[AMPS] NCL-2000 comments
km1h@juno.com
km1h@juno.com
Wed, 30 Dec 1998 16:14:21 -0500
On Wed, 30 Dec 1998 10:39:46 -0800 Rich Measures <measures@vc.net>
writes:
>
>
>>>A 20w resistor in a circuit where the dissipation is typ. 0.13a^2 x
>20
>>>ohms = 0.34w?
>>
>>
>>I suggest you consult the schematic to determine the location of
>RFC-2
>>Rich.
>
>€ Thanks, Carl. The max. diss. would be 0.8a^2 x 20-ohms = 12.8w, so
>a
>20Wer would be a good choice.
I am pleased that you agree Rich.
>>........
>>>>73 Carl KM1H
>>>>Amplifier Repairs and 6M Conversions our Speciality
>>>>National Radio 1963-69 Part of NCL-2000 Design Team, Service Mgr
>>>>1965-69
>>>>
>>>The NCL-2000 circuit design:used a killer screen-supply.
>>
>>Separate winding on the xfmr, common useage for the times. Also was
>per
>>RCA recommendations including the surge and fuse resistors used.
>>
>Many screens got toasted.
Many screens got toasted from poor tube design, not the PS. Early 8122's
had no support for the screen, a little bit of current and it walked
right over to the plate. Later versions used ceramic spacers.
The Eimac 8122W was a very strong tube as was the Amperex version.
The NCL screen supply is no better or worse than the competition of the
era.
>
>>>2. did not protect the 8122's unusually delicate screen from
>>>excessive >screen current.
>>
>>Screen trip ckt was in the prototypes. RCA really tucked it to
>National
>>with the early 8122 mfg problems.
>>
>>>3. ran grid current (Class AB2 grid-driven) which made ssb-doodoo.
>
>>
>>With ALC connected it was simple to limit grid current and give
>>acceptable doo doo. There is only 1dB difference in IMD3 between AB1
>and
>>AB2 with the 8122.
>
>€ [chortle] Apparently not simple enuff for trogs in the land of the
>
>fruits and nuts. There were plenty of 'em who ran several mA of grid
>current, and thereby made abundant daytime forty-meter feculence. //
>
>How much grid current did the manual say was ok?
A barely perceptible wiggle. " until the grid current just flicks off
zero occassionally..."
>>>4. ignored a distortion-lowering circuit recommendation from RCA's
>>>8122 tech info. sheet.
>>
>>Not according to RCA, suggest you get reading glasses.
>>
>€ As I recall, RCA recommends a rf-nfb R in an unbypassed cathode,
>like
>Eimac recommends for the 4cx600, like Svetlana recommends for the
>4cx1600. The NCL-2000 did not.
The NCL strictly followed RCA recommendations right down the line. The
cathode resistor is suggested as an option in Class AB1 and at 2000V or
less ONLY.
I tried ur QST mod many years ago ( 198 something) and it brought the
amp up into parasitic land.
You also have to read the fine print in many spec sheets.
The cathode resistor has never been used to my knowledge in a VHF amp due
to the stability problems associated with a big inductor hanging out
there.
I much prefer a big fat low L strap to gnd and let the IMD suffer a bit.
Who is going to hear a 5 dB difference on most HF bands anyway, the
typical rice box exciter sets the pace.
I have rebuilt the screen supply with G3SEK's circuit this past summer.
Standard IMD tests show a 5-6 dB improvement in my 6M version where IMD
becomes important.
Voice tests with the peak hold function on the analyzer were similar. ( I
fed Rush Limbaugh in as the "voice" and let him rant for about 20
minutes) Maybe I should have used my Muddy Waters CD.
>>
>>>5. as I recall, used no low-L screen capacitor/collet bypass to
>>>improve vhf stability.
>>
>>That is on the prototypes also.
>>
>€ another design change by bean-counters?
YEP.
>
>>As I stated here and to you in the past, what was designed in Engr is
>not
>>what got built after the Marketing VP screwed around.
>
>€ R, R, R
>
>>One engr quit in
>>disgust. I transfered to the Svc Dept, wrote NCL service bulletins
>and
>>was soon promoted to Svc Mgr. over the objections of the idiot in
>>Marketing. He left years before I did.
>>
>€ If I came with an amplifier design that was subsequently changed by
>
>schmucks, I would not want my name associated with their mistakes.
>- cheers.
Schmuck is correct, you dont know how right you are (- :
The big dollars were put into the external appearance and all that fancy
extruded aluminum plus rear cover ads in most ham rags. I admit the
NCL-2000, NCX-5 and HRO-500 series were great looking products and won
many industrial design awards. But the user suffered.
At least my wife likes the looks of the HRO-500's in the bedroom and
living room. She objected strenuously to the NC-303 and HRO-60 that used
to reside respectively.
I dont dare bring the 51J4 out of the basement!
73 Carl KM1H
73 Carl KM1H
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