----- Original Message -----
From: "Gary Schafer" <garyschafer@comcast.net>
To: "'jeremy-ca'" <km1h@jeremy.mv.com>; "'Amps @Contesting.com'"
<amps@contesting.com>
Sent: Tuesday, March 18, 2008 8:21 PM
Subject: RE: [Amps] Power transformer for 600 watt rig
>
> Filtering isn't the problem. Dynamic regulation is a problem with a choke.
> You get severe voltage drops when current is drawn at an audio rate from
> the
> power supply.
That is in complete disagreement with reality.
A swinging choke is even worse than a regular choke. They
> should never be used in an SSB power supply.
Tell me the difference between a Class B amp and a Class B modulator
requirements.
> Put a scope on the high voltage output of the supply with a choke (thru
> appropriate divider resistors) and you will see some pretty nasty looking
> voltage drops with modulation.
I have many times over the past 4+ decades. A well designed swinging choke
input PS has none of those problems. I stress "well designed".
> Only a tuned choke is desirable as it does not have the problems of a
> regular choke.
W8JI thru a lot of monkey wrenches into that myth on here over the years.
Putting into practice what looks good on paper isnt that easy.
A real problem with a swinging choke is that there are very few people still
alive that know how to design one. Peter Dahl built one for me in 1983 that
worked just great with a pair of 4-1000A modulators. Last I heard that
complete amp, modulator and both PS were still on the air.
>
> Series resistance of the transformer is the second problem for voltage
> regulation in a power supply used for SSB. We want as low a resistance as
> we
> can get. Most of the older power transformers are not well suited for SSB
> operation because of their rather high series resistance.
Very true but only when someone tries to get the full secondary voltage in a
bridge and also expects the full wave CT config current using SS and a cap
input.
If a builder actually understands the manufacturers transformer specs and
doesnt apply some halfwit ham super optimistic rating to it AND designs
accordingly it will perform just fine. I burnt up a few learning that a long
time ago.
Carl
KM1H
>
> 73
> Gary K4FMX
>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>> Behalf Of jeremy-ca
>> Sent: Tuesday, March 18, 2008 5:43 PM
>> To: garyschafer@comcast.net; 'Pat Barthelow'; 'Jim Tonne'; 'Amps
>> @Contesting.com'
>> Subject: Re: [Amps] Power transformer for 600 watt rig
>>
>> SSB is less critical than a Class AB or B modulator as far as PS
>> requirements which is why a single capacitor is capable of sufficient
>> filtering.
>>
>> For a modulator a choke input is used and it is not a fixed value
>> smoothing
>> choke nor is it a tuned choke at amateur power levels. What is used is a
>> swinging choke that maintains critical inductance at a light load but
>> changes (swings) as the current is increased. These are typically built
>> over
>> a 5:1 ratio; 4-20; 5-25, 6-30 Henries, etc.
>>
>> By maintaining critical inductance the voltage will not soar with a light
>> load.
>>
>> All you ever need to know about designing this style of supply is found
>> in
>> the old Handbooks from the AM days, especially the Bill Orr series of
>> Handbooks.
>>
>> By using a choke input filter SS rectifiers can be used with the old
>> style
>> transformers designed for tube rectifiers without cooking them as usually
>> happens with a single fat cap.
>> Instead of a unloaded DC voltage of 1.4X RMS with a bridge and a cap the
>> output will be .9. However the regulation will be far superior to the cap
>> version which may drop well below .9 on peaks.
>>
>> Swinging chokes in the 500-1000 ma CCS range are readily available on the
>> used and surplus market. I recently picked up a 5-25H @ 1A with 7500V
>> insulation for $70. I cant wait to watch the 304TL's glow on voice peaks!
>>
>> Carl
>> KM1H
>>
>> ----- Original Message -----
>> From: "Gary Schafer" <garyschafer@comcast.net>
>> To: "'Pat Barthelow'" <aa6eg@hotmail.com>; "'Jim Tonne'"
>> <tonne@comcast.net>; "'Amps @Contesting.com'" <amps@contesting.com>
>> Sent: Tuesday, March 18, 2008 3:14 PM
>> Subject: Re: [Amps] Power transformer for 600 watt rig
>>
>>
>> > Hi Pat,
>> >
>> > The biggest problem with a choke input filter is the transient response
>> of
>> > the choke with SSB. It will allow the voltage to dip quite a bit on
>> > some
>> > of
>> > the voice peaks as the amplifier demands current. A supply with no
>> > choke
>> > doesn't have those kind of problems. A tuned choke on the other hand
>> will
>> > act like a capacitor input filter and will not have the transient
>> problems
>> > either.
>> >
>> >
>> > 73
>> > Gary K4FMX
>> >
>> >> -----Original Message-----
>> >> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
>> On
>> >> Behalf Of Pat Barthelow
>> >> Sent: Tuesday, March 18, 2008 12:12 PM
>> >> To: garyschafer@comcast.net; 'Jim Tonne'; 'Amps @Contesting.com'
>> >> Subject: Re: [Amps] Power transformer for 600 watt rig
>> >>
>> >>
>> >> This is quite informative...Question, From Gary's comment about
>> Secondary
>> >> Resistance, and choke input power supplies, not sufficient for SSB
>> >> dynamic
>> >> regulation, if one has available an older power supply, that is choke
>> >> input, you need relatively low secondary resistance....Does the choke
>> >> resistance have a lot of influence there also? What are some typical
>> >> values of HV choke resistances? If so, then I think what you are
>> >> saying,
>> >> is some (most?) choke input power supplies will have regulation
>> >> issues
>> >> with SSB.
>> >> Yes/No?
>> >>
>> >> All the best,
>> >> Pat Barthelow (916) 315-9271
>> >> aa6eg@hotmail.com
>> >> http://www.jamesburgdish.org
>> >>
>> >>
>> >> > From: garyschafer@comcast.net
>> >> > To: tonne@comcast.net; amps@contesting.com
>> >> > Date: Tue, 18 Mar 2008 11:08:59 -0400
>> >> > Subject: Re: [Amps] Power transformer for 600 watt rig
>> >> >
>> >> > Hi Jim,
>> >> >
>> >> > No I don't have LTspice.
>> >> >
>> >> > What I was saying about what type of service the power supply is to
>> >> expect
>> >> > to see matters a great deal. A transformer (a good one) that is to
>> >> > be
>> >> used
>> >> > with a voltage doubler might have a secondary resistance in the
>> >> neighborhood
>> >> > of 15 ohms.
>> >> >
>> >> > A transformer to deliver the same power supply voltage using a choke
>> >> input
>> >> > filter can get by with a transformer secondary resistance of a
>> >> > couple
>> >> > of
>> >> > hundred ohms.
>> >> > The dynamic regulation of the latter will be fine for an AM or FM
>> >> > rig
>> >> but
>> >> > not acceptable for SSB.
>> >> >
>> >> > 73
>> >> > Gary K4FMX
>> >> >
>> >> >
>> >> > > -----Original Message-----
>> >> > > From: amps-bounces@contesting.com
>> >> > > [mailto:amps-bounces@contesting.com]
>> >> On
>> >> > > Behalf Of Jim Tonne
>> >> > > Sent: Monday, March 17, 2008 9:47 PM
>> >> > > To: garyschafer@comcast.net; 'Amps @ Contesting.com'
>> >> > > Subject: Re: [Amps] Power transformer for 600 watt rig
>> >> > >
>> >> > >
>> >> > > Gary:
>> >> > >
>> >> > > Do you have LTspice? I will plug those numbers
>> >> > > into the transformer model to complete the design.
>> >> > > The numbers I quoted are adequate for the problem
>> >> > > as stated.
>> >> > >
>> >> > > - Jim Tonne
>> >> >
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