Heater voltages

[timmy]

How is it that in a string of about 5 tubes one is only 5 vac but befor that one and after the voltages are up around 6.5 and 7 vac. I tried several tubes in that socket and the voltage changed very little. The string resistors are new.

[old_coot88]

Originally Posted by timmy

How is it that in a string of about 5 tubes one is only 5 vac but befor that one and after the voltages are up around 6.5 and 7 vac.

What's the type number of that tube? And what are the type numbers of the other tubes in series with it?

[jr_tech]

What tube is it, and where is it used? Perhaps the oscillator tube in the pilot???

jr

[timmy]

Yes the pilot, 4 - 6au6 in a row and switched around and now it changed low voltage on another one so I guess it's difference in resistance between tubes but I hope at 5 vac there is enough for the tube to conduct.

[jr_tech]

Does the low voltage occur on the same tube independent of which socket it is plugged into, or is the voltage always low at a particular socket no matter which tube you plug into it?

jr

[Eric H]

Are they all clearly marked 6AU6 and not one of the odd voltage versions like a 4AU6 which has a higher current draw?

[N2IXK]

6AU6 vs. 6AU6A may make a difference in series circuits, as well.

In general, an "A" suffix means controlled warmup time for series string use.

[Tubejunke]

In a series heater string each tube heater is actually a resistance. Each resistance drops or uses a certain voltage. The voltage drops must add to approximate the supply voltage. A good way to check this out is to look inside of an old transformerless tube type radio. You can add the first two numbers of the tubes which are your operating voltages and come up with somewhere near line voltage.

You may want to get to know the basics of electronics to get a decent understanding of things like series circuit arrangements as opposed to parallel. There are even combinations of the two which is a bit more difficult to grasp. Frankly, this knowledge IMO is essential to anyone expecting to be a radio or TV doctor. We live in a plug and play age of electronics, but really the old stuff I think required a good knowledge base of the understanding of circuits, components, and the tools of the trade and how to use them being volt, ampere, and resistance meters to keep it basic.