Moskido - Hybrid Aikido/MOSFET amplifier

[Stef]

Francios - did you by chance implement the tube gain clone?

I a friend has asked me to build him a guitar amp but wants a valve like sound with some power (and cheap) - If so do you recommend this that and do you have a schematic and any tips?

Stef

[JC951t]

Hi Guys,
Need your advice again. Getting ready to build the
Moskido but am thinking of using noval tubes instead.
Driver side, I"ve decided on using the 6n6p but for the
input I can't find any that has a mu of 70. If I were to use
a 6n2p which has a mu of 100, would the gain be too much ?
I'm leaning more to Russian tubes for cost & ready availabilty.

Thanks in advance

[Francois G]

Please check John Broskie's website for known tube variations and gain. See http://www.tubecad.com/Nine-Pin_Aikido_PCB.pdf I think it would be wise to stick with the tried tube variations.

For the regular 9-pin board he shows:
outputs) V1, V4 =
6AQ8, 6BQ7, 6BS7, 6DJ8, 6CG7, 6GM8, 6H30, 6FQ7, 6N1P,
6N27P, 12AT7, 12AU7, 12BH7, 12DJ8, 12FQ7, 5963, 5965,
E80CC, ECC81, ECC82, ECC83, ECC86, ECC88, ECC99

(inputs) V2, V3 =
6AQ8, 6BQ7, 6BS7, 6DJ8, 6CG7, 6GM8, 6FQ7, 6N1P, 6N27P,
12AT7, 12AV7, 12AU7, 12AX7, 12BZ7, 12DJ8, 12FQ7, 5751,
5963, 5695, 6072, E80CC, ECC81, ECC82, ECC83, ECC86,
ECC88

If you must change the tubes:

I know the MOSKIDO calls for a tube with amplification of 70 in the input, but I believe one could get away with less gain. On the low end of gain I would guess that 6n6p (with amplification of ~22) on both input and output would be enough to make your Moskido sing. I don't know the best operating point though.

A 6N1P (amplification ~30) should work too. and if you hard wire the 6N3p give you amplification of ~35

Good luck.

[Francois G]

Originally posted by Francois G


A 6N1P (amplification ~30) should work too. and if you hard wire the 6N3p give you amplification of ~35

Good luck.

Just to be clear - the 6N3p has a different pinout than the PC boards - that is the reason for my "hard-wire" comment. Additionally, the cathode-to-heater voltage needs to be considered in this tube-on-top-of-tube topology.

Unless you are an experience builder and have time on your hands I 'd say stick with the tried and true PC board and tube sets. John Broskie's boards are things of beauty and very reasonable at $39.

On the other hand, if you go with the 6N3p we would like to be kept informed. The 6N3p has an amplification factor (mu) of about 35 and is reported to be a very good sounding tube. I have not used them but people with trusted ears like them (better than the common 12**7s). Note, I have not checked the cathode-to-heater voltage for 6N3p. (It is a 2C51/5670 equivalent if you have difficulty finding data for 6N3p.)

Success with your Moskido!

[DC2100]

Hi folks, I started reading this thread on friday night, mon morn now and I dont know were the weekend went! I have been bartering on ebay for tubes and have enjoyed the stages this project has gone through, up to the point were it reaches its end for me, I really didnt want to put a relay in the signal path. I am guessing the Aikido can be tagged on to most designs from reading so I was wondering if someone could have a look at this and tell me if there would be much work to do to. I have a pair of JLH monoblocks I built nearly ten years ago and they are stuffed with vishay/caddocks/film caps and the same transisters used in michell alecto, they were so good I stopped looking for anything better. Untill now, I shelved the hoods a couple of years ago and stopped listening to music, I am looking for a new diy project and I figured why leave them on the shelf, I spent a fortune on cerafine reservoir caps, 1k transformers and other parts.
I realise I will need to install the output cap as i will no longer be able to adjust the DC offset and I think I need to implement the Bias parts, can any see any reason why this would not work?

Thanks for starting the thread beau.

Alan

[JC951t]

Hi Francois,
Thanks for the advice. I re read the whole Moskido thread
& I think the 6n3p will not be able to drive the amp from
a CD source as the gain of the 6n3p will be cut into half
using the Akido front end. Will try out the 6n2p & see how
it would turn out. Many thanks again

[Valverine]

Francois G wrote:

On the low end of gain I would guess that 6n6p (with amplification of ~22) on both input and output would be enough to make your Moskido sing.

I'm now calculating a hybrid amp (Aikido driver with a different topology MOSFET output stage) and in fact I'm wondering why a high gain is needed at all. With 6n6p the gain should be around 10 (22/2 minus some losses at the cathode follower). With a 1V amplitude input signal from CD this gives 10V at the MOSFET gate; BUZ900 is rated for the max. +/-14V gate-source voltage, so that is fine.

But looking at BUZ900 datasheet (http://www.magnatec-uk.com/pdf/magnatec/BUZ900.pdf) I'm wondering how it can be biased that high! The Typical Output Characteristics graph shows that for 1A idle current Vg curve is about 2V, so wouldn't input sensitivity be too high (even with the low gain tube) and the volume control would have to be kept all the way down not to clip? Or do you guys have a different set of curves?

Good advice is always appreciated

[beau2317]

Not sure what the gate-to-source voltage has to do with it. It's a source follower so the source voltage follows the gate, so it's never more than a couple or four volts.

The important thing is how much voltage you develop at the output and whether that's enough to drive whatever speakers you use.

Is 10Vpp enough ? Depends on how sensitive your speakers are, and what impedance (4 or 8 ohm).

[Valverine]

Oh, I see - missed the point on the source follower. And still missing another point: you previously calculated the output power as I*I*R, so why the drive voltage is important?

Thanks!

[beau2317]

V = I * R