Amen and thank you. Now lets discuss G2DAF and super cathode grounded grid
amps.
73 de Hans SM5KI
>Från: "Lamb" <k7fm@teleport.com>
>Till: "AMPS" <amps@contesting.com>
>Ämne: Re: SV:SV:SV: [AMPS] Tetrode Amp Help
>Datum: ons 15 dec 1999 14.43
>
>
>We have probably beat the screen regulation issue to death - but the very
>nice Collins S-line and M-2 series did not use regulated screen voltage on
>their final 6146's.
>
>As a matter of fact, they were poorly regulated - but the Collins always
>sounded superb - partly because they used rf feedback which improved the imd
>by 10 db and actually reduced distortion.
>
>Bill Orr ran an article in Ham Radio and scrutinized the 3rd order imd of
>the Collins. He noted that by removing the screen from the original
>configuration of a series resistor and attaching it to the low voltage
>supply (which had less variation), he reduced imd by a few db.
>
>Unless the driver transceiver uses feedback or high voltage transistors,
>almost any amp (except a sweep tube amp) will have better imd specs than the
>driver - meaning the results will be irrelevant no matter how the screen is
>regulated if a proper tube is used. The 4CX1000 is a poor tube to use
>without feedback. The 4CX1500 is excellent. Today, many of the high end
>transceivers have superb 3rd
>order imd specs, meaning that the amp is now becoming the weak link.
>Amateurs are still way behind commercial units. The standard for ham gear
>is a -30 db whereas I believe most commercial equipment is a -45 db. If you
>listen on the ham bands, you can tell the difference.
>
>The bottom line is that amateurs are experimenters. Excellent tetrode amps
>can be made without a regulator - if the builder is prepared to test and
>document the amp. under actual conditions of use. Without the testing, it
>is better to follow the lead of someone else.
>
>A real advantage of the screen regulator circuit is that it provides
>absolute protection in case the plate voltage is lost for some reason. I
>have built amps without electronic regulation on the screen that had
>excellent imd performance - but there was no protection for loss of plate
>voltage until I used a relay operated by the plate bleeder to give some
>protection. However, if the rf choke had opened, I would have been in
>trouble. There are some fine regulator circuits and boards available and
>they are highly recommended.
>
>Colin K7FM
>
>
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>
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