Filament voltage amperage question

[ALBATROS1234]

I have a chassis taken from a 1959 Conn organ. It had a 5U4 with an 0A3 regulator the rest of the tubes are 12 volt filaments including 4- 12V6gt's 2-12AX7's and a 12BH7. I was thinking I could use one half of the 12 winding with the center tap to make an amp with 6 volt tubes. My question is about the allowable amperage if I did this. My first instinct is that the winding wire gauge determines this period and I should be able to power as many amps of filament power regardless but I feel that I need consult the guru's to make sure I am not mixed up. Am I delusional thinking this? I realize that a 6volt tube will use more amperage due to ohms law but in my mind I think if I add up the filament current for the 4- 12v6's and the preamp tubes I should get the allowable amperage and therefore as long as I do not exceed this at 6 volts I am fine. I am thinking of perhaps a push pull EL84 amp being that I have some early 60s Telefunken 7189's begging for an amp to shine in and I have amps using 6V6's, 6L6's, 6AQ5's, and 6973's. But I digress are my thoughts flawed?

[sluckey]

Rather than trying to figure out how to run the filaments on 6v think about running on 12V. All the 12??7 tube family can easily be run on 12V filaments. As for a pair of EL84s, or a pair of 6L6s, etc, you can wire the filaments for the pair in series and operate from 12V. Think about that for a bit.

[ALBATROS1234]

True, I could run a pair of 6 volt tube filaments in series on a 12 volt supply. That's another possible solution. Granted I have a quad of RCA 12V6's but I was thinking of not being limited by 12 volt tubes or the "6V6" family albeit the thought crossed to do JMP with 4 12V6s in ppp.

Regarding the original question I am still.wondering/curious if using a leg to the center tap is possible and in my understanding of transformers it is the gauge of the winding which determines how many amps it can handle. In my mind I imagine a winding which handles say 3 amps at 12 volts would handle 3 amps at 6 volts but due to ohms law for instance a 12ax7 at 12 volts uses .15amps and at 6 volts use .3 amps also a 6v6 uses .45 amps vs a 12V6 using .225 amps so my thinking is at 6 volts I could only use a pair of power tubes vs a quad at 12 v like the original did. But I should be able to calculate total amps that were being used at 12v and as long as I do not exceed that amperage at 6v I should be fine. At least that is my thoughts.

[kagliostro]

Yes, 3A at 12.6v will be 3A at 6.3v, the tickness of wire rules

Unfortunately the two semi windings can not be connected in parallel

However if you do what Sluckey says (use 12.6v tubes and if 6.3v tubes connect It in series) will result in a bit less humm, prefer the less current path

Franco

[sluckey]

Regarding the original question I am still.wondering/curious if using a leg to the center tap is possible

Yes, you can do that. I suggest you calculate the current requirements of the Conn amp as is just so you know what the PT can handle. Then calculate the filament requirements of the project you have in mind to see if the PT is capable.

Most of the old Hammond PTs are very robust and can easily handle adding an additional amp of filament current. I suspect the Conn PTs are similarly rated.

[tubeswell]

True, I could run a pair of 6 volt tube filaments in series on a 12 volt supply. That's another possible solution. Granted I have a quad of RCA 12V6's but I was thinking of not being limited by 12 volt tubes or the "6V6" family albeit the thought crossed to do JMP with 4 12V6s in ppp.

Regarding the original question I am still.wondering/curious if using a leg to the center tap is possible and in my understanding of transformers it is the gauge of the winding which determines how many amps it can handle. In my mind I imagine a winding which handles say 3 amps at 12 volts would handle 3 amps at 6 volts but due to ohms law for instance a 12ax7 at 12 volts uses .15amps and at 6 volts use .3 amps also a 6v6 uses .45 amps vs a 12V6 using .225 amps so my thinking is at 6 volts I could only use a pair of power tubes vs a quad at 12 v like the original did. But I should be able to calculate total amps that were being used at 12v and as long as I do not exceed that amperage at 6v I should be fine. At least that is my thoughts.

Lots of examples on the web of 12V filament wiring. For 6V tubes in series, the current draw of each tube needs to be the same because of Kirchhoff’s law. (i.e. don’t put a EL84 and a 6V6 heater in series)
2 x 6V6s in series require 12.6VAC @ 450mA in total. 2 x 6L6s, 900mA in total

[66Strat]

I don't understand the impetus to switch to 6 volt heaters. New old stock 12V6GTs are readily available at bargain basement prices. The NOS 12V6 tubes are most likely better tubes than any new production 6 volt tube offerings.

[ALBATROS1234]

66strat that is a fair observation. I actually pulled four 1959 RCA 12v6s out of this amp.To be honest It would take some doing to calculate the exact amount of 12.6v current this beefy xfrmr can handle because in addition to the 4 12v preamp and 4 12v power tubes this amp had close to 50 other preamp tubes. most of which are 12AU7 sylvanias from 1959 as well. I was just trying to verify what I thought to be true that I could theorhetically take the CT and a leg at 6.3 v and make a standard amp using the hundreds of tubes I have in hand which are 6.3v as long as I don't exceed the current the xfrmr was designed for. That question has been answered as I expected it to be so the option is open to use 6v tubes if I wish. Like I figured x-amps=x-amps and although a 12 volt tube will use less amps at 12 v to heat said tube. Which is probably why they chose to design this amp as such. They figured if they needed x-amps at 12 v and a considerable bit more at 6v they are better off financially if the tubes are at 12V using .15amps per tube rather than .3amps per 6v tube. If you have literally 50 12AU7s this would make a huge difference in the wire gauge for the winding and make this big ass honking xmfr that much bigger if they were to use the 6v filament option.

[66Strat]

Is the amp in this link similar to the one than you have?
https://el34world.com/Forum/index.php?topic=11597.0

Some thoughts:

According to the datasheet, 12V6GT tube heater filaments draw .225 amps per tube. The datasheet for 6VGT tubes indicate a current dray of .45 amps per tube. The 12AX7 datasheet indicates filament current draw to be .15 amps at 12 volt series operation and .3 amps at 6 volt parallel operation. The tubes draw tubes draw twice the current operating at 6 volts as they do at 12 volts. Intuitively, this indicates that the transformer should support at least half of the number of tubes at 6 volts heater supply as the number of tubes at 12 volts.

One could measure (vernier caliper or micrometer) the diameter of the heater wire leads to determine the wire gauge and current capacity of the transformer filament wire leads. This would be one way to estimate the upper limit of the current capacity of the transformer. See attached link (https://www.powerstream.com/Wire_Size.htm)

[sluckey]

in addition to the 4 12v preamp and 4 12v power tubes this amp had close to 50 other preamp tubes. most of which are 12AU7

       So why even bother to try to calculate the current capacity? You're not likely to stress that PT filament winding.