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Old April 9th 12, 03:58 PM posted to
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Default Drake TR-4 questions

Thanks Bill! Every once in awhile I accidentally surprise myself

Good catch, Ernie.

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Old April 9th 12, 04:52 PM posted to
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Default Drake TR-4 questions

On Sun, 08 Apr 2012 07:45:57 -0500, Ernie wrote:

Problem found.

Actually two problems.

In addition to the atypical grid voltage readings on the IF tubes
leading me to suspect AVC involvement, R195 (68 ohms) that feeds the
cathodes of the IF tubes (V11 and V12) and is delivered to those tubes
from a jumper from V5 (6BA6) was open. Once replaced, I still had very
low voltage (1/2 volt) instead of 1.5 volt on the cathode. What else can
be left? The filament? Hey those things NEVER go bad, right? So I
checked the filament voltages and, while V12 was good (12.8 VAC), the
1st IF (6BZ6) was missing. Back and forth a hundred times checking the
little white wire from V5 that feeds the filaments too but it was good.
I look at the filament string on the schematic and there's a 0.005 uF
capacitor in parallel with the filament of V11 which was good. Here's
the very odd thing: Of course the filament for V11 uses only one side of
the leg of the filament string to develop its voltage BUT MY VOLTAGE
CHART SHOWS IT SHOULD BE 12.8 VAC. In addition, it is clearly
silk-screened on the chassis of V5, "12BA6." But yet the voltage chart
refers to V5 as a "6BA6." Figuring I'd better double check the 6BA6 or
12BA6 or whatever was in there I discovered it was a 12BA6 with its
lettering almost rubbed off. Voila. Exchanging the 12BA6 for a 6BA6
immediately returned my filament voltage on V11 to 6.3 VAC (so I notated
the correction on the manual's voltage chart), cathode voltage returned
to a healthy 1.5 VDC, S-meter easily zeroed and worked and finally

This transceiver was given to me by a gentleman who said the receiver
didn't work very well. I think I know why.

Thanks to Scott, Richard and Garey for your suggestions. They were all
good ones but I think Richard's crystal ball may have been closest when
he stated, "check the obvious."

I remember reading an article in Readers Digest or some other popular-
press magazine with a bunch of factoids about TV repair. One of the
things I remember reading is that 50% of service calls were at that time
(early 1970s) because the TV wasn't even plugged in.

Then I grew up to be an electronics engineer, and while you'd think I'd
have known better, I can't count the number of times I've had the back
off of a piece of electronics, or was getting ready to, before I
discovered that it just wasn't plugged in, or some switch had been
flipped, etc.

"Check the obvious" is good advise -- and advise that isn't always easy
to remember to follow!

My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software

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