Valvecaster troubles

[danamoose]

Sorry, new to the forum and realized I wasnt following the rules so here is the proper help set up.

I recently built the 9v Valvecaster (no tone) based on Renegadrians layout here: http://imageshack.us/f/245/valvecasternotoneog3.jpg/

All component values are a match, no sustitutions. Running a JJ 12AU7/ECC82 tube. It turns on, tube glows, appears to function.....but the output is very low. At 100% volume and 100% gain it is just a touch quieter then the bypass volume. The break up is more of a crunch also....doesnt sound right. I dont hear any hum or noise....just not loud enough and doesnt sound right....nothing like the versions I have heard and seen on youtube. Looking at other posts.....it seems my pin1 voltage is too high but not really sure what could be causing it. Have seen Ricks 12v voltages but not sure how running mine on 9v changes what I should expect.

Here are my voltages: (volume/gain 100%....about the same #s at 0% v/g)

9.42v power supply, 1400mA

1-8.68
2-.159
3-.001
4-.001
5-9.41
6-8.85
7-.173
8-0
9-4.64

Here are some pics of the pedal:

2012-02-06_10-39-08_549 by danamoose, on Flickr

2012-02-06_10-38-46_103 by danamoose, on Flickr

2012-02-01_11-21-40_981 by danamoose, on Flickr
Please help

[rutabaga bob]

 right off the top of my head...you should have no voltage at pin 9.  it's supposed to be unconnected in this circuit.  the heater connection is usually +9 volts to pin 4, and pin 5 is to ground.  regards, larry s.

[rutabaga bob]

d'oh!  you would read 1/2 supply at pin 9 - center tap, but it's not connected. 
nice-looking build!

[crane]

right off the top of my head...you should have no voltage at pin 9.  it's supposed to be unconnected in this circuit.  the heater connection is usually +9 volts to pin 4, and pin 5 is to ground.  regards, larry s.

It IS supposed to be unconnected BUT.... but it's not true that there should be no voltage. As it is the middle point of two heaters it should be about 1/2 of the heater voltage (supply voltage is 9V, ping 9 voltage is 4.64 so it's almost perfect).
You should try to run this on a 12V supply to be able to deliver sufficent heater voltage. I've built this one and it worked fine, but with 9V supply the cathode is just hot enough to function properly.

[danamoose]

Ok seems to be a common consensus that it should be 12v. I was hoping to keep it at 9v but looking like I dont have much choice but to raise it . So I raised the voltage to 12 and gave it another shot. I am now getting the level of boost I expected, but the break up still does not sound how I expected. I expected something alot smoother/warmer, but what I am getting is a scratchier crunchier type of break up....it is not pleasing to the ear at all. Here are my new voltages running it with a 12v P/S.

11.9V and P/S rated at 200mA
1- 9.97
2- .260
3- .001
4- .001
5- 11.73
6- 10.15
7- .310
8- 0
9- 5.77

Ricks Frequency Central Voltages: (On a working valvecaster)
Pin 1: 3.02v
Pin 2: -0.518v
Pin 3: 0.00v
Pin 4: 0.00v
Pin 5: 11.97v
Pin 6: 8.21v
Pin 7: -1.285v
Pin 8: 0.00v
Pin 9: 5.91v

Comparing mine to Ricks, it looks like the largest difference is at Pin 1 but I am not quite sure where to go with that. What could be causeing my pin 1 voltage to be so much higher? Thanks!

[rutabaga bob]

perhaps check plate resistor value?
i have  built a 9 volt valvecaster, but used a 9au7 tube...not quite as nice as the 12 volt version.
@crane:  yes - see 2nd post!  thought of it after i posted.  (this has not been one of my better days

[iccaros]

Ok seems to be a common consensus that it should be 12v. I was hoping to keep it at 9v but looking like I dont have much choice but to raise it . So I raised the voltage to 12 and gave it another shot. I am now getting the level of boost I expected, but the break up still does not sound how I expected. I expected something alot smoother/warmer, but what I am getting is a scratchier crunchier type of break up....it is not pleasing to the ear at all. Here are my new voltages running it with a 12v P/S.

11.9V and P/S rated at 200mA
1- 9.97
2- .260
3- .001
4- .001
5- 11.73
6- 10.15
7- .310
8- 0
9- 5.77

Ricks Frequency Central Voltages: (On a working valvecaster)
Pin 1: 3.02v
Pin 2: -0.518v
Pin 3: 0.00v
Pin 4: 0.00v
Pin 5: 11.97v
Pin 6: 8.21v
Pin 7: -1.285v
Pin 8: 0.00v
Pin 9: 5.91v

Comparing mine to Ricks, it looks like the largest difference is at Pin 1 but I am not quite sure where to go with that. What could be causeing my pin 1 voltage to be so much higher? Thanks!

This could be tube specific, and rolling to a different 12au7 may give you more what you are looking for or for me its a 5751, or 12at7. Warm is a definition in the ear of the beholder, I have found that this design sounds really good and warm if the gain is not above 75% and the amp its going to is a tube amp already close to overdrive, I have only liked the distortion if I used a Valvemaster design, higher voltage (I have 60v now) and two tubes.. 
200ma is close, the tube pulls 150ma for heaters, but you should have headroom unless it really can not put out that current. I go with 500ma to stay close

[PRR]

If the tube hasn't been run for many years: power up and leave it cooking for a day, a week.

The grid voltages suggest gas. Not enough to matter in 300 Volt use, but at 9V/12V it matters.

Over years of storage stray wisps of gas come out of the metal and glass. There's stuff inside the tube to absorb stray gas. It only works when hot. So a long-cold tube may need a hundred hours of hot to clean-up and work its best.

[danamoose]

Its a brand new JJ tube. I bought it tested and matched for this project. Despite that I did run it on for a day from your advice. Havent noticed any change at all.

I realize my limited knowledge but a bad tube would not contribute to my high Pin 1 voltage though right?
That pin 1 voltage leads me to believe something else is going on.
Is that correct?
Thanks!
Dana

[PRR]

> a bad tube would not contribute to my high Pin 1 voltage though right?

Sure would. Pull the tube. There is no path for current in the plate resistor. The plate terminal will pull-up to full supply voltage. Putting a meter on this fairly high 220K resistance will load-down slightly, giving near-supply readings such as you report.

The readings are consistent with a tube drawing little or no current.

Dumb question. Is the tube lighting up? Does it get warm?

[danamoose]

Interesting
Yes it does light up, and does get slightly warm.....when I left it on all day it never got hot but always just warm to the touch.
I have some other 12au7s in a Fender amp I have.....will have to pull one out of there and try it out. Only have 12ax7s laying around not being used but I hear they are simply no good for this project.
Thanks will let you know what happens with a different 12au7 as soon as I can get to it.

[Govmnt_Lacky]

What is that around the tube? Doesn't look like a grommet.

Did you glue a rubber seal around the cut-out for the tube?

[PRR]

> does get slightly warm.....

Depends on your fingers, but I'd call a happy-hot 12A_7 more than "slightly warm".

> some other 12au7s in a Fender amp

12AX7 or 12AU7 will run the same temperature. Is your Valvecaster's tube running as hot as the small tubes in the Fender?

Maybe a hair cooler since there is a LOT of other heat in the Fender.

If it isn't coming up real close to 1,000 degrees on the cathode, the electrons won't flow and the plate voltages won't pull-down good.

[danamoose]

Govmnt_LackyThe ring around the tube is just a tube dampening ring I grabbed when I bought the tube. Just thought it would give the pedal a cleaner look.

PRR-I will compare the heat of the tubes and swap them out tomorrow if I can find some time and let you know my findings thanks for all the advice!
Dana

[danamoose]

Is your Valvecaster's tube running as hot as the small tubes in the Fender?

So I compared temp to the 12au7 in the Fender amp....big difference! The Valvecaster is just warm where as the Fender amp is hot. The Fender amp tube glows alot brighter too.
I swapped the tubes out trying the 12au7 from the amp in the Valvecaster....same issues. Barely warm and much dimmer glow now.

Voltages on the new tube are about the same:
1-9.38
2-.366
3-.001
4-.001
5-11.69
6-10.65
7-.476
8-0
9-5.80

Sound quality is the same - With V/G at 100% I do get a decent boost but the break up sounds very bad....and the low end I notice is terrible! Bypassed I get great low end but engaged it just farts out. The break up sounds more like a crackle than nice overdriven tube. When I roll the gain back to 50% I no longer get any boost....it is about the same or just under the bypass level even though the Volume is still at 100%. Something definitely still going on in there just cant put my finger on what exactly. I still suspect that pin 1 voltage is telling me something I just dont have experience to say what lol. Any help is appreciated!
Thanks!
-Dana

[PRR]

> I compared temp to the 12au7 in the Fender amp....big difference! The Valvecaster is just warm where as the Fender amp is hot. The Fender amp tube glows alot brighter too.

> 5-11.69
> 6-10.65
> 9-5.80

Hummm. They seem to be getting the same heat. The "12"A_7 heater is really two 6V heaters on three pins. Fender typically runs them in parallel at 6V. Yours are series and 12V.

The "right" voltage is 12.6V, but that's not very critical. +/-10% is understood, so 12.6 11.4V is quite legal. Many commercial designers run 11V. People have seen this ValveCaster work on 9V.

I'd accuse you of mis-wiring, except pin 9 is the center of the series heat, shows half-voltage, and there's no way that would happen except proper voltage at both ends.

11.7V would be detectably dimmer but essentially the same surface temperature.

So I don't know.

[mrmoo1337]

I still suspect that pin 1 voltage is telling me something I just dont have experience to say what lol. Any help is appreciated!
Thanks!
-Dana

Have you checked the value of the resistor going to pin 1?  I can't make out a 220k looking at your pictures.  A close up of the board and the back of it too would help. 

[danamoose]

2012-02-18_22-40-20_529 by danamoose, on Flickr

2012-02-18_22-38-29_994 by danamoose, on Flickr

Not my best work for sure but not noticing any errors. Yes I have verified that resister several times and just reverified to be sure.
Anyone have any other ideas?

[MichelP]

This is probably the answer you´re not waiting for...
The JJ ECC82 doesn´t function well in the valvecaster knock off´s I´ve made. Several discussions on a German forum (Tube-Town)  also suggest that the JJECC82 doesn´t work with the topology of the valvecaster.
But don´t throw away that JJ tube !  It functions flawlessly with a higher anode voltage (> 32 V) or if you want to stay with 12 V you can build a nice clean booster with it !
I built a nice clean tube-booster by  putting  a JFET buffer before  the   tube  line stage mentioned in Merlin Blencowes article "Triodes at low voltage" schematic fig. 9. 
With this I tried several brands and types of tubes (EH12AU7, China12AU7, 5963, nos Philips ECC81, JJ ECC81 and JJECC82) : best sound -> JJECC82 !
Web links
http://www.muzique.com/lab/buffers.htm
http://www.freewebs.com/valvewizard2/Triodes_at_low_voltages_Blencowe.pdf

[danamoose]

Ok as odd as this sounds I am willing to buy another tube to rule this out. I am scanning the main valve caster thread but not seeing specific brands of tubes mentioned in functional pedals. Anyone care to share the best BRAND 12au7 for the low voltage set up in the valve caster?