Octal Fatness In A Box?!

[Michael Allen]

Does anyone know what the multiplier is on the voltage doubler? I'm sure it's not exactly 2 right? I looked up a voltage doubler in an electronic book and it's a multiplier of 2.8.

So here's my math: 115V x 2.8 = 322. So then it's full wave rectified: 322 x 1.41 = 454V !!! Wow, I only need 250V for the Hotbox i want to throw down. So what should I do to lower the voltage. And for Paul, how are you going to go about getting only 150? Just full wave rectify the raw 115V?

Thanks

[Paul Marossy]

Aharon - thanks.  

Michael - Yeah, basically. With 120VAC to start with, I'm estimating that it would be somewhere in the ballpark of 150V after being full wave rectified and after the filter caps do their thing.

[Aharon]

Does anyone know what the multiplier is on the voltage doubler? I'm sure it's not exactly 2 right? I looked up a voltage doubler in an electronic book and it's a multiplier of 2.8.

So here's my math: 115V x 2.8 = 322. So then it's full wave rectified: 322 x 1.41 = 454V !!! Wow, I only need 250V for the Hotbox i want to throw down. So what should I do to lower the voltage. And for Paul, how are you going to go about getting only 150? Just full wave rectify the raw 115V?

Thanks

Math aside all I can tell you is that I used the circuit  for my HotBox and got 280V or so unloaded.Once the tubes were in it came down to 260V or so which is just peachy for the HB.
Aharon

[mjones99]

Paul, the octal fatness amp started out as just a preamp in a small chassis on the floor running into an old peavey PA head, so I could have something to play guitar through, then, it used an xfrmr available from www.tubesandmore.com that produces 125V and 12.6V with enough current to power 2 preamp tubes heaters n all, and I used a 6SJ7 and 12AX7, series heaters for 12.6, and just parts I had lying around, then I decided to build a champ poweramp and stick the whole thing together in one chassis, and that became what we know as the OF today.  It was like a stompbox but with no bypass, cause, well, why would you want to bypass it?  Sounds great! Lets motor right?  Originally the pentode had grid leak bias like the old 5C1 champ preamp, but that dont sound good with overdrive pedals, so I went to cathode bias on the 6SJ7.  Dougs version has a different tone stack than mine, and I think he uses EL34 power too, I have since gone KT66, the oringial tonestack had strange values, it was just the pots and caps that I had laying around for the tone stack.  I have gone to the modded VOX stack in my builds now just because you can get TMB versitility with just 2 knobs.  ok rambling...better stop now, point I was trying to make is that vendor probably still makes that xfrmr and you could just run the tubes with series heaters for 12.6V with only one 15-16 dollar pwr xfrmr.

[Doug_H]

I'm glad you two got together. I was going to suggest that.

Not that it contributes to this discussion in any way, but for the record I started using a 6L6 in my OF a few weeks ago. I run it completely clean now (MV nearly dimed) and use my pedals for distortion. It gives me more flexibility this way, the clean sound is amazing (I found a nice black plate 6L6 in my stash), and I'm happy with my pedal distortion sounds. The amp is pretty flexible though. I was driving it with a Rangemaster for a while and I've gigged it with no pedals at all and just rode the volume control.

[swt]

excuse my ignorance...but, can i use just 2 110/6volts instead of the 12v to get the same purpose, but use it for the paralell filaments?. Also...i think a voltage doubler cuts the current of the tranny by two, so you need to duplicate it...does this apply to the two transformers?. Thanks a lot!

[Paul Marossy]

Not that it contributes to this discussion in any way, but for the record I started using a 6L6 in my OF a few weeks ago. I run it completely clean now (MV nearly dimed) and use my pedals for distortion. It gives me more flexibility this way, the clean sound is amazing (I found a nice black plate 6L6 in my stash), and I'm happy with my pedal distortion sounds. The amp is pretty flexible though.

Yeah, I also usually run it clean (OK maybe slightly dirty) and use distortion pedals with it. At home, I like to use the amp's distortion sometimes because I love the way that it sounds! 

[mjones99]

yes you can use 2 back to back 110/6v xfrmrs no problems there, you only NEED around 100V to power this preamp, the max on the 6SJ7 is like 150 at most, it sounds good with like 100-140V supply, the 12AX7 loses a bit of headroom but thats cool.  gives a browned up sound, it would probably make a real nice tube overdrive, also just the 6SJ7 with a mosfet source follower, irf810 or so, to lower the high output Z, or even without the follower, sounds NICE as a booster with some natural compression...I think way back in the day some esoteric HiFi stuff used the 6SJ7, I got my stash of RCAs (Alabama Manufacture!) from a guy that does repairs at a high dollar stereophile store, conrad johnson and so forth.  If you can pop for a telefunken, phillips red, NOS 5751, mullard 12AX7, (insert other high dollar 12AX7 type here), that will open it up nicely too.  There are also military 6SJ7 equiv that are slightly better than a 6SJ7, I would say go metal can if possible too. The screen resistor can go anywhere from 1M to 2M2, lower values give less compression and more output, the cap hanging off the screen makes a difference in the tone too, it can be like .02-.22, I just like .047 the best but .1 is also a common value, man this post just keeps getting longer...at any rate happy soldering!

[Paul Marossy]

There are also military 6SJ7 equiv that are slightly better than a 6SJ7, I would say go metal can if possible too.

I have metal can 6SJ7s in mine. I still have to try some of my NOS 6V6s in it, too.