The 6146B Story – Fact & Opinion

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.
Glen, K9STH       Website: http://k9sth.com
 
 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, K9STH         Website: http://k9sth.com
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
 
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5 thoughts on “The 6146B Story – Fact & Opinion

  1. Dear AB1VL,
    thank you for publishing all these useful info; am asking for yr help re. following:
    -I recently bought 2 matched pairs of Siemens QE05/40 from http://www.tubes.rs, quite cheap, I would say, but
    some friends and yr news possibly got me stuck in the “confusion corner”, hi hi !
    Yr comments clearly state that 6146 and “b” are not the same tube, I presently have to replace pa tubes in a TS520S and an FT-101 ZD and would like to store a matched trio of “b” for my new FT-102.
    TS520s handbook clearly says (thanx God) that no matched pair is necessary, whereas neutralization is enough.
    The confusion really started this morning when a friend suggested the idea that QE05/40 Siemens is equivalent to 6146 and not “b”…. Please lighten my foggy day… with many thanx in advance and
    best ’73
    Fabrizio
    I-VE611
    (in the wonderful Dolomites)

    • Thanks for your post. I don’t have knowledge of the QE05/40 so I cannot comment on that tube. My information is based on correspondence with Glen Zook, which I have quoted after his review. Perhaps he can help if you have further questions. However, I can say that when I replaced a mixture of A and B types with all B types, in my TS-530S, there was no apparent difference in the basic transmit operation of the rig. I still get good signal reports on SSB regardless of which tubes I use. I did not have the instrumentation required to probe the signal path and discover any real (but probably subtle) differences, however.

      After reading many often-contradictory discussions on the topic I decided Glen Zook’s recommendations were the most succinct and posted them for others to review. That is, his point was to debunk a lot of internet lore and highlight the fact that there was a change to US military specifications that might go undetected if one were not careful to verify manufacturing dates and markings. I also concluded that “matched” tubes would probably NOT stay that way for very long in a practical use, so it was not worth it to me to resolve it any further. Please let me know how your experiments with the QE05/40 tubes go.

      73, chuck AB1VL

    • I should add that matched pairs or quads will usually not be matched the same after two or three weeks of actual use anyway, but it helps to have them at least matched within 10%-20% for transconductance, plate current, and grid emissions, when you start. The closer the better! Eventually they will usually kind of settle into what works, and good tube, when not ask to operate too far beyond design specs should give a nice long service life. Modern production tubes will only provide “maybe 25%” the service life of the older USA/UK & Western European made tubes. I am using a Shuguang 8877 in one linear amp, and a used Eimac 8877 in another, two Salt Lake City Varian 3-500Z Eimacs, in another Amp Supply Lk500ZC linear, & 3 in another LK550ZC, and 3 Shuguangs 3-500ZG graphite plate 3-500Z “G” for graphite in my home brew. The tubes in my Heathkit, & Kenwood amps are RCA 6146Bs. One pair is old date code A specs, so the amp would neutralize. Some modifications to the amp & now it will use either one. The HW101 sold very well, and is a simple but tried & true design with many modifications. 6146 & 6146B are NOT the same tube. The HW101 calls for straight 6146s but mine came with 8298s in it. I changed some components in the rig, so it can use either one now. The power supply was also modified for selectable low voltage “different bias voltages”.

    • A “bit” late to the topic but maybe someone else reading this will find it useful.
      QE05/40 is identical to 6146B. I have 2 of those (Siemens) in my FT-901 and I have no issues.
      I believe those tubes you got are from the same source as mine (military surplus) although I got them from a different retailer here in Serbia (and also got a “local” price 🙂
      73 from YT3ART

      Thanks for your input.

  2. On the obverse, a 6146B will not neutralize in some of the transmitters that use 6146As without some modifications. I am running 8298s in an old Heathkit HW101, and 6 Ampeg SVT public address amplifiers which through their popularity with bass players morphed into the later SVT Classic & Heritage bass guitar amplifiers. Ampeg dumped the 6146B for the 6550, and the SVT dropped from 360 watts to 300. Telefunken was developing an incredible tube in response to the 6146B/6146W, but it never went beyond a few very rare prototype engineering samples. I have modified Tektronix 576 and 371B curve tracers & a Triplett 3444A, so I can match just about anything in the audio & amateur radio realm, as far as tubes and transistors. True 6146Bs or 6146W will generally not match each other or with a 6146 or 6146A. The, at the time, inexpensive sweep tubes used in transmitters & transceivers, mostly made in Japan, were powerful, but usually quite far from being anywhere close to linear. The 6146 variants were good dependable tubes, and I am still using them in the old Heathkit HW-101, to power a pair or trio of 3-500Zs, or an 8877, in various linear amps, from 1980s designs, whether bought or built by myself. 73s, KI7AQJ.

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