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In Reply to: RE: Stereomour vs other 2a3/45 designs? posted by Frank Mena on June 11, 2020 at 14:27:58
I'd ask how it compared to the original Paramour with similar upgrades (Constant Current Source, etc.).
Which reqresented good value for $$$ back in the day.
Preferred the sound of the Paramount and would wonder how much better (if at all) the new MonAmour is when compared to the original Paramount
Follow Ups:
MonAmour has DC filaments, better iron, and a more linear driver tube, compared to the original Paramount. It is not direct coupled, which the 2A3 version of Paramount was.I am limited in what I should say on this forum; best to post on the Bottlehead Forum if you want details.
Edits: 06/13/20
Sorry, thought both the Paramount and the MonAmour used the 5670 series of tube as a driver (good!). Maybe only later Paramounts? Maybe the tube is the same but the circuit is different?
Also, I am very sure that answering a couple technical questions about products one designs is allowed my the management as is well within the prescribed rules of behavior by a manufacturer.
Yes, answering questions is OK - and I am happy to do it.
You used the term "original Paramount" - that used a 12AT7. There were some issues in certain specific cases which led to a revision incorporating a slow-start driver power supply and a few other tweaks. We switched to the 5670 at that time. There was an upgrade kit for earlier amps.
Incidentally, we did do a few before-and-after distortion measurements. I was pleased to find that both drivers produced essentially the same distortion harmonic spectrum at the output, suggesting to me that the distortion was dominated by the output tube - the current source plate load made the 12AT7 more linear than a [Sovtek] 2A3.
Like Ivan303, I also think there's something special going on with the 5670. I am probably one of the few outside of Bottlehead who has heard the Stereomour with the premium iron that comes with BH's Kaiju 300B and Monomour 2A3 amps. I installed my Kajiu iron in a Stereomour. It appreciably improved the sound (to my ears), but the Stereomour still fell considerably short of the Kaiju. Other than the driver tubes (12AT7 in the Stereomour, 5670 in the Kaiju), the amps were essentially identical (besides the output tubes -- but I used very nice EML tubes in both). In fact, the Stereomour with Kaiju iron arguably had an advantage: installed in the Stereomour, the Kaiju plate choke could be used full winding (I think 60H?), whereas in the Kaiju only a partial winding is used (40H?).
Which leads me to think that it's the 5670 that makes (much of) the difference. The only other potential explanation I can think of is the spacious layout of the Kaiju - perhaps greater distances between iron and other components is a contributing factor.
I suspect that there's something not captured by distortion measurements going on here. The Kaiju just sounded "bigger and better".
I would imagine that the Monomours, which take advantage of the full plate choke winding and use 5670 drivers, sound very good indeed.
cheers, Derek
Derek
IIRC, I have a number of 5670 types somewhere in storage. Maybe even some WEs.
Also recall the weak link in the Paramour was the 'stock' choke? At the time the Paramour was a 'starter' kit ($500?) and a number of friends built them, later upgrading the 'iron' and even going so far as to change the 12AT7 driver tube.
My Edgar Hours would be perfectly happy with 3 measly watts, and yes, EML tubes are 'nice'!
Yes, the weak links in the original Paramour from 20 years ago were the plate chokes - and the output transformers. (That's a big part of what made it inexpensive, of course ...)
It's a long story, but the original Paramour had a 10H choke at 4K load, for 2.5H per kOhm (that's what counts). The original output transformers had limited bass power bandwidth, something like 3.5 watts above 50Hz, 1.75 watts at 35Hz. Current Stereomour is 20 henries, power band 3.5 watts at 22Hz.
Some customers (e.g. Deke609) have indeed experimented successfully with various mods to the iron and driver.
and that with a WE tube of some sort.Sounded very good, IIRC it was a 2A3 version of the amp driving Cain & Cain Abbys. Might have been a 300B version but do remember the WE tube,
Long time ago.
Edits: 06/15/20
That's the 396A.
Only a bag full of 'tested' WE 417A's and a dozen or so Raytheon and Amperex 5842's. :-(
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