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Author Topic: looking for a Central Electronic 10B for parts  (Read 932 times)
AK0B
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Posts: 375




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« on: December 08, 2018, 10:16:55 AM »

Looking for a basket case CE 10B as a part source.

What do you have cheap?  my QRZ address is correct. The other thing I am interested in --- back in the 50s or 60s I seem to remember fellows using 6AG7s (several of them) as a GG linear.  Interested in finding a QST etc that has a circuit for doing so.

thanks, 73 de Stan AK0B


   
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K4PF
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Posts: 17




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« Reply #1 on: December 09, 2018, 09:03:06 PM »

Hi, Stan

Re: Your query for grounded-grid 6AG7 amplifier info - you might be remembering the 4-tube 6L6 grounded grid amplifier by Norm McLaughlin, W6GEG.

See page 34 of https://www.americanradiohistory.com/UK/Amateur-Radio/Amateur-Radio-1983-11.pdf

That same circuit was shown in the CQ "New Sideband Handbook" by Don Stoner (1958).
Stoner gives the coil values as follows: rfc 1 & 3 are 2.5mH 500mA.
RFC-2 is a parasitic choke, 50 Ohm 1 Watt resistor wound end to end with enameled No. 16 wire.
C1 is ceramic 500pF 10KV TV doorknob type.
C-2 is Johnson 200L15 200pF .030" spacing.
L-1 is B&W type 40 JEL (for use on 75 meters). Tap about 4 turns from bottom.

He fed the amp with 750VDC.

73,
Ed Knobloch
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AK0B
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Posts: 375




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« Reply #2 on: December 09, 2018, 10:10:26 PM »

Thanks Ed,   That was the information I needed.  I have several 6CL6 so might try them as replacements for the the 6L6s. Not looking for a lot of power just wanted to get above what the 10B would put out.

Merry Christmas, 73 de Stan AK0B
 
PS   the amateur radio book was also of interest.  First time I had seen a copy of it..
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KM1H
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Posts: 5516




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« Reply #3 on: December 10, 2018, 01:41:16 PM »

My first 10A amp was 4 6AG7 in GG and maybe from a CQ article around 1956. It later became a 10B with a modified 1625 in GG driving 4 more, 837's could also be used without having to select modifiable 1625's. Lake Shore Industries sold the LA-400 amp with a choice of tubes.The 10A went to a 2M transverters,  the 10B to the same on 6M, and a 20A was used on HF. In 59 a 4 year hitch in the USN curtailed the fun stuff, and in 63 I went to work for National Radio.

In 65 a CE 100V arrived and is still in use.

Carl
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AK0B
Member

Posts: 375




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« Reply #4 on: December 11, 2018, 08:34:22 AM »

Thanks Carl,   why did they modify the 1625  and how?   I have box of them both new and used.

de Stan AK0B
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N2EY
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Posts: 5093




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« Reply #5 on: December 11, 2018, 08:54:58 AM »

why did they modify the 1625  and how?   I have box of them both new and used.

The problem with using 1625s in grounded-grid is that the beam-forming plates and the cathode are connected to the same base pin, and the resulting interelectrode capacitances cause problems in GG operation.

In QST for June, 1955, page 21, there is an article "A 200 Watt Grounded Grid Linear Amplifier" by R. L. Peck, W9MOW and E. L. Hoover, W9SAR. Very simple design using four 1625s as zero bias triodes, with 816 rectifiers.

Peck and Hoover discovered that some 1625s had the cathode and beam forming plates brought out of the bulb with separate wires, rather than being bonded internally. So they removed the base of the tubes, separated the wires, determined which was which, put the beam forming plate wire to an unused base pin, and reattached the base. The tubes could then be used successfully in GG by grounding the grid, screen and beam forming plates.

Peck and Hoover's company, P&H (not Lakeshore Industries) made manufactured versions of this amplifier under the name "LA-400". The manual for the LA-400B can be found here:

http://bama.edebris.com/manuals/ph/la400b

P&H sold modified 1625s, and also made a version using 837s which did not require modification because they have the suppressor brought out to its own pin already. Their modified 1625s could be had with a 6 pin base, too, because the 7 pin Medium socket isn't the most common junkbox item around.

There's more!

In QST for September, 1955, in a Stray on page 10, W7GND tells that National Union 1625s are suitable for modification, and can be modified without removing the tube base by drilling a hole above the cathode pin, heating the pin and pulling out the wires, separating them and attaching to different pins. Tells how to determine which is which electrically, too.

In those days, 1625s could be had for as low as 19 cents each in surplus. Like the 807 they are pretty rugged, and at those prices, if a quad lasted only a few months, you wouldn't break the bank on replacements.

73 de Jim, N2EY
« Last Edit: December 11, 2018, 08:57:33 AM by N2EY » Logged
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