differences in 6146 A and B

[Craig Buck]

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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