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Author Topic: Looking for 6KD6 tubes  (Read 15841 times)
K9AXN
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« Reply #15 on: June 04, 2016, 09:18:13 AM »

Greg,

What is the radio and does it have a screen balance adjustment?

Kindest regards Jim K9AXN
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KD0FAT
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« Reply #16 on: June 04, 2016, 05:31:16 PM »

Try the esrcvacuumtubes.com website.  They have new 6KD6's for $38, and used ones for $20 each. You can get finals for your rig for less than a carton of cigs, and you don't have to listen to online criticism. 73  Al.
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KB4MNG
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« Reply #17 on: June 04, 2016, 07:18:31 PM »

Yeah, go ahead and buy them on ebay. They are not that much and will more than likely outlast you. I know guys that have been burned at hamfest buying bad tubes. And they were the audio nuts paying $50 a tube. I mainly buy tubes off ebay and have never been burned. Most are very honest and they have to be.

You'll probably spend more eating out for a week than you will for those tubes...
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W5INC
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« Reply #18 on: June 06, 2016, 10:11:38 AM »

 Go to Surplus sales web page linked down below. NOS RCA matched pairs of 6KD6s are 72.00 and single tubes are 34.00. These folks have plenty of these tubes available and do stand behind what they sell. Never had a problem getting tubes from these folks. Good Luck in your project.

https://www.surplussales.com/Tubes-Sock-Acc/6/TubesListed_6-4.html
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G3RZP
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« Reply #19 on: June 06, 2016, 01:55:11 PM »

Jim K9AXN

Quote
What is the radio and does it have a screen balance adjustment?

Could you explain exactly what you mean by this, please?
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K9AXN
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« Reply #20 on: June 06, 2016, 05:13:20 PM »

Jim K9AXN

Quote
What is the radio and does it have a screen balance adjustment?

Could you explain exactly what you mean by this, please?

Pete,

Screen balance is a differential adjustment for screen voltage implemented in some transceivers to effect match for the final pair.

I've seen it primarily in transmitters that use sweep tubes i.e. the Hallicrafters SR-400A.  The sweep tubes are capable of immensely higher current than the 6146 and have a far wider range of current at a specific bias making it very difficult to find a reasonable match.

I believe you knew that before you asked and think that I missed something in the question???

A great day to you --- Kindest regards Jim      
« Last Edit: June 06, 2016, 05:22:07 PM by K9AXN » Logged
G3RZP
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« Reply #21 on: June 07, 2016, 01:13:10 AM »

Jim,

Thanks. I thought it might be that. I've always used separate grid bias pots to get around the matching problem, but it does the same job. I know there was a Collins aircraft tx that had one adjustment for the common screen volts on three 4CX250Bs, and then individual bias controls for the three tubes, all because of the matching business.

Very few manufacturers of ham gear seem to have taken tube matching into account, and when you buy a load of tubes which all are from the same production batch, they do tend to match pretty well, although you cannot guarantee it. But that's of no help when it comes to servicing the equipment!

There was an ARRL designed sweep tube amplifier back in the 1970s where they used individual bias pots for each of four sweep tubes....they also used four cathode current meters. Actually unhooking plate caps and putting something like a Simpson 260 in to measure and set plate current would probably frighten a lot of people off these days....
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K9AXN
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« Reply #22 on: June 09, 2016, 07:47:40 PM »

Pete,

Was that amp was running AB1 or AB2?

Kindest regards Jim
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G3RZP
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« Reply #23 on: June 10, 2016, 08:54:22 AM »

In the '69 Handbook, it just says "in the Class AB region". As the bias pots were 10kohm, I suspect AB1.  When I fitted separate pots on a FL1000 and substituted 6LQ6s for 6JS6s, I used 100 ohm 3 watt wire-wound pots for bias adjustment to keep the bias fairly stable if it ran into grid current.
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K9AXN
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« Reply #24 on: June 10, 2016, 01:27:17 PM »

Pete,

I meant the amp using the 4cx250Bs.

Regards Jim
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G3RZP
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« Reply #25 on: June 11, 2016, 01:14:03 AM »

Jim,

AB1. Actually 7580, but much the same as a 4CX250B, driven by a pair of parallel 6CL6, auto-tune, NFB over the two stages.

The 7580 data sheet says you need individual screen or bias adjustment for multiple tube amplifiers.

73 Peter G3RZP
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WB5LFV
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« Reply #26 on: June 14, 2016, 07:14:58 PM »

so what radio are these going in?Huh
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K9AXN
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« Reply #27 on: June 15, 2016, 08:27:51 AM »

Have to Guess,

Probably an FTDX560 ---- don't believe Greg is going to answer.

Have a good day --- Kindest regards Jim
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K9AXN
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« Reply #28 on: June 20, 2016, 09:47:16 AM »

Note:  The RCA 6KD6 with 274 manufacturing code stamped on it or the box will work in just about any Class AB1 grid driven amp.  It's a handpicked tube with parameters that fit into the quadrant 2 beam tetrode ranges of values for bias and inter electrode capacity.  Otherwise it will be a 1 in 4 chance to select an appropriate tube for your radio.  

Whether a 6KD6 tube will work in your radio has little to do with the manufacturer or batch but everything to do with the bias and inter electrode capacity range they fit.

The design parameters are far tighter for the 6KD6 as compared to the 6146 because a pair of 6KD6'S will equal 5 to 6 --- 6146'S.  The combined plate to grid capacity for the 6146'S will be .44pf and the 6KD6'S 1.6pf --- four times the capacity.  

Kindest regards Jim K9AXN  

« Last Edit: June 25, 2016, 08:02:04 AM by K9AXN » Logged
KD8IIC
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« Reply #29 on: June 24, 2016, 04:23:45 AM »

Fair Radio, Lima Ohio has them NOS.
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