Re: [Drakelist] AC-4R Surprise
True. I've seen 3-500Z's die that way, too, but that failure is usually a lot more exciting! You won't find a short with the ohmmeter, but you'll get a nice bang when you put the 3kV to the plate :) Steve, W1ES/4 -Original Message- From: Garey Barrell k4...@mindspring.com Sent: Dec 21, 2011 10:11 PM To: Steve Wedge w1es1...@earthlink.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Steve - Extremely high gain tubes mean extremely closely spaced grids! :-) -- 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: If you can find a tube tester, test it. I find that 6HS6's get shorts more than most other tubes. They won't show up until you light the filament. My TV-10-D/U puts line voltage on the pins to check for shorts (to light a neon bulb), so you wouldn't necessarily see a short with no power to it. Not sure why I see so many: if it's something in the design or just because many people when they find these tubes are on the way out try to milk them for as long as they can because they're so expensive. From: rhule...@comcast.net Sent: Wednesday, December 21, 2011 8:54 PM To: Drakelist@zerobeat.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
Does the glass envelope actually break? 73, Lee -Original Message- From: Steve Wedge w1es1...@earthlink.net To: k4oah k4...@mindspring.com Cc: Drakelist Drakelist@zerobeat.net Sent: Thu, Dec 22, 2011 8:42 am Subject: Re: [Drakelist] AC-4R Surprise True. I've seen 3-500Z's die that way, too, but that failure is usually a lot more exciting! You won't find a short with the ohmmeter, but you'll get a nice bang when you put the 3kV to the plate :) Steve, W1ES/4 -Original Message- From: Garey Barrell k4...@mindspring.com Sent: Dec 21, 2011 10:11 PM To: Steve Wedge w1es1...@earthlink.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Steve - Extremely high gain tubes mean extremely closely spaced grids! :-) -- 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: If you can find a tube tester, test it. I find that 6HS6's get shorts more than most other tubes. They won't show up until you light the filament. My TV-10-D/U puts line voltage on the pins to check for shorts (to light a neon bulb), so you wouldn't necessarily see a short with no power to it. Not sure why I see so many: if it's something in the design or just because many people when they find these tubes are on the way out try to milk them for as long as they can because they're so expensive. From: rhule...@comcast.net Sent: Wednesday, December 21, 2011 8:54 PM To: Drakelist@zerobeat.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
No, but all such failures I'd seen were in Heathkit SB-220's. When the short occurs, it causes immediate and catastrophic flameage of the grid RF choke. Because those chokes usually have some sort of waxy coating, they make nice candles :) The smoke will fill the room quickly. -Original Message- From: kc9...@aol.com Sent: Dec 22, 2011 11:49 AM To: w1es1...@earthlink.net, k4...@mindspring.com Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Does the glass envelope actually break? 73, Lee -Original Message- From: Steve Wedge w1es1...@earthlink.net To: k4oah k4...@mindspring.com Cc: Drakelist Drakelist@zerobeat.net Sent: Thu, Dec 22, 2011 8:42 am Subject: Re: [Drakelist] AC-4R Surprise True. I've seen 3-500Z's die that way, too, but that failure is usually a lot more exciting! You won't find a short with the ohmmeter, but you'll get a nice bang when you put the 3kV to the plate :) Steve, W1ES/4 -Original Message- From: Garey Barrell k4...@mindspring.com Sent: Dec 21, 2011 10:11 PM To: Steve Wedge w1es1...@earthlink.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Steve - Extremely high gain tubes mean extremely closely spaced grids! :-) -- 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: If you can find a tube tester, test it. I find that 6HS6's get shorts more than most other tubes. They won't show up until you light the filament. My TV-10-D/U puts line voltage on the pins to check for shorts (to light a neon bulb), so you wouldn't necessarily see a short with no power to it. Not sure why I see so many: if it's something in the design or just because many people when they find these tubes are on the way out try to milk them for as long as they can because they're so expensive. From: rhule...@comcast.net Sent: Wednesday, December 21, 2011 8:54 PM To: Drakelist@zerobeat.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
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 ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
I still believe that R61 and the AC-4 were both victims of the same failure. And I still would not trust that 6HS6. Did you recheck the resistances with the 6HS6 removed? 73, Bob WW3QB 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 ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
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 vswitches biasshunt scale buttonmin reading 6HS66.3 JR3-567212 --- D P3 3000 6AU66.3 JR3-567210 --- 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 ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
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 vswitches biasshunt scale buttonmin reading 6HS66.3 JR3-567212 --- D P3 3000 6AU66.3 JR3-567210 --- 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 ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
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 vswitches biasshunt scale buttonmin reading
6HS66.3 JR3-567212 --- D P3 3000
6AU66.3 JR3-567210 --- 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 Wedgew1es1...@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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Re: [Drakelist] AC-4R Surprise
I've checked all of the tubes with my old emission tester, all test good except for the OA2 which lights up but tests bad. Not sure how valid that is. And with V8 removed, the resistance at pin 6 is still 15k rather than 90k per the manual. I'm in process of resistance checking the rest of the tubes. Sorry for the stream of consciousness dialog about this, I'll let all know if the cause of resistors opening in the power supply and shorting in the rig is ever found. 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
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 vswitches biasshunt scale buttonmin
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 Wedgew1es1...@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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Re: [Drakelist] AC-4R Surprise
Curt - The 0A2 is always difficult to test, as most inexpensive testers don't have enough high voltage DC to fire. As I said earlier, I think you have a problem with your Pin 6 of V8 resistance measurement. There is a 6.8k and 6k resistor in series between that pin and the +250 bus. Depending upon ohmmeter polarity, you have either an electrolytic cap or a diode to ground at that point. I rarely use the resistance charts, as they are just too reliable on what meter was used to derive them. When a resistance check is off, do a reality check by looking at the DC path.. -- 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 rhule...@comcast.net wrote: I've checked all of the tubes with my old emission tester, all test good except for the OA2 which lights up but tests bad. Not sure how valid that is. And with V8 removed, the resistance at pin 6 is still 15k rather than 90k per the manual. I'm in process of resistance checking the rest of the tubes. Sorry for the stream of consciousness dialog about this, I'll let all know if the cause of resistors opening in the power supply and shorting in the rig is ever found. 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
Hello Gary, Yes, that is what I've concluded too though haven't confirmed with measurements yet. I know at one time you repaired Drake equipment (maybe you still do), so would appreciate any words of wisdom about finding and correcting a short in the B+. Nothing obvious on visible inspection, seems finding a short in the B+ will likely be nearly impossible, a lot of area to cover. Maybe need to inquire whether anyone needs a parts rig. It's a shame, the cosmetics and until now the performance of this T-4X has been pretty nice. Thanks in advance, 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
Curt, before you throw in the towel, have you tried pulling all the non-final tubes to be sure it's not an internal short in one of them? It's exceedingly rare in receiving tubes but not impossible if something came loose internally. To break up the problem into manageable chunks (assuming the tubes are okay), follow the B+ line and unhook it half-way from the source and re-check. Continue splitting the bad side 'til you get there. Hard shorts are blessings: they generally stay around until you find them! 73, Steve, W1ES/4 -Original Message- From: rhule...@comcast.net Sent: Dec 21, 2011 8:17 AM To: Gary Poland gpola...@cinci.rr.com Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Hello Gary, Yes, that is what I've concluded too though haven't confirmed with measurements yet. I know at one time you repaired Drake equipment (maybe you still do), so would appreciate any words of wisdom about finding and correcting a short in the B+. Nothing obvious on visible inspection, seems finding a short in the B+ will likely be nearly impossible, a lot of area to cover. Maybe need to inquire whether anyone needs a parts rig. It's a shame, the cosmetics and until now the performance of this T-4X has been pretty nice. Thanks in advance, 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
A good first step is use the resistance chart in the manual for the tube sockets. I would also check the relay. 73, Bob WW3QB Curt, before you throw in the towel, have you tried pulling all the non-final tubes to be sure it's not an internal short in one of them? It's exceedingly rare in receiving tubes but not impossible if something came loose internally. To break up the problem into manageable chunks (assuming the tubes are okay), follow the B+ line and unhook it half-way from the source and re-check. Continue splitting the bad side 'til you get there. Hard shorts are blessings: they generally stay around until you find them! 73, Steve, W1ES/4 -Original Message- From: rhule...@comcast.net Sent: Dec 21, 2011 8:17 AM To: Gary Poland gpola...@cinci.rr.com Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Hello Gary, Yes, that is what I've concluded too though haven't confirmed with measurements yet. I know at one time you repaired Drake equipment (maybe you still do), so would appreciate any words of wisdom about finding and correcting a short in the B+. Nothing obvious on visible inspection, seems finding a short in the B+ will likely be nearly impossible, a lot of area to cover. Maybe need to inquire whether anyone needs a parts rig. It's a shame, the cosmetics and until now the performance of this T-4X has been pretty nice. Thanks in advance, 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
It's interesting that the pin 6 resistance to ground is so low since it passes through a 82K resistor. Do the values change if you remove V8? I sense a tube short. 73, Bob WW3QB Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
If you can find a tube tester, test it. I find that 6HS6's get shorts more than most other tubes. They won't show up until you light the filament. My TV-10-D/U puts line voltage on the pins to check for shorts (to light a neon bulb), so you wouldn't necessarily see a short with no power to it. Not sure why I see so many: if it's something in the design or just because many people when they find these tubes are on the way out try to milk them for as long as they can because they're so expensive. Typical eBay prices for them are around $30 but you should be able to find a local provider who will sell them for $15 each or so. Sometimes I get lucky and find them in $2/each assorted tubes boxes :) Funny to see a resistor fail shorted. Not typical. Congrats on your find! 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: rhule...@comcast.net Sent: Wednesday, December 21, 2011 8:54 PM To: Drakelist@zerobeat.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
Curt - If this is a 'new' transmitter to you, the most likely cause of a crispy R61 is that someone shorted one of the trimmer caps in the PreSelector plate circuit to the chassis. Easy to do, especially when guys use a metal screwdriver to adjust those trimmers through those little holes. Only takes a momentary short to do it! R21 and R26 are also subject to this problem! Of course a Plate / Suppressor short will also do it, but those don't usually 'clear' after a failure. -- 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 rhule...@comcast.net wrote: Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
Steve - Extremely high gain tubes mean extremely closely spaced grids! :-) -- 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: If you can find a tube tester, test it. I find that 6HS6's get shorts more than most other tubes. They won't show up until you light the filament. My TV-10-D/U puts line voltage on the pins to check for shorts (to light a neon bulb), so you wouldn't necessarily see a short with no power to it. Not sure why I see so many: if it's something in the design or just because many people when they find these tubes are on the way out try to milk them for as long as they can because they're so expensive. From: rhule...@comcast.net Sent: Wednesday, December 21, 2011 8:54 PM To: Drakelist@zerobeat.net Cc: Drakelist@zerobeat.net Subject: Re: [Drakelist] AC-4R Surprise Well, my nose detected burnt smell in vicinity of T4. R61, a 150ohm 1/2 resistor in the 250 volt line to V8's plate is burnt to a crisp, resistance is zero. But why? Resistance to ground on V8 pin 5 is 15k per spec. But pin 6 screen grid resistance to ground it 15k, vs 90k spec. Any advice? 73, Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
A short in the B+ line within the T-4X will open the resistors. It used to happen a lot when people would change the blue filter in S meter of TR-4’s and pinch the wires reassembling the metal cover on the S meter. Look for a short in your T-4X. 73, Gary http://home.roadrunner.com/~w8pu R-4A T4-X R-4B T4-XB R-4C T4-XC MS-4 L-4B 2A 2B 2C 2NT 2CQ 2AS 4-LF TR-4 TR-4C TR-4CW/RIT RV-4C TR-7 RV-7 CW-75 MS-7 WH-7 W-4 WV-4 MN-2700 MN-4C MN-2000 UV-3 PS-3 PRN1000 TR-22C TR-33C AA-10 AC-10 MMK-22 TR-6___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC-4R Surprise
Curt, Does not surprise me...is it a supply that has had a full update (Heathkit shop or other)?? If not I would do that right now. Everything in there is getting old. 73, Lee -Original Message- From: rhulett1 rhule...@comcast.net To: Drakelist Drakelist@zerobeat.net Sent: Tue, Dec 20, 2011 8:25 pm Subject: [Drakelist] AC-4R Surprise My T-4X quit working today, the 250V supply was gone. Filament, bias, and 650V supply normal. On investigating the AC-4R board in the AC-4, found two parallel 5W 200ohm metal oxide resistors in the 250V supply circuit OPEN. Suspected a shorted capacitor, but the cap is not shorted. Anyone else experience similar behavior? 73 Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
