"Bill Carpenter" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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I tested the tubes on my tube tester. I know this is not always conclusive
but the meter on the tester did not move at all on either tube.
----- Original Message -----
From: "Garey Barrell" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, January 01, 2008 11:31 AM
Subject: Re: [drakelist] T4B Trouble
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist
gang
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Bill -
OK. Those no load voltages are fine. I'd check the rest of the path to
the final grids. Perhaps a bad power cable or connector wiring / short?
Typical failure scenario you described is that the bias voltage fails,
causing the T/R relay to pull in, keying the transmitter (grounding the
final cathodes) and with no bias the tubes conduct as much as they or the
power supply or the cathode resistors can handle until one or the other
opens up.
Open cathode resistors are certainly a symptom of extreme overload of the
PA tubes. You say the finals were "bad". How did you determine that they
were "bad".
I guess I'm stubborn. I still say the bias supply failed, somewhere
between the AC line and the PA grids! :-)
My next guess is that the Cinch connector(s) have a problem, e.g., short
or open of the bias line. Possibly intermittent?
73, Garey - K4OAH
Glen Allen, VA
Bill Carpenter wrote:
"Bill Carpenter" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Power supply seems OK. Bias adjusts from -49 to -90 and voltages at 279
and 682. Both a little high but seem OK to me. Anything else I should
check before I try replacing the cathode resistors? Gotta wait to order
some anyway.
----- Original Message ----- From: "Garey Barrell" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, January 01, 2008 10:34 AM
Subject: Re: [drakelist] T4B Trouble
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist
gang
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Yep, that's it. It's adjustable to set the idle current for the finals.
No bias voltage = full plate current!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Bill Carpenter wrote:
"Bill Carpenter" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Thanks Gary, I'll look at the AC-4 though I replaced the electrolytics
a few years ago. Which pin is the bias measured on? It looks like pin
9 to me at -45 to -65 volts against pin 1 which is ground?
----- Original Message ----- From: "Garey Barrell"
<[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, January 01, 2008 9:46 AM
Subject: Re: [drakelist] T4B Trouble
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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Bill -
Sounds like you lost the bias supply in the AC-4, electrolytics and/or
rectifiers. There has been some discussion of this over the last few
weeks on here.
The AC-4R kit from The Heathkit Shop is the best answer for AC-4's
that still have their original electrolytics.
You got lucky in that the cathode resistors opened! Carbon comp
resistors are pretty hard to find. Best replacement is the Ohmite OX
ceramic composition resistor available from Mouser and others.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Bill Carpenter wrote:
"Bill Carpenter" <[EMAIL PROTECTED]> made an utterance to the drakelist
gang
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I was enjoying SKN last night on 40M with my Bline but decided to
switch to my K2/100 to use a more effective NB against bad powerline
noise that has popped up here recently. I left the Bline on and was
happily CWing away when the Bline kind of "blinked" so I turned it
off. Later I found no output at all so suspecting finals I checked
them and yes they were bad. I put good ones in and still no output.
There had been no noise, smoke or burned sound so I had not looked
under the finals. I did that this morning and found R32 and R33 (1
watt 15 Ohm) both burnt and testing very high or open. Obviously I
need to replace these but is there anything else I should check first
to see what may have caused this to happen?
Any help appreciated.
Happy New Year! 73
Bill
NZ0T
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