Hi!
First and foremost, sorry if this is explained elsewhere. I'm working on fixing my very first tube gear. Analog electronics is pretty new to me. Reading whatever I can find, "Youtube university" etc. My background is in IT and digital logic, so some concepts I understand fine, whereas certain basics most certainly have eluded me.
Ok, so back to the question at hand - voltage levels on tubes, and how to understand the spec sheet. I'm fixing up a Conrad Johnson preamp using 6922 triodes, and discovered there were no plate voltage. Traced it back to a couple of faulty transistors (used for power regulation, I assume). Ok, fine.
However, when checking all the pins on the tube sockets, I discovered the heaters were running on everything from 45-60v. This preamp consists of dual monoblocks, so I can use the working channel as a control - and lo and behold, it was approximately in the same range.
If I check the data sheet for the 6922 (http://www.tubebooks.org/tubedata/HB-3/Receiving-Type_Industrial_Tubes/6922.PDF), it said heater voltage should be 6.3v +/- 0.6v. However, it also states that, relative to the cathode, it can be from -60v to 120v.
How should I read this? Does the tube really have such a wide tolerance? If so, why do they state 6.3v?
Apparently, the tubes work fine at ~50v for the heaters, since the working channel has no issues. I've measured relative to ground, but the cathode has about 1.3v relative to ground, so no big difference.
Any input is greatly appreciated!
First and foremost, sorry if this is explained elsewhere. I'm working on fixing my very first tube gear. Analog electronics is pretty new to me. Reading whatever I can find, "Youtube university" etc. My background is in IT and digital logic, so some concepts I understand fine, whereas certain basics most certainly have eluded me.
Ok, so back to the question at hand - voltage levels on tubes, and how to understand the spec sheet. I'm fixing up a Conrad Johnson preamp using 6922 triodes, and discovered there were no plate voltage. Traced it back to a couple of faulty transistors (used for power regulation, I assume). Ok, fine.
However, when checking all the pins on the tube sockets, I discovered the heaters were running on everything from 45-60v. This preamp consists of dual monoblocks, so I can use the working channel as a control - and lo and behold, it was approximately in the same range.
If I check the data sheet for the 6922 (http://www.tubebooks.org/tubedata/HB-3/Receiving-Type_Industrial_Tubes/6922.PDF), it said heater voltage should be 6.3v +/- 0.6v. However, it also states that, relative to the cathode, it can be from -60v to 120v.
How should I read this? Does the tube really have such a wide tolerance? If so, why do they state 6.3v?
Apparently, the tubes work fine at ~50v for the heaters, since the working channel has no issues. I've measured relative to ground, but the cathode has about 1.3v relative to ground, so no big difference.
Any input is greatly appreciated!
You can easily check whether the heater terminals are isolated from the cathode. As far as the little I know, heaters have usually dedicated/isolated terminals. This means, the cathode can be at any voltage relative to the heater provided such voltage does not cause a flow of electrons where it shouldn't. Heater voltages for valves are usually low like 6.3V. When specifications state otherwise, double or triple check. It is far better to be a paranoid rather than destroy expensive hard to find components.
Umm,
First the heaters of the 6922 are on pins 4 and 5 of the socket. Measure the voltage directly on them, not to ground. That is the 6.3 volts you should read. (It might be AC or DC, I do not know the circuit.) Anything else will be a problem, too little the valve will not perform correctly, too much and it will burn out ...
Often the 6.3 volts is referenced to the ground or 0 volt line through a centre tapped transformer or 2 resistors. But sometimes to comply with the insulation requirements between the heater and cathode (-60 -to +120v) because of the circuit design, the heater supply is elevated above chassis or ground by a DC voltage. I suspect that is what you are measuring?
Some info here: The Valve Wizard
First the heaters of the 6922 are on pins 4 and 5 of the socket. Measure the voltage directly on them, not to ground. That is the 6.3 volts you should read. (It might be AC or DC, I do not know the circuit.) Anything else will be a problem, too little the valve will not perform correctly, too much and it will burn out ...
Often the 6.3 volts is referenced to the ground or 0 volt line through a centre tapped transformer or 2 resistors. But sometimes to comply with the insulation requirements between the heater and cathode (-60 -to +120v) because of the circuit design, the heater supply is elevated above chassis or ground by a DC voltage. I suspect that is what you are measuring?
Some info here: The Valve Wizard
Aha! Now that makes a lot more sense, and explains the differences between heater pins. Since they were labeled heater pin 1 and heater pin 2, I thought both was positive voltage for heaters, one for each triode in the tube. Which seemed strange, but what do I know. Of course, since it can be AC, i get it now why they don't label it with polarity.
Thanks!!
Thanks!!
That book ("Designing High-Fidelity Valve Preamps") seems both comprehensive and accessible. Would you recommend it?
It is an excellent book well worth having, but not knowing your current understanding it is difficult to advise.
If you are looking for the basics of valves (tubes) then there are simple books (old but still relevant) like ''Basic Electronics 1955'' volumes 1 - 5, on line here: http://sportsbil.com/other/Basic Electronics, Volumes 1-5, (1955).pdf.
Through to 'Foundations of Wireless' by Scroggie.
As in all things you need to pick out the parts you need.
If you are looking for the basics of valves (tubes) then there are simple books (old but still relevant) like ''Basic Electronics 1955'' volumes 1 - 5, on line here: http://sportsbil.com/other/Basic Electronics, Volumes 1-5, (1955).pdf.
Through to 'Foundations of Wireless' by Scroggie.
As in all things you need to pick out the parts you need.
Got the book, and I think this will be with me for many years to come. So far, he has a nice balance between an academic and a practical approach. I will need to brush up on my math skills though, some of the topics are heavy for a guy like me. As with most hobbyists, I have gaps in my basic understanding (which he does try do address). I still get an immediate value, with more to come as my understanding increases.
"Free for me!" Available gratis on the WWW, NEETS is U.S. Navy training material.
While you will have to dust your differential equations off, a copy of either the 1st or 2nd edition of "Basic Electronics for Scientists" by James Brophy is (IMO) a worthwhile investment. Lots of "goodies" (both tubes and SS) here, including the foundation stones of digital electronics.
While you will have to dust your differential equations off, a copy of either the 1st or 2nd edition of "Basic Electronics for Scientists" by James Brophy is (IMO) a worthwhile investment. Lots of "goodies" (both tubes and SS) here, including the foundation stones of digital electronics.
As always, I'll link to this great resource from 1955...
Basic Electronics, Volumes 1-5 (1955) : Van Valkenburgh Nooger & Neville : Free Download, Borrow, and Streaming : Internet Archive
EDIT: I see Alan linked to an alternative source - My bad.
Basic Electronics, Volumes 1-5 (1955) : Van Valkenburgh Nooger & Neville : Free Download, Borrow, and Streaming : Internet Archive
EDIT: I see Alan linked to an alternative source - My bad.