New Stereomour II

[Alonzo]

Just finished the Shunt Regulator and DC Filament install.  Initial power test worked, got filaments lit for all 4 tubes and all 8 LED's on.  Saw wisps of white smoke from around 13U so shut it down for tonight and I'll troubleshoot it tomorrow.  Since the fuse didn't blow I'll poke around and check the wiring in that area, solve it before going on to the voltage checks.
Some pics of the build.

[denti alligator]

Nice colors!

[Alonzo]

Thanks,
The base has 3 or 4 more coats of stain before finishing. The pale grey is just the bottom coat. The darker stains first layer is on.  I'm hoping to get the grey to come thru, I'm going for a weather beaten sand scoured beach wood look for the base.  If that doesn't work I'll get a Blumenstein case to match my other amps.

[Sugar Man]

Interested as to your thinking on using 10uF capacitors - isn't that quite a bit outside of PJ's design parameters? I'm using 1.5uF Jupiter Flats in that spot, which is at the low end of his range.  I went a little lower, so I could also try them in the Eros, which shipped with 1.5uF Solens.

[Alonzo]

The circuit is in the middle of a configuration change.  I changed the output transformer to a BH5 Ni which is 3K impedance.  I remember a formula from here of 2*L/R*R where L is the plate choke Henries and R is the impedance of the output, with a range on either side of the micro farad solution of half to double.  A standard Stereomour (stock) would be 2.5uF (supplied with a 3.3) so when I changed the outputs I put the final value I'm going for in place.  My setup will be BCP-15's at 40H and TFA-2004 pinstriped Sr at 3K so 80/9 (throwing out the zero's) for 8.8uF.  So I should be good for a range of 4 to 17 or so.
I think I got this right (if not someone please correct).

[Doc B.]

I hate to keep saying this, but the theory is only good up to a point. The proper way to determine the value is measure the amp's bass into the intended nominal speaker load and look at the bass response. Too small a value and there will be a hump in the mid bass. Too big and you won't get the nice little knee that extends the bass response smoothly, you will see a dip and a hump below it. If you don't do the due diligence and measure the response you can use any value you want, because you won't really have a clue what it is doing anyway.

[Jamier]

I'm asking this question from a position of complete ignorance: I know that the BH-5 was an aftermarket part designed for the Paramour. Is it appropriate for use in the Stereomour II? If so do you also need to change the plate chokes?

Jamie

[Alonzo]

There aren't any approved upgrade outputs for the Stereomour.  I like to experiment and if it sounds good I keep it, whether or not it is scoped and measured.  It's not hard to trace the genealogy from the Paramour, Paramount, Stereomour to find items that may work but are not in the business scheme of Bottlehead.  The stock outputs aren't bad but if you want to try nickel or pinstriped metals you have to go to other companies.

[Paul Birkeland]

The original Paramour monoblocks used off the shelf parts for the plate choke and output transformer.  This helped us keep the price reasonable for these amplifiers, and upgrading the iron brought about a huge jump in performance.

Luckily for us, and ultimately for our customers, those off the shelf parts became no longer available.  This brought about a major improvement in the stock iron, taking the plate choke from 10H in the Paramour to 40H in the Stereomour (same inductance as the MQ choke mentioned in this thread).  The output transformers were also designed from the ground up and absolutely bury the Speco units used previously. 

There are lots and lots of aftermarket transformers that you can try in our amps.  As Alonzo mentioned, if you want to try exotic lams in your transformers, you'll have to contact Magnequest or Sowter.  Other than those two companies, I would expect any other transformer substitution to be a journey in the wrong direction. 

[howardnair]

Alonzo. It a little late for this advice for the weathered look unless you sand the paint off. You take primer and paint it on and wipe it off   In your case you would use grey then you can finish over it it's a simple process akin to Pickeling. The stain over may work I would be tempted to try a solid stain maybe wiping it off or use a stiff brush and give it some grain
Sanding until the wood starts showing through may work also

Howie

[Alonzo]

Thanks Howie,
I have a sander so it won't be that much of a problem removing the paint.  I'll have to look up Pickeling, only done that with jalapenos or cucumbers.

[Paul Joppa]

I'm asking this question from a position of complete ignorance: I know that the BH-5 was an aftermarket part designed for the Paramour. Is it appropriate for use in the Stereomour II? If so do you also need to change the plate chokes?

Jamie

PB's history summary is accurate. I'll just add the Magnequest part of the history.

The BH-5 is a 3K impedance part, actually a variant of the TFA-2004 Junior with some special internal touches. It was built for the Paramount. The Paramour/Stereomour is designed around a 4K impedance, originally because that was what was available as an off the shelf 70v PA system line transformer (the Speco). I never could talk Mike into making a 4K transformer, and I didn't want to change the operating points, so for a short period we had a custom unit made for upgrades. We had some quality control issues with the custom winder, so I accepted the BH-5 as close enough, counting on the high inductance of the BH-6 choke to provide enough bass goodness to make up for the modest impedance mismatch. It is clearly an upgrade from the Speco.

We were also using the Speco in the stereo SEX amp, so when it went out of production (actually the design changed but kept the model number, which kind of blindsided us), I elected to design our own transformer and choke for the SEX and the Stereomour.

[Alonzo]

Latest update;  TFA2004's installed.  Tight fit.

[Paul Joppa]

Latest update;  TFA2004's installed.  Tight fit.

The TFA-2004 transformers' coil axes are aligned with the power transformer, and thus likely to pick up a good deal of hum. If you rotate them 90 degrees, the hum will null out, and it won't be such a tight fit either. Two birds, one stone!

[Alonzo]

Thanks Paul,
I looked at that 3 times trying to figure it out and still chose wrong.