Tube boost + overdrive running off a 9 volt battery

[capes83]

It's this one..

http://www.electricalmate.co.uk/proddetail.php?prod=Monacor-PM-2%2F1MA-Moving-Coil-Panel-Meter&gclid=CNbt44eM_rwCFSUUwwodqU4ASQ

And I've just seen it's internal resistance in 200. Balls. Is there anyway I can just take that shunt out and replace it with a 1ohm? I couldn't get a reading on my mm either, on the output pot it was showing, but not on the gain. I'll have a look at moving coil meter calibration now, thanks for your help mate.

[duck_arse]

ahh, no need for balls. that 200R is the exact number you will need to plug the equation. you're nearly there.

[capes83]

I found this, which explains the resistances etc...

http://sound.westhost.com/articles/meters.htm

But I still don't understand why I'm not getting a reading? Am I just placing the meter in the wrong place? Surely if I just placed the meter in with no additional resistor, then the needle would fly up? Sorry if I'm missing something stupidly obvious, still trying to wrap my head around all of this!!

[duck_arse]

tell me again, exactly what current, and where, are you wanting to measure/indicate?

[capes83]

I'm want the meter to show the effect of turning the gain pot, on pin 3. Which I think is the bias??

[duck_arse]

in this circuit? I'm not the person to ask about valve currents. however, if you have a dmm, it will measure whatever is there to measure, within reason. you need to insert the meter set to (milli)amps dc in series with either R2 or VR1.

the same applies for the moving coil meter. if you have calculated your shunt resistance (if it is needed), it goes across the meter terminals, and then in series with that which you want to measure.

[vigilante397]

in this circuit? I'm not the person to ask about valve currents. however, if you have a dmm, it will measure whatever is there to measure, within reason. you need to insert the meter set to (milli)amps dc in series with either R2 or VR1.

the same applies for the moving coil meter. if you have calculated your shunt resistance (if it is needed), it goes across the meter terminals, and then in series with that which you want to measure.

Excellentely put. Measuring current is different than measuring voltage or resistance because voltage and resistance can be measured with the leads in parallel to the circuit, whereas current MUST be measured with the leads in series.

[capes83]

in this circuit? I'm not the person to ask about valve currents. however, if you have a dmm, it will measure whatever is there to measure, within reason. you need to insert the meter set to (milli)amps dc in series with either R2 or VR1.

the same applies for the moving coil meter. if you have calculated your shunt resistance (if it is needed), it goes across the meter terminals, and then in series with that which you want to measure.

Yeah, that's the one, except for a few cap changes and 60V and 6V to the heaters on pin 5. I tried with my dmm on R2, it gives a reading over the resistor, but then when I put the meter in, the circuit still works, but no reading. Pretty annoying. The dmm is responding to changes on the gain pot too. Scratching my head doesn't come close at the min! Will try and crack it tonight. Thanks again for your help..

Excellentely put. Measuring current is different than measuring voltage or resistance because voltage and resistance can be measured with the leads in parallel to the circuit, whereas current MUST be measured with the leads in series.

Hi mate, I've been placing it in series, pretty sure I'm doing it right. Any chance you could explain how you'd go about it?

[vigilante397]

Hi mate, I've been placing it in series, pretty sure I'm doing it right. Any chance you could explain how you'd go about it?

Measuring in series can be tricky because it usually means you have to take apart your circuit. The current needs to be flowing through the DMM, not just across it. I drew some diagrams to make it more clear because I'm terrible at explaining

Excuse the crude artwork; I'm on my work computer and the only graphics software I have is Paint

Parallel measuring (i.e. for measuring resistance, voltage, etc.) -  https://www.dropbox.com/s/ibq3degnyn9ttxl/parallel.JPG

Series measuring (i.e. for measuring current) - https://www.dropbox.com/s/crmqtlcjgl9sh0c/series.JPG

Hope this helps

[capes83]

Yeah, that's what I've been doing. Can't seem to get it working. Where abouts on the schematic would you put it? I've tried it before and after R2, and before and after the gain pot. Do you think the current is just too small to read? Weirdly, if I place my digital meter over the resistor at R2, so in parallel, it works. My brain hurts.

[mth5044]

What are you measuring with the DMM?

[capes83]

It's set to read mA.

[duck_arse]

someone on this forum said it was not enuff to know ohms law, but to know when to apply it. or something similar.

and always is the time to apply it, but it never seems to occur to me till the next day. gets yr dmm, measure yr volts dc at the top of R2, the supply voltage. measure the voltage at the other end of same resistor, the anode/plate voltage. subtract the smaller number from the larger, and divide by the resistance. this will give you the current into the valve. if it is more than 1mA, you'll need to re-shunt yr moving coil meter. if it is less than 1mA, you'd expect the needle to move by one 0.1 marking on the meter for each 100uA. less than 100uA, and you'll probably need a meter amp.

with no signal, turn the gain pot while measuring the plate voltage. does it change? by how much? put the highest and lowest # you get through the resistor calc, and that's your current. seeing as the second stage is ac connected, it won't draw any dc current from the first stage, so what goes in at the top will also dribble out the bottom.

you can prove this by measuring the kathode voltage as you vary the gain pot, and work the I=V/R there too. don't divide by nought, tho.

[froglicker]

so i've read about 30 pages so far and i really want to start on this. i play through an active bass though. can i change a couple things in the circuit or do i need to run something in front of it to lower the input signal?

[vigilante397]

so i've read about 30 pages so far and i really want to start on this. i play through an active bass though. can i change a couple things in the circuit or do i need to run something in front of it to lower the input signal?

I've never had any problems with active pickups through this one. You would definitely want to change the input and output capacitors to higher values so they don't filter out the low end of your bass.

[froglicker]

alright thanks. will do. i just figured somethings would need to be changed because of past experiences with boosts and od's.

[dynotouch]

hey all, Im new to this site. Thank you DIYstompboxes for accepting my registration: I ended up at this forum while searching ways to build a guitar boost circuit using one tube. I know there are probably tons already built and/or written to choose from both commercially and diy's but i'm kinda particular about it and like the idea of gaining experience in this sort of build because i have other ideas for projects in my head and down on paper that i would like to accomplish and it's remarkable how close this discussion is to being exactly what i was looking for. I think as a starter i will take on this particular 12au7 boost project first and then maybe see what can be done when using 18v rather than 9v ...maybe the added headroom will be a little closer a range supportable for a 12ax7, at least it will bring the middle of voltage sweep to a solid 9vdc rather than 4.5 which might not be too bad. Is this idea totally lame or ??.. any thoughts ideas? Somewhat familure with dual triode preamps but don't know this circuit at all as i've yet to even see how its possible to heat, bias & output an 12au7 with 9vdc?!?! Thanks for any input

[vigilante397]

hey all, Im new to this site. Thank you DIYstompboxes for accepting my registration: I ended up at this forum while searching ways to build a guitar boost circuit using one tube. I know there are probably tons already built and/or written to choose from both commercially and diy's but i'm kinda particular about it and like the idea of gaining experience in this sort of build because i have other ideas for projects in my head and down on paper that i would like to accomplish and it's remarkable how close this discussion is to being exactly what i was looking for. I think as a starter i will take on this particular 12au7 boost project first and then maybe see what can be done when using 18v rather than 9v ...maybe the added headroom will be a little closer a range supportable for a 12ax7, at least it will bring the middle of voltage sweep to a solid 9vdc rather than 4.5 which might not be too bad. Is this idea totally lame or ??.. any thoughts ideas? Somewhat familure with dual triode preamps but don't know this circuit at all as i've yet to even see how its possible to heat, bias & output an 12au7 with 9vdc?!?! Thanks for any input

First of all, welcome This was my very first DIY build, and i think it's a very good introduction to building.

Second, I never run tube pedals on anything less than 12V. I've also found that the lower the current rating of a power supply the noisier it is. I first tried it with 9v 300mA and it was dreadful, so I used 12v 300mA and it was better, but I ended up settling on a 12v 1000mA power supply, and it runs amazingly. I have heard a lot of people say they prefer it with an 18v supply for the headroom just as you mentioned.

Welcome again and good luck

[Jdansti]

^Just a reminder to keep the heaters at 12V in series or 6V in parallel.

[vigilante397]

^Just a reminder to keep the heaters at 12V in series or 6V in parallel.

+1