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Author Topic: 6146 In place of 6JB6 in Drake T4X  (Read 14571 times)
WA4JQS
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Posts: 280




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« on: February 15, 2018, 04:08:48 PM »

I recall some time back that someone had taken an old t4x and upgraded to 6146's. just wondered if anyone else had done this or had found another tube to replace the sweep tubes drake used.

73 Tony WA4JQS
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WA4NJY
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« Reply #1 on: February 15, 2018, 05:43:30 PM »


 Tony,

 Try a Google of K5DKZ.   He has some info on doing the conversion along with several other articles. There may be others out there.

  Ed WA4NJY
  Bradenton, Fl
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WA4JQS
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« Reply #2 on: February 15, 2018, 05:56:00 PM »

thanks ed
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AK0B
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« Reply #3 on: February 15, 2018, 09:13:43 PM »

I would not do it.   The 6JB6 is a more rugged tube than 6146.  The 6146 is very critical of grid current and will go bad if you don't watch it when tuning.  Remember the Drakes are tube rigs and not transistor and need to be carefully tuned.  The 6JB6 as they get weak so you have a few watts less power.

Even if you drop by 50 watts it still a nice transmitter and will take punishment.

If you power has dropped the first place I would check it the cap in the power supply.

Stan AK0B



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KD8IIC
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« Reply #4 on: February 16, 2018, 01:22:15 AM »

 Would advise against it as well.
The 6JB6 PA is a proven es rugged design.
This is not a hammy hambone project to undertake.
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K8BYP
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Posts: 256




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« Reply #5 on: February 16, 2018, 10:00:16 AM »

" The 6JB6 is a more rugged tube than 6146."

FALSE INFORMATION

Notice none of these Posters posting this nonsense are quoting tube specs.. it means they know nothing about it

READ THE TUBE SPECS.

The 6146 will withstand more plate dissipation 35 watts for the 6146 and 17.5 for the JB6. Therefore the 6146 is "more rugged"

PS theres no such metric as "rugged"- thats someone making it up...

If "rugged" is important, that implies mechanical, and the 6146 comes in a W grade that can withstand high vibration.

https://frank.pocnet.net/sheets/049/6/6146B.pdf

See, I can quote specs, I know something about this topic!


The JB6es are VERY sensitive to grid current, they are not allowed to draw any. (neither tube should draw grid current)

been there, tested that, I deliberately burned  6 12JB6es to the ground by allowing them to draw grid current (I did it deliberately as a test)

The engineers (not Trolls on a website) that designed the TR3 limited the 12JB6 grid current to about 1.5 mA max... then the TX AGC kicks in to limit grid drive.

The 6146 is a low end transmit tube. The JBs are horizontal output tubes from TVs, they are not transmit tubes. They are receiving tubes.


Ive seen 6146 data sheets that had operating points identical to the JB6es.

Point is, read the data sheets for yourself.

beware, this is an AMATEUR radio site and quite often you get bad info like this- the universal indicator of "bad advice" is "they cant discuss specs"

Youre getting opinion, not facts.
« Last Edit: February 16, 2018, 10:07:18 AM by K8BYP » Logged
N2EY
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« Reply #6 on: February 16, 2018, 12:03:35 PM »

It has been done successfully in a number of rigs that used "sweep tubes", including the 6JB6. However, it is usually more involved than just changing the sockets. Expect some loss of power output because the plate voltage of the T-4X is not optimum for 6146s.

Which tube is "more rugged" is an opinion question.

The "sweep tube" ratings in most tube manuals are for use as a horizontal deflection amplifier in a TV set. Such operation is very hard Class C conditions, continuous duty, inside the poorly ventilated HV compartment of a TV set that may be left on for several hours every day. A real hard-knock life! So ratings such as plate dissipation ratings of "sweep tubes" were determined based on giving reasonably long service under those conditions. 

Drake and others used "sweep tubes" because they saved money and were more available back-then. A 6JB6 was not only less expensive than a 6146 back in 1965, but the 6JB6 would give the same power output with 100-150 volts less plate voltage. That meant savings in the power supply and other components. More watts per dollar!

All turned upside-down, now.

There's an easier way, though......

The 'JB6 family of tubes was made in a wide variety of heater voltages. With the addition of a separate heater transformer of appropriate rating, you can use almost any of the xJB6 tubes that you can find.

---

If you could go back in time and talk to the Drake people that, in 2018, hams would still be using their rigs.....they'd never believe you.


73 de Jim, N2EY

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WA4JQS
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« Reply #7 on: February 16, 2018, 02:04:32 PM »

Jim and Crew"
thanks for the info. BTW i do a little more the hammy ham repairs. i have been restoring rigs for over 50 years.. and have seen a lot of sweep tubes replaced by 6146's in other brands. i was just wondering if anyone had done it with the Drake gear. seems a K5 has done this and yes a lot more involved then just changing a few wires. Yep think Bob would have a wide grin on his face if he could see the number of Drakes still on the air in 2018. i have 3 complete sets on the air. and my 4 L4B's are still full output with the org. tubes. i have found that adding a fan to the T4 transmitters seems to help tube life. guess ill see if i can pick up an old T4X and convert it over as i am running out of projects hi hi..
Again thanks guys.
73  ZUT
WA4JQS
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W8JX
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« Reply #8 on: February 16, 2018, 02:32:41 PM »

I recall some time back that someone had taken an old t4x and upgraded to 6146's. just wondered if anyone else had done this or had found another tube to replace the sweep tubes drake used.

73 Tony WA4JQS

Check out link below

Click Here
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AC5UP
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Posts: 4546




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« Reply #9 on: February 16, 2018, 05:19:19 PM »

It should also be noted the horizontal sweep frequency for old-school NTSC (color) TV is 15.750 KC.........  And those of you old enough to remember when your ears were young could hear a high pitched whistle coming off the back side of your TV.

Sweep tubes were popular as HF finals based on cost and availability.  Not their RF characteristics as a TV never took them above dog whistle audio.

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W8JX
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« Reply #10 on: February 16, 2018, 06:22:43 PM »

And those of you old enough to remember when your ears were young could hear a high pitched whistle coming off the back side of your TV.

I well remember it!
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
G3RZP
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Posts: 1278




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« Reply #11 on: February 17, 2018, 02:04:22 AM »

K8BYP said:

Quote
The 6146 will withstand more plate dissipation 35 watts for the 6146 and 17.5 for the JB6.

The 6146, 6146A and 6146W are all 25 watts plate dissipation: the 6146B is 35 watts. They are all rated at between 3 and 4mA of grid current maximum in Class C, and generally speaking, are more linear than sweep tubes in SSB service.

The 6JB6 presumably draws some grid current in sweep tube service to get the 550mA peak cathode current, but as the maximum grid cathode resistance is quoted as 1 megohm, it can't be very much to get the minus 55 volts of grid bias quoted.

The 6146 family has a defined range of plate current, but no range is available for the 6JB6, so unless tubes come from the same batch, you could have problems. I know my fathers FL200B with 6JS6Cs in did - the one drawing most current would fuse the cathode lead open!

Although the power will be less because of the lower plate voltage, I figure that 6146s will be around for longer than 6JB6s.....
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KX4OM
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« Reply #12 on: February 18, 2018, 03:31:51 PM »

An article by Doug DeMaw, W1FB in the October 1980 QST contained a list of 6 Sylvania sweep tubes that the company tested in 1964 for RF service up to 30 MHZ. Among them was the 6JB6. There are 3 tables in the article with the detailed data from Sylvania's tests, along with a schematic of the test circuit. The 6JB6 had a probable upper frequency limit of 175 MHz, based on its output self-resonant frequency of 200 MHz.

The other two tables were of the data collected for ICAS CW operation and Class AB operation. The tubes were tested at 500 VDC plate, and W1FB mentioned that amateurs who were using sweep tubes in parallel were more likely to run them at 900 VDC.

It took me awhile to realize that I had a copy of the article. For ARRL members, the 4 page article, including W1FB's own experiences with sweep tubes can be downloaded from the ARRL web site.

Ted, KX4OM
« Last Edit: February 18, 2018, 03:34:04 PM by KX4OM » Logged
K5WLR
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Posts: 311




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« Reply #13 on: February 18, 2018, 03:58:03 PM »

Neat article, but it's in the February 1980 QST, not the October 1980 QST as mentioned above.

73

Will Rogers
K5WLR
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KX4OM
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Posts: 366




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« Reply #14 on: February 18, 2018, 05:06:24 PM »

Yeah, I missed that. Following this thread all week, I was doing some reading to see if the 6HF5 sweep tubes in my Galaxy V Mk2 can be expected to hold up under the 850 VDC plate from my AC-400 supply. Turned out that the 6HF5 tubes are on the Sylvania list. The highest rated plate dissipation at 35W, in fact. The rig was originally designed for the AC-35 power supply, which delivers 800 VDC on the plate. Galaxy kept upping the power on the Galaxy transceiver line and changing the PA tubes, and they released the AC-400 for the Mk3 and the later GT-550. With my line voltage, I got about 900 on the plate in standby when I rebuilt the AC-400. I then took the Mk2 down for some refurbishing. In the brief time I ran it, it was on CW only. I think now is a good time to finish the AC line buck transformer for my boatanchors. My HW-101 runs high on plate voltage as well.

Ted, KX4OM
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