"PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube

[frequencycentral]

soundclips of this bad boy yet?

Believe it or not, I'm not planning to build this one. Designing the PentaBoost was just a stage on the way to designing the PentaDriver. I built the PentaDriver, which can also function as a clean boost. So I'll leave it to someone else (Adriano ?) to post soundclips.

[Renegadrian]

Why not, give me some days then...

[mth5044]

While a sound clip isn't really necessary, it would sure help for me and other people to get a feeling as to what it sounds like. Is it a clean boost? I heard the pentadriver, and it was sick, but if that was only one extra tube, I'm imagining just half the gain from it.

[Renegadrian]

Yeah, I'd say clean booster with a little breakup if hit it harder...I'll try to post a sound clip anyway, but I'd say it reminds me those sounds - Still loving you intro - Knockin' on Heaven's Door intro - House of the Rising Sun intro (but cleaner than the Animals)

[frequencycentral]

While a sound clip isn't really necessary, it would sure help for me and other people to get a feeling as to what it sounds like. Is it a clean boost? I heard the pentadriver, and it was sick, but if that was only one extra tube, I'm imagining just half the gain from it.

What's happening in the PentaDriver is that the first pentode is boosting the signal relatively cleanly, the boosted signal hitting the second pentode is too much for it's input to handle, so it clips. Not so different from how a FF works really.

[Renegadrian]

Here's my version...



After I successfully breadboarded it, decided to draw a vero layout by myself, now in my gallery,
and decided to build and box it somehow...Found a little wooden box at Leroy Merlin while shopping
for spray cans, so I thought "WHY NOT?!" 
So here it is...It uses a 5678 tube and it's powered by a 9V and a 1.5V AAA for the heaters.

[frequencycentral]

Very nice and unique build Adriano - such a thrill when someone builds my design too!!

[mth5044]

Very cool, as usual.

[sweetwilly]

Was just warming the iron up to get my 1st effort finished when I saw Adriano's.  Mine's not anywhere near as pretty, but hopin it'll sound sweet just the same!

[frequencycentral]

Lookin good...radical in that Boss housing. Might be an idea to use a loop of wire to stop the tube moving about, soldered either side and bracing it. I like how you've mounted that tube on it's side though. Sweet.

[sweetwilly]

cheers rick, got it working pretty much 1st go, but have a slight oscillation problem due to some poor lead dress!  will fix tomorrow and post sound clips.  not a huge boost on it's own - my wife said "all that effort for THAT?" - but when I stuck it in front of an EH English Muff'n with a 12AU7 in the gain stage it just pushes it's tubes beautifully.  can't wait to hear it in front of my amp!

nice work rick!

edit - dig the boss joke rick, outtasight...

[frequencycentral]

Excellent - try a LPB in front of the Pentaboost, drive it hard and listen to it break up really nicely.

[mth5044]

cheers rick, got it working pretty much 1st go, but have a slight oscillation problem due to some poor lead dress!  will fix tomorrow and post sound clips.  not a huge boost on it's own - my wife said "all that effort for THAT?" - but when I stuck it in front of an EH English Muff'n with a 12AU7 in the gain stage it just pushes it's tubes beautifully.  can't wait to hear it in front of my amp!

nice work rick!

edit - dig the boss joke rick, outtasight...

This is all the motivation I need to actually get off my lazy ass and build the dual valvecaster with pentaboost in front of it. Thanks!

Oh and soundclips. 

[sweetwilly]

cheers rick, got it working pretty much 1st go, but have a slight oscillation problem due to some poor lead dress!  will fix tomorrow and post sound clips.  not a huge boost on it's own - my wife said "all that effort for THAT?" - but when I stuck it in front of an EH English Muff'n with a 12AU7 in the gain stage it just pushes it's tubes beautifully.  can't wait to hear it in front of my amp!

nice work rick!

edit - dig the boss joke rick, outtasight...

This is all the motivation I need to actually get off my lazy ass and build the dual valvecaster with pentaboost in front of it. Thanks!

Oh and soundclips. 

i'm planning the exact same thing.  this build was a practice run and a b'day present rolled into one.  really simple design with great results. 

i was planning to use Renegadrian's Twincaster layout - you?

Rick - I ended up with LM317Ms not Ts.  with the 100R resistor I get 1.2v from Pin 2.  how much difference would 0.05v make here?  and my tube does get a nice amber glow going - simple things...

[mth5044]

i'm planning the exact same thing.  this build was a practice run and a b'day present rolled into one.  really simple design with great results. 

i was planning to use Renegadrian's Twincaster layout - you?

Rick - I ended up with LM317Ms not Ts.  with the 100R resistor I get 1.2v from Pin 2.  how much difference would 0.05v make here?  and my tube does get a nice amber glow going - simple things...

I'm not making a 'twincaster' per se, but it will be two cascaded valvecasters with the pentaboost out infront. Although, the second valvecaster will not be avaliable unless the first one is on. It has a clever switching scheme with a clever name, but I will not reveal that until its done  Plus I like having lots of control and I'm pretty sure the twincaster had dual knobs for some of them.

[Renegadrian]

Nice board Willy!!! I like the way you placed things...And oh that ugly enclosure!!! Aahahah 

[sweetwilly]

I'm not making a 'twincaster' per se, but it will be two cascaded valvecasters with the pentaboost out infront. Although, the second valvecaster will not be avaliable unless the first one is on. It has a clever switching scheme with a clever name, but I will not reveal that until its done  Plus I like having lots of control and I'm pretty sure the twincaster had dual knobs for some of them.

I eagerly await the revelation!!!

Nice board Willy!!! I like the way you placed things...And oh that ugly enclosure!!! Aahahah 

Cheers Adriano, had to do something with the dead tremolo I had!  Waste not...

[frequencycentral]

Rick - I ended up with LM317Ms not Ts.  with the 100R resistor I get 1.2v from Pin 2.  how much difference would 0.05v make here?  and my tube does get a nice amber glow going - simple things...

The 5672 data sheet quotes 1.25 volts +/- 20%, so the minimum is 1 volt, the maximum is 1.5 volts. I don't think that 0.05 will make any difference. Adriano used a 1.5 volt battery for the heater in his build - and 9 volts for the plate. I'd be interested to know if there is any sonic difference there.

Damn - your tube glows?? Mine doesn't!! Damn!!

Yesterday I played about with asymettrical diode clipping at the Pentaboost's output, I tried loads of different diodes but only got reasonable results with a couple of germanium (I have no idea what they are). The sound was good, a very soft but pleasing overdrive, but failed to achieve unity with the bypassed signal. Now I'm trying to figure how to get more gain from a single 5672. Any ideas anyone?

[sweetwilly]

Have been pulling hair out all morning trying to find the source of this high pitched squeal I get when I turn mine on.  It fades away within 10 seconds mostly, and oscillates sometimes so thought it might be wires running too close.  After a bit of poking about think it might be the tube itself.  A little tap increases the squeal significantly.  Out with it, and in with a new and we'll see how it goes!

[sweetwilly]

Well, somehow turned a working Pentaboost into a brick and cannot figure out why!  Audio probed and racked mind but think that it's prob something to do with all the 2nd hand bits'n'pieces I used!

Figure I'll scratch this effort and try, try again!