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
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
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
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!
----- Original Message -----
From: "Gary Schafer" <firstname.lastname@example.org>
To: "'Pat Barthelow'" <email@example.com>; "'Jim Tonne'"
<firstname.lastname@example.org>; "'Amps @Contesting.com'" <email@example.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
> 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
> Gary K4FMX
>> -----Original Message-----
>> From: firstname.lastname@example.org [mailto:email@example.com] On
>> Behalf Of Pat Barthelow
>> Sent: Tuesday, March 18, 2008 12:12 PM
>> To: firstname.lastname@example.org; '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
>> 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
>> is some (most?) choke input power supplies will have regulation issues
>> with SSB.
>> All the best,
>> Pat Barthelow (916) 315-9271
>> > From: email@example.com
>> > To: firstname.lastname@example.org; email@example.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
>> > to see matters a great deal. A transformer (a good one) that is to be
>> > with a voltage doubler might have a secondary resistance in the
>> > of 15 ohms.
>> > A transformer to deliver the same power supply voltage using a choke
>> > 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
>> > not acceptable for SSB.
>> > 73
>> > Gary K4FMX
>> > > -----Original Message-----
>> > > From: firstname.lastname@example.org
>> > > [mailto:email@example.com]
>> > > Behalf Of Jim Tonne
>> > > Sent: Monday, March 17, 2008 9:47 PM
>> > > To: firstname.lastname@example.org; '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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>> > Amps@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
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