[Heathkit] 6146Bs

[Glen Zook]

Nope!  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


________________________________
 From: Charles Yahrling <cfytech24x7 at gmail.com>
To: heathkit at mailman.qth.net 
Sent: Friday, March 22, 2013 11:56 AM
Subject: [Heathkit] 6146Bs
 
Not much on the web. I'd like to get a new, matched pair found a ham
in England with a set (intl shipping and possible tariff might be a
killer) and another stateside outfit that has no contact info, so I'm
reluctant to take a risk.  Both sets were in the 80-$100 range for two
tubes, plus shipping.

If you find an hw100 with tubes you might be in luck - it used 6146Bs.