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Author Topic: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube  (Read 60453 times)

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frequencycentral

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"PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« on: September 04, 2008, 03:22:05 PM »
I just started playing with these 5672 submini pentodes on the breadboard tonight, basically to check that they work. I bought four - they were manufactured in 1958! They are tiny, and are completely dwarfed by my 6111 submini dual triodes.

They require a 1.25 volt heater voltage (at only 50ma), I used a LM317 to provide that.

When I hooked up the heater voltage I expected to see a glowing tube..............but...........nothing.

So I rigged up a simple test circuit to check out if the tube was actually functioning - it was!

All of a sudden I was overdriving my VJ clone to saturation - basically what I usually use an LPB to do.

Here's the circuit, the clean boost is about 10db - and very tubey:

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mth5044

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #1 on: September 04, 2008, 03:30:33 PM »
Weird, I was just about too search for something along these lines. Can't wait to see other responces. Very nice  :icon_mrgreen:
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Renegadrian

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #2 on: September 04, 2008, 03:51:44 PM »
Rick, I got a space charge 12bl6 tube - got to take out something from that tube...cheap and easy to find on the bay...
still I love to see how pentodes can be used!!!Gotta learn from your circuit!  :icon_wink:
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frequencycentral

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #3 on: September 04, 2008, 03:54:25 PM »
Quote from: Renegadrian on September 04, 2008, 03:51:44 PM
Rick, I got a space charge 12bl6 tube - got to take out something from that tube...cheap and easy to find on the bay...
still I love to see how pentodes can be used!!!Gotta learn from your circuit!  :icon_wink:

Didn't you buy a submini pentode a while back? I remember you mentioned it but I can't remember it's name (began with a 5 though) - maybe if you check the pinout against the 5672 you could use it in this circuit.
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Renegadrian

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #4 on: September 04, 2008, 04:07:22 PM »
Yes Sir, I got 5678 and 6205. :icon_wink:
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frequencycentral

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #5 on: September 04, 2008, 04:59:23 PM »
Quote from: Renegadrian on September 04, 2008, 04:07:22 PM
Yes Sir, I got 5678 and 6205. :icon_wink:

I don't think the 5678 is a pin for pin replacement for the 5672 (the specs are similar though). The heater pins are the opposite way round. In both tubes Grid #3 is connected to the filament pins. You should be able to work something close out though........ :icon_biggrin:
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ambulancevoice

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #6 on: September 04, 2008, 05:11:07 PM »
have you tried other pentodes???
just to see what they sound like
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frequencycentral

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #7 on: September 04, 2008, 05:13:44 PM »
Quote from: ambulancevoice on September 04, 2008, 05:11:07 PM
have you tried other pentodes???
just to see what they sound like

5672 are the only ones I have right now........

..........and for sure I will be cascading them - for a "PentaDrive" !!
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Steben

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #8 on: September 05, 2008, 04:21:41 AM »
AFAIK,

pentodes have similar response curves to MOSfets (harmonic contents), more logarithmic, where triodes are square root.
Yet I think they still clip softer than any semiconductor.
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~arph

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #9 on: September 05, 2008, 04:42:27 AM »
..the odds,

I just received 10 of these tuesday... I expected glowing too, none of that but they do work!
I'll try your heater supply, I was having troubles with it..

Regards,

a

EDIT:  btw, I allready figured out that these tubes do not have enough gain to do a PSO (for an all tube vibracaster)
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frequencycentral

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #10 on: September 05, 2008, 06:42:30 AM »
Quote from: ~arph on September 05, 2008, 04:42:27 AM
..the odds,

I just received 10 of these tuesday... I expected glowing too, none of that but they do work!
I'll try your heater supply, I was having troubles with it..


10 you say - maybe cascade the lot!!
« Last Edit: September 05, 2008, 08:35:39 AM by frequencycentral »
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~arph

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #11 on: September 05, 2008, 06:57:25 AM »
(read again)   :(
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frequencycentral

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #12 on: September 05, 2008, 05:14:54 PM »
I realised that the 100k resistor from pin 3 of the pentode to earth is completely pointless - don't know how that got there! So i have removed it from the schematic.

Rick

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sweetwilly

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #13 on: September 10, 2008, 02:10:15 PM »
1st attempt at a layout using Bancika's layout creator.  Apart from the LM317t needing a heatsink and the extra space that that will require does this look ok?



  I'm working on a layout with both the 5672 and pot on board to cut wiring (thanks Rick!).
« Last Edit: September 10, 2008, 02:32:10 PM by sweetwilly »
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Renegadrian

Breadboard report
« Reply #14 on: September 13, 2008, 06:24:13 AM »
Spent this saturday morning breadboarding, I tried the Pentaboost with the submini pentode I have, the 5678.
It works, and the 5678 is a good sub(mini)substitute.
I am powering the heaters with a AAA battery. It should be easy to wire the neg. to the input jack to cut it out when not connected, as all the other battery  powered pedals...
As for the valvy I am surprised to get a good sound out of a stupidly simple circuit...That's the beauty of DIY...
Rick, as I am looking for more gain, should I try the Pentadriver?
« Last Edit: September 13, 2008, 06:26:02 AM by Renegadrian »
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frequencycentral

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Re: Breadboard report
« Reply #15 on: September 13, 2008, 06:38:35 AM »
Quote from: Renegadrian on September 13, 2008, 06:24:13 AM
Spent this saturday morning breadboarding, I tried the Pentaboost with the submini pentode I have, the 5678.
It works, and the 5678 is a good sub(mini)substitute.
I am powering the heaters with a AAA battery. It should be easy to wire the neg. to the input jack to cut it out when not connected, as all the other battery  powered pedals...
As for the valvy I am surprised to get a good sound out of a stupidly simple circuit...That's the beauty of DIY...
Rick, as I am looking for more gain, should I try the Pentadriver?

Hi Adriano - pleased you have success with that. I thought it might work with a 5678 too.

More gain you say? Metal head!!   :icon_twisted:

I think you would be pleased with a PentaDriver. Maybe I should do some A/B/C soundclips of the Valvecaster, Pepper Shredder and PentaDriver.

You should maybe try your PentaBoost in front of your Valvecaster - or you Valvecaster in front of the Pentaboost. Could be interesting!

Adriano - you're a Veroboard man (I don't use Vero) - could you verify sweeywilly's layout - or suggest your own layout?

EDIT: I think if should be possible to mount both the tube and the pot on the Veroboard.

« Last Edit: September 13, 2008, 07:02:10 AM by frequencycentral »
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Renegadrian

Re: Breadboard report
« Reply #16 on: September 13, 2008, 07:05:02 AM »
Quote from: frequencycentral
More gain you say? Metal head!!   :icon_twisted:
YEAH!!!

Quote
Adriano - you're a Veroboard man (I don't use Vero) - could you verify sweeywilly's layout - or suggest your own layout?

Well, I breadboarded right from the vero layout posted by Willy...It seems correct all the way, so yep, I'd say

VERIFIED


Maybe he wired the VOL backwards? Usually is OUTPUT-->pin 3 and pin 1-->ground. Just flip the two wires.
« Last Edit: September 13, 2008, 07:14:01 AM by Renegadrian »
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sweetwilly

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #17 on: September 13, 2008, 08:59:09 AM »
Yup, more than likely.  Seem to have a habit of reversing pot wiring.  Pin outs - fine, but pots?!??!?!

Thanks for the verification on the layout Adriano!

Rick, I'll incorporate at least the tube on the board in next version!
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frequencycentral

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Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #18 on: September 13, 2008, 12:30:30 PM »
Just a bump to publish the final schematic. I've been deleting and re-uploading the schematic in Photobucket when I have made changes - but it occurs to me that 'cookies' might prevent the viewing unless you click 'refresh'.

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mth5044

Re: "PentaBoost" - 12 volt Pentode Booster using Submini 5672 tube
« Reply #19 on: September 13, 2008, 01:54:26 PM »
soundclips of this bad boy yet?
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