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Old 9th August 2006, 08:10 PM   #21
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Default here the ec8010-vt52

Beautiful, but not as good as the ugly Loftin White,
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Old 9th August 2006, 08:16 PM   #22
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Default the ugliest but ultra sound

This has highest fidelity than the capacitor coupled ec8010-VT52 (good but not so good as this ultra performer).
Gian Luca
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Old 9th August 2006, 08:25 PM   #23
kevinkr is offline kevinkr  United States
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I have Jean Hiraga's book (in French) which has been an inspiration to me on numerous ocassions.

I recently designed and built a 2A3 amplifier based on a loose interpretation of the Loftin White approach. Mine has a choke assisted mu follower driver direct coupled to the 2A3 output tube. The driver tube is a 7N7 (6SN7 loctal version) I have box plate Kenrad 2A3 from the 1940's. The power supply and output tube cathode bypass caps are 100uF ASC PPIO, supply is CLC with GZ32 rectifier. It was just great with a pair of JBL Rhodes C37 speakers and works well, but not great with my current Onken bass /JBL4333 mid horn /JBL2402 ART setup.

Gain is a bit marginal, but ok in my system and given the amplifier's limited output power.

Here is a pix of it. A very simple design..
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Old 10th August 2006, 02:18 PM   #24
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Default Schematic

Kevin,
Can I ask you for the schematic...
I always curious with the sound of 2A3 and 6SN7....


Thank you very much

Ferry
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Old 11th August 2006, 02:15 PM   #25
kevinkr is offline kevinkr  United States
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Hi Ferry,
This design will be featured in an upcoming article in Positive Feedback Online.. I'll let you know when the schematic is available for download.

Kevin
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Old 14th August 2006, 03:24 AM   #26
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Default beautiful

It is a nice work.
this is my amp,Loftin White.
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Old 15th August 2006, 05:32 PM   #27
5u4 is offline 5u4  United States
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This thread seems to keep resurfacing with lots of nice L-W photos! Also interested to see the circuit Kevin has come up with.

Wondering what capacitors you L-W amp builders are using?

Been doing some cathode bypass cap rolling the last couple of days. Bypass caps make a very noticable difference to the sound of my L-W.

Here are my subjective findings with the caps I had on hand.

2A3 (100uf 250V)
#1 Panasonic NHG
#2 Panasonic EB (rolled off highs, distorted)

6SL7 (100uf 16V)
#1 Panasonic NHG
#2 Panasonic FC (similar sound to NHG, but slightly irritating)
#3 Nichicon Muse ES Bipolar (rolled off highs, dull)

The NHG's for both output & driver sound the best to me of the limited number of caps I tried.

Comments?
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Old 15th August 2006, 06:56 PM   #28
kevinkr is offline kevinkr  United States
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Hi 5U4,
I noticed much the same thing in designing my amplifier. I tried several panasonic electrolytics and they all sounded harsh.

Ended up with ASC 100uF PPIO (motor run cap) on the output tubes from cathode to ground and 20uF Solen from cathode to B+ (ripple cancelling) adding the solen made a big difference - things just opened up and also got a lot cleaner sounding. The ASC by itself sounded clean, but rolled off.

Driver stage uses relatively cheap rubycon blackgate for cathode bypass.
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Old 15th September 2013, 04:29 PM   #29
drlowmu is offline drlowmu  United States
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Quote:
Originally Posted by Mas Penk View Post
Kevin,
Can I ask you for the schematic...
I always curious with the sound of 2A3 and 6SN7....


Thank you very much

Ferry

Hello Ferry,

The two tubes you mention are each LOVELY performers, very neutral. However, it is an error to combine them in a two stage DC amp, as there is NOT enough gain.

Ohh yes, the amp will pass a signal, but it will only sound good when pushed....which gets "old" fast. The most livable two stage L-W type tube choices would use a mu of 70 or higher triode as the driver tube.

This will be perceived as being a LIVELY and vivacious sounding amp, even at low levels.

A wonderful and easy choice with a 2A3 would be 1/2 of a 12AX7 ( mu of 100 ) operating at 170 to 195 VDC Ea, 1.70-1.80 VDC Ek, and about .0006 Ia. It will sound very engaging....good, even at low listening levels. Half a 6SL7WGT is also a candidate, prefer the 12AX7's gain however, with a 2A3.

Jeff Medwin
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Old 15th September 2013, 05:13 PM   #30
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Hi Jeff
I have a bunch of 12SF5, Have you tried them and if so how they compare to the 12AX7 in a LW circuit ?
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