[Hallicrafters] SX-32 audio amp question.

[Richard Knoppow]

     Let me clarify, the tubes need only a rough match, they should not 
be radically different but any two tubes in reasonable condition should 
match well enough.
     There are circumstances where a close match is necessary, for 
instance in a Class B amplifier but not in Class A or AB1 amps. If you 
want absolutely minimum distortion you must match everything, resistors, 
capacitors, tubes, transformer windings, etc. Not needed here. The SX-32 
is an interesting receiver. Evidently a cost reduced version of the 
SX-28 but with nearly equal performance.

On 11/8/2015 8:14 PM, Richard Knoppow wrote:
> Unless the tubes are very different they do not need to be matched.  
> The amp in the SX-32 runs AB1, very nearly Class A. Also, the cathode 
> resistor is unbypassed so there is a little feedback which tends to 
> compensate for any distortion from unbalance.  Its worth checking the 
> values of the resistors in the audio circuit to make sure they are 
> close to the right values.  If you want to be fussy you can check the 
> tubes for similar mu on a tube checker but exact match is not necessary.
>
> On 11/8/2015 9:38 AM, Karel J wrote:
>> Hi, writing this on my phone from the ladies clothing store. Please 
>> forgive
>> crappy formatting.
>>
>> I moved fairly recently and have been working to get my hamshack up and
>> running.
>>
>> My sx-32 needed some minor repairs and alignment. No problem, but I 
>> noticed
>> one of the 6V6 tubes was not lit.
>>
>> The other was quite hot, and audio sounded OK. I slapped in a 
>> replacement,
>> and the radio is again happy.
>>
>> Since these are two 6V6 in push-pull, do I need to worry about matched
>> tubes? They were the same brand, which leads me to think they may 
>> have been
>> a matched pair.
>>
>> Getting on fleabay shows me a few options for tubes. Normally, I buy 
>> NOS or
>> good tested tubes from hamfests or a place in Vancouver. Anyway, I am
>> seeing these *new* tung-sol branded tubes.
>>
>> Back from a few years ago, you could still get Svetlana 12ax7s (the 
>> winged
>> c logo, I think) and they were great quality.
>>
>> So, should I bother worrying about matched tubes? If so, new or verified
>> used? Or NOS?
>>
>> Thanks everyone.
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>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL