[Heathkit] [Heath] 6146B Issues

Mon Oct 14 14:30:02 EDT 2013

The Japanese rigs were designed to use the 2001A which is the same tube as the 6146B/8298A.  As such, no problems at all.

I have run into problems with the Heath HW-100, HW-101, SB-100, SB-101, SB-102, SB-110A, DX-100, TX-1 Apache, VHF-1 Seneca, Hallicrafters HT-32, HT-37, B&W 5100, and a number of other rigs.  Again, not every transmitter was unhappy with the 6146B/8298A.  However, the majority of those transmitters were definitely unhappy.

As for the Collins S-Line and KWM-2- series:  In late 1965 or early 1966, Collins did change the neutralization circuit so that the 6146B/8298A and the "new" 6146W tubes could be used.  The easiest way to tell if the transmitter can use the 6146B/8298A is to look at the neutralization capacitor inside the final amplifier cage.  If it is an air variable, then the neutralization is the "new" type and the 6146B/8298A can be used without any problems.  If the neutralization capacitor is a ceramic trimmer, then there is well over a 95% chance that the neutralization capacitor will "burn up"!

All Collins 32S-1, 32S-2, and the earlier 32S-3, 32S-3A, KWM-2, and KWM-2A units were manufactured with the ceramic trimmer neutralization capacitor.  Collins did come out with a field modification kit for the military to change the neutralization circuit in the units that were already in the field as well as changing all units that were in production to the "new" circuit.  Any Collins transmitter manufactured after early 1966 will have the "new" neutralization circuit as well as those units which have been modified.

The commercial FM two-way equipment that was designed for the earlier tubes definitely has problems with the newer tubes.  Remember, those transmitters were manufactured with a fixed neutralization circuit and that circuit could not be modified because of "type acceptance".  Of course, for those units that were adapted to amateur radio use, the circuits could be modified without any problems.  It was just for those used in commercial applications that could not be modified.  I have definitely run into serious problems with commercial equipment that was designed for the earlier tubes and in which the later tubes were installed.

As for the transmitters designed with a single 6146:  A goodly number of those, like the Heath DX-35 and DX-40, were designed not to be neutralized by "loading down" the grid of the 6146.  The result was that the final amplifier tube is much less likely to "take off" and, as such, they did not have a separate neutralization circuit.  Most of those transmitters seem to work fine with the 6146B/8298A.

I "point out" in the article on the 6146 family of tubes, that the 6146B/8298A can be tried in the transmitter.  If the tubes can be neutralized, and if that neutralization "holds", then using the tubes is fine.  But, if the tubes cannot be neutralized, then, unless one is willing to modify the neutralization circuit, it is best to go back to the 6146, 6146A/8298, or 6293 tubes.  It all comes down to "plug and play".  If the transmitter is unhappy with the 6146B/8298A, and, if the person is not willing or able to modify the unit, then it is best to go back to the earlier tubes.

If the person is willing or able to do what is necessary to use the later tubes, then there is absolutely nothing wrong with using them!

For example, the original Heath DX-100 does not have a neutralization circuit.  A neutralization circuit such as used in the Heath TX-1 Apache can be added with only a moderate effort.  If the transmitter's owner is willing to make this modification, then it is much easier to use the 6146B/8298A.  If the owner doesn't want to make the modification, then I certainly recommend using the earlier tubes.

As I keep saying, I definitely believe that some people have had absolutely no problems using the 6146B/8298A in transmitters designed for the earlier tubes.  But, there are even more people that have had problems.

There are those who criticize the designers of the transmitters that tend to be unhappy with the later tubes because of the problems.  However, one has to remember that the quirks of the 6146B/8298A were unknown when the design took place.  As such, since the differences were not known, the designers had no way of anticipating the differences and could not design the circuits to compensate for the later tubes.

Glen, K9STH

Website:  http://k9sth.com

On Monday, October 14, 2013 12:42 PM, Glen Zook <gzook at yahoo.com> wrote:

I never said that the 6146B/8298A cannot be made to work in all rigs.  What I do say is that those tubes are problematic in many transmitters and, as such, using them is not always "plug and play"!

I also said that there are those who have had absolutely no problems using the 6146B/8298A in transmitters designed for the 6146 and 6146A/8298.  However, there are plenty of examples where using the later tubes have caused problems.  

I also agree that the "numbers" on the 6146B/8298A are basically the same as the earlier versions.  However, the 6146B/8298A tubes are harder to neutralize in many situations.  Why that?  I have no idea!

I have, somewhere in my files, a letter from RCA acknowledging the fact that the later tubes are not suitable for use in commercial FM two-way transmitters that were designed for the earlier tubes because of the neutralization.

Glen, K9STH

Website:  http://k9sth.com

On Monday, October 14, 2013 10:50 AM, L L bahr <pulsarxp at embarqmail.com> wrote:

You know, Pete, I have been saying this for years.  However, as soon as you state there is no problem, here comes the famous 6146 again .  The problems stated in this paper have to do with Motorola VHF/UHF equipment and the fact Collins changed their inadequate neutralization capacitor which really had nothing to do with changing over to 6146B tubes.  If you look at the published RCA spec sheet, you will see the differences between both type tubes is extremely minimal.  (I think maybe RCA knows what they are talking about since they invented both the 6146A and 6146B type tubes and also state they are interchangeable.  Then you hear RCA retracted this statement.  However if you ask the person who says they retracted the statement for a copy of the RCA retraction, NONE IS EVER PRODUCED!)  There is no way a ham HF rig will have a problem stemming from moving over to 6146B tubes. If they have a problem, it is because of some other rig problem in the
rig and not caused by using 61
46B tubes.  So let the lemmings believe their myth.  Both you and I know the truth about this subject.

Lee, w0vt

----- 

I've never run across any of the rigs that I've owned over the last 50
years where 6146B's would not work in place of 6146's and A's and that
includes Heathkit (my original Apache has been running 6146B's since the
70's), Hallicrafters, B&W, Johnson, Kenwood, and others. I won't refute
Glen's original findings (obviously he had a problem with them back then)
but for anyone to say they won't work in all rigs as a replacement is
highly exaggerated. 

Pete, wa2cwa

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