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Old 18th June 2003, 08:29 PM   #1
zobsky is offline zobsky  India
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Default preamp-amp tap - would this work

For a typical SE / PP tube integrated (random schematic stolen from the www), ...could the following tap work as either a pre-amp out (fed out to a seperate power amp) or as a main in (to run the amp in question as a power amp). there are no switches to break any flow of current.

thanks,
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Old 18th June 2003, 08:44 PM   #2
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Default YOU WHISH.

Hi,

Unless you design for that kind of service from scratch, no.

Consider the load and I'm confident you'll see why.

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Old 18th June 2003, 08:53 PM   #3
Joel is offline Joel  United States
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If it's as an input, then what's wrong with the front end that's already there?

If it's as an output, then the .022 cap is rather small - and you'll still be feeding signal to the 6V6.
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Old 18th June 2003, 10:24 PM   #4
SHiFTY is offline SHiFTY  New Zealand
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This is similar to what I was trying to do in a guitar amp. Basically you can certainly use the second stage after the coupling cap as an input, but if you want a "line out" from the preamp you really need to use a cathode follower to get a low enough output impedance.

Check this schematic (It is a guitar preamp but the same principles apply.)

http://www.kbapps.com/audio/tubeamps/preamp.html

So you would need another triode section per channel to do this. Not too hard at all.
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Old 19th June 2003, 01:08 PM   #5
zobsky is offline zobsky  India
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i see, ... thanks

rom the looks of things, it just might be easier to use a switch to isolate the desired section of the amp
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Old 19th June 2003, 02:40 PM   #6
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Frank,

Why not?

If he does not hook up a speaker to it, and puts a dummy load on the output, or even pulls the out the 6V6 altogether, he can drive a high impedance load.

If he puts another source, provided it is a lower impedance, he can drive the 6V6.

Both can be done without necessarily having to do much doctoring. I would say just use a 10K resistor in series with the "hot" wire (as opposed to the gound one) as a kind of buffer/isolater. As long as high impedances are maintained.

Why would not this work? This is exactly how the phase inverter in some P-P amps work. The inverter takes the signal from that point (the grid of the output tube).

But... the switch idea is the best. The follower would be ideal, but only really needed with low impedance loads.

My .

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Old 19th June 2003, 09:33 PM   #7
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Hi Gabe,

Under your conditions, yes it can be done.

I must have misread the original post and jumped to the wrong conclusions...still, not something I would do for audio use but for anything else, why not?

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Old 20th June 2003, 04:28 AM   #8
zobsky is offline zobsky  India
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wow, ..i never realized there were so many ways to look at such a simple idea,

the reason i thought of this is i have a pair of vintage monoblock PP tube integrateds (pilot aa-903). i thought of modding, as described in my post, one of the inputs to the pre-amp 12ax7.

this (reversible) change would still maintain the stock appearance of the amp.

cheers
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