tubes age 179
in several stages. Pick from the tubes you have in hand the best one as rated
on signal to noise ratio. Put the best one forward in the circuit. Different tubes
from the same manufacture have whole ranges of signal to noise. I have new
tubes with very bad signal to noise. I have brought known pulls and used tubes
at swap meets and found some to be better than new tubes. Not all and not
everyone. But I cannot tell a good tube by looking at the item.
6C4 are not the only tube in this class. Every tube in the R390's come in the full
range of noise flavors. Every tube circuit in the receiver will benefit from tube
selection on the signal to noise test. Some circuits in the receiver (forward
circuits) provide a better place to test tubes than other circuits (back end) but
always rank all the tubes. Install the bet you have and place the best ones
forward.
If you do not own enough tubes to do signal to noise testing and own enough
good tubes so that you do not need to think about which circuit to place the
tubes into you do not own enough tubes. You will just have to listen to what you
own until you find some more good tubes. Real life is that you will likely buy
more bad tubes before you find more good tubes.
I have purchased brand new tubes that had more noise than the tubes I already
had. Going off to the store is no sure bet that you will come home with a better
tube. So a good many folks not knowing the variation of tubes from
manufactures, dates and batches have found a good tube marked as and a
bad tube marked as and just declared all tube marked as are not as good as
the other flavor. In fact is was just two random of 12 random tubes compared
and a declaration make. Another run from the same manufactures may have
completely different results.
Back in the 68 - 75 era I would get new JAN tubes out of supply and find bad
tubes. Likely if we found a new tube to be noisy, every thing we had in stock
would also be from the same production run and also bad. Life was hell then.
You just could not toss 20 tubes in the trash and ask for more. There was no
way to send them back.We had to find a circuit to use them in where we could
get enough good tubes around then to make the receiver pass minimum
acceptable tests. Other than 6DC6's you can like with a noisy tube type some
where in the receiver. Roger.
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Date: Sun, 23 Apr 2006 13:52:42 EDT
Subject: Re: [R-390] Re: 6C4? 6C4W? 6C4WA?
I like Tim's following points: All the 6C4's are used as mixers. <snip>
(14 pages)
(10 pages)
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