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Old 25th March 2010, 05:04 PM   #1
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Default 6n6p tube as output tube for small guitar amp

I am hoping to attract Waveborne's attn with this -- but of course I am open to all input.

I would like to use the 6n6p in a "flea-power" guitar amp like the AX84 firefly. I have asked folks in that forum -- but no one seems to have the experience with the 6n6p. Among my questions are:

1. Best output impedence for the 6n6p in this application. Given that it is a guitar map - some level of mild saturation is desired.
2. Recommendations for preamp tubes to "overdrive" but not necessarily distort the 6n6p.
3. Boosting 2nd harmonic - what would be the best way to boost the 2nd harmonic of this tube when used at the output? I want to tune this amp for use with single coil pickups which benefit IMHO from a "dark" sounding amps.

Thx much.
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Old 25th March 2010, 06:20 PM   #2
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My thought is to parallel the two sections to get a reasonable output impedance. For hi-fi, the triode seems to like a lower voltage, higher current idle condition (maybe 20mA, 110V) which also necessitates a low grid voltage. For your application, a higher voltage lower current idle condition will satisfy your drive/2nd harmonic requirements better. But this makes the output impedance suffer. Hence the suggestion to parallel sections.
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Old 25th March 2010, 07:42 PM   #3
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You will get more 2nd harmonic distortion in SE mode than PP, but you will also get more susceptance to line frequency noise coupled from the PS.

Operating in the non linear portion of the plate curve will give more even harmonic distortion as well, but it limits output current as it pushes you into a lower bias configuration. As zifgzagflux stated, operate with higher voltage and lower current. The tubes are relativly cheap, so you could parallel two tubes (4 triodes).

I don't think the impedance is that crutical since you can choose the OPT to support it, unless you are thinking OTL.

How much power do you want to achieve?
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Old 25th March 2010, 07:51 PM   #4
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Sure, if to go for 2'nd harmonic SE amp is desired; and paralleled triodes will give you more power.

A typical isolation transformer with 120V secondary will give you 170V rectified, it is what you need for 6N6P output.

I would try a typical 4K SE transformer, individual 390 Ohm in each cathode, or 6V 15 mA bulbs instead of them.
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Old 25th March 2010, 07:54 PM   #5
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I just happen to have a firefly sitting on my desk untested. You may need to tweak the bias, and account for the 6.3v heaters and pinout of the 6n6p's but otherwise I think the circuit would work just about as-is.

If you're just trying to save $ you can use 9AU7's for the output. They can be found for $1 but you'll need a separate heater voltage.
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Old 25th March 2010, 08:07 PM   #6
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Quote:
Originally Posted by Wavebourn View Post
typical 4K SE transformer, individual 390 Ohm in each cathode, or 6V 15 mA bulbs instead of them.
Thank you much - that will save me many hours - much appreciated. What Russian triode(s) would you recommend trying to *over*drive (and *mildly* distort) the 6n6p?

Gimp -- I would say anything over .75W would be *gravy*. Also -- I AM thinking OTL as well - I guess - but isn't one of the main reasons for OTL more linear response with LESS distortion -- wouldn't it defeat my purpose in the end or is there a way to allow the 2nd harmonic through in OTL? That being said -- I am REMAIN interested in 6n6p OTL -- it is still of interest for a mostly clean sort of amp or preamp. thx.

Thanks much to all -- I successfully snared the two gents I wanted to talk to about this .
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Old 25th March 2010, 08:11 PM   #7
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Originally Posted by whitelabrat View Post
If you're just trying to save $ ...
Yes you could say that ... sure ... but more broadly I want to find more uses for the great bounty of Russian triodes in instrument amplification in general -- I have purchased a few and want to learn more about them ...
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Old 25th March 2010, 08:20 PM   #8
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Default Is the 6n6p really a ECC99?

Seems to me there is much confusion about Russian triodes -- take 5 EBAY vendors and they all claim different "equivalents" for the various tubes ...

For example -- the latest seems to call the 6n6p a ECC99. What is the opinion here? I am not sure I really have a reference point to know *what* a ECC99 is? Some places I read say it is an audiophool's 12AU7 but the specs don't seem to support that.

At least in my mind it is time to look at these tubes as themselves. Waveborn has made the statement in other threads that -- they sound great if you only know how to use them? Guess that is what I am here to find out starting with a simple design like the firefly. Although that is only a starting point -- that design was meant for different tubes.

http://www.ax84.com/index.php/oldpro...ect_id=firefly
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Last edited by moonbird; 25th March 2010 at 08:29 PM.
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Old 25th March 2010, 08:28 PM   #9
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Default Sorry --

Quote:
Originally Posted by Wavebourn View Post
I would try a typical 4K SE transformer, individual 390 Ohm in each cathode, or 6V 15 mA bulbs instead of them.
Is the 4K for the SEP (two parallel tridoes) configuration?? thx
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Old 25th March 2010, 08:36 PM   #10
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Yes, for parallel triodes.
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