The TS-530S uses two 6146B beam power tubes for final RF amplification. When I got mine I saw it had one 6146B and one 6146W, so I immediately started the search to find at least one, and preferably two NEW in box 6146B tubes. Someone suggested I get an electrically MATCHED SET of tubes, but my research leads me to believe that would be an unnecessary expense. Anyway, I want to present you with the information as I discovered it by probing around the net and asking Hams who seemed to be the most knowledgeable.
The long story presented in short form is:
1. In the 1964-1965 time frame the 6146B made its debut, and for a time some were marked 6146B but produced to 6146A specifications. Hence, there may be some old tubes out there that are mismarked and you should take pains to verify the production date of any 6146B you put in your rig.
2. Sometime during 1965, driven by updates to the federal procurement specs for military radios, 6146Bs and their 6146W milspec counterparts were produced to the later, higher power specifications.
3. The most important thing is not to mix a genuine 6146A with a genuine 6146B or 6146W. Later spec 6146Bs and 6146Ws can be mixed. My rig is proof of that, as are many others.
4. You may be able to use 6146As in a rig designed for 6146Bs but must run them at a significantly lower power to avoid condemning them to a short life. There may be some risk to equalization circuitry when using 6146B or 6146W tubes in rigs designed for earlier 6146 series tubes.
Here are the facts as I learned them from Glen Zook, who was commenting on tube choices for the Heath HW-100 transceiver. Note his comments about using “matched pair” tubes:
The Heath HW-10X series used 6146A/8298 tubes. Heath did have a special “run” of tubes marked 6146B/8298A made by General Electric that were, in fact, 6146A/8298 tubes. However, the kits in which those tubes were included had a warning NOT to use any other 6146B/8298A tubes.
Using a matched pair of 6146 tubes in a transmitter which has the final amplifier tubes running in parallel does nothing more than to increase the profit margin of the seller. When the tubes are used in push-pull, matching can make a difference. In most cases, after a few hours of operating the tubes in parallel, they are no longer “matched”. None of the manufacturers ever shipped units with “matched” 6146 family tubes.
Many transmitters designed for the 6146 or 6146A/8298 tubes are unhappy with the 6146B/8298A. In many of those transmitters the final amplifier will not neutralize without modifying the neutralization circuitry. As such, contrary to what RCA originally said about the 6146B/8298A (or 6146W tubes which any with a code date after around mid 1964), those tubes are not universally compatible with the earlier versions. RCA had to withdraw the universally compatible statement. Yes, if the neutralization circuitry is modified when difficulty is present, the 6146B/8298A and 6146W tubes can be used. But, as a “plug and play” option, one has to be very careful. That is why I don’t generally recommend using the later tubes in transmitters designed for the earlier versions. I know that there have been a number of operators that have had absolutely no problems using the later tubes and I also know of quite a few operators who have had all sorts of problems. I have run into situations where 3-transmitters, with serial numbers within 10 of each other, where 1-transmitter has been very happy with the later tubes and 2-transmitters have been very unhappy. I believe that the differences in the transmitters were due to component tolerances.
If one feels that they can handle any modifications to the neutralization circuitry necessary to use the 6146B/8298A and 6146W tubes, then they should not have any problem. But, if the operator is any bit “queasy” about modifying the neutralization circuitry if there are problems, then I definitely suggest going with 6146, 6146A/8298, or 6293 tubes. The 6293 is a version of the 6146A/8298 that was made for pulse modulators and have a plate dissipation (when used as pulse modulators) of 1000-watts. The 6293 makes an excellent replacement for the 6146 and 6146A/8298 and, when operated under the same operating conditions as those tubes, has a life span between 5 and 10-times of the original tubes.
I asked Glen for clarification on mixing 6146Ws with 6146Bs because I was concerned that my rig, though tuning and sounding OK, might be in jeopardy. Here is his response:
Since the 6146W and 6146B/8298A tubes are supposed to be the same, there is usually no problem mixing them. However, NEVER mix a 6146 or 6146A/8298 with a 6146B/8298A or 6146W. You can mix a 6146 with a 6146A/8298.
The Japanese transceivers usually came with 2001A tubes installed. Those are the same as the 6146B/8298A and 6146W. The Japanese 2001 tube is the same as the 6146A/8298 and should never be mixed with an 2001A.
Most rigs are neutralized on 10-meters which usually holds very well on lower frequencies. If the rig is neutralized on 10-meters, don’t worry about how the other bands tune!
Glen has an excellent site and an impressive resume, so I believe his information to be correct. I should add that it also jives with the FAQ information about 6146 series tubes in Ken, k4eaa’s, site at http://www.k4eaa.com/faq.htm