[Boatanchors] 6146 question

[Paul Christensen]

Back in 1973, I had horrid results when changing from 6146A to a 6146B tubes in a Heath HW-101.   With the B tubes, I couldn't neutralize the PA and get stable 15m and 10m performance.  On those bands, the transmitter would "take off" as the mic gain/carrier control was advanced while simultaneously producing a high pitch screech from the PA.   I tried multiple sets of B tubes and had identical results.  Switching to a new set of A tubes solved the problem.  Back then, a pair of 6146 tubes from our local wholesaler was about $10.  As I recall, Heath published a service bulletin with a warning to only use 6146A tubes.

Given this experience, there's no way I'd consider all versions as universally interchangeable.  Possibly better results would have been attained with a slightly larger variable neutralizing cap value but that's not something I would have considered at age 13.  That said, I believe there's value in the work reported by K9STH and K9AXN.  

Paul, W9AC        

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> On Behalf Of Jeff Blaine
Sent: Sunday, January 28, 2024 9:03 PM
To: boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] 6146 question

I would not say that the 'B can be swapped for the 'A in all cases.