Tube boost + overdrive running off a 9 volt battery

[blown240]

This is my first post here, but I have been lurking for a while.  There is definitely some good info here!

I just finished building a dual valve caster.  I built it per the schematic, and once I got it to stop picking up AM radio, it sounds real nice.

I have noticed that when I have both gains all the way up, there is a TON of sag.  So much so that it cuts out sometimes.  Its a smooth in and out, and ALMOST sounds like a noise gate.  What could be causing this? 

I am using a 12v 1250ma wall wart, and vintage Raytheon tubes.

Here is a pic:



The extra hole is from a previous build and the extra switch does nothing yet.

[iccaros]

it could be a few things
1) your power supply is not really able to handle 1.2 amps as it says
2) you are not hearing sag but cut off
3) something is wired wrong
4) your vintage tubes are dead and need replaced

[Govmnt_Lacky]

Where did you find those RED anodized aluminum knobs??

Me likey 

[blown240]

it could be a few things
1) your power supply is not really able to handle 1.2 amps as it says
2) you are not hearing sag but cut off
3) something is wired wrong
4) your vintage tubes are dead and need replaced

1.  Thats entirely possible. Whats the minimum that a dual valve caster needs?
2.  Thats probably true too, what causes cutoff?
3.  I double checked it all, and i am pretty sure its all correct.
4.  I ran them thru a tube tester and they are good, old but good.  They are well above minimum spec.

I got the red knobs from a dead Carvin bass amp.  They may sell the seperatly.

[iccaros]

it could be a few things
1) your power supply is not really able to handle 1.2 amps as it says
2) you are not hearing sag but cut off
3) something is wired wrong
4) your vintage tubes are dead and need replaced

1.  Thats entirely possible. Whats the minimum that a dual valve caster needs?
2.  Thats probably true too, what causes cutoff?
3.  I double checked it all, and i am pretty sure its all correct.
4.  I ran them thru a tube tester and they are good, old but good.  They are well above minimum spec.

I got the red knobs from a dead Carvin bass amp.  They may sell the seperatly.

1)you should need about 312 ma (heaters are 150 each tube , and about 3 ma per triode max which there are 4 triodes in this design)
2) cut off happens when you exceed the inputs ability to conduct anymore, this leads to distortion at one level, and to complete cutoff at another. Since a guitar puts out more than one frequency at a time, you could cut off a single band of audio while another is not, so you may loose some treble or bass, while the other frequencies are not in cut off. You may have to loose some gain between stages, adding a bigger resistor, or change capacitor values to filter out frequencies that cause issues.   
3)cool, post voltages around the tube please...
4) I am not touching that 

[runmikeyrun]

Quick question- I am having a hum issue on my Valvy.  When people say to wire your heater grounds separate from your signal ground, where am I supposed to ground the heaters?  To the DC jack itself?  I ground my signal and heaters on the vero, on the same strip.  I'm having some hum issues.

[iccaros]

its very unlikely that you will get noise off DC heaters, that is a problem with AC heaters, but everything is possible.
But to your question, I have a capacitor to ground from the input of the power supply and that ground lead I connect to all signal grounds and I connect all power grounds to the jack. I believe that makes zero difference on this design as there is little room from a loop. In any case its a star like network and not everything connecting to the closest part this is also connected to ground.

For versions with a Voltage multiplier, signal ground comes from the last capacitor of the multiplier, while power ground (heaters, voltage multiplier, LED) come from the power jack.

Tubes can be noisy, but also things like voltage regulators can create noise, or in my first pedal a bridge rectifier I put in place to correct polarity before the pedal CKT.

Bad solder joint, signal wires running parallel in close proximity, noisy power supply

[blown240]

3)cool, post voltages around the tube please...

Here are my voltages:


Tube 1

1=.61
2=.53
3=0
4=12
5=.63
6=.62
7=.36
8=0
9=not used

Tube 2

1=.59
2=.41
3=0
4=12
5=.62
6=.6
7=.35
8=0
9=not used

[iccaros]

Here are my voltages:


Tube 1

1=.61
2=.53
3=0
4=12
5=.63
6=.62
7=.36
8=0
9=not used

Tube 2

1=.59
2=.41
3=0
4=12
5=.62
6=.6
7=.35
8=0
9=not used

Those are not right in any way.. pin one a plate at 12v should show 7v about and 6 should be close to the same. The others are ok, can you send a picture? but it looks like plates are not connected through a resistor to V+, if you pull the tubes you should read 12v on pin 6 and 1 to ground. 
Reading pin 4 and 5 should be between them, but to ground is ok for this. I see a .62 rise in your ground to ... ground. In this design that will change how the tubes are biased, as the first stage will not boost much.

pin 2 and 7 should be a DC 0 volts, to ground and a negative voltage to pin 3 and 8 respectively.
This could be a ground issue

[blown240]

The only thing I can see that may be wrong is that I have the 470k resistor from pin 7 going to pin 8 and then to ground.  Basically I am using the pin 8 ground to ground pin 7.  could this be messing me up?  also the meter is set to 20v...

[iccaros]

in order to have dc voltage on pin 2 and 7, you have to have DC leaking from the Grid or from the coupling capacitor. But that is not bothering me, its the .6 volts on the plates.. The tube can not work with that low a voltage. if you draw 1mA across a 47K resistor you would drop about 4.5 volts so you should see about 7 volts on the plates Pin 1 and pin 6.

can you take a picture and post it?

[blown240]

Here are some pics.  I know its ugly, but I am new at this.  (you should have seen the first amp I built  )

Its odd that it sounds so good for the voltages being so far off.  Even my amp snob brother in law thinks it sounds great.  He wants me to build him one.

[iccaros]

hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

Why does it sound so good, I have no ideal, unless you are not making a good ground connection when reading voltages, but consistent on pin 4... 
With so much solder there could be a lot of flux messing up the readings. if you pull the tube and read voltages from the tube side what do you get?

[runmikeyrun]

its very unlikely that you will get noise off DC heaters, that is a problem with AC heaters, but everything is possible.
But to your question, I have a capacitor to ground from the input of the power supply and that ground lead I connect to all signal grounds and I connect all power grounds to the jack. I believe that makes zero difference on this design as there is little room from a loop. In any case its a star like network and not everything connecting to the closest part this is also connected to ground.

For versions with a Voltage multiplier, signal ground comes from the last capacitor of the multiplier, while power ground (heaters, voltage multiplier, LED) come from the power jack.

Tubes can be noisy, but also things like voltage regulators can create noise, or in my first pedal a bridge rectifier I put in place to correct polarity before the pedal CKT.

Bad solder joint, signal wires running parallel in close proximity, noisy power supply

Cool, thanks man, I will try another PS and see what happens.  I already have a 1000uF cap on the power terminals. 

[kurtlives]

its very unlikely that you will get noise off DC heaters, that is a problem with AC heaters, but everything is possible.
But to your question, I have a capacitor to ground from the input of the power supply and that ground lead I connect to all signal grounds and I connect all power grounds to the jack. I believe that makes zero difference on this design as there is little room from a loop. In any case its a star like network and not everything connecting to the closest part this is also connected to ground.

For versions with a Voltage multiplier, signal ground comes from the last capacitor of the multiplier, while power ground (heaters, voltage multiplier, LED) come from the power jack.

Tubes can be noisy, but also things like voltage regulators can create noise, or in my first pedal a bridge rectifier I put in place to correct polarity before the pedal CKT.

Bad solder joint, signal wires running parallel in close proximity, noisy power supply

Cool, thanks man, I will try another PS and see what happens.  I already have a 1000uF cap on the power terminals. 

Do you have regulation?

[buildafriend]

Regarding the 386 amp, that's the route I'm taking with my wired tube socket thing. Trying to fit it in a small plastic case.

For the questions about using a tube other than the 12AU7, as said earlier, they are higher gain and won't work nicely unless you modify the circuit, I don't know how to do that part.

tubesandmore.com has the tube and sockets, it is the standard 9-pin tube socket you would use for guitar amp preamp sections.

Here is a rough *unverified* wiring diagram for anyone who wants to try it.

Wow very cool. I will build this and post back. I have most if not all parts on hand.

[JRM]

Hi guys, I've just discover another starved plate tube driver circuit that realy sounds well.
The main differences are: They have an opamp before the valve to raise the signal level and drive the valve into distortion easier (my guess, waiting for the designer to confirm) and they run the heaters out of an AC 16V tap. Running the heaters with AC prevents hum and could be a nice solution to add to the Valvemaster.
I'd rather build the Valvemaster as it would fit better in my rig: I could run the Laney Cub 12 preamp at low gain for a total clean/big headroom sound and add the Valvemaster as an additional gain stage either before the amp input or in the effect loop (in this case the additional stage it will be placed after the 4 inicial stages, gain and EQ controls and before the last 2 pre-amp stages, tone control and power stage).

[iccaros]

JRM

to fix your statements, a Buffer before the tube has been done,as you know, but some people want an all tube solution. The Dual Caster does this in effect, if you take the first tube and make it a cathode follower, you may see better drive of the second, at least more consistence between tubes.
as for using AC. I would doubt they would run the heaters using 16v ac, as that will kill the tube quickly, they are rated at 6.3 parallel or 12.6 series.

as for "with AC prevents hum and could be a nice solution to add to the Valvemaster"
This is not true, you can not get HUMM from DC as you can not hear DC. It would be common to run heaters in a tube amp with DC, but there is a lot of expense in rectification, and dealing with ripple, its just easier to use 6.3 ac. In a dual triode it is common to use the second half as the first gain stage as its less likely to carry over noise generated from AC heaters.

[JRM]

Sorry iccaros, I might haven't explained myself well enough. They run the heaters in series from an 16V AC supply but they have a resistance to decrease the voltage. The claim that it solves hum problems isn't mine but the builder's as I don't even have the knowledge about valves to know it (although I've understood your explanation about the impossibility of DC being the culprit of hum!).
On the other hand, many thanks for your answer as it helped me to decide that I'll build a Valvemaster as soon as I finish my other projects: it's simpler and will work better in my effects chain as I can use it alone or to boost my Big Muff or Fuzz Face. Another thing that I'll try is to use the Valvemaster after my powerboost (in a clean boost setting) as I think it will raise the signal level enough to overdrive the Valvemaster.

[iccaros]

JRM
Do you have a link to that build
Thanks