112a driver stage.

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pre65
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#1 112a driver stage.

Post by pre65 »

This was to be part of the mosfet follower driver for the mighty 833a (still is I hope) but I'm making part of it to try as a valve driver for the MoFo amp.

In essence it's a 112a valve with a Rod Coleman filament bias module and a Hammond 126C interstage transformer. I have all the parts needed (if I can find them) so now that the chip amp casing project has finished I can start on this soon.

Some long time ago Mike H gave me four aluminium panels with three edges folded down. The flat portion is 12" X 7" and the folded edge is 1". I've cleaned them up (been laying around in the lean-to for years) and they could form the base and top held together with Delrin rod and M8 threaded rod in each corner. If I need more space I can make an intermediate level from BBP or 3mm alloy sheet. I can fill in the sides with blue acrylic sheet as is my wont.

When the next bout of enthusiasm strikes I'll start laying out the components and see how things lie.
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)
JamesD
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#2 Re: 112a driver stage.

Post by JamesD »

Hi Phil,

QUick reminder on the importance of connecting the 126C the right way around :D

Hammond 126C – how to connect it up.
Secondary black is hot and green cold the reverse of the Hammond documentation -this yields better bandwidth and less distortion see: https://www.bartola.co.uk/valves/tag/hammond-126c/

ciao

James
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Paul Barker
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#3 Re: 112a driver stage.

Post by Paul Barker »

JamesD wrote: Sun Jun 12, 2022 4:17 pm Hi Phil,

QUick reminder on the importance of connecting the 126C the right way around :D

Hammond 126C – how to connect it up.
Secondary black is hot and green cold the reverse of the Hammond documentation -this yields better bandwidth and less distortion see: https://www.bartola.co.uk/valves/tag/hammond-126c/

ciao

James
Actually it’s a pile of crap the wrong way round. So easy to diagnose. Muddy recessed mid’s no top end, too much but completely out of control bass.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#4 Re: 112a driver stage.

Post by Paul Barker »

Edited a few hundred times due to my dyslexia and the apple spell checking bastard who is a total dick these days! Apple has fallen a long way behind and is no longer a simpler faster medium. I’m sick to the eye teeth of Apple today. And I have no functioning windows device. Probably Linux is best option going forward.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#5 Re: 112a driver stage.

Post by Paul Barker »

Phil if you only need low mu you’re plan is fine, if more mu required maybe 5687 or triode d3a for mucho plenty gain and very good sounding. Can’t go pentode if using interstage.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Nick
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#6 Re: 112a driver stage.

Post by Nick »

Now here is a thing that I only realized with Paul amp at Owston. I am not sure that Hammond docs are in conflict. The problem is how we tend to draw diagrams.

The hammond diagram shows I assume that the phase dots would be on Brown and Green

https://www.mouser.co.uk/datasheet/2/17 ... 389799.pdf

And that would be correct for phase if the drawing was done how it used to be done with B+ coming from the bottom, so the anode would be on Brown and B+ on Blue. The output taken from Green, with Black being earth/0v. That puts the transformer in phase.

We have got into the habit now of drawing the transformer above the valve and without thinking connect Brown to B+ and Blue to the anode. So inserting without noticing a phase switch around.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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pre65
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#7 Re: 112a driver stage.

Post by pre65 »

Paul Barker wrote: Sun Jun 12, 2022 4:47 pm Phil if you only need low mu you’re plan is fine, if more mu required maybe 5687 or triode d3a for mucho plenty gain and very good sounding. Can’t go pentode if using interstage.
Thanks Paul. I think it will be OK for the MoFo amp. On the 833a there will be a mosfet follower stage that James D designed for me, so again, I'm sure that will work well.

If not, I'll bear your comments in mind.

Thanks for your interest. :D
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)
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pre65
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#8 Re: 112a driver stage.

Post by pre65 »

JamesD wrote: Sun Jun 12, 2022 4:17 pm Hi Phil,

QUick reminder on the importance of connecting the 126C the right way around :D

Hammond 126C – how to connect it up.
Secondary black is hot and green cold the reverse of the Hammond documentation -this yields better bandwidth and less distortion see: https://www.bartola.co.uk/valves/tag/hammond-126c/

ciao

James
Thanks James, I'll make a note. How is the recovery going ?
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)
JamesD
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#9 Re: 112a driver stage.

Post by JamesD »

Hi Phil,

Recovery is going OK but very slowly... although the Consultant and support staff say its going as well as can be expected and ahead of track.... so I'm just impatient :D

No stamina or ability to think for longer than 15 mins at a time but I feel fine until I do something and them I go to sleep!

ciao

JAMES
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pre65
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#10 Re: 112a driver stage.

Post by pre65 »

I've now got the basics for the anode power supply on the 112a. Enough to start laying out parts on the bases.

Next up is to get a power supply for the Rod Coleman filament bias module. I'll start on that when,

A) I get the table cleared and read through Rod's notes.

B) The next bout of enthusiasm pops up. :)
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)
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