Good quality coax. With SHV connectors.
|
Akek, That worked! Thanx. My Kenwood has a soft start in it already (Kessler). My Henry (2K-3) about once every three months will trip the breaker when turned on. I can live with that I guess. The amp was built in 1968 so I guess it can stay the way it is. Plus for my "test" amp, I use the MFJ external step start, ICP-240. I think the Henry is about maximum for that MFJ.
So you're using the NTC in place of a resistor in the soft start. I never thought of that but obviously it works.
The NTC in my Astron RS-50 is always in the circuit. 7 years or so used just about everyday and it's obviously holding up. Yep, different than an amp though.
73, Bob W4JFA
Hi Bob
Search for
100A 4000W High-Power
Soft Start Circuit Power Board for Class A Amplifier Amp
73, Alek.
On 9/12/2024 10:00 pm, Bob via
wrote:
Alek, Angus, I couldn't make those ebay numbers
work but if you do a search on ebay for "NTC resistor" you get
several.
I had to use one in my 50 amp Astron (RS-50) linear power
supply. It would sometimes trip the breaker. at start up The
one I used is...
SL322R025. It solved?the problem. It's been at least 7
years with no problems. Here's a link...
I originally got the info from "repeater builder"?
73, Bob W4JFA
G'day Angus.
Sorry for the delay. I missed your email and I'm just
cleaning up my emails and noticed this one.
Yes, the NTC works. I use them in this form for a lot of
amps that I build. See Ebay Item number 402565661699.
They are compact and work extremely well.
I've never bothered with soft starts for the little
Yaesu amps, as all the Yaesus I've worked on, have
excessive filament voltage at the filament pins when
connected to our AC mains.
A low value of resistance made up of 5W wirewound
resistors in parallel in series with the filaments
brings the volts back from around 6.9 - 7.0V back down
to the nominal 6.3V. This resistance, usually around
0.15 Ohms, also provides a measure of inrush protection
to the filaments. This is very important when using
Chinese valves, which hate excessive volts on the
filament.
Cheers from sunny Binningup, Western Australia.
Alek VK6APK
On 16/11/2024 5:06 am, AngusGM6AGC via wrote:
Hi Alek,
I trust you are well.
Have you done the step start mod ?¡°A
simple but effective delay can be done with an NTC
resistor. The
primary winding of the transformer is only a few
Ohm, so that a 1Ohm/20A NTC is sufficient to limit
the large momentary switching currents of uncharged
HV elco's and cold filaments.¡±
Is
it effective? Other soft step start arrangements seem
more complex.
I
look forward to hearing from you.
Best
wishes
Angus
?
|
Hi Bob
Search for
100A 4000W High-Power
Soft Start Circuit Power Board for Class A Amplifier Amp
73, Alek.
On 9/12/2024 10:00 pm, Bob via
groups.io wrote:
toggle quoted message
Show quoted text
Alek, Angus, I couldn't make those ebay numbers
work but if you do a search on ebay for "NTC resistor" you get
several.
I had to use one in my 50 amp Astron (RS-50) linear power
supply. It would sometimes trip the breaker. at start up The
one I used is...
SL322R025. It solved?the problem. It's been at least 7
years with no problems. Here's a link...
I originally got the info from "repeater builder"?
73, Bob W4JFA
G'day Angus.
Sorry for the delay. I missed your email and I'm just
cleaning up my emails and noticed this one.
Yes, the NTC works. I use them in this form for a lot of
amps that I build. See Ebay Item number 402565661699.
They are compact and work extremely well.
I've never bothered with soft starts for the little
Yaesu amps, as all the Yaesus I've worked on, have
excessive filament voltage at the filament pins when
connected to our AC mains.
A low value of resistance made up of 5W wirewound
resistors in parallel in series with the filaments
brings the volts back from around 6.9 - 7.0V back down
to the nominal 6.3V. This resistance, usually around
0.15 Ohms, also provides a measure of inrush protection
to the filaments. This is very important when using
Chinese valves, which hate excessive volts on the
filament.
Cheers from sunny Binningup, Western Australia.
Alek VK6APK
On 16/11/2024 5:06 am, AngusGM6AGC via wrote:
Hi Alek,
I trust you are well.
Have you done the step start mod ?¡°A
simple but effective delay can be done with an NTC
resistor. The
primary winding of the transformer is only a few
Ohm, so that a 1Ohm/20A NTC is sufficient to limit
the large momentary switching currents of uncharged
HV elco's and cold filaments.¡±
Is
it effective? Other soft step start arrangements seem
more complex.
I
look forward to hearing from you.
Best
wishes
Angus
?
|
In the soft start device I'm talking about, it gets switched out
of circuit by the 100A relay, just like the resistor in a normal
slow start.
Alek VK6APK
On 9/12/2024 11:04 pm, Bill K3HZP via
groups.io wrote:
toggle quoted message
Show quoted text
I have mixed emotions about NTC resistors.? I tried one on my
SB-220 and found that the resistance would change between idle
and full plate current.? The large current change caused the
filament voltage to change since it uses the same transformer.?
Because of the filament voltage change under load, I took it
out.?
Bill K3HZP
|
The SB220 has a separate filament transfomer but since the line feeding it and the plate transformer is the same, any sag on the line voltage due to plate primary current drawn by the plate transformer will affect the filament voltage.
On Monday, December 9, 2024, 10:04 AM, Bill K3HZP via groups.io <hzp_electronics@...> wrote: I have mixed emotions about NTC resistors.? I tried one on my SB-220 and found that the resistance would change between idle and full plate current.? The large current change caused the filament voltage to change since it uses the same transformer.? Because of the filament voltage change under load, I took it out.?
Bill K3HZP
|
I have mixed emotions about NTC resistors.? I tried one on my SB-220 and found that the resistance would change between idle and full plate current.? The large current change caused the filament voltage to change since it uses the same transformer.? Because of the filament voltage change under load, I took it out.?
Bill K3HZP
|
Alek, Angus, I couldn't make those ebay numbers work but if you do a search on ebay for "NTC resistor" you get several. I had to use one in my 50 amp Astron (RS-50) linear power supply. It would sometimes trip the breaker. at start up The one I used is... SL322R025. It solved?the problem. It's been at least 7 years with no problems. Here's a link...
I originally got the info from "repeater builder"?
73, Bob W4JFA
G'day Angus.
Sorry for the delay. I missed your email and I'm just cleaning up
my emails and noticed this one.
Yes, the NTC works. I use them in this form for a lot of amps
that I build. See Ebay Item number 402565661699.
They are compact
and work extremely well.
I've never bothered
with soft starts for the little Yaesu amps, as all the Yaesus
I've worked on, have excessive filament voltage at the filament
pins when connected to our AC mains.
A low value of
resistance made up of 5W wirewound resistors in parallel in
series with the filaments brings the volts back from around 6.9
- 7.0V back down to the nominal 6.3V. This resistance, usually
around 0.15 Ohms, also provides a measure of inrush protection
to the filaments. This is very important when using Chinese
valves, which hate excessive volts on the filament.
Cheers from sunny
Binningup, Western Australia.
Alek VK6APK
On 16/11/2024 5:06 am, AngusGM6AGC via
wrote:
Hi Alek,
I trust you are well. Have you
done the step start mod ?¡°A
simple but effective delay can be done with an NTC resistor.
The
primary winding of the transformer is only a few Ohm, so
that a 1Ohm/20A NTC is sufficient to limit the large
momentary switching currents of uncharged HV elco's and cold
filaments.¡±
Is
it effective? Other soft step start arrangements seem more
complex.
I
look forward to hearing from you.
Best
wishes
Angus
?
|
G'day Angus.
Sorry for the delay. I missed your email and I'm just cleaning up
my emails and noticed this one.
Yes, the NTC works. I use them in this form for a lot of amps
that I build. See Ebay Item number 402565661699.
They are compact
and work extremely well.
I've never bothered
with soft starts for the little Yaesu amps, as all the Yaesus
I've worked on, have excessive filament voltage at the filament
pins when connected to our AC mains.
A low value of
resistance made up of 5W wirewound resistors in parallel in
series with the filaments brings the volts back from around 6.9
- 7.0V back down to the nominal 6.3V. This resistance, usually
around 0.15 Ohms, also provides a measure of inrush protection
to the filaments. This is very important when using Chinese
valves, which hate excessive volts on the filament.
Cheers from sunny
Binningup, Western Australia.
Alek VK6APK
On 16/11/2024 5:06 am, AngusGM6AGC via
groups.io wrote:
toggle quoted message
Show quoted text
Hi Alek,
I trust you are well. Have you
done the step start mod ?¡°A
simple but effective delay can be done with an NTC resistor.
The
primary winding of the transformer is only a few Ohm, so
that a 1Ohm/20A NTC is sufficient to limit the large
momentary switching currents of uncharged HV elco's and cold
filaments.¡±
Is
it effective? Other soft step start arrangements seem more
complex.
I
look forward to hearing from you.
Best
wishes
Angus
?
|
I¡¯ll take a look at this, thanks a bunch.
|
Re: Need advice on HV connectors
SHV connector is ....'safe high voltage'.? It's basically a reverse gender BNC connector.? ?Typ rated for 5 kv @ 2 amps.?
A HN connector is a ...'high powered N connector'.?
|
Here is some info about the TU-6B board designed and sold by W7DS (SK). I was able to source a board from a guy on e-bay, but I don't think he has any left. Hope this helps.
?
?
Hope this helps,
73, N0NC
?
|
Re: Amp Supply LK800 Meter/ALO Board Question
Lower the screen voltage on the radio not the amp to lower the drive to the amp.
All-
It's a grounded grid triode amplifier - three 3CX800A7s.
Many thanks,
-Mark
On Wed, Nov 27, 2024 at 11:22?AM mike repinski via <mikflathead= [email protected]> wrote:
Any chance you could lower the screen voltage? Assuming it's a tetrode or pentode. A string of zeners?
On Wednesday, November 27, 2024 at 09:45:32 AM EST, Omni < selcor@...> wrote:
If you do use an attenuator, which I do here for one of my amps, you will have to find a way to bypass it in receive or you will have 3dB attenuation of the receive signal. ? ? All- Thank you for the information.? I do not recall having a spectacular failure like that, but perhaps the person I loaned the amp to did.? Regardless, it still appears to be working.? Thank you for your help! Regarding manually tuned gear in an automatic station, I fully agree.? My main amp is an Alpha 9500 for that reason, as the antennas and rig are interfaced, and all switching is done whenever I change band on the radio.? This amplifier is being driven by a Swan 350B, which is manual everything - my first radio?that my father bought me when I was a kid.? That brings me to my next question: The?Swan puts out 50-100W, and I need to detune the driver as the only method?for bringing the power down.? Is there a simple mod that will allow this amplifier to accept more power?? If not, then I will buy a 3 dB attenuator to put between the radio and the amplifier (rated for at least 100 W - they're pretty inexpensive).
|
Re: Amp Supply LK800 Meter/ALO Board Question
Pad the input to the final tube? Lot's of ways. Good luck. Listening on 10 on my 50 year old Siltronics 1011C. Memories from High school.?
All-
I'm willing to accept the 3 dB on receive, although it is not great.? I have a separate question?on the Swan forum to see if there?is an easy way to put an RF output adjustment on the radio.? I suspect that will be the easier of the mods to make.
-Mark
If you do use an attenuator, which I do here for one of my amps, you will have to find a way to bypass it in receive or you will have 3dB attenuation of the receive signal. ? ? All- Thank you for the information.? I do not recall having a spectacular failure like that, but perhaps the person I loaned the amp to did.? Regardless, it still appears to be working.? Thank you for your help! Regarding manually tuned gear in an automatic station, I fully agree.? My main amp is an Alpha 9500 for that reason, as the antennas and rig are interfaced, and all switching is done whenever I change band on the radio.? This amplifier is being driven by a Swan 350B, which is manual everything - my first radio?that my father bought me when I was a kid.? That brings me to my next question: The?Swan puts out 50-100W, and I need to detune the driver as the only method?for bringing the power down.? Is there a simple mod that will allow this amplifier to accept more power?? If not, then I will buy a 3 dB attenuator to put between the radio and the amplifier (rated for at least 100 W - they're pretty inexpensive).
|
Re: Amp Supply LK800 Meter/ALO Board Question
All-
It's a grounded grid triode amplifier - three 3CX800A7s.
Many thanks,
-Mark
On Wed, Nov 27, 2024 at 11:22?AM mike repinski via <mikflathead= [email protected]> wrote:
Any chance you could lower the screen voltage? Assuming it's a tetrode or pentode. A string of zeners?
On Wednesday, November 27, 2024 at 09:45:32 AM EST, Omni < selcor@...> wrote:
If you do use an attenuator, which I do here for one of my amps, you will have to find a way to bypass it in receive or you will have 3dB attenuation of the receive signal. ? ? All- Thank you for the information.? I do not recall having a spectacular failure like that, but perhaps the person I loaned the amp to did.? Regardless, it still appears to be working.? Thank you for your help! Regarding manually tuned gear in an automatic station, I fully agree.? My main amp is an Alpha 9500 for that reason, as the antennas and rig are interfaced, and all switching is done whenever I change band on the radio.? This amplifier is being driven by a Swan 350B, which is manual everything - my first radio?that my father bought me when I was a kid.? That brings me to my next question: The?Swan puts out 50-100W, and I need to detune the driver as the only method?for bringing the power down.? Is there a simple mod that will allow this amplifier to accept more power?? If not, then I will buy a 3 dB attenuator to put between the radio and the amplifier (rated for at least 100 W - they're pretty inexpensive).
|
Re: Amp Supply LK800 Meter/ALO Board Question
Any chance you could lower the screen voltage? Assuming it's a tetrode or pentode. A string of zeners?
If you do use an attenuator, which I do here for one of my amps, you will have to find a way to bypass it in receive or you will have 3dB attenuation of the receive signal. ?
From: [email protected] < [email protected]> On Behalf Of Mark KE1IU via groups.io Sent: Wednesday, November 27, 2024 9:23 AM To: [email protected]Subject: Re: [ham-amplifiers] Amp Supply LK800 Meter/ALO Board Question ? All- Thank you for the information.? I do not recall having a spectacular failure like that, but perhaps the person I loaned the amp to did.? Regardless, it still appears to be working.? Thank you for your help! Regarding manually tuned gear in an automatic station, I fully agree.? My main amp is an Alpha 9500 for that reason, as the antennas and rig are interfaced, and all switching is done whenever I change band on the radio.? This amplifier is being driven by a Swan 350B, which is manual everything - my first radio?that my father bought me when I was a kid.? That brings me to my next question: The?Swan puts out 50-100W, and I need to detune the driver as the only method?for bringing the power down.? Is there a simple mod that will allow this amplifier to accept more power?? If not, then I will buy a 3 dB attenuator to put between the radio and the amplifier (rated for at least 100 W - they're pretty inexpensive).
|
Re: Amp Supply LK800 Meter/ALO Board Question
All-
I'm willing to accept the 3 dB on receive, although it is not great.? I have a separate question?on the Swan forum to see if there?is an easy way to put an RF output adjustment on the radio.? I suspect that will be the easier of the mods to make.
-Mark
If you do use an attenuator, which I do here for one of my amps, you will have to find a way to bypass it in receive or you will have 3dB attenuation of the receive signal. ? ? All- Thank you for the information.? I do not recall having a spectacular failure like that, but perhaps the person I loaned the amp to did.? Regardless, it still appears to be working.? Thank you for your help! Regarding manually tuned gear in an automatic station, I fully agree.? My main amp is an Alpha 9500 for that reason, as the antennas and rig are interfaced, and all switching is done whenever I change band on the radio.? This amplifier is being driven by a Swan 350B, which is manual everything - my first radio?that my father bought me when I was a kid.? That brings me to my next question: The?Swan puts out 50-100W, and I need to detune the driver as the only method?for bringing the power down.? Is there a simple mod that will allow this amplifier to accept more power?? If not, then I will buy a 3 dB attenuator to put between the radio and the amplifier (rated for at least 100 W - they're pretty inexpensive).
|
Re: Amp Supply LK800 Meter/ALO Board Question
If you do use an attenuator, which I do here for one of my amps, you will have to find a way to bypass it in receive or you will have 3dB attenuation of the receive signal. ?
toggle quoted message
Show quoted text
From: [email protected] < [email protected]> On Behalf Of Mark KE1IU via groups.io Sent: Wednesday, November 27, 2024 9:23 AM To: [email protected]Subject: Re: [ham-amplifiers] Amp Supply LK800 Meter/ALO Board Question ? All- Thank you for the information.? I do not recall having a spectacular failure like that, but perhaps the person I loaned the amp to did.? Regardless, it still appears to be working.? Thank you for your help! Regarding manually tuned gear in an automatic station, I fully agree.? My main amp is an Alpha 9500 for that reason, as the antennas and rig are interfaced, and all switching is done whenever I change band on the radio.? This amplifier is being driven by a Swan 350B, which is manual everything - my first radio?that my father bought me when I was a kid.? That brings me to my next question: The?Swan puts out 50-100W, and I need to detune the driver as the only method?for bringing the power down.? Is there a simple mod that will allow this amplifier to accept more power?? If not, then I will buy a 3 dB attenuator to put between the radio and the amplifier (rated for at least 100 W - they're pretty inexpensive).
|
Re: Amp Supply LK800 Meter/ALO Board Question
All-
Thank you for the information.? I do not recall having a spectacular failure like that, but perhaps the person I loaned the amp to did.? Regardless, it still appears to be working.? Thank you for your help!
Regarding manually tuned gear in an automatic station, I fully agree.? My main amp is an Alpha 9500 for that reason, as the antennas and rig are interfaced, and all switching is done whenever I change band on the radio.? This amplifier is being driven by a Swan 350B, which is manual everything - my first radio?that my father bought me when I was a kid.? That brings me to my next question: The?Swan puts out 50-100W, and I need to detune the driver as the only method?for bringing the power down.? Is there a simple mod that will allow this amplifier to accept more power?? If not, then I will buy a 3 dB attenuator to put between the radio and the amplifier (rated for at least 100 W - they're pretty inexpensive).
Many thanks,
-Mark
Many thanks,
-Mark
On Wed, Nov 27, 2024 at 8:02?AM Louis Parascondola via <Gudguyham= [email protected]> wrote:
FWIW, I have changed those series resistors on those amps quite a few times before.? They are rather small resistors and are probably sacrificial to save the meter in a fault.? ??
On Tuesday, November 26, 2024, 7:51 PM, Dave w6de <w6de@...> wrote:
Plate/Grid flash over.?
With a manual tune amplifier, a likely suspect is a band change and failure to tune the plate and load at low power.?
Another way is returning to from a break in operation then upon return switching bands or switching antennas without retuning the amp¡ªwith Steppir antennas this is an easy mistake to make. Specially when you have automatic antenna selection from your
rig to the antenna switch and/or automatic band selection to the Steppir.
?
The worst thing for a shack is to have a manual operation set-up required in an otherwise fully automatic switching shack from
a modern transceiver.
?
73,
Dave, w6de
?
All-
I gave the amplifier a try tonight at very low drive, slowly working my way up to legal limit to ensure the meter did not peg to the right due to an incorrect resistor value.? Everything seems normal (grid current of ca. 30 mA when tuned,
and turning the load control clockwise reduces it), so that resistor R29 is indeed 18 ohms.? If anyone knows why that might have?blown, I would?be interested in your thoughts.
?
The PDF file here works for me.? I have seen this manual before.? It has no information on the ALO/metering board.? Yes, there are two meters in the schematic, but my LK800a does not have the same wiring of those meters.
?
?
I have an Amp Supply Company LK800A amplifier that puts out full power.? However, I noticed recently that it shows no grid current reading when transmitting on multiple bands.? This is odd behavior, as the grid current normally runs ca.
20-50 mA from my past experience.? I know the meter is fine, because when I turn the meter switch to measure plate voltage, I get the expected reading.? I looked at the meter/ALO board and found that R29 was somewhat charred and had a reading of 180 K ohms.?
No other parts look visibly damaged.
The LK-800 series manual does not have a schematic for this board.? I was able to find one at
.? While the manual is for the LK-400 / LK-500 series, it does have a description of the ALO/Meter board.? The resistor R29 is in the grid current metering circuit and
is claimed to have a value of 18 ohms (p. 27 and 29).? I suspect this is the problem.? The other parts on my board seem to match what is listed on p. 29, and the parts list on p. 29 suggests the board works in the LK-800 series amps because it references the
heavy resistor R30 as being unique to the LK-800 (and is present on my board).
My question - can someone verify that R29 should indeed be 18 ohms?? I would hate for there to be a misprint in the manual and find my grid current meter to be blown when I try this out, as I suspect they are very difficult to obtain.?
Also, do you have any insights as to what would blow this resistor?? A current of 120 mA through that resistor would deliver 0.25 watts...? I have always kept the grid current low, but I did loan the amplifier out a few years ago and don't know if the other
user experienced an issue.
|
Re: Amp Supply LK800 Meter/ALO Board Question
FWIW, I have changed those series resistors on those amps quite a few times before. ?They are rather small resistors and are probably sacrificial to save the meter in a fault.? ??
On Tuesday, November 26, 2024, 7:51 PM, Dave w6de <w6de@...> wrote:
Plate/Grid flash over.?
With a manual tune amplifier, a likely suspect is a band change and failure to tune the plate and load at low power.?
Another way is returning to from a break in operation then upon return switching bands or switching antennas without retuning the amp¡ªwith Steppir antennas this is an easy mistake to make. Specially when you have automatic antenna selection from your
rig to the antenna switch and/or automatic band selection to the Steppir.
?
The worst thing for a shack is to have a manual operation set-up required in an otherwise fully automatic switching shack from
a modern transceiver.
?
73,
Dave, w6de
?
All-
I gave the amplifier a try tonight at very low drive, slowly working my way up to legal limit to ensure the meter did not peg to the right due to an incorrect resistor value.? Everything seems normal (grid current of ca. 30 mA when tuned,
and turning the load control clockwise reduces it), so that resistor R29 is indeed 18 ohms.? If anyone knows why that might have?blown, I would?be interested in your thoughts.
?
The PDF file here works for me.? I have seen this manual before.? It has no information on the ALO/metering board.? Yes, there are two meters in the schematic, but my LK800a does not have the same wiring of those meters.
?
?
I have an Amp Supply Company LK800A amplifier that puts out full power.? However, I noticed recently that it shows no grid current reading when transmitting on multiple bands.? This is odd behavior, as the grid current normally runs ca.
20-50 mA from my past experience.? I know the meter is fine, because when I turn the meter switch to measure plate voltage, I get the expected reading.? I looked at the meter/ALO board and found that R29 was somewhat charred and had a reading of 180 K ohms.?
No other parts look visibly damaged.
The LK-800 series manual does not have a schematic for this board.? I was able to find one at
.? While the manual is for the LK-400 / LK-500 series, it does have a description of the ALO/Meter board.? The resistor R29 is in the grid current metering circuit and
is claimed to have a value of 18 ohms (p. 27 and 29).? I suspect this is the problem.? The other parts on my board seem to match what is listed on p. 29, and the parts list on p. 29 suggests the board works in the LK-800 series amps because it references the
heavy resistor R30 as being unique to the LK-800 (and is present on my board).
My question - can someone verify that R29 should indeed be 18 ohms?? I would hate for there to be a misprint in the manual and find my grid current meter to be blown when I try this out, as I suspect they are very difficult to obtain.?
Also, do you have any insights as to what would blow this resistor?? A current of 120 mA through that resistor would deliver 0.25 watts...? I have always kept the grid current low, but I did loan the amplifier out a few years ago and don't know if the other
user experienced an issue.
|
Re: Amp Supply LK800 Meter/ALO Board Question
Plate/Grid flash over.?
With a manual tune amplifier, a likely suspect is a band change and failure to tune the plate and load at low power.?
Another way is returning to from a break in operation then upon return switching bands or switching antennas without retuning the amp¡ªwith Steppir antennas this is an easy mistake to make. Specially when you have automatic antenna selection from your
rig to the antenna switch and/or automatic band selection to the Steppir.
?
The worst thing for a shack is to have a manual operation set-up required in an otherwise fully automatic switching shack from
a modern transceiver.
?
73,
Dave, w6de
toggle quoted message
Show quoted text
From: [email protected] <[email protected]>
On Behalf Of Mark KE1IU via groups.io
Sent: 26 November, 2024 23:24
To: [email protected]
Subject: Re: [ham-amplifiers] Amp Supply LK800 Meter/ALO Board Question
?
All-
I gave the amplifier a try tonight at very low drive, slowly working my way up to legal limit to ensure the meter did not peg to the right due to an incorrect resistor value.? Everything seems normal (grid current of ca. 30 mA when tuned,
and turning the load control clockwise reduces it), so that resistor R29 is indeed 18 ohms.? If anyone knows why that might have?blown, I would?be interested in your thoughts.
?
The PDF file here works for me.? I have seen this manual before.? It has no information on the ALO/metering board.? Yes, there are two meters in the schematic, but my LK800a does not have the same wiring of those meters.
?
?
I have an Amp Supply Company LK800A amplifier that puts out full power.? However, I noticed recently that it shows no grid current reading when transmitting on multiple bands.? This is odd behavior, as the grid current normally runs ca.
20-50 mA from my past experience.? I know the meter is fine, because when I turn the meter switch to measure plate voltage, I get the expected reading.? I looked at the meter/ALO board and found that R29 was somewhat charred and had a reading of 180 K ohms.?
No other parts look visibly damaged.
The LK-800 series manual does not have a schematic for this board.? I was able to find one at
.? While the manual is for the LK-400 / LK-500 series, it does have a description of the ALO/Meter board.? The resistor R29 is in the grid current metering circuit and
is claimed to have a value of 18 ohms (p. 27 and 29).? I suspect this is the problem.? The other parts on my board seem to match what is listed on p. 29, and the parts list on p. 29 suggests the board works in the LK-800 series amps because it references the
heavy resistor R30 as being unique to the LK-800 (and is present on my board).
My question - can someone verify that R29 should indeed be 18 ohms?? I would hate for there to be a misprint in the manual and find my grid current meter to be blown when I try this out, as I suspect they are very difficult to obtain.?
Also, do you have any insights as to what would blow this resistor?? A current of 120 mA through that resistor would deliver 0.25 watts...? I have always kept the grid current low, but I did loan the amplifier out a few years ago and don't know if the other
user experienced an issue.
|
Bob
Bill K3HZP