...and now, the "PentaDriver" 12 volt Pentode Overdrive using Submini 5672 tubes

[svstee]

Updated version. I'll build it on Friday, if anyone wants to try it please do so and let me know the results. I made up these layouts for aa couple of reasons, I need more practice at vero layouts, and I think most beginners might find the LM317/heatsink/heater voltage thing a little complicated, and the resistor makes things less intimidating as well as a lower/cheaper part count. I think people are more likly to have 1 watt resistors in stock than lm317's, and you don't have to deal with all the variants like lm317, lm317t, all that.

[frequencycentral]

Updated version. I'll build it on Friday, if anyone wants to try it please do so and let me know the results. I made up these layouts for aa couple of reasons, I need more practice at vero layouts, and I think most beginners might find the LM317/heatsink/heater voltage thing a little complicated, and the resistor makes things less intimidating as well as a lower/cheaper part count. I think people are more likly to have 1 watt resistors in stock than lm317's, and you don't have to deal with all the variants like lm317, lm317t, all that.

I know this is a submini tube project - but I'm having trouble reading your submini layout!

[Renegadrian]

 

[svstee]

I really hate photobucket

I didn't do anything different this time, no idea what was going on.

[frequencycentral]

Hre's a slightly neater version of yours, the pots are a bit further apart.

[svstee]

Thanks a lot, You have been a huge help in my submini questing.
I'll try to build it tonight. I just picked up a shipment of 40 6111 tubes and I have 18 5672's left, so I won't run out of glass bottles any time soon. I'll be drawing up some layouts for you Murder One, and when I get my caps in I'll build it.

[svstee]

Built it, but ran int some problems.
P2 is acting like an inefficient gain control.
P1 is acting like a volume/treble control, but is working backward (getting louder with more bite as pot is turned left), and when turned all the way backward kills all sound.
I used your layout, frequencycentral.

[frequencycentral]

Built it, but ran int some problems.
P2 is acting like an inefficient gain control.
P1 is acting like a volume/treble control, but is working backward (getting louder with more bite as pot is turned left), and when turned all the way backward kills all sound.
I used your layout, frequencycentral.

Ok, can you post some voltages at all pins of each 5672?
Are you getting about 1.25v at pin 3 of each tube?
Did you remember all the (4) jumpers?
And all the cut tracks (5) ?
Are all the resistor/cap values correct?
Both tubes in the right was around?

My layout seems correct. The differences between my build and yours are:
- voltage, mine is 12v
- 1uf cap, mine are polarised
- heater power, I used LM317

[svstee]

My layout seems correct. The differences between my build and yours are:
- voltage, mine is 12v
- 1uf cap, mine are polarised
- heater power, I used LM317

I did all these differences on my pentaboost build and it works great.

Ok, can you post some voltages at all pins of each 5672?
Are you getting about 1.25v at pin 3 of each tube?
Did you remember all the (4) jumpers?
And all the cut tracks (5) ?
Are all the resistor/cap values correct?
Both tubes in the right was around?

I'll get voltages soon, but Pin 3's are about 1.40v each, pretty close.
Got all the jumpers and cuts for sure, I'll go over the resistors with an ohmeter to double check values when I get the voltages. Caps are correct, I used multilayers for the 1 uf and poly for the .047's.
Tubes are in correct, grounding is good.

[frequencycentral]

Hmm. Frustrating. I've checked my layout again and it looks OK. Maybe check for shorts/solder bridges? It also occurs to me that at 9 volts this circuit will have less drive than at 12 volts, as the first stage will not be driving the second stage quite as hard. Whereas with the 'Red Star Drive' there should be more drive at 9 volts because the clipping diodes will have more effect.

Are you sure you have the jumper between g5 and f5?

[svstee]

I'm sure about the jumper. checked for solder bridges as well as shorts. I even ran the pentaboost in front of this and it didn't have much effect, same problems.

[frequencycentral]

I'm sure about the jumper. checked for solder bridges as well as shorts. I even ran the pentaboost in front of this and it didn't have much effect, same problems.

Ok, post your voltages, I'll replicate you circuit on breadboard at 9 volts and see what voltages I come up with.

[frequencycentral]

I'm sure about the jumper. checked for solder bridges as well as shorts. I even ran the pentaboost in front of this and it didn't have much effect, same problems.

Ok, post your voltages, I'll replicate you circuit on breadboard at 9 volts and see what voltages I come up with.

I've replicated your circuit as close as I can on breadboard, running a 9 volts (9.08v actually). I still used an LM317 for the heaters as I dont have the correct value cap. For the 1uf caps I used non-polarised as you did, and you're right there, it doesnt make any difference.

5672 #1

1.   5.81
2.   7.28
3.   1.26
4.   -0.012
5.   0.103


5672 #2

1.   5.78
2.   7.36
3.   1.26
4.   -0.065
5.   0.101

As I suspected there would be, there is much less gain at 9v than at 12v. It did work really nicely once I added the 'turbo mod' though - makes it a very useable effect at 9 volts.

Turbo Mod: While I was breadboarding I decided to add a 10uf cap between the base of the BC557 and ground, this gets rid of some hiss you may experience. It also seems that the 68K resistor should maybe be a 100K trimpot, to take account of which BC557 you use, some need a lower resistor value than 68K, I measured 57K on the trimpot with one BC557 I tried.

[frequencycentral]

Seeing as I breadboarded the PentaDriver again to get voltages at 9 volts for svstee, I thought I'd have a little tweak too.

- I added a 10uf cap between the base of the BC557 and ground (as mentioned above), which gets rid of some hiss and improves sustain.

- I added a Big Muff style tonestack with values tweaked to suit the impedance of this circuit. The tone control goes from nicely muffled through to ear piercingly tinny!

When I originally designed the PentaDriver I was thinking of added a Big Muff tonestack - what stopped me was that this tonestack is pretty lossy, and I didn't want to compromise the effect. So I went with a simple treble cut tone control. Since I added the Turbo Mod to my pedal I rarely have the volume above 2 on the dial, so it probably has too much boost available - hence the addition of the Big Muff tonestack, which tames the volume without sacrificing any gain. I wouldn't recommend the addition of this tonestack to an 'un-Turbo modded Pentadriver' though.



There! It's actually nice to see this design gradually improving and rounding out. It's certainly a lot different now to the pedal it was when I first built it. And it's quite easy to mod the old tonestack into the new one. Let me know if you build it!

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EDIT: Just finished modding my pedal to this new spec - it's a lot more fun now, lots of different tones available than with the original tonestack - I'm really pleased!

[Renegadrian]

Actually, the turbo DOES work on the the valvecaster. I just tried it.

It DOESNT work on the first stage, and i think it has something to do with the way the "gain" is adjusted on a 'caster. Im guessing that if one implimented a regular style gain then it would work.

but i tried it on the second stage and we get a bit more Ooomph.

I made a small layout and followed that indication, I connected it to pin 6 - it is boomy and loud, but not in a good way...too noisy, it isn't a keeper for sure...BTW how is it supposed to work?! thx

[frequencycentral]

Adriano - I don't quite understand your layout - what's the component under the word 'Mod'? It is the collector of the transistor that should be directly connected to pin 6.

It works in place of the plate resistor, it's a constant current source (CCS) which has a high impedance (of about 1 meg), but with a resistance of less then 1K so you do not use up your B+ across the plate resistor. So the voltage at the plate is much higher than if you used the 100K resistor instead.

[Renegadrian]

Rick, the one on the left is a switch.
Basically you have 12V going right to the 100k res that goes at the pin 6 of our valve (so to be stock Valvy) - the other way of the switch is the 12V going thru the tranny - I just followed your schem on the page before.
PS I measured 11.98V on both OUT points of the circuit (right side, first and last tracks)...

[frequencycentral]

Ah, a switch - of course! I should have realised. Maybe instead of the 68K you should try a 100K trimpot. The mod in the V2 thread might work better though: http://www.diystompboxes.com/smfforum/index.php?topic=71864.0

[Renegadrian]

Nope my friend, do you remember I tried to build the V2 some months ago with a 12au7, and a trimmer, but no that didn't work...

[frequencycentral]

Nope my friend, do you remember I tried to build the V2 some months ago with a 12au7, and a trimmer, but no that didn't work...

Yeah - I didn't continue with the V2 because the extra gain wasn't really enough to make it a 'different' circuit to the Valvy - and that was before I started messing with voltage multipliers. I think you will have more luck with the voltage multiplier that you posted last week than with the PNP CCS. Higher voltage is good.