Tube boost + overdrive running off a 9 volt battery

[iccaros]

And what does "re-bias" mean? What should I change here? [\quote]
The original design created distortion buy changing the  bias adjustment on the cathode of the first stage. I think its better to A) control gain with a opamp before the first stage, or B) add a pot between the stages and adjust the "gain" or C) A&B

I am going to a tube amp - but thats why I piut the buffer at the end. Does this not help?

yes, it helps get a consistent signal and loading for the pedal.

Going strait to a tube amp should not need the buffer, and if you raise the gain a lot, you will start over-driving your preamp stage sooner, AKA tubescreamer
if you have a pedal after you may need the buffer as the gain from this pedal may be too much for the following on pedal.
So I am suggesting that if you have  a opamp at the output of the pedal, give your self some way to adjust its gain, so that you may add more or less boost, or control the input from the tube to the opamp to not cause it to overdrive.

If

[Dongle]

Alright!
I got it!
Thanks again! I will than go for A and B - and adjust the buffer also with a trimpoti...

[thereminator]

Interesting article about triodes at low voltages:

http://www.freewebs.com/valvewizard2/Triodes_at_low_voltages_Blencowe.pdf

[ayayay!]

Interesting article about triodes at low voltages:

http://www.freewebs.com/valvewizard2/Triodes_at_low_voltages_Blencowe.pdf

That really is a good read.  Nice. 

[iccaros]

http://www.diystompboxes.com/smfforum/index.php?topic=91745.0
This was my take on low voltage with a pentode out..

[sco01]

Hi!

I have been lurking for a while and this is my first post here. The Valvecaster is my second build in total and my first scratch build and I got it working on the first try. I like the sound in general but I thought it would be fun to add a charge pump to see what would happen. I have built the perfboard design by Rick Holt and it gives just under 80v unloaded: http://www.diystompboxes.com/smfforum/index.php?topic=74729.0
The charge pump works fine but I am not sure about how to hook it up to drive the plates. Here's my idea on how it should be done:




Can you guys let me know if I'm on the right track here? Also, do I need to change the values of R2 (220K) and R3 (100K)? Anything else that needs to be changed?

Regards,
Stefan

[frequencycentral]

^^^

You're hookup is correct. I'd be interested to see what voltages you read at the anodes though, as in my experience grounded cathodes make for low voltage at the anodes no matter how much you pump into them. I refer you to the Valvemaster on the previous page for a circuit more suited to 80v.

[sco01]

Thank you Rick. It worked beautifully. The voltage across the anodes is ~50v with this setup.
At first i noticed some weird noises and I then discovered that the old 12at7 I have been using had gone microphonic. This was with a tube that I had replaced in an amp some time ago. It has worked in my valvecaster until now but I think the voltage increase pushed it over the edge. I replaced it with a new 12au7 and now it works perfectly.

This is fun. I think I will have to put the Valvemaster on my build list.

Regards,
Stefan

[norim_13]

Hi!
I read somewhere that  for this pedal, if we power it with 12v, instead of 9v, it would be better for the valves. Is this true?
Sorry if this is something already discussed, but I couldn't almost anything using the search.

Regards

[iccaros]

Hi!
I read somewhere that  for this pedal, if we power it with 12v, instead of 9v, it would be better for the valves. Is this true?
Sorry if this is something already discussed, but I couldn't almost anything using the search.

Regards

The heaters wired for 12v ran on 9v is fine, there was talk it could hurt the tube.. I see no evidence of this as long as it is wired for 12V heaters (series)

Running at 12V gives more headroom.. 24 is better, 75V would be awesome..

[norim_13]

Thanks
For higher DC voltages, does the schematic change? Or can I just replace the 9v power supply with 12v?

BTW, does this affect the sound in anyway?

Regards

[iccaros]

Thanks
For higher DC voltages, does the schematic change? Or can I just replace the 9v power supply with 12v?

BTW, does this affect the sound in anyway?

Regards

no changes for 12v, as for sound you get a little more volume, not much but for some tubes you also get more levels of dirty...

if you go above 12v you need to think about how to give the tube heaters only 12v.

[Dongle]

you can change the design to get ride of the DC noise on the pot, if you Bias the cathode with between 2 - 10K (inplace of VR1) , and place the pot between the tirode stages  after the cap, so replace R4 with a 500K audio pot

+1 on that, so I introduce you to the Valvemaster:



- interstage gain pot - no more crackle - like a 'real' tube circuit.  
- proper cathode biasing of both triodes - like a 'real' tube circuit.  

Would be worth playing around with the values of R2 and R3, as well as the (nominal) 1K and 10uF cathode biasing. Quite why it's taken 131 pages to get rid of the crackle and get some proper biasing......

Hi!
I have a question for this layout:
The 10uF at the cathode... this is a highpass to ground, right? So for all frequencies above a certain threshold, there is no resistance... And as 10uF is a quite high value, there is basically no resistance for the interesting frequencies?!? Did I get something wrong here?

[iccaros]

10uf is standard in most HIFI designs.. you can change it to what you like.. 
edit..
10uf will pass almost all audio for a guitar or bass. if you want to start bypassing go lower

for a 10u with 1K at 100K load you get about this.. you can do the math to see if the graph is correct.

[bassmannate]

Hey, does anyone know if the sockets over on Small Bear are PCB mount or if they're solder lugs?

[runmikeyrun]

forgive me if this has been asked, but has anyone tried a 12AT7 or 12AY7 in a valvecaster?

[Bill Mountain]

forgive me if this has been asked, but has anyone tried a 12AT7 or 12AY7 in a valvecaster?

I've tried a Ruby AT7 and it worked just fine.  Infact, it was my favorite unilt I got some NOS AU7's.  I used mine for bass and would roll of the lows at about 70Hz to keep from getting hardcore blocking distortion.

[rutabaga bob]

There have been both pro and con opinion regarding higher-gain tubes in the stock valvecaster...some folks like them, others don't.  My 2 cents says, if you're going to the trouble of building a box for a higher-gain tube, use a supply that puts higher voltage on the plates.    Larry

[iccaros]

forgive me if this has been asked, but has anyone tried a 12AT7 or 12AY7 in a valvecaster?

my experience.. Standard valve caster 12v
12ax7 no real gain.. ok.. but no boost..
12au7 good boost, when gain maxed really farts out.
12u7 -- good sounding, mod gain, no difference adding more voltage.
12at7 -- more distortion (good in my eyes)
ECC99 .. my GOD... best sounding for me.. Good distortion, turn down to "warm" overdrive.. lots of boost, would not turn master volume past 1/4
5751 -- Good sounding low boost, nice warm overdrive but bad when gain turned more than 75%

@24v
12ax7 -- useable, more boost.. but still lower boost than the rest --- accadently broke the glass, these JJ's seem touchy
12au7 -- more headroom (more clean before distortion)
12u7 -- no change..
12at7 -- Full on Distortion pedal, with good gain, my NOS at7 had noise, so while I loved the tone, did not like the whine
ECC99... if it was not so big and get so hot (pulls more 400ma for heaters) this would be what I would use.. with the heat of the tube and voltage regulator for heaters this pedal got hot.. just a note
5751 -- good sounding, good boost.. nice warm overdrive but bad when gain turned more than 75%

I also use the Russian (like most new tubes are not made there) needed to adapt for 6.3 on heaters so more heat from the voltage regulator..
6N6P --- same as ECC99 but less costly, more heater current.
6N2P -- close to the 5751.. a little better sounding but I believe my 5751 is going micro-phonic..

as for more voltage..

you can add more voltage and get more clean.. you may have to watch output voltage as the swing gets bigger, into a tube amp is really no big deal but a poorly created SS amp would have issues.
if more clean is not what you want, then an AT7 really created a good distortion in my case, too bad I like it in my Firefly better.. Ricks drawing above is a better way to make this pedal.. Add a voltage mutiplyer and you are in even better shape, for more clean and slamming a tube amp into full distortion.

[runmikeyrun]

I started work on a *yipes* quadcaster tonight.  I used two twincaster vero layouts next to each other.  I am building it for bass, so I am socketing the input and coupling caps along with the anode and cathode resistors.  I'm going to try the stock valvecaster values first, then try the valvemaster values and see which sounds better.  I am making a couple of mods- I am using a 500k gain pot in between the first and second gain stages instead of the standard 50k pots on the cathodes.  I'm also considering making a switchable JFET buffer stage at the input because I have an active bass, but honestly I don't even think I need it.

I ordered (3) JJ 12AU7s and (1) JJ 12AT7.  I will be using this on bass and I really like the way JJs sound in my bass amp.  I might try the 12AT7 in V1 to see what happens, I really want to go for higher gain. 

I am taking photos and will post a build report when finished just in case anyone wants to build one.  I'll also work on sound clips.  Eight gain stages.... even though they're not high gain tubes it should still be fun!