Question for Dan and Paul

[ebag4]

When you were developing the Stereomour you had to design to a price point.  What were some of the options you decided not to go with due to cost?

I am loving my Stereomour but I am on the lookout for way to make it better.  Any input is appreciated.

Best,
Ed

[Jim R.]

Ed,

One thing you can try is to remove the cathode bypass electrolytics from the power supply board, and their wiring to the pins on the 2a3s, and put a film cap of at least 47 uF 100v directly across the cathode resistors, and upgrade the resistors themselves if you haven't done so already..

You can also try to upgrade the 100 uF 450 v power supply caps to film caps if you can get them to fit, and replace the two diodes on the psu board with CREE SiC types of suitable ratings.

And then we'll all wait for some fancier iron :-).

There's just not that much to do to this one other than what you have already done.  Maybe a better current setting resistor on the CCS boards -- can't remember the value now, but it is generally the lowest value ones on the board -- 2 of them, one for each side.

HTH,

Jim (pretending to be Doc and/or PJ) :-)

[Grainger49]

Just a little more to add to Jim's post.  The cathode resistor might sound better if it were non-inductive.  You can find non-inductive wire wound resistors a number of places.

I modified my Paramours by going to a 76 tube for the driver.  That would require some space on a Stereomour and a little more heater current.  PJ or Doc would know if it is there.

Upgrading the cathode bypass cap is a good suggestion, and oddly the only stock cap I think is left in my amps.  I guess I will need to do that too!

[Paul Joppa]

The parafeed (3.3uF/630v) and coupling (0.1uF/630v) capacitors are located near each other on the terminal strips near the front edge. Calculated optimum values for the parafeed cap are 2.5uF for 2A3, 5uF for 45 (based on which choke tap is used). The range from half to twice the optimum is considered suitable, which is why the stock 3.3uF is used for either tube.

**the following paragraph was edited Sept. 6, 2012, to correct the terminal numbers**

The output tube cathode bypass capacitor (which is on the PSU board) can by bypassed with a film cap across the cathode resistor, T6-T16 and T10-T20. To completely replace the electrolytic, simply remove the wires from T1 and T5 to the PSU board "K" connections.

The best place for film bypass capacitors in the power supply would be from the B+ outputs on the PC board, to the nearby cathode resistors at T1 and T5. An extra hole is provided on the PC board for this.

**in the following paragraph, the switch board is nw in production**

The output transformers can be wired for 2, 4, 8, or 16 ohms. It is possible to wire them to two DPDT switches (each channel) to provide this choice. We are developing a PC board for the Smack that will be available for this application as well. This is a convenience upgrade, with little or no sonic difference, of course  :^)

Eventually the driver C4S board will be converted to the latest version, which will allow bias voltage to be adjusted so that other tubes can be more easily used. The 5670 comes to mind, since we use that in the latest Paramount version.

Shunt regulating the driver high voltage would be a more exotic modification. It would be cool to use a pair of 0A2 glow tubes in series, though I haven't thought about where you would put them, or the extra C4S to feed them power.

The driver heater supply is 12.6v, and can supply 0.5 amps RMS. This could be rectified and possibly regulated - not sure if that would be an audible improvement or not, it probably depends on the particular tube being used.

[ebag4]

Guys, thanks for the replies.  I am going to get the LDR volume control running then revisit this thread and start making a few of these mods. 

Any thoughts on which mods would gain the biggest improvments are welcome but I would imagine the answer is subjective as is much in audio, still recommendations are appreciated.

Best,
Ed

[howardnair]

jim and paul-why can you go with a lower film cap value on the cathode bypass cap and what would be the optimum value[47uf??-i am building a second stereomour for my daughter-if i were to put in a film [a  m- tube cap]  i would have to  use a clamp on chassis-it seems i would want to connect it  to  where the  neg of the electrolytic on pc board and then directly to 16u and 20u--and just how beneficail woul this be---howie

[Paul Joppa]

There is no optimum capacitance. Bigger is better, limited only by practical considerations such as the start-up voltage sequencing, physical size of the cap, or high-frequency cap problems (generally worse the larger the cap). There is a minimum size, set mostly by the low frequency limit and the margin you choose. The analysis for a minimum size is pretty complicated because it involves the output circuit (plate choke, parafeed cap, OPT, and power supply) as well as the load (speaker impedance function). In practice, 47uF is good. I've seen lower values down to 20uF but I would not try it myself unless I could audition alternatives in the target system.

We use the larger value of 220uF or 270uF because we use hundreds of those caps - they are in most of our products, one place or another - and by buying in quantity they are cheap.

The late John "Buddha" Camille at onetime advocated much larger caps in this position, around 5000uF if I recall correctly. I've never listened to such an amp myself though.

[Thoburn]

And then we'll all wait for some fancier iron :-).

I would be very interested in fancier iron!    I wonder what all nickle would cost.

[ajp]

Does anyone have a suggestion for a speaker kit that would work well with this amp? One of similar quality.

[Jim R.]

How big is your room and what and how do you listen?  That info will help for making a better recommendation.

-- Jim

[ajp]

Its about 10x12. Its an home office. I would have them on the desk that runs across the wall which I sit facing.

[Jim R.]

Well, then eve some smallish monitors should work fine -- I'm guessing.  This is kind of offtopic for this thread, but take a look in the speakers forum and read the post on Blumenstein Ultra-Fi -- again, I'm just guessing, but the little Orcas, with or without a small sub might do the trick.  I plan to get a pair myfelf to use with my s.e.x. amp on my office desk.

HTH,

Jim

[Grainger49]

How about the Blumenstein speakers Doc has really liked.  I see a small pair in that thread:

http://www.bottlehead.com/smf/index.php/topic,1943.0.html

BTW, we also need to know your budget.