Tube question

[simonsez]

I'm sorry for asking a lot of question, many thanks for your kindness...

1. What is five star tube meaning?
2. What is different between GL and non-GL tube? What is GL mean?
3. What about Japanese NOS Tube like Toshiba, National? Any good? comparing to USA NOS tube?

 

[simonsez]

Anyone?? :

 

[rodabod]

1. 5-star was GE's premium selection mark from what I remember.

2. This question is out of context. What valve? 6L6? 5881?

3. I've never used them.

 

[simonsez]

Thanks Rodabod, I have two data sheet for 5670, and 5670GL, the data is slightly different. So I wonder what "GL" mean?

 

[PRR]

> I wonder what "GL" mean?

5-star and GL mean less than the "EX" badge on my Honda. 5-star and GL were G.E. trade-marks for a higher priced tube which had stricter inspection limits. It may be a better tube, or it may be a regular 5670 originally sold at a higher price.

In microwave systems with hundreds of tubes, a better-inspected tube might be worth the money in reduced system maintenance costs. In simple audio systems, you buy and try several, no big deal like finding one weak tube in a large rack.

 

[simonsez]

Thanks PRR, so it's not really a big deal in audio system. I just found an old local tube store, they have a lot US NOS and Japanese NOS tube, Thanks guys..

 

[simonsez]

Again... another newbie question, This is from tube datasheet,

1. What is that mean?
2. How can i measure that?
3. "Elevated heater supply", when i should do that?

 

[rodabod]

1. These look like maximum ratings.They are what they say they are.
2. With a volt meter so that you are measuring between the cathode and heater. Or just ball-park it by looking at the circuit.
3. If you approaching max ratings (say you had a cathode follower and the cathode was sitting at a high voltage) you could lift the heater voltage up (eg. 50V, 56.3V) to lower the potential differnce. Alternatively, you may also lift the heater voltage to reduce noise in some instances.

 

[simonsez]

Many thanks Rodabod, I built this simple preamp, i measure voltage between cathode and heater, it's 122 VDC, in the data sheet max cathode to heater voltage is 100v.  I use 12 VDC regulated for heater/filament supply (7812- heater in series).  what should i do? lowering B+? do i need to elevating the heater supply?

 

[rodabod]

Either find a valve that can handle that sort of heater-to-cathode voltage, or change the heater supply so that it is referenced to say 100V instead of ground. Looking at a schematic would make this easier.

Try and find an existing PSU schematic to see how this is done; it'll depend a little on if you are wanting to use a regulated supply or not.

 

[simonsez]

Thanks, this is the PSU schematic that I'd use. I reduce the HT voltage to 180V. But still got about 113V heater to cathode voltage. I don't want to change the valve. How can I modified this PSU?

 

[simonsez]

I think the problem solved. I increase the plate resistor to 47k, now i got 94V heater to cathode voltage. I think it save now. Isn't it? Thanks rodabod.

 

[rodabod]

Simon, was that the cathode resistor which you changed on the second stage? The second stage does not have an anode resistor.

Changing these values affects the gain, distortion and the bias level (relatively). What is this circuit for?

 

[simonsez]

Not the cathode resistor, but the anode resistor of the first triode (v1). I don't know why that can lowering the heater to cathode voltage. I use this circuit for make up gain in my 16ch resistive summing mixer (with 100k resistor}. i add global negative feedback to reduce gain . It works good now, distortion is very low. 40hz square wave looks pretty good. Unless you see something wrong here, please tell me. Many thanks...

 

[rodabod]

Ah, ok I see what you mean now. Well, assuming that the amplifier still works well (not too much distortion, suitable gain range, and good level handling) then I'd say all is good. It might suggest adjusting the first cathode resistor to compensate for the change in the anode resistor, but if it works well, it works well.

Just remembered that the 5670 is an equivalent of the 6N3P... I'm going to be doing a small project with a couple of them soon.

 

[simonsez]

Yes, i like this little cute tube, it's equivalent of WE396A/2C51 too. It's good and cheap. Well..thank you very much for your help rodadob!

 

[skipwave]

Ummmm, positive feedback from the output cathode to the input grid?

EDIT: Or I'm just sleep deprived.  :  Which is proof that on a day to day basis being in school is actual making me dumber, because I am not only too tired to recall any of my newly acquired knowledge, but I actually lose access to facts long since known to me. 

 

[simonsez]

Positive feedback? Ampex MX-35 use that kind of feedback and in the manual it's said negative feedback. Do you see something wrong here?

 

[MagnetoSound]

Negative feedback, surely? The signal is only inverted once, in the first triode.

 

[simonsez]

Thanks God it's negative...