|
Hi Everone,
I've owned this amp about 5 years but used very little. The amp was refurbished (new tubes, and relays) by a guy in north Idaho about 2017, just before I bought it. I have tried to contact him but get no response.
A couple weeks ago in the middle of a QSO I sensed some unusual heat from the amp and noticed the tubes were both cherry red. I shut it down immediately.? I have tuned it up a couple times since and the symptoms reoccur. ? I am (obviously) not an amp guy or much of a technician so I have 2 questions.? 1.? Is this a symptom of something that might be easily confirmed and repaired by me, ? and if not ? 2.?? Is there anyone in the Portland-Seattle-Vancouver BC area I might take it to for repair?
Thanks for any help or ideas
John
W7SWB
Does
|
Sounds like one of the 3-500s has a grid to cathode short. Remove them one at a time to find the bad one be VERY CAREFUL the plate meter is at zero before you touch anything. HV KILLS! ? 73 Mike N2LYM ? ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of John Roland
Sent: Tuesday, November 28, 2023 5:44 PM
To: [email protected]
Subject: [ham-amplifiers] Need Help with Amp Supply LK500ZC ? Hi Everone,
I've owned this amp about 5 years but used very little. The amp was refurbished (new tubes, and relays) by a guy in north Idaho about 2017, just before I bought it. I have tried to contact him but get no response.
A couple weeks ago in the middle of a QSO I sensed some unusual heat from the amp and noticed the tubes were both cherry red. I shut it down immediately.? I have tuned it up a couple times since and the symptoms reoccur. ? I am (obviously) not an amp guy or much of a technician so I have 2 questions.? 1.? Is this a symptom of something that might be easily confirmed and repaired by me, ? and if not ? 2.?? Is there anyone in the Portland-Seattle-Vancouver BC area I might take it to for repair?
Thanks for any help or ideas
John
W7SWB
Does
|
Turn amp on and observe two things, as soon as?you turn it on look for your grid meter going negative and or the plate meter reading positive. ?Look for you tubes starting to gest up in a minute or two. ?If any of these happen report what you see. ?You may have developed a tube short or a loss of cut of bias. ?Report the findings here when you have them. Lou
On Tuesday, November 28, 2023, 11:43 PM, John Roland <johnroland51@...> wrote: Hi Everone,
I've owned this amp about 5 years but used very little. The amp was refurbished (new tubes, and relays) by a guy in north Idaho about 2017, just before I bought it. I have tried to contact him but get no response.
A couple weeks ago in the middle of a QSO I sensed some unusual heat from the amp and noticed the tubes were both cherry red. I shut it down immediately.? I have tuned it up a couple times since and the symptoms reoccur. ? I am (obviously) not an amp guy or much of a technician so I have 2 questions.? 1.? Is this a symptom of something that might be easily confirmed and repaired by me, ? and if not ? 2.?? Is there anyone in the Portland-Seattle-Vancouver BC area I might take it to for repair?
Thanks for any help or ideas
John
W7SWB
Does
|
Lou, Mike and all,
I turned it on and watched it with no drive.? At around 5 minutes the plates began turning red. See hopefully attached pictures.? I got no reading (0) on the plate and grid current meters.? I haven't yet tried removing the tubes.
|
FWIW? Here are the pictures I intended to attach to my previous post.?? The top is after about 1 minute and bottom is at about 5 minutes.? No drive.? No meter readings.? Adrian I got your note and will try to work through your suggestions I am able to in the next few days.??? Thanks everyone.?? /John? W7SWB 
|
That tube is bad. Remove that tube and just try the other tube by itself to see what it does.
On Wednesday, November 29, 2023, 7:12 PM, John Roland <johnroland51@...> wrote: FWIW? Here are the pictures I intended to attach to my previous post.?? The top is after about 1 minute and bottom is at about 5 minutes.? No drive.? No meter readings.? Adrian I got your note and will try to work through your suggestions I am able to in the next few days.??? Thanks everyone.?? /John? W7SWB 
|
Verify that your meters are working correctly. Bob W4JFA?
Lou, Mike and all,
I turned it on and watched it with no drive.? At around 5 minutes the plates began turning red. See hopefully attached pictures.? I got no reading (0) on the plate and grid current meters.? I haven't yet tried removing the tubes.
|
Especially the PLATE VOLTAGE meter it must measure 2400 to 3000 and decay to zero with the AC line power switched off.? Do NOT touch anything if it doesn’t work this way! ? One more thing – when you get to the part when you want to remove a tube be sure the plate cap off the tube you removed doesn’t touch the chassis and completely UNPLUG the AC power cord before opening it up. ? Mike N2LYM ? ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Bob
Sent: Wednesday, November 29, 2023 9:16 PM
To: [email protected]
Subject: Re: [ham-amplifiers] Need Help with Amp Supply LK500ZC ? Verify that your meters are working correctly. ? Lou, Mike and all,
I turned it on and watched it with no drive.? At around 5 minutes the plates began turning red. See hopefully attached pictures.? I got no reading (0) on the plate and grid current meters.? I haven't yet tried removing the tubes.
|
Lou, on the 2nd pix, it looks like BOTH tubes are going red.? My guess is.... it's a grid to cathode short on one or both tubes.?
The baffling part is..... his grid and plate current meters are still reading zero.?
More baffling is..... it takes 5 mins for the problem to manifest itself.?
Typ with a grid to cathode short on just one tube.....? BOTH tubes will go red asap, as soon as you turn on the amp.
?
On a related note, on Eimac 3-500Z's, they typ hi-pot test 5 kv? from grid to cathode ( good tube).? ?On all the chinese ( good tube)? 3-500Z's.... they all only hi-pot test 1 kv from grid to cathode.?
|
Jim, it could be ?reflection. The OP didn’t give much information like if the amp works, reads hi voltage, gives idle current if keyed up, etc etc. ?I?agree with you but I’m just trying to get the OP to do something to obtain more data. ?Yup you are correct I have hi pot brand new Chinese tubes right out the box and some will conduct at just over 400volrs. ?I like to see around 1500. ?I’ve test some old ?Eimacs G-F to almost the P-G amount. ?Rare but I have seen it. ?Chinese are mostly ok P-G upwards of 7kv. ?If you didn’t accept just above 500v G-F you’ll be rejecting lots of tubes!
On Thursday, November 30, 2023, 7:08 AM, Jim VE7RF <jim.thom@...> wrote: Lou, on the 2nd pix, it looks like BOTH tubes are going red.? My guess is.... it's a grid to cathode short on one or both tubes.?
The baffling part is..... his grid and plate current meters are still reading zero.?
More baffling is..... it takes 5 mins for the problem to manifest itself.?
Typ with a grid to cathode short on just one tube.....? BOTH tubes will go red asap, as soon as you turn on the amp.
?
On a related note, on Eimac 3-500Z's, they typ hi-pot test 5 kv? from grid to cathode ( good tube).? ?On all the chinese ( good tube)? 3-500Z's.... they all only hi-pot test 1 kv from grid to cathode.?
|
Lou, Mike, Jim, Adrian and all, I removed the tubes one at a time.? I let the amp idle (no drive) for 10 minutes with each tube in place individually.?? No signs of anything overheating.? I then replaced both tubes and let it set another 10 minutes, still no sign of overheating.?? I then applied about 20 watts of drive in RTTY mode and was getting around 200 watts out.? (I'm still using my Heathkit watt meter circa 1978)? Attached is a photo of my grid and plate current with that 20 watt drive.? The meter shows 2900 volts when idling and drops to about 2600 when transmitting.?? (I'm operating 240 volts on about a 20 foot length of 12 AWG from the panel.)? The pictures below are 1.? the front tube at 10 minutes.? 2. the rear tube at 10 minutes? 3. Both tubes back in place after 10 minutes.? 4.? A picture from yesterday of both tubes just after switching off the power (light) which looks to me like both tubes are overheated. 5.? A picture of my meters with 20 watts RTTY drive applied.? The Plate volt meter does return to 0 when switched off. So it now looks like I may have some kind of an intermittent ?? Thanks again /John? W7SWB     
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John, you just might have a worn out contact that switches bias on the antenna relay. ?If the contacts are severely pitted they might not make up too good sometimes and other times ok. ?You need to inspect the that set of contacts in particular. ?If you carefully remove the rear spring on the relay you can lift the armature off and inspect all the contacts. ?The contacts that switch the RF can be cleaned gently, the contacts on the bias may be in bad shape, there may be a tiny point on the armature contact and a tiny depression on the body contact. A gentle filing to remove the “pit” and a cleaning should restore reliable contact. ?It’s not unusual at all to see the bias contact hood bad with the age of thst amp especially being used on CW a lot. ?Seen it quit often and by doctoring up the bias? contact that problem went away. ?Lou
On Thursday, November 30, 2023, 3:58 PM, John Roland <johnroland51@...> wrote: Lou, Mike, Jim, Adrian and all, I removed the tubes one at a time.? I let the amp idle (no drive) for 10 minutes with each tube in place individually.?? No signs of anything overheating.? I then replaced both tubes and let it set another 10 minutes, still no sign of overheating.?? I then applied about 20 watts of drive in RTTY mode and was getting around 200 watts out.? (I'm still using my Heathkit watt meter circa 1978)? Attached is a photo of my grid and plate current with that 20 watt drive.? The meter shows 2900 volts when idling and drops to about 2600 when transmitting.?? (I'm operating 240 volts on about a 20 foot length of 12 AWG from the panel.)? The pictures below are 1.? the front tube at 10 minutes.? 2. the rear tube at 10 minutes? 3. Both tubes back in place after 10 minutes.? 4.? A picture from yesterday of both tubes just after switching off the power (light) which looks to me like both tubes are overheated. 5.? A picture of my meters with 20 watts RTTY drive applied.? The Plate volt meter does return to 0 when switched off. So it now looks like I may have some kind of an intermittent ?? Thanks again /John? W7SWB     
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There are burnishing tools for exactly this purpose.?
Using finger nail files and files for this purpose is risky, as the potential damage of removing too much contact material is high.
?
I have one of these:
Here are two more:
?
?
Burnishing tools have very fine almost invisible teeth.?
Using a burnishing tool is a safe method for cleaning relay contacts.?
Every radio amateur that works on equipment with open frame relays should have one in his tool kit.
?
73,
Dave, w6de
?
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Show quoted text
From: [email protected] <[email protected]>
On Behalf Of Louis Parascondola via groups.io
Sent: 30 November, 2023 22:56
To: [email protected]
Subject: Re: [ham-amplifiers] Need Help with Amp Supply LK500ZC
?
John, you just might have a worn out contact that switches bias on the antenna relay. ?If the contacts are severely pitted they might not make up too good
sometimes and other times ok. ?You need to inspect the that set of contacts in particular. ?If you carefully remove the rear spring on the relay you can lift the armature off and inspect all the contacts. ?The contacts that switch the RF can be cleaned gently,
the contacts on the bias may be in bad shape, there may be a tiny point on the armature contact and a tiny depression on the body contact. A gentle filing to remove the “pit” and a cleaning should restore reliable contact. ?It’s not unusual at all to see the
bias contact hood bad with the age of thst amp especially being used on CW a lot. ?Seen it quit often and by doctoring up the bias?contact that problem went away. ?Lou
?
On Thursday, November 30, 2023, 3:58 PM, John Roland <johnroland51@...>
wrote:
|
Very often, all that is necessary is to run a bizness card
between the contacts. A card with a particularly-rough finish is
great, but don't use a card with an epoxied smooth or glossy
finish on one side. If you do, then try to stick a sheet of
ordinary notebook paper to that side of the card so it doesn't
contact the relay contacts. The epoxy or gloss may rub off onto
the relay contact and make the problem even worse.
When you run a bizness card thruogh the contacts and examine it,
you will notice gray or black residue is left on the card.
However, the card will not clean up a burned or pitted contact
very well.
73,
Steve K0XP
On 11/30/2023 3:46 PM, Dave w6de wrote:
There
are burnishing tools for exactly this purpose.?
Using finger nail files and files for this purpose is
risky, as the potential damage of removing too much contact
material is high.
?
I
have one of these:
Here
are two more:
?
?
Burnishing
tools have very fine almost invisible teeth.?
Using a burnishing tool is a safe method for cleaning
relay contacts.?
Every radio amateur that works on equipment with open
frame relays should have one in his tool kit.
?
73,
Dave,
w6de
?
?
John,
you just might have a worn out contact that switches bias on
the antenna relay. ?If the contacts are severely pitted they
might not make up too good sometimes and other times ok.
?You need to inspect the that set of contacts in particular.
?If you carefully remove the rear spring on the relay you
can lift the armature off and inspect all the contacts. ?The
contacts that switch the RF can be cleaned gently, the
contacts on the bias may be in bad shape, there may be a
tiny point on the armature contact and a tiny depression on
the body contact. A gentle filing to remove the “pit” and a
cleaning should restore reliable contact. ?It’s not unusual
at all to see the bias contact hood bad with the age of thst
amp especially being used on CW a lot. ?Seen it quit often
and by doctoring up the bias?contact that problem went away.
?Lou
?
On Thursday, November
30, 2023, 3:58 PM, John Roland <johnroland51@...> wrote:
--
See my QRZ.com page at
|
Steve, Dave, Lou, and allOne of my problems is that I'm doubtful that I have a complete schematic for this amplifier.?? Best I've been able to find is from a 1988 users manual I found? . The previous owner who refurbished the amp replaced what I believe is the relay you refer to with what I was told are high-end vacuum relays, which if so, I wouldn't expect to be the problem and if it is, I wouldn't think burnishing contacts would be feasible. I'm also not understanding on how a bad relay would relate to the overheating when the amp was idling??
I have on my to-do list the task of reconciling the schematic with the existing circuitry, which is not something I feel I'm very good at.? I was told the QSK circuitry was bypassed (removed?) ("They're nothing but trouble")? and I've never seen the ALO light come on so not sure it hasn't also been disabled.? Other questions I have about the amp are whether it is good on the WARC bands and how to tell if it has a soft-start circuit which I read somewhere were factory installed on later models but I don't recognize in the schematic I have.
And to clarify my earlier post, the tubes were refitted not replaced.? Thanks Adrian.
Cheers for now.
/John
|
Here's the photo of the relays that I tried to attach to my last post.
|
Not all LK500 amps had QSK and vacuum relay output, it was an option. ?Some had a standard 3PDT relay like an SB220 et Al. ?Even if your amp has a QSK option it’s not working and the previous owner did a CF modification as is clearly shown by those outboard coaxial relays. ?That?said whoever did that probably has a third relay inside the amp for bias switching. ?REGARDLESS OF HAVING THE QSK OPTION OR NOT, THE BIAS SWITCHING IS NOT DONE DIRECTLY WITH ANT TRANSISTOR, THE BIAS IS STILL RELAY SWITCHED WITH CONTACTS IN EITHER?CASE. ?Don’t get bogged down with a bad transistor. ?Now that we know this amp has had the golden screwdriver done to it, it’s time to pop the top and show a photo of the rest area so we can see how the “ tinker” handled the bias switching.
On Thursday, November 30, 2023, 7:44 PM, Adrian Fewster <vk4tux@...> wrote:
The comments about a bad bias contact do not make sense to me ;
If K1C contact was welded (closed #) , which is highly unlikely
in such a low current circuit unless a fault current came through,
then that may be a possibility.
The issue was in standby , with relay open. If K1C is open and
not #; R1 (I requested check in earlier post) would need to be
shorted as that provides resistor bias cutoff.
D3 would probably need to be defective as well. The meters seems
to work so plate current should be checked on TX with and without
drive to check bias current? ?
73
vk4tux
On 1/12/23 09:46, Dave w6de wrote:
There
are burnishing tools for exactly this purpose.?
Using finger nail files and files for this purpose is
risky, as the potential damage of removing too much contact
material is high.
?
I
have one of these:
Here
are two more:
?
?
Burnishing
tools have very fine almost invisible teeth.?
Using a burnishing tool is a safe method for cleaning
relay contacts.?
Every radio amateur that works on equipment with open
frame relays should have one in his tool kit.
?
73,
Dave,
w6de
?
?
John,
you just might have a worn out contact that switches bias on
the antenna relay. ?If the contacts are severely pitted they
might not make up too good sometimes and other times ok.
?You need to inspect the that set of contacts in particular.
?If you carefully remove the rear spring on the relay you
can lift the armature off and inspect all the contacts. ?The
contacts that switch the RF can be cleaned gently, the
contacts on the bias may be in bad shape, there may be a
tiny point on the armature contact and a tiny depression on
the body contact. A gentle filing to remove the “pit” and a
cleaning should restore reliable contact. ?It’s not unusual
at all to see the bias contact hood bad with the age of thst
amp especially being used on CW a lot. ?Seen it quit often
and by doctoring up the bias?contact that problem went away.
?Lou
Sent from
the all new AOL app for iOS
?
On Thursday, November
30, 2023, 3:58 PM, John Roland <johnroland51@...> wrote:
|
Running any kind of paper currency or?business card or the like will only help the RF rx side of the switch contacts which are the NC contacts. ?NO or NC contacts on the??armature contacts C on the bias can develop a “ pit” and “tit” scenario on the contacts. ?They can not be clean with any miracle spray goop of paper treatment. ?A mild file is needed to fix up those contacts and followed with a buffing. ?If done correctly contact surface can be?successfully?restored. ?The contact flashing isn’t?needed so much on the bias contacts as it is needed on the NC contacts in the receive path! ?Dentron amps are specifically?prone to the issue. ?I’ve had to restore damaged bias contacts several times before.
On Thursday, November 30, 2023, 7:18 PM, Steve <k0xp@...> wrote:
Very often, all that is necessary is to run a bizness card
between the contacts. A card with a particularly-rough finish is
great, but don't use a card with an epoxied smooth or glossy
finish on one side. If you do, then try to stick a sheet of
ordinary notebook paper to that side of the card so it doesn't
contact the relay contacts. The epoxy or gloss may rub off onto
the relay contact and make the problem even worse.
When you run a bizness card thruogh the contacts and examine it,
you will notice gray or black residue is left on the card.
However, the card will not clean up a burned or pitted contact
very well.
73,
Steve K0XP
On 11/30/2023 3:46 PM, Dave w6de wrote:
There
are burnishing tools for exactly this purpose.?
Using finger nail files and files for this purpose is
risky, as the potential damage of removing too much contact
material is high.
?
I
have one of these:
Here
are two more:
?
?
Burnishing
tools have very fine almost invisible teeth.?
Using a burnishing tool is a safe method for cleaning
relay contacts.?
Every radio amateur that works on equipment with open
frame relays should have one in his tool kit.
?
73,
Dave,
w6de
?
?
John,
you just might have a worn out contact that switches bias on
the antenna relay. ?If the contacts are severely pitted they
might not make up too good sometimes and other times ok.
?You need to inspect the that set of contacts in particular.
?If you carefully remove the rear spring on the relay you
can lift the armature off and inspect all the contacts. ?The
contacts that switch the RF can be cleaned gently, the
contacts on the bias may be in bad shape, there may be a
tiny point on the armature contact and a tiny depression on
the body contact. A gentle filing to remove the “pit” and a
cleaning should restore reliable contact. ?It’s not unusual
at all to see the bias contact hood bad with the age of thst
amp especially being used on CW a lot. ?Seen it quit often
and by doctoring up the bias?contact that problem went away.
?Lou
Sent from
the all new AOL app for iOS
?
On Thursday, November
30, 2023, 3:58 PM, John Roland <johnroland51@...> wrote:
--
See my QRZ.com page at
|
Another thing not to be overlooked which is prevalent in many Ameritron amps is a shorted bypass cap on the bias line anywhere along it’s length?.??In rare cases, but possible,?a bypass cap that’s shorted on the filament choke can cause such issues. ?If ?shorted?however in the second test he did it seemed like the tubes behaved which would rule out a short and point to something intermittent like a moving contact perhaps.
On Thursday, November 30, 2023, 9:21 PM, Louis Parascondola via groups.io <Gudguyham@...> wrote:
Not all LK500 amps had QSK and vacuum relay output, it was an option. ?Some had a standard 3PDT relay like an SB220 et Al. ?Even if your amp has a QSK option it’s not working and the previous owner did a CF modification as is clearly shown by those outboard coaxial relays. ?That?said whoever did that probably has a third relay inside the amp for bias switching. ?REGARDLESS OF HAVING THE QSK OPTION OR NOT, THE BIAS SWITCHING IS NOT DONE DIRECTLY WITH ANT TRANSISTOR, THE BIAS IS STILL RELAY SWITCHED WITH CONTACTS IN EITHER?CASE. ?Don’t get bogged down with a bad transistor. ?Now that we know this amp has had the golden screwdriver done to it, it’s time to pop the top and show a photo of the rest area so we can see how the “ tinker” handled the bias switching. Sent from the all new AOL app for iOS
On Thursday, November 30, 2023, 7:44 PM, Adrian Fewster <vk4tux@...> wrote:
The comments about a bad bias contact do not make sense to me ;
If K1C contact was welded (closed #) , which is highly unlikely
in such a low current circuit unless a fault current came through,
then that may be a possibility.
The issue was in standby , with relay open. If K1C is open and
not #; R1 (I requested check in earlier post) would need to be
shorted as that provides resistor bias cutoff.
D3 would probably need to be defective as well. The meters seems
to work so plate current should be checked on TX with and without
drive to check bias current? ?
73
vk4tux
On 1/12/23 09:46, Dave w6de wrote:
There
are burnishing tools for exactly this purpose.?
Using finger nail files and files for this purpose is
risky, as the potential damage of removing too much contact
material is high.
?
I
have one of these:
Here
are two more:
?
?
Burnishing
tools have very fine almost invisible teeth.?
Using a burnishing tool is a safe method for cleaning
relay contacts.?
Every radio amateur that works on equipment with open
frame relays should have one in his tool kit.
?
73,
Dave,
w6de
?
?
John,
you just might have a worn out contact that switches bias on
the antenna relay. ?If the contacts are severely pitted they
might not make up too good sometimes and other times ok.
?You need to inspect the that set of contacts in particular.
?If you carefully remove the rear spring on the relay you
can lift the armature off and inspect all the contacts. ?The
contacts that switch the RF can be cleaned gently, the
contacts on the bias may be in bad shape, there may be a
tiny point on the armature contact and a tiny depression on
the body contact. A gentle filing to remove the “pit” and a
cleaning should restore reliable contact. ?It’s not unusual
at all to see the bias contact hood bad with the age of thst
amp especially being used on CW a lot. ?Seen it quit often
and by doctoring up the bias?contact that problem went away.
?Lou
Sent from
the all new AOL app for iOS
?
On Thursday, November
30, 2023, 3:58 PM, John Roland <johnroland51@...> wrote:
|
|
|
Bob