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What's the best series feed output you offer for the 2A3`

68.158.247.151
Posted on September 15, 2009 at 19:30:58
rickmcinnis@dogwoodfabrics.com
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Posts: 723
Location: Atlanta
Joined: December 15, 2003
 I want to buy something from you (out of patriotic fervor?. I have embarked on a Medwin inspired Loftin-White, by way of Shishido, 2A3 circuit.

What is the best output you can offer at this time?

I do not care about response below 500 hz (too much) first order c/o to a TAD 4001 and a TAD 2001 above 10K is all the amp has to drive.

I am ready to order, though not in a hurry to take delivery.

Please, let me know,

Thanks,

Rick McInnis
How does one order from you?, posted on September 25, 2009 at 10:41:18
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 723
Location: Atlanta
Joined: December 15, 2003
 I see nothing at BOTTLEHEAD anymore.

I sent a note, but maybe I accidentally deleted your reply with the massive number of "enlargment" emails I get everyday.

Also, of the RH series which one would be "the one"?

Let me know, thanks,

RE: What's the best series feed output you offer for the 2A3`, posted on September 17, 2009 at 20:10:14
mqracing
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Posts: 3314
Joined: June 29, 2000
Contributor
  Since: May 7, 2004
 Hi Rick:

On the series feed front we offer the DS-025, QS-025 and FS-030 outputs. Each would work quite well with the 2A3 tube.

You can think of the DS-025 and the QS-025 as from our "small block" series. These have a nominal primary impedance of 2500 ohms and 4, 8, and 16 ohms (some variants omit the 4 ohm tap). The QS designation is for an all silver wire (the real thing, pure silver--- not silver plated copper) version of our DS-025. Both the DS-025 and QS-025 are gapped for 60 mils of DC plate current. These come in bell end caps.

The FS-030 is our "big block" series feed 3,000 ohm pri impedance output... it's secondary can be arranged for 4, 8, or 16 ohms. It too is airgapped for 60 mils of dc plate current.


The DS-025 has graced the top plates of many a great 2A3 amp... as just a few examples... the Baby O amp by Gordon Rankin (and in the public domain), Don Garber's FI 2A3 often sports this output, and Dennis Fraker's 2A3 amp uses this same output transformer.

Pricing info can be found at www.magnequest.us

fire away if you have any more questions.

Mike





Builder of MagneQuest™ & Peerless™ transformers since 1989
What about the ES-025? Nt, posted on September 18, 2009 at 19:42:32
Caucasian Blackplate
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Posts: 4444
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 Nt

RE: What about the ES-025? Nt, posted on September 18, 2009 at 20:26:21
mqracing
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Posts: 3314
Joined: June 29, 2000
Contributor
  Since: May 7, 2004
 Hello. The ES-025 is not a catalog item and is only available by special order. Until I get caught up on my current backlog of special orders I am not accepting any new non-catalog work.

Mike



Builder of MagneQuest™ & Peerless™ transformers since 1989
Thanks,, posted on September 18, 2009 at 11:36:48
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 723
Location: Atlanta
Joined: December 15, 2003
 I wanted to be sure there was not some behind the scenes variant.

The silver wire version is not listed.

What would be the price for this, this week? I know you have to price it based upon the market. I would like to get an idea is this is even a possibility for my budget.

RE: Thanks,, posted on September 18, 2009 at 20:23:39
mqracing
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Contributor
  Since: May 7, 2004
 Hello.

The DS-025's are $200 each and delivery would be approx four to six weeks.

The QS-025's are $3200 a pair. We have these in stock.


If the DS-025 is outside your budget... then I would recommend our Robin Hood series ($99 each). But you will need to derive a set of operating points for the 2A3 working into a 5,000 ohm load impedance.

If PJ tunes into this thread... I think he has previously posted some suggested operating points for a 2A3 with 5,000 ohm primary.


Mike







Builder of MagneQuest™ & Peerless™ transformers since 1989
Tuning in, posted on September 19, 2009 at 13:02:57
Paul Joppa
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  Since: July 1, 1999
 (Been out of town)

Looks like the question is settled, and the DS-025 at 2500 ohms is well suited to the standard operating conditions from the tube manuals sso it should be easy.

But this is as good a place as any to respond to Mike's hint. So here's my analysis or high-impedance operating conditions for 2A3s:

My approach starts with a nominal operating point, fixed by the load impedance and bounded by the maximum current, maximum plate dissipation, and/or maximum voltage. The 2A3 is rated for 15 watts and/or 300 volts; I've never seen an official maximum current rating so I would not exceed 60mA (the highest specified for typical operation). With a very linear tube, such as a (well-made!) 45, 2A3, or 300B, the distortion will be about 5% at full power.

Here are some examples of my estimated conditions at 15 watts plate dissipation:

60mA 250v 2262 ohms *** n.b. RCA recommends 2500 ohms at this condition ***
55mA 275v 3040 ohms
50mA 300v 3975 ohms

Without exceeding the plate voltage limit, the following operating points are calculated:

45mA 300v 13.5 watts 4570 ohms
40mA 300v 12.0 watts 5320 ohms
35mA 300v 10.5 watts 6290 ohms
30mA 300v 9.0 watts 7600 ohms

If you change the load impedance from the above, a lower impedance will product more power at greater distortion, while a higher impedance will reduce both power and distortion. For example, we recently operated a 2A3 at 300v, 50mA, into a 6500 ohm impedance transformer. The result was a very sweet and extended sound, but only 2 watts. In my opinion, any load from 2/3 to 3/2 of the calculated impedance is quite acceptable. It will change the power by only a small amount - less than a dB - and the distortion will remain reasonable, between 3% and 10% usually.

Operating the tube at lower power dissipation will probably extend the life of the tube and is recommended by some. Many 2A3s however are already rated very conservatively, in which case this effect will be small.

And again,, posted on September 19, 2009 at 11:18:19
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 723
Location: Atlanta
Joined: December 15, 2003
 I just had to ask about the silvers.

The DS are certainly affordable. I will have to wait for my next life to be able to have the "others".

Thanks for the advice.

Rick McInnis

I'm interested in the answer too., posted on September 18, 2009 at 19:28:41
nc
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Posts: 315
Location: San Francisco, CA
Joined: November 19, 2003
 Thanks

Did you look at Mike's Robin Hood line?, posted on September 16, 2009 at 20:29:44
VoltSecond
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Posts: 2423
Location: Arizona
Joined: October 14, 2000
 http://www.magnequest.com/products.htm

Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.

. . .Oh!. . .Remember: Modifying things voids their warranty.
They all seem to be 5K, posted on September 17, 2009 at 09:01:35
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 723
Location: Atlanta
Joined: December 15, 2003
 figured I should go with 2.5 to 3K.

Power is not a consideration. Do you think I would get better sound quality with the higher impedance?

All advice is appreciated.

RE: They all seem to be 5K, posted on September 18, 2009 at 20:30:32
VoltSecond
Audiophile

Posts: 2423
Location: Arizona
Joined: October 14, 2000
 I like the sound of 5K on the plate. It is a little tighter than 2.5k, but not too tight.

Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.

. . .Oh!. . .Remember: Modifying things voids their warranty.
RE: They all seem to be 5K, posted on September 18, 2009 at 21:03:57
mqracing
Manufacturer

Posts: 3314
Joined: June 29, 2000
Contributor
  Since: May 7, 2004
 Hi Voltsec:

Can you recommend a set of operating points (plate volts, grid bias, dc plate current, etc) for the 2A3 working into a 5K ohm load for Rick to consider?

The Robin Hoods can be gapped for 40 mils (40H) or 60 mils (30H).

MSL



Builder of MagneQuest™ & Peerless™ transformers since 1989
2A3 5K load, posted on September 21, 2009 at 20:33:08
VoltSecond
Audiophile

Posts: 2423
Location: Arizona
Joined: October 14, 2000
 260V Plate-Cathode with 40mA bias current ~53V cathode to ground should give a clean 2-3W output. (Cathode resistor of 1.3K, plate voltage of 313V)

The plate will be at 10.4W so the tube will last a long time.

Remember, for something to sound twice as loud takes about 10X the power. The volume difference between 2 and 4W isn't that much.

Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.

. . .Oh!. . .Remember: Modifying things voids their warranty.

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