piggy back pre-amps?

[Gremlin]

I'm multi tasking here :loco while trying to fix one amp I am building another. I mean if I built my guitar why not build my own amp.

DISCLAIMER:KEEP IN MIND I'M A NOOB TO GUITAR AMP CIRCUTS.

I can understand and follow schematics, know transistor values, know what most of the parts are and the basics of what they do and my soldering skills are decent. I am in the process of building a LM3886 mono amp from Chipamp.com

I have ordered these two kits and was wondering if anyone has any experience with either of these pre-amps?

http://secure.oatleyelectronics.com/files/K261notes.pdf
http://secure.oatleyelectronics.com/files/K270notes.pdf

Anyway here is the thought process of what I'm thinking of doing.
Guitar > k261 preamp > gain > k270 preamp > volume > LM3886 amp.
My theory is to use the k261 like a gain channel. I have a transformer from a powered speaker (9 volt 1 amp) that I can power both preamps with by changing a couple resistors on the k261. Is this a do-able setup? Or am I setting myself up for failure?

[galaxiex]

Oh Oh... I recently bought those exact kits from Oatley and both kits have microphonic tubes.

They have a disclaimer on their site that mentions this (the tubes being microphonic) and recommend putting rubber grommets over the tubes to stop the "ringing" sound.

I did this to no avail... even encased the whole tube in heat shrink and still have microphonic ringing.
The boards are basically unusable.

The fault is with the tubes themselves. I don't know if these are factory "seconds" or what, or just inherent in those particular tubes.
Maybe I just got a couple of bad one's?

I don't think so... so beware... if you decide to order them anyway... I hope you have better luck than me.

[Gremlin]

Thanks for the reply galaxiex. I am kind of stuck with them as I already ordered them. Something I gleened from another site on these:

"Hi, i have some experience with the Jan6418 tubes - i've designed a few circuits around them now....

Firstly the Oatley kits set the impedance way to low at around 200k - i have tried 2 kits prior to designing my own...

Setting impedance at 1Meg solves the issue of microphony - i currently have my new preamp exposed with tubes just in grommets with none of the high pitched ringing associated with the oatley kits.... with my speakers up quite loud

Also for the tubes to work as per the datasheet impedance needs to be at 1Meg as eg... optimal plate voltage is at around 18-22v (for maximum gain - with 1Meg resistors)... setting impedance at around 200k or lower lowers the maximum gain voltage to around 14 or less - this also produces the unpleasant ringing even at normal listening levels...

I made the mistake of assuming the Oately designs were right and initially desiged a preamp around their circuit - it rang even in a solid metal enclosure..."

So now the question is how to set the impedance to1Meg?

[galaxiex]

Well! Thanks for that!  :dbtu:
All that is good to know, and hopefully Roly will see this and chime in. I'm sure he can help.