[Jukebox-list] Moron vacuum tube question.

[Don]

Hey Wes!
'ats right.
Injecting a sinusoidal waveform then checking the cathode and plate voltages 
is a good basic test for the 6L6's assuming no leaky coupling cap(s).
don

----- Original Message ----- 
From: "The Jukebox Junkyard" <jukeboxjunkyard at cox.net>
To: "Jukebox mailing list" <jukebox-list at lists.netlojix.com>
Sent: Thursday, April 12, 2007 7:20 AM
Subject: Re: [Jukebox-list] Moron vacuum tube question.


    Hi Don. A stupid simple way to test the output tubes is to check the 
cathode voltage of each tube individually. If it reads near the same for 
each, both tubes are OK. A leaky coupling capacitors will unbalance the 
circuit. It is best to replace the caps first. First a thermal check is in 
order. Wes
----- Original Message ----- 
From: "Don" <dontutt at telus.net>
To: "Jukebox mailing list" <jukebox-list at lists.netlojix.com>
Sent: Thursday, April 12, 2007 1:03 AM
Subject: Re: [Jukebox-list] Moron vacuum tube question.


> Hi Kyle,
>
> Hum....
> So.... how do you know the 6L6 is "dead"..... no filament glow?? (assuming
> its glass envelope)
>
> Without the schematic I will assume the two 6L6s are connected in a push
> pull circuit. If one of the two 6L6's is really dead the other should be
> able to drive one side of the primary and you will get "some" sound. 
> Again,
> without the schematic I risk a skate on thin ice here so maybe the folks
> with a schematic for your unit will correct me.   However, invariably when
> we see two 6L6's they are both "driving" or energizing the output
> transformer's primary winding and that winding, in such a situation is
> usually center-tapped with the center-tap connected to the B-plus high
> voltage supply.
>
> Given the truth of all this in your situation.... then.... if you have one
> dead 6L6..... what you might consider is installing two "new" 6L6 tubes of
> equal or almost equal strength. These would be called a "matched pair" and 
> I
> think Antique Electronics will sell you matched 6L6's..... for a 'bit' 
> more
> dough.   Theoretically these "same strength" tubes will drive the o/p xfmr
> primary symetrically, ergo you'll get the least distorted sound.
>
> On the other hand if you test the remaining good 6L6 and it washes up just
> fine as a good strong tube, then try to find a match for it.....  ie. a 
> 6L6
> that gives similar test results on the SAME tube tester.  I  do this 
> easily
> since I have a really good tube tester.
>
> Anyway, I hope this helps.
> Don
>
>
> ----- Original Message ----- 
> From: "Jackie" <etreble7 at verizon.net>
> To: "Jukebox mailing list" <jukebox-list at lists.netlojix.com>
> Sent: Wednesday, April 11, 2007 5:22 PM
> Subject: Re: [Jukebox-list] Moron vacuum tube question.
>
>
>> Kyle,
>> just kidding.............DON'T answer that, LOL
>> love ya,
>> Jackie
>>
>> ----- Original Message ----- 
>> From: "Mechanical Music of S.F." <mechanicalmusic at hotmail.com>
>> To: <jukebox-list at lists.netlojix.com>
>> Sent: Wednesday, April 11, 2007 8:14 PM
>> Subject: [Jukebox-list] Moron vacuum tube question.
>>
>>
>>>
>>> OK, in the G120 I just finished up, one of the two 6L6 tubes is dead.
>>> Juke still plays loud and (what I think is) pretty clear.
>>> What gives?  Are the pair some kind of oscillator or something?
>>>
>>> Have another one on the way....
>>>
>>>
>>> Kyle ~
>>> Mechanical Music of San Francisco
>>>
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