112A bias options.

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pre65
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#1 112A bias options.

Post by pre65 »

I've been thinking again. :shock:

I plan to use a 112A and Hammond 126C interstage to drive the A2 buffer that will drive 833a (GU-48).

Original plan was to use filament bias on the 112A, but I read somewhere (can't find it now :( ) that cathode bias (and filament bias ?) was not compatible with using an interstage transformer. Any ideas on that ?

When I did a 26 preamp years ago I did grid bias with a 9v battery (-9v) and used a Rod Coleman module for the filament.

Any opinions would be welcome. :)
Life is what happens to you while you're busy making other plans. John Lennon

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Nick
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#2 Re: 112A bias options.

Post by Nick »

Any opinions would be welcome.
My opinion is there is a lot of rubbish written on the internet. (he writes on the internet)
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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#3 Re: 112A bias options.

Post by JamesD »

Self referential - I like it - Shall we start a Hofstadter thread on Godel, Escher, Bach: an Eternal Golden Braid?

For external reference, since I suggested it to Philip, have a read of Thomas Mayer on Filament Bias https://vinylsavor.blogspot.com/search?q=filament+bias
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Nick
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#4 Re: 112A bias options.

Post by Nick »

JamesD wrote: Fri Jun 12, 2020 1:31 pm Self referential - I like it - Shall we start a Hofstadter thread on Godel, Escher, Bach: an Eternal Golden Braid?

For external reference, since I suggested it to Philip, have a read of Thomas Mayer on Filament Bias https://vinylsavor.blogspot.com/search?q=filament+bias
As a programmer from the late 70's I prefer recursive solutions where ever possible.
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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Paul Barker
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#5 Re: 112A bias options.

Post by Paul Barker »

112a’s very rare in my lab, I’ve killed too many with direct coupling that went wrong. It was a momentous task to balance up a direct coupled capacitorless full amp from a capacitor less power supply.

But the rewards were worth it , just a shame I doubt I have a single working *1a *2a and I think my only pair of 71a.

But when it all worked out in the end it was worth it.

But it’s history, tomorrow is another day.

I know nothing of the things you asked about so I’ll let you google it instead of being you’re google parrot.
"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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pre65
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#6 Re: 112A bias options.

Post by pre65 »

Paul Barker wrote: Fri Jun 12, 2020 2:25 pm I know nothing of the things you asked about so I’ll let you google it instead of being you’re google parrot.
Thanks Paul.

Using Google (other search engines are available, or are they ?) is all well and good, but as Nick suggests there is an awful lot of crud to sift through.

I asked the question on here because I respect the opinions of those most likely to respond.
Life is what happens to you while you're busy making other plans. John Lennon

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#7 Re: 112A bias options.

Post by Paul Barker »

I expect it’s all there, but harder to find these days.
"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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#8 Re: 112A bias options.

Post by Paul Barker »

I start researching alone then ask other views when I find I’m stuck. Prefer to fix my own lack of knowledge alone!
"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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pre65
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#9 Re: 112A bias options.

Post by pre65 »

Paul Barker wrote: Fri Jun 12, 2020 5:01 pm I start researching alone then ask other views when I find I’m stuck. Prefer to fix my own lack of knowledge alone!
Well yes, I was happy to go with filament bias until I read something that put doubt in my mind with regards using it in conjunction with an interstage.
Life is what happens to you while you're busy making other plans. John Lennon

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#10 Re: 112A bias options.

Post by Paul Barker »

Sounds like an experiment in waiting. Always better to hook it up for yourself and judge for yourself and you’re decisions more informed. If a picture paints a thousand words an ear speaks to you truth, many of the words you’re other point of reference will throw at you are worthless and deceptive.
"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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