SR45 amplifier

[Jim R.]

Pj,

Another quick regulator technical question:  Since the Ddowdy is more than 3 times the inductance of the  bpc-15 that's in the amps now, will that appreciably lessen the load on the regulator?

And count me in as wanting to hear any impressions on the feastrex speakers under development by Clark and Molly.  If I can afford it, this would be the only speaker I'd really consider upgrading to at some point in the future.

-- Jim

[Paul Joppa]

Yes, a larger choke will reduce the fluctuation in the regulator current at any given frequency, or perhaps you can say it will have the same fluctuation at a lower frequency.

As to the Feastrex speakers, it's way too early to say anything beyond "they seem promising." We heard them in some cabinet that was on hand, not at all intended for these drivers, and they had (I think) less than 10 hours on them.

[Jim R.]

Paul,

Thanks for confirming the larger choke concept.

As for the speakers, sorry, I thought these were the new cabinets and Clark's well-seasoned drivers.  Yes, can't tell much given what the configuration was.  Guess we'll just have to wait for Clark to get some prototype cabs done.


-- Jim

[xcortes]

Jim and Aaron:

http://www.ebay.com/itm/Pair-Magnequest-TFA-2004-Jr-Cobalt-Transformers-Pinstripe-version-M4-/261140242206?pt=Vintage_Electronics_R2&hash=item3ccd2bdf1e

The price is stupid (I guess) but maybe sending the guy an offer?

And another maybe even sweeter?

http://www.ebay.com/itm/Pair-Magnequest-EXO-36-Cobalt-Transformers-/261140247083?pt=Vintage_Electronics_R2&hash=item3ccd2bf22b

[xcortes]

Paul,

I'm thinking of using a huge pair of BAC100 chokes (in my stash already) for the PS instead of the good ol' triads. I don't have the DCR handy but the BAC80s is 325 ohms so assuming this one is not far away it wouldn't deviate much from the 270 of the triad. Any concerns?

Thanks

[Jim R.]

Xavier,

Thanks for thinking of me but I won't have that kind of cash until we sell our other house, besides, even if I had the money, not sure I'd pay that much for these.  Wonder what they sold for originally, or what they'd cost new today?

-- Jim

[xcortes]

I don't expect them to sell for that much. But you never know!

[Jim R.]

Aaron, you  should pick up those EXO-36s -- if you use the 16 ohm tap they will have 5k equivalent primaries.  A cool 3 grand for a couple of transformers you can drop in your shirt pocket :-).

-- Jim

[johnsonad]

That's just crazy talk Jim! I know where a pair of full blue 2004 jr's are hiding if your heart is set on a pair but they would still be expensive. I'm considering silver wire with M3 depending on the price

[tsingle999]

I was told the full cobalt tfa 2004 jr went for 1$k. The m4/co stripe jr's $800. I much prefer the m4/co stripe to the full cobalts. You get better bass from m4 and take advantage of cobalts crisp airy highs. I would go for those before the 36's plus theyre cheaper. But honestly full nickel is very similar to my ears. Fwiw. Taran

[Hank Murrow]

My 2A3 stereo power amp uses the MQ TFA 2004 Jr's with M4, and ten slices of cobalt in the middle of the coil. They are 'the Bomb' in my opinion. I think I got my pair for $600 back when Mike released stats for them noting 80% of the inductance of the full cobalt stack. I can testify(now that I have the Orcas and a pair of BUF subs) that they really extend the bass and highs are clean. You can see the cobalt slices in the middle of the coil in this pic:

[xcortes]

I measured the BAC 100s dcr at 250 ohms so they are drop-in vs the triads. These are going to be heavy amps.

[howardnair]

is there a difference between the magnequest TFA 2004 and the TFA 2004jr??-and how about the EXO 45-i am ready to purchase some output transformers for the SR45 along with the plate chokes which the bcp-15 is called for --there has been discussion of the dowdy chokes!!! looking for some input--thanks howie

[Jim R.]

Hi Howie,

The difference between the tfa-2004 and the junior is the size of the lamination stack -- and thus the poer handling.  For a 45 or 2a3, the jr is plenty robust enough and *may* have a slight advantage for a lower power amp as it will have less core losses.

The EXO-45 is a 5k primary (instead of 3K fpr te 2004s) and I believe has a maximum power handling capability of 3 watts -- still enough for the 45 but may be pushing it with a 2a3, but it's not a typical primary impedance for a 2a3.

For th bpc-15 you want the 50 henry, 40 ma flavor for the sr-45, or as you mentioned, the Dowdy.  Downside to the dowdy is that it may not fit on an existing chassis (it mounts on top and has endbells), and with a 3k primary impedance on the tfa-2004/jr, the parafeed cap will have to be fairly large -- midpoint is about 28 uF -- and at 630volts, that's a biggie!

Hope this helps,

Jim

[howardnair]

 hi jim -thanks for responding-i think the dowdy choke would be out-not due to its size as this will be my first scratch build and the chassis will be custom- 28uf now  thats a lot of cap-a little pun eh!!!!--magnequest does not show the 2004 jr- so the 2004 or the exo 45 would be the options -is there a advantage to having the 5k over  the 3k impedancel-howie