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Old 4th May 2009, 07:15 PM   #1
pointy is offline pointy  United Kingdom
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Default anything that can go as a Rp.....

hi
I have been thinking of making a preamp up out of some bits and using ecc83 valves. now the thing that I wish to try to do with this preamp is to have as many different types of anode resistor replacement circuits as I can find on two selector switches one for each tube. and so I was looking for any suggestions.
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Old 6th May 2009, 08:58 AM   #2
Arnulf is offline Arnulf  Europe
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You mean different types of loads, say a resistor, a choke, an interstage transformer (unlike choke this avoids coupling capacitor) and some kind of active load (CCS) ? There are many variations on the latter.

What would be the purpose of such exercise ?
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Old 6th May 2009, 11:35 AM   #3
kevinkr is offline kevinkr  United States
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Because of the high rp of the ECC83/12AX7A the only practical loads are resistors, gyrators or CCS. Chokes and transformers with sufficient inductance for such a high rp (66 - 80K) are impractical.
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Old 6th May 2009, 03:53 PM   #4
pointy is offline pointy  United Kingdom
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i was thinking of something a little more dynamic like mr black used to design and any new stuff. it was just to see which combinations would sound best
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Old 9th May 2009, 01:04 PM   #5
pointy is offline pointy  United Kingdom
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Well I can only guess that all the fantastic dynamic enhancement designs of the late 60s and early 70s must have been lost in the old books and magazines so that they no longer exists . Which means its a very sad day, while searching for stuff I did find one amplifier design of those days which may just jog the memory of someone.

<http://www.geocities.com/tjacodesign.../valveamp.html>

not the best amp in the world but does give the flavour of thems days.
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Old 9th May 2009, 10:05 PM   #6
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Hi,

I can't see any obvious connection between your stated objective:
Quote:
to have as many different types of anode resistor replacement circuits as I can find
and the example in your last post.
Quote:
Well I can only guess that all the fantastic dynamic enhancement designs of the late 60s and early 70s must have been lost in the old books and magazines so that they no longer exists .
This is not true at all. There have been many innovations in tube circuitry in recent years, especially since high voltage BJTs and FETs became available.

What sort of suggestions are you looking for? Is it about the types of load that could be suitable, as addressed by Arnulf and Kevin, or something else?

One obvious thing to mention is that, if you're planning on using selector switches to change from one plate load type to another, you will need to ensure that the switches you use are suitable for the plate voltages you will encounter. The switch body and knob should be grounded and properly insulated, so there is no risk of a shock or sparking
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Old 10th May 2009, 12:32 AM   #7
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by pointy
Well I can only guess that all the fantastic dynamic enhancement designs of the late 60s and early 70s must have been lost in the old books and magazines so that they no longer exists . Which means its a very sad day, while searching for stuff I did find one amplifier design of those days which may just jog the memory of someone.

<http://www.geocities.com/tjacodesign.../valveamp.html>

not the best amp in the world but does give the flavour of thems days.

Sorry to burst your bubble, but that design is much more recent than you seem to realize, the use of mosfet based current sources for biasing output tubes is a fairly recent practice. The rest of the design is in no way innovative as far as I can see.

Not much has been lost, anything that was done in the 1960s and 1970s was at least as well documented as the earlier stuff. With the internet some searching will turn up lots of stuff, but make no mistake the focus of "thems" days was on solid state not tubes.
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Old 10th May 2009, 01:03 PM   #8
pointy is offline pointy  United Kingdom
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ray_moth you are right that there is no common ground between the amp web site address and my request. but in the late 60s and through the 70s I had ''a collection of magazines'' and the ''last of'' amp was something I remember from them. they also contained many dynamic devices, I am also interested in any new designs. I think the reason so many good designs appeared in magazines around then is because it was the only place the designers could make money.
as for switching I was looking at a roller bar (earthed) with micro-switch cams. this way if something does blow it only takes changing one or two switches.
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