Hello
Exploring CRT circuits, found a couple of televisions that their filament heaters are powered with 4.3VAC. Checked with two voltmeters, showing same reading. I used to believe the filaments were 6.3V and vacuum tubes with other voltages showed it on the first two digits. Example 35W4 as 35 volt; 12AX7 as 12 volt. Am in doubt if picture tubes had their numbering starting with the filament voltage or the size.

Can anyone confirm the CRT numbering relation to heater voltage; and if the typical 6.3V was changed to 4.3V at some point ? Or 15KHz derived is playing something here ?

 

Hello
Exploring CRT circuits, found a couple of televisions that their filament heaters are powered with 4.3VAC. Checked with two voltmeters, showing same reading. I used to believe the filaments were 6.3V and vacuum tubes with other voltages showed it on the first two digits. Example 35W4 as 35 volt; 12AX7 as 12 volt. Am in doubt if picture tubes had their numbering starting with the filament voltage.

Can anyone confirm the CRT numbering relation to heater voltage; and if the typical 6.3V was changed to 4.3V at some point ?

There were all kinds of tubes with different filament voltages. Remember that these were often unregulated AC voltages straight from the secondary winding on the transformer. The 6 and the 12 series were common along with the tubes in the "All American Five" including the 50C5. The sum of the filament voltages was 120 VAC -- what a coincidence they were all wired in series.

 

TV tubes were designed to have their filaments operated in series from the mains, just as the "All American Five" radio.
The high power tubes (e.g. horizontal drive) had a high filament voltage rating, and the lower power tubes had a lower voltage rating.
The sum of the filament voltages added to 120V.
I think there may have been more than one series string for all the tubes in a TV.

 

The 6.3 volt and 12 volt heater voltages were chosen for comparability with automotive electrical circuits of the day. Not many CRTs were designed with automobile electrical systems in mind, and only them from the late 1960’s, and they were not very common.

I can say that numbering for color tubes do not directly reflect the heater voltage.

4.3 VAC sounds odd but there is no reason to think it is incorrect.

 

If the part code starts with a number (and it is American made) then it is likely to be the heater voltage. European valves start with E if they are 6.3V.
Most of the data sheets are here.
https://frank.pocnet.net/

 

Thanks, gentlemen.
Learned something today ! The 6.3 and 12 V derived from automotive circuits.

Narrowing the search for color TV picture tubes only; anyone knows of a link for heater filament voltages table/data ? These B&W found show a bunch of voltages I did not expect :

Stumbled onto a good book if someone wants to read ----> https://www.effectrode.com/wp-content/uploads/2018/08/getting_the_most_out_of_vacuum_tubes1.pdf

 

Hello,

The following booklet has a lot of CRT tubes data:
https://archive.org/details/sencorecrttestersetupbook1984edition/mode/2up

Bertus

 

I disagree with crutchow about TVs with series string heaters. MOST of the decent quality sets did not do that, but quite a few of the "consumer junk" sets did use series strings, and a hot chassis as well. It did reduce the weight and eliminate the expensive power transformer. Also eliminated a bit of quality AND PRODUCT LIFETIME.

 

The basic reason for 6V and 12V filaments would have been to run them from batteries. 6V from 3 lead-acid cells or 4 dry cells. Radio was popular long before electric lighting reached every home.

 

You need one of these
https://cdn.pixabay.com/photo/2017/06/29/15/43/radio-2454584_960_720.jpg
for the HT supply!