[Boatanchors] 6146 question

[Gary Schafer]

I learned from the same experience many years ago on a Collin’s 32S1.
I chased my tail around for weeks and finally tried increasing the neutralizing capacitance.

73
Gary K4FMX
Gary Schafer


> On Jan 28, 2024, at 9:17 PM, Paul Christensen <w9ac at arrl.net> wrote:
> 
> 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.
> 
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