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Author Topic: Viking 2  (Read 17542 times)
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DMOD
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« Reply #25 on: January 01, 2016, 12:01:48 PM »

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Hi all, I just picked up a Viking 2 last week that's in beautiful condition . It has very little grid current 2 mills until I turn the drive to 9.  Than there is 7/8 mils of current. There are mods instead of 6au6's there are 12ax7's driving a 6cl6. , 807's to 6146 . I made a mistake trying to tune and had the drive to far and plate current and took out the 5v4ca  rectifer . This is mated to a HRO 50t ,also the Viking has a trans relay the coax to the back  of the case and one that plugs into the two small holes at the bottom. This is my first AM transmitter and I don't want destroy it.


This is a common problem with both older Heathkit and EF Johnson transmitters.

The modification is as follows:

1). Replace the 25k 4W potentiometer with a 25k, 5 Watt unit.

2). Add a 10k to 15k, 10W series resistor between LV B+ and the Drive Potentiometer

3) Add a 22 uF, 450 Volt electrolytic at the junction of the drive potentiometer and the New 10k to 15k, 10W resistor.


Below is the Buffer-Driver Stage modification schematic:

* Generic Drive Pot Modification.pdf (39.05 KB - downloaded 259 times.)
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w1vtp
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« Reply #26 on: January 01, 2016, 05:01:49 PM »

It's a Viking 2 that was manufactured on April first   Grin - - - - or was the other way?Huh?
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N8ETQ
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Mort


« Reply #27 on: January 01, 2016, 08:27:07 PM »

Yo'


In June of 1950 the US started support of the South Korean Government (Ironically created
by the Allied  Coalition at the end of WWII) VS. the Soviet/Chinese who supported the North.
With the “Viking” (Introduced in 1949) originally designed with a 4D32 PA this meant big
trouble.  The USAF bought up ALL the 4D32's overnight making them really expensive.

In response, Johnson had little choice other than to find a substitute tube for the PA.  They
chose the 829B (Probably  because it used the same socket) and similar voltages. It wasn't
until the late 1980's that the USAF “Dumped” thousands of 4D32's on the surplus market.

The Korean conflict pretty much wound down by July of 1953. The Viking II was introduced
in 1952 and was available to 1957 sporting 2 X 6146 in the PA.

https://en.wikipedia.org/wiki/Korean_War

http://www.radioing.com/museum/tx4.html

/Dan

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DMOD
AC0OB - A Place where Thermionic Emitters Rule!
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« Reply #28 on: January 03, 2016, 06:50:01 PM »

Quote
Hi all, I just picked up a Viking 2 last week that's in beautiful condition . It has very little grid current 2 mills until I turn the drive to 9.  Than there is 7/8 mils of current. There are mods instead of 6au6's there are 12ax7's driving a 6cl6. , 807's to 6146 . I made a mistake trying to tune and had the drive to far and plate current and took out the 5v4ca  rectifer . This is mated to a HRO 50t ,also the Viking has a trans relay the coax to the back  of the case and one that plugs into the two small holes at the bottom. This is my first AM transmitter and I don't want destroy it.


This is a common problem with both older Heathkit and EF Johnson transmitters.

The modification is as follows:

1). Replace the 25k 4W potentiometer with a 25k, 5 Watt unit.

2). Add a 10k to 15k, 10W series resistor between LV B+ and the Drive Potentiometer

3) Add a 22 uF, 450 Volt electrolytic at the junction of the drive potentiometer and the New 10k to 15k, 10W resistor.


Below is the Buffer-Driver Stage modification schematic:

I had almost forgotten about the other solution to the Drive Potentiometer problem
which is found at:

http://amfone.net/Amforum/index.php?topic=32895.0

in case you cannot find the 25k, 5W wirewound Potentiometer.

The transistor can be a TT-2062 or NTE 2300, 2669, etc.

http://www.nteinc.com/specs/2300to2399/pdf/nte2300.pdf


Phil - AC0OB
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N9axl
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« Reply #29 on: February 13, 2016, 10:11:07 PM »

I'm having to re tube my Viking 2 CDC. It came with no tubes except a pair of 807s. I have a jackson 648 tube tester so I can run some kind of check on what I buy. 

Is there any benefit to using a 6293 in place of the 6146? I know it's basically ruggedized 6146 but as the starting goal is to get this operating as stock per manual will this cause issues? Shoukd I neutralize these tubes? The rest of the tubes seem standard.

6aq5. X2
6au6. X3
6al5
5V4g
5r4gy. X2
6j6

So far this is going fine.  I just need to get some dual caps for the power supply. This seems easier to work on than the Viking Ranger.

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« Reply #30 on: February 14, 2016, 05:43:42 PM »

I have a number of 6293's and use two Marconi 6293's in mine and they they work just fine but:

Testing the transconductance of various tubes, I find the RCA and Sylvania 6146B's have transconductances of 7500 umho's, whereas all the 6293's all check out between 5800 and 6500 umho's, in deference to the published spec of 7300 umho's.

I have used both tube types during testing and cannot see any real output power differences.

I don't see any problems with neutralization as both tubes have the same interelectrode cap specs.

I would replace the 6AU6's in the first speech amp and the Oscillator with 6AH6's.

Phil - AC0OB

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Charlie Eppes: Dad would be so happy if we married a doctor.
Don Eppes: Yeah, well, Dad would be happy if I married someone with a pulse.NUMB3RS   Smiley
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