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Old 27th October 2006, 09:05 PM   #11
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Manual is by Robert C. Wolpert, "Audio Transformer Design Manual" It is very detailed on the exact and practical methods of designing and building audio transformers with many examples and lots of supporting data and tables in the appendix. He also wrote an equally good manual on power transformers. Unfortunately, these manuals seem to be out of print. I bought mine from Ram Sales in the early 1990's. Ram Sales is a wonderful source for bobbins, transformer hardware, surplus lams from time to time, and also coil winding equipment. I have done business with them for 30 years or so and they are at the top of my list. They fill smaller orders for me. Their phone number is 800-423-2985
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Old 27th October 2006, 10:28 PM   #12
bembel is offline bembel  Europe
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I confirm EC8010 thoughts.
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Old 28th October 2006, 07:32 AM   #13
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Paul (7N7) The idea of using acorn tubes, I assume for show, is unique. I would have never thought of it. If you get back into amp construction and need any tubes that I have in my junk collection and am not using, I will send them to you.

I have several tube types that I want to try and probably won't part with. I have a several 212 tubes which are old theater amp tubes from the 1930's. I even have sockets. I believe they have a plate dissipation of about 250 watts. How I came by them is a good story. Several years ago, I went to an estate sale near Microsoft in Redmond, Washington. There was a pile of stuff outside about 50 feet long and 3 feet high, covered with blue tarps and plywood, all in bad condition. I could see a few antique electronic items, so I offered $100 for anything I could salvage from the pile, and my offer was accepted. Most everything was rain soaked for years but there was a box containing 17 each WE-205d's as well as 8 each Duovac NIB 205d's with factory test sheets and warranty cards, all at the bottom of the pile. This is also where I found the 212 tubes. I gave the 205d's to my friend who told me about the sale. About half of the tubes turned out to be fine. This is the type of good luck that seldom happens to me.

I have thought about trying something with 304tl's and 450tl's. I have a few of them. If it doesn't work out, they make nice lamp stands.

Sparky
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Old 28th October 2006, 04:18 PM   #14
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Response to email by "Bear" I am not familiar with the 417a, what do they look like? I have boxes and boxes of tubes than I have not gone thru yet. A lot of my friends who came over to see the estate stuff started drooling. In fact, their personalities changed temporarily when they saw the Western Electric tubes. I kept some of them for myself. We also pulled rack mount complete WE amplifiers out of the junk. They were rough on the outside, but pristine inside. I hauled home 4 navy shipboard 6 ft full rack size transmiters. One was a "TBM-8" I believe. There was a Breting 12 communications receiver and a good story behind it. Inside one of the sheds I found the receiver chassis which was installed in a high boy 1920's Sonora console radio cabinet with spindly legs, doors, etc. In spite of lack of the original cabinet, I negotiated for the receiver and finally bought it for $15. Later in the day when I was going through the outdoor mound of stuff, I found the original Breting cabinet along with a little cloth tobacco sack tied to the cabinet with the harware in it. You have to understand that this equipment was found mostly ouside in western Washington where it is damp or rains frequently and consequently the physical condition was poor. There were literally truck loads of neat stuff. I don't expect to ever find anything like this again.

Sparky
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Old 28th October 2006, 08:55 PM   #15
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I have found this http://www.tube-fullmusic.com/produc...oduct0-805.htm
It seems the curve of a pentode
do these tubes normally work in class A2 or AB2 (with grid current) ?

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Old 29th October 2006, 06:35 PM   #16
7N7 is offline 7N7  United Kingdom
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Quote:
Originally posted by sparky813
Paul (7N7) The idea of using acorn tubes, I assume for show, is unique. I would have never thought of it. If you get back into amp construction and need any tubes that I have in my junk collection and am not using, I will send them to you.

I have several tube types that I want to try and probably won't part with. I have a several 212 tubes which are old theater amp tubes from the 1930's. I even have sockets. I believe they have a plate dissipation of about 250 watts. How I came by them is a good story. Several years ago, I went to an estate sale near Microsoft in Redmond, Washington. There was a pile of stuff outside about 50 feet long and 3 feet high, covered with blue tarps and plywood, all in bad condition. I could see a few antique electronic items, so I offered $100 for anything I could salvage from the pile, and my offer was accepted. Most everything was rain soaked for years but there was a box containing 17 each WE-205d's as well as 8 each Duovac NIB 205d's with factory test sheets and warranty cards, all at the bottom of the pile. This is also where I found the 212 tubes. I gave the 205d's to my friend who told me about the sale. About half of the tubes turned out to be fine. This is the type of good luck that seldom happens to me.

I have thought about trying something with 304tl's and 450tl's. I have a few of them. If it doesn't work out, they make nice lamp stands.

Sparky

Helo Sparky, and thanks for the offer.

I doubt if I will be building yet though. Yes the acorns did fascinate me for appearance reasons, and I alsways loved anything that was old and "modern" at the same time: cutting-edge 30s technology. But it's worth looking at the example circuits that RCA devised. For example they knew about bypassing heater supplies at the valve, with small capacitors o get rid of RF noise.

However, when I tested the 955s aspecially as diff pairs I found that the distortion was very low, and as I wrote earlier the prototype pre-amp was very good. With 6SN7s I got -3dB at about 100kHz (I think) adn 180kHz with the 955s.

212s I have forgotten about; more info please!

Paul
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Old 29th October 2006, 06:51 PM   #17
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Quote:
Originally posted by 7N7
However, when I tested the 955s aspecially as diff pairs I found that the distortion was very low, and as I wrote earlier the prototype pre-amp was very good. With 6SN7s I got -3dB at about 100kHz (I think) adn 180kHz with the 955s.

Paul

In SE the 955 is an excellent performer, as a differential pair it has the potential to be amazing:

955 Acorn tubes

Love the 9002 equiv in the front end of my little 6CW5 SE. Also agree on the general recommendations here of 900-950 volts and ~-90 bias on the 813 trioded. At least with a modern Chinese sample voltages above around 975 greatly raised the level of higher harmonics regardless of standing current. This was driving a Hammond 1628Se, 5K:8 with an 8 ohm load on the 4 ohm tap for ~10K plate load.

And thanks for the triode curves!
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Old 29th October 2006, 07:34 PM   #18
Tweeker is offline Tweeker  United States
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Cutting-edge 30s technology: Westinghouse high power audio amplifier, the large tubes are 849s, smaller 211s. I just love the look of this sort of gear. 3 phase 6 pulse "low power rectifier" at left, note the 6 diode tubes.

Click the image to open in full size.

Amperex 849A datasheet.


1936 Western Electric 212E datasheet.

1945 Amperex 212-E datasheet.
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Old 29th October 2006, 08:10 PM   #19
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Tweeker,

As you know, that was only the input stage to a 250KW to 350KW audio amp used to plate-modulate an RF power amp in the old WLW AM radio station. Here's the output stage of that same audio amp:
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Old 29th October 2006, 08:18 PM   #20
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And a simplified schematic for those that plan to build one:
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File Type: jpg wlw audio power amp simplified schematic.jpg (36.6 KB, 853 views)
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