Another Asteroid/K60 Build

[Synchu]

Right - after popping into an Asteroid build thread and doing the research, it seemed like an excellent sounding quick build while rigging up for the SSS chassis sitting patiently aside.
Nothing extraordinary here except that the amp, as I am sure, all know sounds absolutely amazing I couldn't believe on the touch responsiveness and great guitar volume interactiveness that was coming out of the speakers.
Didn't have any troubles with the excellent layout (that I had to flip as usual, because of the chassis source I am using - Europe is limited in this respect and the chassis I am using has the power input hole pre-punched on the wrong side sort of).
I am using Tung Sol RI 12AX7 at V1 and Sovtek's 12AX7 LPS for V2 and V3. JJ EL34s as power tubes. I will run through few other power tube sets, I have around - 6L6, 5881 and 6CA7, once the initial excitement cools down - just can't believe it can sound any better than now
Another find with this build is an excellent European transformers manufacturer - InMadOut - I sent out the specs and couple of weeks later I had the transformers received and they hit the specs at the plates within 1 volt! Solid and nice looking iron.

Couple of quick recordings, just enjoying touch responsiveness and using the guitar volume like never before

http://soundcloud.com/synchu/synchus-ma ... -impromptu
http://soundcloud.com/synchu/synchus-mars-demos-2

Couple of mods I will try most probably will be some sort of switchable Master Volume or Power Scaling and Mark Knopfler mod.
I called it Mars.

Niki

[njwrecks]

sounds fantastic Man- great work - !!

[stephenl]

Sounds and looks great Synchu.

I built a KF50ish amp with PowerScaling and the LP bootstrapped MV - love it.

What is the Mark Knopfler mod?

[Synchu]

Thanks! I like it quite a lot as well.

MK mod is described here:
http://ampgarage.com/forum/viewtopic.php?t=7665
and it basically consists of:
"Replace the two .02uF PI Caps with .047uF OD's
Replace the two 220K PI>power tube grid/bias resistors to 100K
Change the V2 Plate resistor from 100K to 220K

There you go. Bias it a little hot."
Power tubes used are 5881.

Niki

[passfan]

My favorite from the trainwreck stable. THE HAND OF GOD this amp is and I've built 3 or 4. Man I wish I still had one.

[5dollazz]

Hey man, that looks and sounds great. I dig the shiny transformers. Glad it worked out. I freaking love mine too. It's all I play anymore.

[Synchu]

Thanks for the good words!

..and once more - many thanks for the materials, Ryan!

Trafos are great! I am very happy that I managed to find EU manufacturer able to produce transformers to specs (and very reasonably priced), because of this amp.

I am falling more and more in love with it - still haven't experimented with other power tubes - just can't pull out those JJ EL34s - sound so good!

Niki

[rp]

Looks and sounds terrific. I'm pretty happy to hear a positive report about those Inmadouts especially on TAG. Price and access is great for me, I'll have to give them a shot. I wasn't aware they did custom one offs either. What was the turn around time? BTW did you polish the bells or they came nice and shiny?

[Synchu]

Thanks rp,

The quoted time was 12-15 days and they were delivered to me on the 16-th day. Came with polished end bells already.
That made me polish the aluminum chassis and use the "silvered" knobs as well
Overall - it looks quite shiny in person!
Niki

[stephenl]

Has anyone played both the KF50 and KF60? I'm curious how they compare.

It looks like the biggest difference is the 60 is tube rectified and the attenuation between the 2nd and third stages...but I don't have a schemo for the 60 to look at. I built a KF50ish amp and love it.

[M Fowler]

K50 has same PT but OT is lowered to 4k8 and diode rectified as well as some circuit changes.

K60 has OT of 5k8 and tube rectified

[stephenl]

How do they compare tonewise?

[Synchu]

While going through various measurements and some tube rolling, I noticed that albeit the bias voltage is -45VDC, current draw (measured through 1 Ohm cathode resistors) from EL34 power tubes can't get past 26 -26.5 mA. Doesn't seem quite normal to me.
I double checked that the pot is 50k linear (using Alpha there) and the resistor to ground is 47 kOhm. I can play with resistor to ground values and get more range out of it, but it should be there with these values as well, right?
The other thing that comes to mind is slightly lower voltage from the BIAS tap of the PT - it was 65-70V (from memory, as my notes are at home).
Any other thoughts will be much appreciated.
Niki

[Synchu]

Alright - I changed the bias pot to ground resistor (actually wired 82K in parallel to the 47K one for a total of approx 30K before doing the actual change) and now the bias range is fine. I biased EL34s to 30mA with bias voltage measuring at -42VDC.
Will verify with some 5881 that they bias fine as well and put a 33 or 39Kohm.

N

I got JAN Phillips 6L6WGB on order so soon will check how NOS 6L6 glass sounds with it.
I didn't seem to like 5881 (these were actually russian 6p3s-ev). Will do MK mods and check again

Niki

[passfan]

Watch that GB. It has a lower plate dissipation than a GC