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Stocking up on tubes.




 
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Author Topic: Stocking up on tubes.  (Read 4630 times)
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Ed WA4NJY
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« on: September 04, 2014, 02:09:52 PM »


 I have some Hammarlund receivers to service and maybe keep.  I have had some problems with 6C4 tubes.  Some worked fine and others not so well.  Should I stock up on JAN or a certain brand?  Or is it a crap shoot?

Thanks,

Ed WA4NJY
Bradenton, Fl
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WQ9E
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« Reply #1 on: September 04, 2014, 10:44:17 PM »

Ed,

With Hammarlund receivers it seems to be a crap shoot.  I have a lot of Hammarlund receivers that use a 6C4 HFO and I have never found any type (i.e. W suffix, JAN, or particular brand) that seems consistently better. I think the best bet is just pick up a selection and be prepared to do some swapping to find one that not only works but has good stability. 
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Rodger WQ9E
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« Reply #2 on: September 04, 2014, 10:58:22 PM »

How are you testing the tubes? What kind of tester? Not all of them give the best indication of how well a tube can work in a multitude of circuits.
I assume you already checked the surrounding components and voltages etc.
Ultimately one can say the best tube tester is the actual socket you intend to use the tube in. If you can do it, set up a receiver specifically to be the one to check the tube in.

some general suggestions:

* Sticking to big name brands like RCA, GE, Sylvania, etc.

* Using only NOS tubes, and burning them in for a couple hours in class A service, then checking them.

* JAN are the better tubes.

* Is there a "G.E. Five-Star" version? Usually that is a 4-digit number tube. Dos not have to be GE, the "RETMA" number tubes are industrial/military uses and supposed to be 'best' in various ways because they have improvements over the consumer type. The 6C4's counterpart is the 6135.

* lastly, does the radio manufacturer suggest a particular brand? Some sets may be fussy. 6C4 is a VHF-rated tube, is this in a sensitive area?

Find a case of them.. maybe get lucky that way, like the case of NIB 6J6's I found where all boxes say "Sperry Gyroscope" on them. So they are not junk tubes anyway but selected.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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« Reply #3 on: September 04, 2014, 11:08:18 PM »

A tester is useless for picking tubes for a Hammarlund HFO, it is a well known quirk of this receiver that it is particular about the 6C4 used.  My HQ-170A VHF is running perfectly with a "Servicemaster International" 6C4 and I consider this brand to be lower than K-Mart quality which is saying something, I tried a couple of NOS W spec tubes before settling on what is in it now.  I recall someone stating about a year ago that he was going to investigate and write an article about the Hammarlund 6C4 behavior but I have heard nothing since and maybe he gave up.  It certainly isn't impossible or even difficult to find a "good" 6C4 for a Hammarlund but it does seem to be a trial and error approach.

For a piece of gear in unknown condition I will run the tubes through a tester to weed out those with gross defects (shorts, gas, etc.)  and I like to check/clean the contacts anyway but even though I have a higher end tester I don't use the readings to accept/reject since a tube that tests at the lower end will often work perfectly in a given circuit while one that tests perfect in a tester may well fail to perform at RF.  Many tube defects will appear only when operating at actual equipment temperature which won't occur in a tester.  As Tektronix noted in the manuals for their classic lab grade tube type scopes the only real test of the tube is whether it performs as required in the actual circuit.
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Rodger WQ9E
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« Reply #4 on: September 05, 2014, 02:54:11 PM »

Hi Ed and all..about to correct a kinda similar problem here..replaced the only VT(6C4) in my Sylvania tester in Dec '013..it's acting up with no two readings for the same tube identical it appears when testing..I've got several 6C4s of different makes..some new some not..but I'm puzzled a bit here..concerning 4 digit numbers usually assigned tubes for mil or industrial use..OPCOM OEI says the equivalent 4 digit # is 6135..my cross index list I've relied on for a long time says 6100..actually for 6135 it's equivalent is listed as a 6C5..they are kinda similar but slightly different basing..I really want to be accurate including this cross reference list so what is the answer?
             By the way Ed there is no known sub that I'm aware of for 6C4..with the exception of a 6C4WA..not lookin' to create trouble here.."just the facts sir..just the facts"..was gonna use my 6100 NOS tube but I'll hold off   tnx 73 de DAVE
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AMer livin in "Moose Country"
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« Reply #5 on: September 05, 2014, 03:16:58 PM »

Dave,

Every reference I have seen lists both the 6100 and 6135 as industrial/high reliability alternative identifiers for the 6C4.  I believe that GE started the 6135 type but I am not sure who first produced the 6100, probably RCA.  In any case both should be suitable substitutes.  Where you do have to be careful is in many cases there are European tubes, often preceded by a 2 letter prefix, that are totally different from a U.S. tube with the same 4 digit industrial identifier and to add to this U.S. manufacturers sometimes appended a 2 letter prefix to indicate manufacturer such as the GL-6135 (GE) and the CK-6100 (Raytheon).
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Rodger WQ9E
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« Reply #6 on: September 05, 2014, 03:53:22 PM »


The 6C4 is a neat tube. It can be thought of as a 12AU7 hack sawed in half with a 7 pin base. It has class C ratings making it a nice power oscillator well into VHF. The 6J6 dual triode with common cathode is also a neat tube that can make several watts RF out as an oscillator.

Years ago Texas Instruments had a line of high voltage JFETS. These were depletion mode devices that biased up like a triode. One such device is the 2N6449. This transistor within its ratings is somewhat similar to a 6C4. I have used several of these over the years with good sucess. A simple low level class A audio amplifier with a B+ of 300 volts can provide in excess of +/- 100 volts peak output.

The 2N6449 does still live, and is made by Interfet.

http://www.interfet.com/datasheet/2N6449/

I use a few of these today in high voltage regulators where I wanted constant current feed to a high voltage zener diode. The 2N6449 makes a nice CCS for this need (IDSS 2-10 ma).

I would imagine a 2N6449 could replace the versatile 6C4 in a few applications where the transistor device parameters are not exceeded.

Supertex also has a line of HV JFETS.

Jim
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K9PNP
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« Reply #7 on: September 05, 2014, 07:03:13 PM »

Ed,

With Hammarlund receivers it seems to be a crap shoot. 

That about says it all.  I have a NOS JAN 6C4 in the HQ-170 and it works fine; will not work well in the HQ-110A.

The manual for the HQ-110A, in the "suggested procedure for eliminating common problems" section states in para 3: "Excessive oscillator drift which would be most noticeable on all of the high frequency bands plus a microphonic condition is usually the result of a poor type 6C4 high frequency oscillator or V10 in the schematic diagram.  This tube is also capable of producing a poor beat note that may have a ripple in it, especially noticeable on the high frequency bands."
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73,  Mitch

Since 1958. There still is nothing like tubes to keep your coffee warm in the shack.

Vulcan Theory of Troubleshooting:  Once you have eliminated the impossible, whatever remains, however improbable, must be the truth.
Ed WA4NJY
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« Reply #8 on: September 05, 2014, 07:55:59 PM »


  Thanks to all for the input.  I wonder if other radios use the 6C4 with less problems.

   73, Ed
   
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« Reply #9 on: September 05, 2014, 10:04:13 PM »

The R390A also suffers from the 6C4 syndrome. It uses three of them in the mixers and hand selecting can pay off. The noise and gain varies wildly. How can such a simple tube be so hard to build consistently? Well now you know why electron coupled 6BA6 oscillators are so popular. They are about bulletproof.
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These are the good old days of AM
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