At 55, I still learn stuff. I consider that to be cool.
Garey, I'd be willing to bet you've worked on a lot more tube gear than I
have, so this will go into my mental filing cabinet as a failure mode. Caps
I've seen fail shorted; diodes and transistors, too.
Given what you've said about an overloaded resistor failing shorted, I'd
ditch the 6HS6 or at least set it aside until you can test it properly.
Again, I still maintain that we see even more failures of these than usual
because of previous owners milking them due to their high price. I've even
repaired one R-4B that had a 6AU6 subbed into V8. It was working, but I'd
bet under extreme conditions it would have made its presence known!
Curt, if you can't find a 6HS6 locally, you can sub a 6AU6 into V2 of the
R-4B temporarily so you can borrow the 6HS6 for the T-4X premixer. You'll
have reduced sensitivity. Let me know if you're still looking for a 6HS6
and I can call my local guy and he'll scare one up.
Steve Wedge, W1ES/4
I swear by my life, and my love of it, that I will never live for the sake
of another man, nor ask another man to live for mine.
-Ayn Rand.
All my computers have my signature with various pearls of wisdom appended
thereto.
--------------------------------------------------
From: "Garey Barrell" <k4...@mindspring.com>
Sent: Thursday, December 22, 2011 3:41 PM
To: "Steve Wedge" <w1es1...@earthlink.net>
Cc: <rhule...@comcast.net>; <Drakelist@zerobeat.net>; <kc9...@aol.com>
Subject: Re: [Drakelist] AC-4R Surprise
Steve -
The resistor in question is a 150 ohm decoupling resistor, not a plate
load resistor. It's not all that unusual for the low value carbon comps
to fail shorted. Enough current to melt the binder into a lump of coal
('tis the Season) rather than enough to just vaporize it! Also an
indication of 'some', not 'catastrophic' overload.
By the way, the reason for the wildly out of range Pin to chassis
resistance is sometimes a matter of ohmmeter polarity, need to check both
ways. The other problem is that Drake was not consistent in changing the
Resistance and Voltage charts to reflect schematic changes.
--
73, Garey - K4OAH
St Charles, IL
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Steve Wedge wrote:
I think Garey had mentioned you can fry the plate resistor on V8 if you
short one of the trimmer caps while tuning it.
It's still odd to me to have a resistor fail shorted.
The 6HS6 will have the same switch settings as a 6AU6 but it has quite a
bit more gain and a different bias setting.
TV-10 D/U settings are:
tube fil v switches bias shunt scale button min
reading
6HS6 6.3 JR3-5672 12 --- D P3 3000 6AU6 6.3 JR3-5672 10 --- D P3 2050
The 6HS6 has quite a bit more gain (these are minimum, and I remember
seeing 4200 from typical new ones).
Good luck.
Steve, W1ES/4
-----Original Message-----
From: rhule...@comcast.net
Sent: Dec 22, 2011 1:33 PM
To: Steve Wedge<w1es1...@earthlink.net>
Cc: Drakelist@zerobeat.net, kc9...@aol.com, k4...@mindspring.com
Subject: Re: [Drakelist] AC-4R Surprise
All,
Well my "luck" or lack thereof continues... I pulled the 6HS6 and then
referenced my Eico 625. Of course the 6HS6 isn't mentioned anywhere in
any of the charts I have. So, based on some results of a search, tested
it as a 6AU6 and then a 6HR6. Former showed "good", latter showed
"marginal", neither showed "short".
So, I guess r61 failed sometime in the past but not the cause of the
power supply going south. At least I don't need to try finding another
6HS6, my usual source for tubes shows 6HS6 "out of stock".
I'm certainly old enough to know better, but suppose will just keep
checking tubes as a start while I have the tester out of the cabinet and
on the desk.
73, Curt KB5JO
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