[R-390] Re: 6C4? 6C4W? 6C4WA?

[Barry Hauser]

Roger ...

I seem to remember a thread some years ago about the 6C4  and it being best 
if the tube is not too "hot" -- as if a mediocre-reading (middling, not 
weak) tube was the better choice -- or one that had been worn in elsewhere. 
I don't recall if it got into s/n ratio or whatever.

Anybody else remember that one?

Barry

----- Original Message ----- 
From: <Flowertime01 at wmconnect.com>
To: <r-390 at mailman.qth.net>
Sent: Sunday, April 23, 2006 1:27 PM
Subject: Re: [R-390] Re: 6C4? 6C4W? 6C4WA?


> Glen,
>
> I have found any and all 6C4 of any variety that would test OK in a tube
> tester would
> work in and R390 or R390/A.
>
> But as you say "Of course, there are other factors to take into 
> consideration
> besides the tubes suffix.  Such as Manufacturer and Date of Manufacture, 
> etc.
> "
>
> Once you get past the tube works and you go on to signal to noise and
> receiver sensitive all bets from the tube tester results are off. I have 
> tubes with
> good high tube tester reading that are very noisy in the circuits of the
> receivers. Likewise a low reading is no clue to tube noise either. First 
> find tubes
> that test good in the tube tester as their is no reason to burn out R390
> resistors as a means of checking tubes for shorts. Then as higher reading 
> tubes in
> the tube tester are though to be better tubes, start subbing them into a
> circuit and measure the signal to noise. Start comparing the tubes you own 
> in the
> same circuit. Consider the signal to noise ratio. You can adjust the final
> receiver gain 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 know 
> pulls
> and used tubes at swap meets and found some to be better than new tubes. 
> Not
> all and not
> every one. 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.
>
>
> _____________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/faq.htm
> Post: mailto:R-390 at mailman.qth.net
> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>