differences in 6146 A and B

[Larry Knapp]

Craig - Interesting.  I am not totally sure exactly when the 6146B came on the
scene...based on your response from the Heathkit service bulletins it appears
somewhere around 79....but probably earlier....I know from talking with some
Heath engineers that they had problems with tubes other than RCA primarily in
VHF work (SB-110's for example) but in other applications as well, as the tube
manufacturers were not always "consistent"....that's why they specified RCA.
This is a fact.

Tho many say not, almost any 6146 (be it the 6146, 6146A, 6146W or 6146B) can
be used successfully in SSB, CW or AM service provided that you do not mix
types.  That is, most finals (say the HW-101 for example) use two 6146 type
tubes.  Don't mix a 6146B and a 6146A...keep them the same.  I am currently
using some 6146B's in AM service which some may say that's not a good
idea...but so far they work fine (and have performed great for several
years)....I have a total of nine 6146's in various configurations in my
boatanchor rigs but I never mix types.  That seems to be a general concensus.

I don't know if Heathkit made circuit changes to the production runs of the SB
& HW gear to accomodate the 6146B's...may have, just do not know.  There are
different characteristics among all the different types of 6146's...that's why
you should never mix types together.  An ARRL handbook or a good tube book
shows those differences (subtle but different).  Hope this clarifies some.

73, Larry, KC8JX

--- K4IA at aol.com wrote:
> To further complicate matters:
>
> Two 1978 Heathkit service bulletins say that the HW-101 should only use 6146A
>
> tubes to prevent neutralization problems on 10 and 15.  HW-101-18 and 39.
> Then bulletin HW-101-49 (May 1979) says 6146As are no longer available from
> the manufacturer and future productions should use the 6146Bs
>
> Bulletin SB-102-3 (March 73) suggests using only RCA brand 6146 tubes to
> prevent low grid drive problems.  No mention of A or B types being acceptable
>
> or unacceptable.  My assembly SB-102 manual calls for 6146 tubes.
>
> I suspect that after 1979 Heathkit made a change to the circuit to
> accommodate the 6146B but I have no idea what they did or when that comes
> into play with the SB-102 model run.  Maybe one of the history gurus can
> answer that question.
>
> There must be some subtle differences going on (at least in the older
> Heathkits).  I think I read somewhere the inter element capacitances were
> different but I can't find it now.
>
> Radio K4IA
> Craig Buck
> Fredericksburg, Virginia USA
> QRP ARCI #2550  FISTS #6702 CC 788
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=====
May your days be full of sunshine and good thoughts fill your head.
From: Larry Knapp, KC8JX, St. Joseph, Mi  49085
  Best 73's

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