[Heathkit] DX-100B on Phone - bad audio distortion / oscillation

[Glen Zook]

What tubes are you running in the final?  Many DX-100 series transmitters definitely do NOT like 6146B/8298A tubes  If you are running 6146B/8298A then try plain" 6146, 6146A/8298, or 6293.  You can mix a 6146 with a 6146A/8298.  But, mixing a 6146 or 6146A/8298 with a 6146B/8298A is just asking for trouble.

If you haven't read the article on the 6146 family of tubes that has been published in several amateur radio publications then go to:

http://k9sth.com/uploads/The_6146_Family_of_Tubes_1.pdf


Neither the DX-100 or the DX-100B has provisions for neutralizing the final amplifier.  A relatively few persons have added neutralization like the circuit in the TX-1 Apache.  Almost always, with the 6146, 6146A/8298, and 6293 there is no need for neutralization.  But, if using the 6146B/8298A neutralization virtually always has to be added.

I know that there are those who have used the 6146B/8298A in transmitters designed for the 6146 or the 6146A/8298 without any problems.  I do believe them.  However, there are a whole lot more transmitters designed for the earlier tubes that are unhappy with the 6146B/8298A than those that work with them, especially unmodified transmitters.  I have worked on the exact same model transmitters, with serial numbers within 10 of each other, 1 of which worked fine with 6146B/8298A tubes and the other 2 were very unhappy with the 6146B/8298A.

By the way, any 6146W with a code date starting in 1965 (some with a code date after mid 1964) are 6146B/8298A equivalents and therefore the same cautions apply to the 6146W unless the code date is before mid 1964.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: Rick Poole <wa1rkt at arrl.net>
To: heathkit at mailman.qth.net 
Sent: Thursday, December 1, 2011 6:13 PM
Subject: Re: [Heathkit] DX-100B on Phone - bad audio distortion / oscillation
 
At 06:55 PM 12/1/2011, Garey Barrell wrote:

>>>>>
>No, it won't hurt anything to reverse them.  Again I don't recall 
>much from the DX-100 schematic, but if is has any audio feedback 
>circuitry reversing the phase of the transformer can cause the audio 
>to oscillate, or not.
<<<<<

Thanks, Garey.  I don't see anything that resembles audio 
feedback.  Anyway, I tried reversing the caps and if anything it made 
the problem worse.  Oh well, back to the drawing board...


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