Valvecaster problem and new member

[Joeandamy]

I do get sound thru the bypass. On the strat if I strum hard as s#'t you can start to hear a faint sound . I will go check and complete the above list , thank you

[GibsonGM]

Yes, be sure the switch is oriented correctly per Jim      If you get any sound when engaged and it's wired right, you are starting to get on the right track.
Keep at it.   Identify the part, and make sure each end is going where it should, then move to the next part.    Make sure the heaters are wired correctly, too (power pin 5, ground pin 4).

Just for reference...it's best to solder parts to a tube socket WITHOUT the tube in, just in case.  And don't use way too much solder, just a tad - no need to overflow and fill in the pin holes, ha ha....

[Joeandamy]

WOW thank you so very much for helping me out everything work great tone , vol, and gain and sounds wonderful. I really appreciate everones help.
This is the new voltage numbers still a negative on pin 7
1)7.14
2)0
3).93
4)0
5)12.19
6)1.53
7)-1.12
8)0
9)5.74
I understand where I went wrong so leason learned I was using the pic on beavisaudio but printed off a parts list from another person , never checked if their "R1" was the same as beavisaudio "R1" .. crap or at least that's where I think I went wrong. I have wired this 6 times solder /de-solder for a week 😂😂😂😂😂

[Joeandamy]

So I have a few follow-up question's lets say a pedal uses 1amp and you had a 5amp p/s could you run all 5 pedals from that in the same box? The reason I ask is I have 2 line 6 long boards that would make a great pedal board nice and neat. Also why are they running as a starve plate is it a safety issue or less noise from the DC or a combo of both. The 12v is nice you don't have to be near as careful 

[GibsonGM]

Just a thought - if you're measuring voltage and don't have the black probe on 'really ground' but which is 'more positive', you might show a negative number at something like a grid, the cathode being elevated by that much.  Not really sure what other case would result in a negative reading (?)  If it's built right, hey...ain't broke, don't fix it

Almost no pedals would come anywhere near 1A!  The VC probably uses about .16A at best, or 160mA.  Less than 1/5 amp.  If your PS can deliver 5A, in theory yes, you could run 5, 1A pedals from it, though.  Nobody would want to come THAT close to the rating, so let's say 4.    
Are you saying the Line 6 boards have their own power supply you want to use inside them?  You could to that...Especially non-tube circuits, transistorized things tend to use way less current - the tube pulls .15A just at the heaters, which you don't have with opamp/transistor/jfet type circuits.

These little tube jobs run on starved plate for safety...easy introduction to tube circuits without high voltage...easy to find power supplies for the hobbyist....and when you run them at 'real' voltages like 300V, you need multiple stages to boost up and get real clipping, whereas you have much less headroom at a lower voltage, so they'll distort a lot easier.   If you push the VC with a booster, you'll note that it breaks up very easily.   If you ran the same thing at 300V, you would have much less distortion!   

[anotherjim]

Isn't the grid leak circuit here supposed to generate a negative grid voltage? I thought it depends on doing so.

[GibsonGM]

Negative voltage "As referenced from...?"     

Isn't the grid just "1.12 volts more negative than the cathode"?     If the neg probe were put on cathode, wouldn't you read exactly that?

If you measured the cathode, wouldn't you find it to be 1.12 volts more POSITIVE than the grid? 

[amptramp]

The negative voltage on the grid is called contact potential and it arises because the cathode emits electrons just from being heated.  Some electrons are intercepted by the grid, which goes negative as a result.

In the standard 5-tube AC-DC radios which were built in the hundreds of millions between 1938 and 1970, a 10 megohm resistor from grid to ground of a 12AV6 triode + double diode gave enough negative bias to allow the input signal to take detector-level outputs and amplify them in the linear range.  Since the detector output was negative, the tube remained in the linear region and never pulled grid current.  If the radio had a phono input, this went through a capacitor to the volume control then a grid capacitor and the bias was still provided by the 10 megohm resistor.  In this case, the input went negative and positive but usually never went positive enough to draw grid current.  In these sets, the cathode was grounded with no cathode resistor.

BTW the triode section of the 12AV6 is identical to the triode section in a 12AX7.  Same ratings and performance.

[GibsonGM]

Thanks for that 'missing piece', Ron, the physical reason we get the grid more negative than the cathode. I've always looked at it or seen it described from the cathode side, 'making the cathode x volts more positive' when setting up bias.   Apparently it is a real 'thing', as referenced from ground.  Funny, I've never even looked! 

[anotherjim]

If the cathode is 0v and the grid is 0v, the triode is just a diode. Allowing the grid to charge negative with respect to the cathode moves it toward cutoff for linear operation. I think this only happens with low voltage "starved plate" conditions.
http://valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf
If you read Merlins paper, you may get a surprise when the penny drops that the grid current produced lowers the grid input resistance - quite a bit. The grid resistor is not defining the input impedance at all.

[GibsonGM]

Sure - grid current limiting, abrupt loss of input impedance.  You can have this condition at any voltage, AFAIK.

The way I was viewing the grid voltage (rather, not viewing it!) comes from P 15 of Merlin's "Designing Valve Preamps For Guitar and Bass", "...we are only trying to make the grid more negative than the cathode, which is exactly the same thing as making the cathode more positive than the grid."   

Anytime I mess w/tubes, I am only thinking about what cathode resistor I choose, and why. It works.   After doing the math and playing w/load lines, I've never actually measured the damn thing! 

Lo and behold, there it is.  Should've been intuitive, but I work this stuff like a shade tree mechanic.

[anotherjim]

Well, I wonder what it does to a guitar output into the Valvecaster if the input impedance goes south of 100k (Merlin cites 20k in one condition). At 100Hz the Xc of the 47nF is around 34k and obviously drops above that. Nevertheless, folks are happy with the sound. I've breadboarded one and like it - one day I'll get a round tuit.

[mozz]

My version, didn't want the pot on the cathode, probably would be scratchy.

[GibsonGM]

It might be a 'stupid question, but I was thinking about 'actually have negative voltage at the grid', and it's not trivial at over -1V...how come tube amps with no input cap don't cause guitar pots to make scratching noises?  I guess I always considered the voltage there to be academic...somehow internal (lol)...but no...

The VC is a fun circuit to be sure, esp. if you are using it as a boost!