Basic knowledge.

Mike H · Post by **Mike H** » Mon Jan 14, 2013 12:08 am

IslandPink wrote:But if a choke fails to act like a choke, in the woods, and nobody sees it fail to act like a choke, did it ....

I think we should organise a spying expedition

pre65 · Post by **pre65** » Tue Jan 22, 2013 12:15 pm

Question 4)

When using a valve where the cathode is grounded, but using a 1R resistor to measure cathode current, does that resistor need a bypass cap ?

Mike H · Post by **Mike H** » Tue Jan 22, 2013 12:36 pm

It's so small a value, so no.

Dave the bass · Post by **Dave the bass** » Tue Jan 22, 2013 12:38 pm

I personally wouldn't bother. Its a tiny resistance.

DIET, Mike and me are answer-twins.

DTB

pre65 · Post by **pre65** » Tue Jan 22, 2013 12:41 pm

Dave the bass wrote:I personally wouldn't bother. Its a tiny resistance.

DTB

Not if compared to one micro ohm.

pre65 · Post by **pre65** » Tue Jan 22, 2013 3:48 pm

Question 5)

Grid bias on a 26. I've read up on filament bias for the 26, and it seems there are several persons who say grid bias is far superior. So, the brain is looking into this.

Looking at the curves, and bearing in mind common battery voltages, -9v at 6ma and 140v plate would seem OK. So how does the filament voltage come into the equation ? At 1.5v (or 0.75v mid filament) can it be ignored for the purpose of grid voltage calculation ?

If the grid is at -9v, how does that effect a normal line level input signal, which is less than half grid voltage.

Paul Barker · Post by **Paul Barker** » Tue Jan 22, 2013 6:16 pm

If you ground the centre of the filament it makes no difference.

But you can also have 9.75v or 8.25 volt to tune in the current you want.

Excellent plan to use fixed bias.

Mike H · Post by **Mike H** » Tue Jan 22, 2013 6:20 pm

pre65 wrote:So, the brain is looking into this.

Wow cells A and B are working together now?

pre65 · Post by **pre65** » Tue Jan 22, 2013 7:11 pm

Mike H wrote:
pre65 wrote:So, the brain is looking into this.
Wow cells A and B are working together now?

Certainly are, a new era in co-operation.

pre65 · Post by **pre65** » Wed Jan 23, 2013 10:49 am

If using grid bias on a 26 do I need a small cap between the volume pot and the grid leak resistor ?

And also, with the cathode, does one just ground the negative side of the filament ? Will that affect the filament module, as I thought that was supposed to float.

Mike H · Post by **Mike H** » Wed Jan 23, 2013 1:39 pm

#1. personally I wouldn't, just run the vol pot into the grid direct. I presume that can be done with a 26? I mean it's not that different from other valve types?

#2. no problem assuming heater reg is not simultaneously connected to anywhere else in the circuit. Like, if you've also grounded the neg side of the regulator, then the neg side of the filament will also be grounded.

HTH

Mike H · Post by **Mike H** » Wed Jan 23, 2013 1:41 pm

Hang on "ground the negative side of the filament" ? No cathode bias resistor etc.?

pre65 · Post by **pre65** » Wed Jan 23, 2013 1:46 pm

Mike H wrote:Hang on "ground the negative side of the filament" ? No cathode bias resistor etc.?

Glasses Mike.

I'm talking about grid bias with a 9v battery, so no cathode resistor or cap.

Mike H · Post by **Mike H** » Wed Jan 23, 2013 1:50 pm

No, feeble memory.

Ok so what I wrote for #1 is bollox.

Paul Barker · Post by **Paul Barker** » Wed Jan 23, 2013 6:49 pm

pre65 wrote:If using grid bias on a 26 do I need a small cap between the volume pot and the grid leak resistor ?

No. If you do it as per this diagram the plus side of battery is at ground the grid is -9v relative to ground. I never parallel a pot with a grid leak resistor but I know some of you guys do I suppose if you use break before make contacts on an attenuator you would need it but for continuous pots or make before break attenuators no purpose to the resistor, and it reduces the overall reistance

pre65 wrote:And also, with the cathode, does one just ground the negative side of the filament ? Will that affect the filament module, as I thought that was supposed to float.

See my anser to vertually the same question previously. Depends where you want your 0.75v. So ground Plus of module or minus of module accordingly.

Paul Barker wrote:If you ground the centre of the filament it makes no difference.

But you can also have 9.75v or 8.25 volt to tune in the current you want.

Excellent plan to use fixed bias.

audio-talk

Basic knowledge.

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