It Lives!

M

Mike B

New member
Got my Stereomour a week ago and finished it up yesterday.  Made some mods, deleted the input selector, changed the coupling caps to foil/paper in oil and changed the parafeed cap to 2.7 uF Mundorf Supreme.

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Did the resistance check and everything was OK, plugged it in and the tubes lit and the fuse held.  Set the hum pots for 1-2 mV (spec) and since the tubes lit and hum was spec, I skipped the voltage check and went straight to the music.

Yeah Baby!  Now I know why people love Class A Triodes with zero feedback - :)  Clear, coherent, transparent sound, beautiful!

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The Bottlehead badge does perfect duty covering up that selector switch hole.
 
Nice going, Mike.  I think those mundorf supremes are highly underrated and like them far better than the silver oils that everybody is so crazy about, but to each his own.

I still would recommend going and doing voltage checks, especially the fiilament voltages as too high or too low will compromise the life of your tubes.

-- Jim


 
With a low value, high power resistor as with some of the other kits, but which ones exactly, I can't recall at the moment.

It will take some trial and error to get down to the right value -- probably.  But I wouldn't worry about it until you take the measurement (with the tubes in place.)

--- Jim
 
Thanks.

It cooked for 8 hours yesterday.  No excessive heat, no bad odors, no smoke, just good sound - :)

I am using this in the bedroom with 95 dB / watt Tangband W8-1772's in DIY 25 liter reflex boxes.

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This sounds really good.

Oh, I also painted the transformer cover black and I masked off the plate chokes and hit them too.  Didn't go crazy with buffing & sanding, just primer and paint.  Looks good and was not hard.

Those coupling caps are Russian surplus PIO's.  Mil spec I think, the housing is a solid steel tube.  I heard they sounded good but I also heard that some were badly made and had leaks.  So I tested  them before I soldered 'em in.  Spec is .1 uF 10%.  One measured at .099 and the other at .103.  I soldered 'em w/o further concern - :)
 
Mike,

I buy a fair amount of USSR Military surplus.  I consider that if you sold bad caps/tubes/switches to the military, you would disappear, never be heard from again.  Very high quality control.
 
Mike B said:
Oh, I also painted the transformer cover black and I masked off the plate chokes and hit them too.  Didn't go crazy with buffing & sanding, just primer and paint.  Looks good and was not hard.

Those coupling caps are Russian surplus PIO's.  Mil spec I think, the housing is a solid steel tube.  I heard they sounded good but I also heard that some were badly made and had leaks.  So I tested  them before I soldered 'em in.  Spec is .1 uF 10%.  One measured at .099 and the other at .103.  I soldered 'em w/o further concern - :)
Click to expand...

If the Russky caps are K40Y9's, they are, IMO, some of the best, (construction quality and sonics),  PIO caps ever made! They will go along way in taming the "plastic nasties" of the Mundorf's!

Cheers,
Geary
 
Cool, just looked and that's what they are.  The guy selling them on ebay sold in lots of 4, so I have 2 left.

The Mundorf I ordered at 2.7, because I read here that 2.5 was optimum for 2A3.

Dunno, I'm new to this valve stuff.

I discovered tubes 6 months ago when I built the K12-G kit from S5.  This two hundred dollar wonder sounded better than all my transistor amps with the Tangbands.  Then I bought a Dared I30 just because it looked good.  Sounded good too it's a 16 watt push-pull with 6L6Gs.  Single ended was supposed to be better, so I built an Elekit TU-879.  It was better.  Just a little, but it sounded a little more pure than the PP amp.  It uses feedback, not a lot 8 dB, but it just kept getting better, so I just had to try the holy grail of tube amps the zero feedback triode.

I wish now that I just started off with a Stereomour - :)
 
You got that right.  I've been practicing since I was 10.

I can tell you about the first kit I built.  It never worked.  I couldn't figure out how to fix it either.  It went into the trashcan w/o ever having worked.  Hey, I was 10.  Didn't know anything about soldering.  I probably cooked half the parts.

Now I work slow.  I'm never in a hurry.  If you are in a hurry you will finish last.  Rework takes 5 times as long as doing it right the first time.  Sorta like driving fast.  The traffic ticket costs a lot, you sit and wait while officer friendly writes it, and then you get to spend a whole saturday in traffic school so your insurance rates don't go up.  That's rework.

Here's how to build with just a pdf. 

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Put project on keyboard shelf - :)
 
Had to show you guys my oops.

Whenever I build anything I always screw it up at least once.  No matter how slow I go, it always happens. 

Sometimes so bad I have to redo the whole thing.  But not this time - :)

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Nipped off the excess resistor lead and had the nippers a little too deep and nipped off the resistor too.

This was easy though, a bare lead thru the terminal and solder to the resistor.

Ooups - :)
 
Mike,

Looks like the red wires at 4:00 and 10:00 don't have any solder.  I would make a good mechanical connection on them first.  But, you are an old hand at this too.  I don't imagine that the picture is of a finished tube socket.
 
Yeah, I took that pic right after I fixed it.

I have a question for you experianced valvers re the parafeed cap.  I have changed this to 2.7 uF as 2.5 was said to be ideal for 2A3 in Stereomour.  Compared to the single ended Elekit, with 6L6G and 8 dB of feedback, everything is better.  Except the bass.  Highs are clear, cymbals have more "shimmer", mids are just awesome, but the bass is less. 

Nothing I couldn't help with a slight adjustment of the level and XO freq on the subwoofer amp, but it is there non the less.

Would more parafeed cap help the bass?  But would that come at expense of the mids / highs?

Give me some insight.  Should I add say half a uF with a clip on to one side and see?
 
I would venture that the bass will fill in after a break in period.  The differences in values of those two caps are inconsequential to the bass end.  Of course it might be the cap you changed to has less in the bottom end.  That is hard to say.
 
Man, I shoulda been reading these Stereomore posts a long time ago. There is a lot of info here. I have been reading the Quickie posts and a few others. I will add this to my lisp,  heh he couldn't resist.
 
Hello Mike,

My first suggestion would be to install all of the factory parts (parallel feed capacitor and 0.1uF interstage coupling capacitor), then let the amp burn in for 100 hours.

At that point, you can have a baseline for the performance of the amplifier.

The bass response differences may have to do with the feedback and damping of the other amplifier, but there isn't a good way to know when the amp isn't stock.

-PB
 
I think I'll leave it alone - :)

I can tell you that I'm not going to remove $80 worth of capacitors so I can solder in 8 bucks.  The sound this amp makes now is the best I have ever heard in my house.

As mentioned, it's no biggie.  I just use a little more "fill", and I really mean a little.  I have a 10 inch Dayton DVC in a 40 liter sealed box.  A little plate amp drives one coil and the other coil I have connected to an LPad wired as a rheostat.  I can vary the loading from open circuit to 3 ohms.  I turn down the load and increase the sub level until I can just hear it.  Then I increase the loading until is becomes seamless.  Works really well.
 
Weak or lifeless bass is usually perceived before a cap gets broken in.

Generally speaking, a smaller parafeed cap will result in a higher bass rolloff frequency but greater power handling (gets luder before clipping) in the bass, with the opposite effect for a larger cap. But it does interact strongly with the particular speaker. If you still have the original 3.3uF cap, you can parallel it with the 2.5 to test the effect - but don't make any judgements until the caps are broken in and the performance is stable!
 
Cool, sounds like a plan.

It doesn't have a hundred hours on it yet, I would say about 50.

I'll let it go to at least a hundred and then solder some clips to the Solen and parallel the stock cap.  That will be ~6 uF, so I'll make sure to turn the volume down before I power up.
 
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