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Slightly off topic,
I am using an old Heathkit
antenna switch that has the control voltages riding on the coax.? The series DC blocking capacitor in the outside box has a
piece chipped out of it.? Maybe lighting,
maybe power did it.? It¡¯s an .02 uf ?1.6 KV disk.
?
I bought a .02uf ?3 KV disk Vishay and installed it.? If I run a 1500 watt carrier through it for
about 15 seconds, it gets warmer than lukewarm.?? Warmest on 10 meters as I would expect.
?
Would one expect
the cap to be warm to hot after that amount of time??? Any suggestions on what I should put in
there??? Curiously, the inside control
box uses two of the .02 caps in parallel, not one as the? outside box does.
?
Jim ¨C KR9U
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A total of .01 is more than enough, maybe a blown .02 was already removed in the past
Carl
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----- Original Message -----
From: kr9u@... [ham_amplifiers]
To: ham_amplifiers@...
Sent: Wednesday, June 26, 2019 10:09 PM
Subject: [ham_amplifiers] Series DC Blocking cap.
Slightly off topic,
I am using an old Heathkit antenna switch that has the control voltages riding on the coax. The series DC blocking capacitor in the outside box has a piece chipped out of it. Maybe lighting, maybe power did it. It¡¯s an .02 uf 1.6 KV disk.
I bought a .02uf 3 KV disk Vishay and installed it. If I run a 1500 watt carrier through it for about 15 seconds, it gets warmer than lukewarm. Warmest on 10 meters as I would expect.
Would one expect the cap to be warm to hot after that amount of time? Any suggestions on what I should put in there? Curiously, the inside control box uses two of the .02 caps in parallel, not one as the outside box does.
Jim ¨C KR9U
---
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<<A total of .01 is more than enough, maybe a blown .02 was already removed in
the past>>
Thanks Carl,
It's a stock box and the schematic shows it as I've described. There aren't any dissipation specs on the new cap - therefore the question.
Jim - KR9U
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The choke should be doing most of the work and the cap very little. My HB and Ameritron switches all use a generic Z5 single .01 1KV right up to 1200-1500W on HF for decades of heavy use without failure.
It often is hard to see internal choke damage but do an A:B resistance test with the other one:
What is the model #? I can look tomorrow at the actual circuit.
Carl
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----- Original Message ----- From: kr9u@... [ham_amplifiers] To: ham_amplifiers@... Sent: Thursday, June 27, 2019 6:01 PM Subject: [ham_amplifiers] Re: Series DC Blocking cap. <<A total of .01 is more than enough, maybe a blown .02 was already removed in the past>> Thanks Carl, It's a stock box and the schematic shows it as I've described. There aren't any dissipation specs on the new cap - therefore the question. Jim - KR9U --- This email has been checked for viruses by AVG.
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<Slightly off topic,?
<I am using an old Heathkit antenna switch that has the control voltages riding on the coax.??The <series DC blocking capacitor in the outside box has a piece chipped out of it.??Maybe lighting, <maybe power did it.??It¡¯s an .02 uf??1.6 KV disk. ? <I bought a .02uf??3 KV disk Vishay and installed it.??If I run a 1500 watt carrier through it for about <15 seconds, it gets warmer than lukewarm.?? Warmest on 10 meters as I would expect.
? <Would one expect the cap to be warm to hot after that amount of time????Any suggestions on <what I should put in there????Curiously, the inside control box uses two of the .02 caps in parallel, <not one as the? outside box does.
? <Jim ¨C KR9U
##? 1500? watts? =? 5.5 amps into? 50 ohms.? That's a helluva lot of current.? The problem? with? disc ceramic caps is.... they never post any RF? current ratings on them.? ?Ideally, they should post a? ?CCS? RF? current? vs? freq chart.? ?Actual? current ratings are all over the map...and must be? determined by testing.?
##? Big difference between? a .01 uf? @ 1 kv rated cap... vs a .01uf? @ 2 kv rated cap... the 2 kv? versions are typ bigger diam, like 25mm? OD... vs the smaller diam? 1 kv units.? ?The? 2 kv versions, being bigger diam, handle more current..which testing confirms.? ?Once you get to the? 3+? kv rated units, they don't appear to handle any additional current,? just a greater V? rating.?
##? I bought 2 x doz? .01uf @ 1.3 kv? disc ceramics? from RF parts? last year.? Huge things at? 25mm? OD, and really thick.? ?These things handle loads of current, best yet so far.?
## For? your heath switch box application,? parallel a 2nd cap? in the remote switch box...then re-test.? ?Parallel a 3rd cap if required.? ?You should have zero heat..on any freq.? Dunno if the heath? box is? good up to 6m or not.? ?
Jim? ?VE7RF
|
Capacitors have current ratings too. Voltage is one parameter and
the current rating is another.
Lee, w0vt
?
?
3 KV
disk Vishay and installed it.??If I run a 1500 watt
carrier through it for about <15 seconds, it gets
warmer than lukewarm.?? Warmest on 10 meters as I
would expect.
?
?
##?
1500? watts? =? 5.5 amps into? 50 ohms.? That's a
helluva lot of current.? The problem? with? disc
ceramic caps is.... they never post any RF? current
ratings on them.? ?Ideally, they should post a? ?CCS?
RF? current? vs? freq chart.? ?Actual? current ratings
are all over the map...and must be? determined by
testing.?
##? Big
difference between? a .01 uf? @ 1 kv rated cap... vs a
.01uf? @ 2 kv rated cap... the 2 kv? versions are typ
bigger diam, like 25mm? OD... vs the smaller diam? 1
kv units.? ?The? 2 kv versions, being bigger diam,
handle more current..which testing confirms.? ?Once
you get to the? 3+? kv rated units, they don't appear
to handle any additional current,? just a greater V?
rating.?
##? I
bought 2 x doz? .01uf @ 1.3 kv? disc ceramics? from RF
parts? last year.? Huge things at? 25mm? OD, and
really thick.? ?These things handle loads of current,
best yet so far.?
## For?
your heath switch box application,? parallel a 2nd
cap? in the remote switch box...then re-test.?
?Parallel a 3rd cap if required.? ?You should have
zero heat..on any freq.? Dunno if the heath? box is?
good up to 6m or not.? ?
Jim?
?VE7RF
|
Indeed
they do. The current handling / rating is usually defined by the capacitor¡¯s
Equivalent Series Resistance / ESR and its dielectric losses Dissipation Factor
/ loss tangent which is highly dielectric material dependent.
?
High
K dielectrics tend to be lossy while NPO class dielectric leaded ceramic disk
capacitors generally perform much better where significant RF current is
flowing.
?
Leigh
VK5KLT
?
From:
ham_amplifiers@...
[mailto:ham_amplifiers@...]
Sent: Friday, 28 June 2019 1:53 PM
To: ham_amplifiers@...
Subject: Re: [ham_amplifiers] Re:
Series DC Blocking cap.
?
Capacitors
have current ratings too. Voltage is one parameter and the current rating is
another.
Lee, w0vt
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On 6/27/2019 11:14 PM, jim.thom@...
[ham_amplifiers] wrote:
?
?
?
?
?
?
?
##?
1500? watts? =? 5.5 amps into? 50 ohms.? That's a
helluva lot of current.? The problem? with? disc ceramic caps
is.... they never post any RF? current ratings on them.?
?Ideally, they should post a? ?CCS? RF? current?
vs? freq chart.? ?Actual? current ratings are all over the
map...and must be? determined by testing.?
?
##?
Big difference between? a .01 uf? @ 1 kv rated cap... vs a
.01uf? @ 2 kv rated cap... the 2 kv? versions are typ bigger diam,
like 25mm? OD... vs the smaller diam? 1 kv units.?
?The? 2 kv versions, being bigger diam, handle more current..which
testing confirms.? ?Once you get to the? 3+? kv rated
units, they don't appear to handle any additional current,? just a greater
V? rating.?
?
##? I
bought 2 x doz? .01uf @ 1.3 kv? disc ceramics? from RF
parts? last year.? Huge things at? 25mm? OD, and really
thick.? ?These things handle loads of current, best yet so far.?
?
##
For? your heath switch box application,? parallel a 2nd cap? in
the remote switch box...then re-test.? ?Parallel a 3rd cap if
required.? ?You should have zero heat..on any freq.? Dunno if
the heath? box is? good up to 6m or not.? ?
?
Jim?
?VE7RF
|
LEIGH, When was the last time you ever saw a NPO? ?.01uf? DISC CERAMIC? ????? ? They don't exist, never did.? ? They are typ? Z5u, z5t? etc.?
I have never seen RF? current ratings for? disc ceramics,? ?rf current ratings? vs? freq,? nor? ESR at a freq.??
Jim? ?VE7RF
|
Published current ratings and actual cap ratings may or may not
co exist.? But the fact remains an application may require a cap
with an appropriate capacitor current capability.? I have a
Johnson Valiant as an example.? It had two banks of series silver
mica capacitors in parallel.? (Factory)? One day it gave up the
ghost and I replaced it with just two in series.? Big mistake.? It
blew up.? That was the day I learned about capacitor current
ratings and why Johnson had 4 of them in there instead of one.
Lee, w0vt?
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?
LEIGH, When was the last time you ever saw a NPO? ?.01uf?
DISC CERAMIC? ????? ? They don't exist, never did.? ?They are typ? Z5u, z5t?
etc.?
I have never seen RF? current ratings for? disc
ceramics,? ?rf current ratings? vs? freq,? nor? ESR at a
freq.??
Jim? ?VE7RF
|
Indeed Jim; that limitation of high Q COG / NPO material ceramic to low C
values is correct....generally limited to a few hundred pF to 1 nF or so.
Bottom line is lossy X7R, Z5U, Y5V, etc ceramic disk caps are not meant to
be used in high RF current applications....better to use multilayer RF chip
HV caps like ATC, Murata, AVX, etc. if low ESR and DF dielectric loss is
desired.
Clusters of Hi-K ceramic HV disks are quite OK for bypassing the tank plate
RFC choke, etc.
Similar issue with tank circuit padder LOAD capacitors....choose the wrong
dielectric doorknob cap and they get hot and drift in value and degrade over
time.
Leigh
VK5KLT
________________________________________
From: ham_amplifiers@... [mailto:ham_amplifiers@...]
Sent: Saturday, 29 June 2019 12:19 AM
To: ham_amplifiers@...
Subject: RE: [ham_amplifiers] Re: Series DC Blocking cap.
?Posted by: jim.thom@...
LEIGH, When was the last time you ever saw a NPO?.01uf? DISC CERAMIC? ?????
? They don't exist, never did.? ?They are typ Z5u, z5t etc.?
I have never seen RF current ratings for disc ceramics,?rf current ratings
vs? freq,? nor? ESR at a freq.??
Jim? ?VE7RF
From: ham_amplifiers@... [mailto:ham_amplifiers@...]
Sent: Friday, 28 June 2019 2:09 PM
To: ham_amplifiers@...
Subject: RE: [ham_amplifiers] Re: Series DC Blocking cap.
Indeed they do. The current handling / rating is usually defined by the
capacitor¡¯s Equivalent Series Resistance / ESR and its dielectric losses
Dissipation Factor / loss tangent which is highly dielectric material
dependent.
High K dielectrics tend to be lossy while NPO class dielectric leaded
ceramic disk capacitors generally perform much better where significant RF
current is flowing.
Leigh
VK5KLT
|
Teflon dielectric discs have been available for decades at least to 1000pf and maybe higher.
Ive used them for decades when modifying amp pi networks to work into high VSWR's on 160-80.
Carl
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Show quoted text
----- Original Message -----
From: 'Leigh Turner' invertech@... [ham_amplifiers]
To: ham_amplifiers@...
Sent: Friday, June 28, 2019 8:39 PM
Subject: RE: [ham_amplifiers] Re: Series DC Blocking cap.
Indeed Jim; that limitation of high Q COG / NPO material ceramic to low C
values is correct....generally limited to a few hundred pF to 1 nF or so.
Bottom line is lossy X7R, Z5U, Y5V, etc ceramic disk caps are not meant to
be used in high RF current applications....better to use multilayer RF chip
HV caps like ATC, Murata, AVX, etc. if low ESR and DF dielectric loss is
desired.
Clusters of Hi-K ceramic HV disks are quite OK for bypassing the tank plate
RFC choke, etc.
Similar issue with tank circuit padder LOAD capacitors....choose the wrong
dielectric doorknob cap and they get hot and drift in value and degrade over
time.
Leigh
VK5KLT
________________________________________
From: ham_amplifiers@... [mailto:ham_amplifiers@...]
Sent: Saturday, 29 June 2019 12:19 AM
To: ham_amplifiers@...
Subject: RE: [ham_amplifiers] Re: Series DC Blocking cap.
Posted by: jim.thom@...
LEIGH, When was the last time you ever saw a NPO .01uf DISC CERAMIC ????
They don't exist, never did. They are typ Z5u, z5t etc.
I have never seen RF current ratings for disc ceramics, rf current ratings
vs freq, nor ESR at a freq.
Jim VE7RF
From: ham_amplifiers@... [mailto:ham_amplifiers@...]
Sent: Friday, 28 June 2019 2:09 PM
To: ham_amplifiers@...
Subject: RE: [ham_amplifiers] Re: Series DC Blocking cap.
Indeed they do. The current handling / rating is usually defined by the
capacitor's Equivalent Series Resistance / ESR and its dielectric losses
Dissipation Factor / loss tangent which is highly dielectric material
dependent.
High K dielectrics tend to be lossy while NPO class dielectric leaded
ceramic disk capacitors generally perform much better where significant RF
current is flowing.
Leigh
VK5KLT
---
This email has been checked for viruses by AVG.
|
BUT there are no .02 NPO caps and there is no reason to have so much C in the RF path.
Anything over 2000pf is overkill.
toggle quoted message
Show quoted text
----- Original Message -----
From: 'Leigh Turner' invertech@... [ham_amplifiers]
To: ham_amplifiers@...
Sent: Friday, June 28, 2019 12:39 AM
Subject: RE: [ham_amplifiers] Re: Series DC Blocking cap.
Indeed they do. The current handling / rating is usually defined by the capacitor's Equivalent Series Resistance / ESR and its dielectric losses Dissipation Factor / loss tangent which is highly dielectric material dependent.
High K dielectrics tend to be lossy while NPO class dielectric leaded ceramic disk capacitors generally perform much better where significant RF current is flowing.
Leigh
VK5KLT
From: ham_amplifiers@... [mailto:ham_amplifiers@...]
Sent: Friday, 28 June 2019 1:53 PM
To: ham_amplifiers@...
Subject: Re: [ham_amplifiers] Re: Series DC Blocking cap.
Capacitors have current ratings too. Voltage is one parameter and the current rating is another.
Lee, w0vt
On 6/27/2019 11:14 PM, jim.thom@... [ham_amplifiers] wrote:
<Slightly off topic,
<I am using an old Heathkit antenna switch that has the control voltages riding on the coax. The <series DC blocking capacitor in the outside box has a piece chipped out of it. Maybe lighting, <maybe power did it. It's an .02 uf 1.6 KV disk.
<I bought a .02uf 3 KV disk Vishay and installed it. If I run a 1500 watt carrier through it for about <15 seconds, it gets warmer than lukewarm. Warmest on 10 meters as I would expect.
<Would one expect the cap to be warm to hot after that amount of time? Any suggestions on what I should put in there? Curiously, the inside control box uses two of the .02 caps in parallel, not one as the outside box does.
<Jim - KR9U
## 1500 watts = 5.5 amps into 50 ohms. That's a helluva lot of current. The problem with disc ceramic caps is.... they never post any RF current ratings on them. Ideally, they should post a CCS RF current vs freq chart. Actual current ratings are all over the map...and must be determined by testing.
## Big difference between a .01 uf @ 1 kv rated cap... vs a ..01uf @ 2 kv rated cap... the 2 kv versions are typ bigger diam, like 25mm OD... vs the smaller diam 1 kv units. The 2 kv versions, being bigger diam, handle more current..which testing confirms. Once you get to the 3+ kv rated units, they don't appear to handle any additional current, just a greater V rating.
## I bought 2 x doz .01uf @ 1.3 kv disc ceramics from RF parts last year. Huge things at 25mm OD, and really thick. These things handle loads of current, best yet so far.
## For your heath switch box application, parallel a 2nd cap in the remote switch box...then re-test. Parallel a 3rd cap if required. You should have zero heat..on any freq. Dunno if the heath box is good up to 6m or not.
Jim VE7RF
---
This email has been checked for viruses by AVG.
|
<Teflon dielectric discs have been available for decades at least to 1000pf?
<and maybe higher.
<Ive used them for decades when modifying amp pi networks to work into high?
<VSWR's on 160-80.
<Carl
##? where? do you buy these teflon caps ?? ? I'm looking everywhere, with not much success.?
Jim? VE7RF
|
I got mine from Amp Supply and later from Bill Edwards, K4BWC (SK) who was their Service Mgr and ran Omega Electronics. After he died I bought several items from his estate.
I believe Ameritron uses them also. Check their big amps and auto tuner.
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----- Original Message ----- From: jim.thom@... [ham_amplifiers] To: ham_amplifiers@... Sent: Saturday, June 29, 2019 4:39 PM Subject: Re: [ham_amplifiers] Re: Series DC Blocking cap. <Teflon dielectric discs have been available for decades at least to 1000pf <and maybe higher. <Ive used them for decades when modifying amp pi networks to work into high <VSWR's on 160-80. <Carl ## where do you buy these teflon caps ? I'm looking everywhere, with not much success. Jim VE7RF --- This email has been checked for viruses by AVG.
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Leigh Turner