic supply but they had none. I will check on line. thanks

Hi Bob,
I wasn't aware that these tubes were designed with integral "fuse tabs". I checked several different tube manuals and this doesn't appear to be a published feature. Do have any literature or specs detailing this design feature?

Just interested.
Gary

:Remember, AC-DC sets are already fused to some extent. The 25Z5, 35Z5 and 45Z5 tubes have cathode connection tabs that are designed to fuse at approximately 140ma. The cathode tabs of the miniature 35Z3 will fuse at about 100ma. This characteristic of the rectifier tube was the only reason that the National Board of Fire Underwriters listed the universal sets without requiring fuses. The Board discussed requiring fuses in the late 1930's and again in the 1950s, but extensive tests showed that the inherent current limiting characteristics of the rectifier tubes provided a more than adequate margin of safety.
:
::::Hi Jim,
:::
::::I usually mount a pig-tail fuse under the chassis, which saves from drilling holes, which preserves the original look of the chassis. When mounting the fuse I use large diameter spaghetti tubing over the fuse to insulate the metal caps on either end.
::::
::::To select the fuse value, calculate the nominal current draw of the radio using the power rating from the name plate.
::::
::::Current = Power / Voltage (I = P / E)
::::As an example, a radio with a 75 watt rating will have a nominal current draw of 75 / 120 = 0.62 amps.
::::
::::Remember that this is the nominal current. The fuse must rated higher than this value. I usually put in a fuse about 2 to 4 times the nominal current. Also, a tube radio will draw significantly higher than nominal current when it is first turned on due to the tube filaments. For this reason a slo-blow fuse is a must.
::::
::::Hope this helps,
::::Gary
::::
:::::I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?
:::
:::
:::Thanks, I asked about pig tail fuses at the local electronic supply but they had none. I will check on line. thanks

The first mention of this feature that I noticed was in a Sylvania News Technical Section article of about 1937. This feature was also mentioned in an article in Radio Engineering of about the same date. I no longer have the original materials at my disposal, as they erre destroyed in a fire, but the NFPA board of Underwriters mentions the requirement for integral current limiting devixes in the primary circuits of transformerless radio apparatus as early as 1935.

:Hi Bob,
:I wasn't aware that these tubes were designed with integral "fuse tabs". I checked several different tube manuals and this doesn't appear to be a published feature. Do have any literature or specs detailing this design feature?
:
:Just interested.
:Gary
:
::Remember, AC-DC sets are already fused to some extent. The 25Z5, 35Z5 and 45Z5 tubes have cathode connection tabs that are designed to fuse at approximately 140ma. The cathode tabs of the miniature 35Z3 will fuse at about 100ma. This characteristic of the rectifier tube was the only reason that the National Board of Fire Underwriters listed the universal sets without requiring fuses. The Board discussed requiring fuses in the late 1930's and again in the 1950s, but extensive tests showed that the inherent current limiting characteristics of the rectifier tubes provided a more than adequate margin of safety.
::
:::::Hi Jim,
::::
:::::I usually mount a pig-tail fuse under the chassis, which saves from drilling holes, which preserves the original look of the chassis. When mounting the fuse I use large diameter spaghetti tubing over the fuse to insulate the metal caps on either end.
:::::
:::::To select the fuse value, calculate the nominal current draw of the radio using the power rating from the name plate.
:::::
:::::Current = Power / Voltage (I = P / E)
:::::As an example, a radio with a 75 watt rating will have a nominal current draw of 75 / 120 = 0.62 amps.
:::::
:::::Remember that this is the nominal current. The fuse must rated higher than this value. I usually put in a fuse about 2 to 4 times the nominal current. Also, a tube radio will draw significantly higher than nominal current when it is first turned on due to the tube filaments. For this reason a slo-blow fuse is a must.
:::::
:::::Hope this helps,
:::::Gary
:::::
::::::I would like to add fuses to some of the tube radios and clock radios I use frequently. On the clock radios I was thinking of putting an in line fuse holder on the ac supply that goes to a switch on the clock (Telechron). On the larger transformer sets I was thinking of putting a fuse mount on the chassis or if not enough room on the cabinet (inside of course). What size fuse should I use and or any comments on adding fuses to tube radios?
::::
::::
::::Thanks, I asked about pig tail fuses at the local electronic supply but they had none. I will check on line. thanks