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Ameritron 240V inrush limiter: any benefit on a KPA500?

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Ron Durie

Ameritron 240V inrush limiter: any benefit on a KPA500?

NO. Solid state amps do not need inrush protection. 73's

Ron WB4OOA
Elecraft K-Line

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Bob McGraw - K4TAX

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

Solid state amps do not require added inrush protection.

And most correctly designed tube amps do not need inrush protection.
In cases where the design, usually HB ones, have excessive current
capacity in the heater or filament transformer, or in cases where HV
transformers have insufficient resistance in the secondary are cases
where inrush protection is desired.

Amps such as SB-200, SB-220, TL-922, L4B, Centurion, Titian, Amp Supply,
Ameritron, and other like commercial amps have sufficient design
implementations such that those do not require inrush protection. At
the same time, many amps using indirectly heated cathodes may have time
delay systems to allow the heater to get the cathode to correct
operating temperature is different than inrush protection

73

Bob, K4TAX

On 1/18/2020 12:06 PM, Ron Durie wrote:

> NO. Solid state amps do not need inrush protection. 73's
>
> Ron WB4OOA
> Elecraft K-Line
>
>
>
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Macy monkeys

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

In reply to this post by Ron Durie

Thanks, Ron! I understand NO, hi!

John K7FD

> On Jan 18, 2020, at 10:06 AM, Ron Durie <[hidden email]> wrote:
>
> NO. Solid state amps do not need inrush protection. 73's
>
> Ron WB4OOA
> Elecraft K-Line
>
>
>
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Roger-3

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

NO amplifier needs inrush protection - it is the POWERSUPPLY that needs it
no matter how it is implemented.
So the answer is not an easy "NO" or "YES" but a definite "it depends"!

Roger, DL5RBW

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Macy monkeys
Sent: Saturday, January 18, 2020 7:42 PM
To: Ron Durie
Cc: [hidden email]
Subject: Re: [Elecraft] Ameritron 240V inrush limiter: any benefit on a
KPA500?

Thanks, Ron! I understand NO, hi!

John K7FD

> On Jan 18, 2020, at 10:06 AM, Ron Durie <[hidden email]> wrote:
>
> NO. Solid state amps do not need inrush protection. 73's
>
> Ron WB4OOA
> Elecraft K-Line
>
>
>
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Bob McGraw - K4TAX

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

"Amplifier" as in all inclusive. The models I referenced all have
internal power supplies, with exception of 2 models. The design of
the transformers in these amplifiers are such that inrush current does
not exceed maximum magnetization current.

73

Bob, K4TAX

On 1/18/2020 12:55 PM, Roger wrote:

> NO amplifier needs inrush protection - it is the POWERSUPPLY that needs it
> no matter how it is implemented.
> So the answer is not an easy "NO" or "YES" but a definite "it depends"!
>
> Roger, DL5RBW
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Macy monkeys
> Sent: Saturday, January 18, 2020 7:42 PM
> To: Ron Durie
> Cc: [hidden email]
> Subject: Re: [Elecraft] Ameritron 240V inrush limiter: any benefit on a
> KPA500?
>
>
> Thanks, Ron! I understand NO, hi!
>
> John K7FD
>
>> On Jan 18, 2020, at 10:06 AM, Ron Durie <[hidden email]> wrote:
>>
>> NO. Solid state amps do not need inrush protection. 73's
>>
>> Ron WB4OOA
>> Elecraft K-Line
>>
>>
>>
>> ______________________________________________________________
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Vic Rosenthal

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

Well, I don't totally agree. The power switch in some of those amps like
the SB220 or TL922 is highly stressed. There is a big "thump" sometimes
when they are turned on at the right point in the cycle. I also believe
that slower application of filament voltage to a 3-500z or similar
lengthens the life of the filament.
But this is about KPA500s, so I suppose the answer is 'no'.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/

On 18/01/2020 21:13, Bob McGraw K4TAX wrote:
> "Amplifier" as in all inclusive. The models I referenced all have
internal power supplies, with exception of 2 models. The design of
the transformers in these amplifiers are such that inrush current does
not exceed maximum magnetization current.
>
> 73
>
> Bob, K4TAX
>
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Jim Brown-10

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

On 1/18/2020 12:14 PM, Victor Rosenthal wrote:
> The power switch in some of those amps like the SB220 or TL922 is highly
> stressed. T

My late '70s vintage Ten Tec Titan amps include circuity to minimize the
turn-on transient, at least some of which is due to charging of the
capacitors in the LV and HV power supplies. A surge to charge these caps
is inherent in any capacitor-input PSU, and the strength of it depends
on where in the 60 Hz cycle it amp is turned on. I own three of these
amps, and the circuit values was a running production change that
evolved over time.

This became a serious problem in large sound systems that included a lot
of big power amps; with several amps on a circuit, it was not uncommon
for breakers to pop when a system was powered up. In the largest
systems, a turn-on at the peak of the cycle could take out the main
breaker! Several schemes were developed; Crown, for example, developed a
circuit to randomly delay the turn-on of their amps, and several
companies developed dedicated sequencers that sat between the amps and
their outlets.

73, Jim K9YC
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K9MA

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

> On 1/18/2020 12:14 PM, Victor Rosenthal wrote:
>> The power switch in some of those amps like the SB220 or TL922 is
>> highly stressed. T

Another cause of high input current is transformer saturation. If the
core happened to be fully magnetized in one direction when last turned
off, and the AC happens to want to magnetize it more in the same
direction at turn-on, the core can saturate for half cycle. It's a
random event, which doesn't happen often, but it's hard on switches. It
can also make that "bong" sound at turn-on.

73,

Scott K9MA

--
Scott K9MA

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k6dgw

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

In reply to this post by Roger-3

10 KW homebrew FM broadcast TX [not kidding -- KPFK 90.7 Los Angeles in
the late 50's, 4 4-1000A's* in parallel driven by a 1 KW stage] had a
step-start using mechanical time-delay relays.** It limited the inrush
current to the filter capacitors of the 5.5 KV plate power supply. It
was part of the power supply in the back room, not the PA.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

* I do *not* recommend 4 ea 4-1000A's in parallel at 90.7 MHz. Things
got very hot.

** Integrated circuits and microprocessors has not been invented then.
Actually, the transistor barely had been.

On 1/18/2020 10:55 AM, Roger wrote:
> NO amplifier needs inrush protection - it is the POWERSUPPLY that needs it
> no matter how it is implemented.
> So the answer is not an easy "NO" or "YES" but a definite "it depends"!
>
> Roger, DL5RBW
>
>

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Vic Rosenthal

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

Just like the 1930s vintage Western Electric at WKOP when I worked there in the early 60s. When you turned it on, it went click-click-click-click BLANG.
Two tubes, 12 kV on the plates, about 1 amp plate current for 5 kW output.

Victor 4X6GP

> On 19 Jan 2020, at 1:45, Fred Jensen <[hidden email]> wrote:
>
> 10 KW homebrew FM broadcast TX [not kidding -- KPFK 90.7 Los Angeles in the late 50's, 4 4-1000A's* in parallel driven by a 1 KW stage] had a step-start using mechanical time-delay relays.** It limited the inrush current to the filter capacitors of the 5.5 KV plate power supply. It was part of the power supply in the back room, not the PA.
>
> 73,
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
> * I do *not* recommend 4 ea 4-1000A's in parallel at 90.7 MHz. Things got very hot.
>
> ** Integrated circuits and microprocessors has not been invented then. Actually, the transistor barely had been.
>
>> On 1/18/2020 10:55 AM, Roger wrote:
>> NO amplifier needs inrush protection - it is the POWERSUPPLY that needs it
>> no matter how it is implemented.
>> So the answer is not an easy "NO" or "YES" but a definite "it depends"!
>>
>> Roger, DL5RBW
>>
>>
>
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Elecraft mailing list

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

Guys,

This is very interesting. Is there a Wiki site where all your explanations are collected together. I am Interested in the magnetization of the iron in the transformers and the effect of the turn on current phase causing an over magnetization of the iron core and drawing too much current at first. This is all new to me. Just an interest as I have never run over 100 watts and usually 5 - 10 watts is enough for me.

Also, how do those inrush devices work? I have seen them offered for the old Heathkit amps.

Thank you.

Dave K8WPE since 1960 always learning something new from you guys and gals.

David J. Wilcox K8WPE’s iPad

> On Jan 19, 2020, at 12:51 AM, Vic Rosenthal <[hidden email]> wrote:
>
> Just like the 1930s vintage Western Electric at WKOP when I worked there in the early 60s. When you turned it on, it went click-click-click-click BLANG.
> Two tubes, 12 kV on the plates, about 1 amp plate current for 5 kW output.
>
> Victor 4X6GP
>
>> On 19 Jan 2020, at 1:45, Fred Jensen <[hidden email]> wrote:
>>
>> 10 KW homebrew FM broadcast TX [not kidding -- KPFK 90.7 Los Angeles in the late 50's, 4 4-1000A's* in parallel driven by a 1 KW stage] had a step-start using mechanical time-delay relays.** It limited the inrush current to the filter capacitors of the 5.5 KV plate power supply. It was part of the power supply in the back room, not the PA.
>>
>> 73,
>> Fred ["Skip"] K6DGW
>> Sparks NV DM09dn
>> Washoe County
>>
>> * I do *not* recommend 4 ea 4-1000A's in parallel at 90.7 MHz. Things got very hot.
>>
>> ** Integrated circuits and microprocessors has not been invented then. Actually, the transistor barely had been.
>>
>>>> On 1/18/2020 10:55 AM, Roger wrote:
>>> NO amplifier needs inrush protection - it is the POWERSUPPLY that needs it
>>> no matter how it is implemented.
>>> So the answer is not an easy "NO" or "YES" but a definite "it depends"!
>>>
>>> Roger, DL5RBW
>>>
>>>
>>
>> ______________________________________________________________
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Vic Rosenthal

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

Vic Rosenthal

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

In reply to this post by Elecraft mailing list

The simplest circuit, which I added to my TL922, is a relay operated
from a DC supply with a capacitor across the coil. The circuit can be
set up to provide from a fraction of a second to a much longer delay.
When the relay is de-energized, a small resistance is inserted in series
with the line to the plate and/or filament transformer. When the relay
pulls in, the resistor is shorted out and the line is connected directly
to the transformers.

I set mine up for about half a second, mostly to increase the life of
the amplifier's on-off switch, and also to provide a more gentle
start-up for the tube filaments. It has a side benefit of preventing the
"thump" which sometimes occurs.

The cold resistance of the filaments is very, very low, and the inrush
current can be very high. As K4TAX said, in a properly designed
amplifier, the transformer itself limits the inrush current to the
filaments and the initial charging current of the capacitors in the
plate supply to a safe value for the tubes, rectifier diodes, and other
components.

But I have had to replace on-off switches in the similar SB220, which
means finding the right switch or it looks ugly. And I believe that the
life of the filament will be longer if it heats up more gradually. In
the big WE transmitter I mentioned in my previous message, there was a
five-step switch to turn on the filaments, and I was told to wait about
a second between steps.

It might be unnecessary, but it was just a few junkbox parts.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
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Roger-3

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

Life sometimes is not as easy as it seems at first glance...............

The heater inrush current topic is a topic by itself and more complex than
what can be read and heard in most of the ham communities. There used to be
a very good treatment of heater management at the BURLE tube company
homepage. Whether the page is still alive or not I don´t know. If alive you
can learn a lot about the Miller-Larson effect, correct soft start for
heating etc.

What is sure is that especially in the case of the TL-922 the heater inrush
current is up to 10!! times the nominal value just like it is the case with
a cold filament bulb. This value has been measured - the only valid way to
make a technical statement anyway. EIMAC requires the inrush current to be
limited to not more than 3 x nominal value therefore inrush current limiting
is a good idea in case you want maximum tube life. Burned powerswitches as
stated elsewhere in this forum are not uncommon with TL-922s without current
inrush limiting. Another very important factor is heater voltage however
this is another story.

Not only the heater benefits from a smart soft start but also the high
voltage powersupply - especially the diodes and after all the filter
capacitor/s could go bad. It may work for a long time without soft start but
it is no good engineering practice unless very "soft" transformers are used.
This would be a disadvantage at least for the high voltage powersupply.

But coming back to the original question:

With switching mode powersupplies (as in the KPA500 and 1500 and most of the
solid state amplifiers with ps included) usually no further measures are
necessary or would help in that respect as most SMPS have soft start
circuits included.

Somebody requested more information on transformers and the magnetizing
mechanism - a good source is the website of any transformer manufacturer.
They usually have pretty good theoretical explanations of this and other
interesting parameters relevant in the world of transformers.

As with many things in ham radio the best thing is to perform measurements
and decide based on the results rather than "feelings" or "I have heard
from someone who have heard from someone........"

Roger, DL5RBW

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Victor Rosenthal
Sent: Sunday, January 19, 2020 1:11 PM
To: David Wilcox
Cc: [hidden email]
Subject: Re: [Elecraft] Ameritron 240V inrush limiter: any benefit on a
KPA500?

The simplest circuit, which I added to my TL922, is a relay operated from a
DC supply with a capacitor across the coil. The circuit can be set up to
provide from a fraction of a second to a much longer delay.
When the relay is de-energized, a small resistance is inserted in series
with the line to the plate and/or filament transformer. When the relay pulls
in, the resistor is shorted out and the line is connected directly to the
transformers.

I set mine up for about half a second, mostly to increase the life of the
amplifier's on-off switch, and also to provide a more gentle start-up for
the tube filaments. It has a side benefit of preventing the "thump" which
sometimes occurs.

The cold resistance of the filaments is very, very low, and the inrush
current can be very high. As K4TAX said, in a properly designed amplifier,
the transformer itself limits the inrush current to the filaments and the
initial charging current of the capacitors in the plate supply to a safe
value for the tubes, rectifier diodes, and other components.

But I have had to replace on-off switches in the similar SB220, which means
finding the right switch or it looks ugly. And I believe that the life of
the filament will be longer if it heats up more gradually. In the big WE
transmitter I mentioned in my previous message, there was a five-step switch
to turn on the filaments, and I was told to wait about a second between
steps.

It might be unnecessary, but it was just a few junkbox parts.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
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ANDY DURBIN

Ameritron 240V inrush limiter: any benefit on a KPA500?

In reply to this post by k6dgw

"With switching mode powersupplies (as in the KPA500 and 1500 and most of the solid state amplifiers with ps included) usually no further measures are necessary or would help in that respect as most SMPS have soft start circuits included."

KPA500 nominal 60 V PSU is not a switching mode supply. About one quarter of the chassis volume is occupied by a toroidal transformer and its output goes to a bridge rectifier.

Andy, k3wyc
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Bob McGraw - K4TAX

OT - Two Kind of Folks

I find there are two type of folks: Those that know what they speak
about, and those that think they know what they speak about. My
suggestion, try to be in the first group.

73

Bob, K4TAX

> "With switching mode powersupplies (as in the KPA500 and 1500 and most of the solid state amplifiers with ps included) usually no further measures are necessary or would help in that respect as most SMPS have soft start circuits included."
>
> KPA500 nominal 60 V PSU is not a switching mode supply. About one quarter of the chassis volume is occupied by a toroidal transformer and its output goes to a bridge rectifier.
>

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Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

In reply to this post by Vic Rosenthal

Edward R Cole

Re: Ameritron 240V inrush limiter: any benefit on a KPA500?

In reply to this post by k6dgw

I used on-rush current limiting series resistors on the 240vac input
to my 4200 volt transformer and one on the 5v filament of my 8877
amplifier. The filament drew normal 11A, so on-rush was
huge. Simple resistor-capacitor time constant timer controlled relay
to short out large 50w and 100w current-limiting resistors. Relays
were 12vdc so a diode rectified the 240vac and I supplied 12v to the
filament relay ckt from amplifier control panel.

I also had a 100-ohm current limiting resistor on the 4200v PS output
to protect from HV arc over's. G3SEK Triode Board was used for bias
and amplifier over current protection; It provided 5-minute warm-up
delay for HV to the 8877.

I've retained my 8877 project web-page for information, though it was
sold in 2018. Now run only sspa's: KXPA100, 1000w Harris on 6m,
1500w W6PQL sspa on 2m, and 600w sspa on 1296. No more "bangs" when
HV goes to ground. SSPA's all use 50v-50A switching PS.

73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[hidden email]

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