[Collins] 30S-1 final 4CX1000 and 4CX1500 poor terminology

[Phil M.]

While I understand and have enjoyed the discussion, I believe the
tube designation terminology has been very careless.  First of all,
people have been talking about the 4CX1500 which is not very
accurate.  The tube suitable for use in the 30S-1 is the 4CX1500B...
please note the B.  According to the 1975 Eimac catalog, there is
a 4CX1500A which has a filament requirement of 5 volts at 38 amps
versus the 45CX1500B which needs 6 volts at 10 amps....a minor
difference :-)  And, as someone pointed out earlier, the 4CX1500B is
listed as designed for SSB with lower IMD.

BTW, the same 1975 catalog lists a 4CX1000K with virtually the
same characteristics as the 4CX1000A but with a solid screen ring....
I've never come across one of these.

73, Phil
W5BVB



----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at storm.weather.net>
To: "pete wokoun, sr." <pwokoun at hotmail.com>
Cc: <collins at mailman.qth.net>
Sent: Tuesday, September 11, 2007 1:32 PM
Subject: Re: [Collins] 30S-1 final


> On Mon, 2007-09-10 at 20:15 -1000, pete wokoun, sr. wrote:
>> The 30S-1 I'm working on has a 4CX1000A final.  The tech manual also 
>> lists
>> this as the final.  I've heard and read about some amps having a 4CX1500B 
>> in
>> there.
>>
>> Is this a later model change?  I see the tubes specs are almost identical
>> except for the plate dissipation and filament current.  Can  they be
>> interchanged in the 30S-1 or do you HAVE to use what's stenciled on the
>> bottom side of the top cover, ie the 4cx1000A?
>>
>> pete KH6GRT
>>
> I don't think the 4CX1500 was ever a factory mod.
>
> Comparing the two data sheets there isn't a great deal of difference
> other than plate and grid dissipation ratings and screen current
> characteristics. The heater currents are the same.
>
> Because of better cathode to grid alignment, the 1500 claims less grid
> interception of the electron stream which allows better linearity with a
> bit of grid current and some grid current is allowed (grid dissipation 1
> watt).
>
> Typical RF amplifier characteristics are with 225 volts on the screen of
> the 1500 and 325 on the screen of the 1000. Since tube gain is directly
> proportional to screen voltage, a mod that raises the screen voltage
> will make the amplifier have more gain but may upset the tuning meter
> and amplifier stability. A different screen voltage also can mean a
> different plate load line is needed to keep the minimum dynamic plate
> voltage is always above the screen voltage, else the screen gets
> overloaded by gulps of current that used to be peak plate current
> suddenly switching to the screen, and its not made for those several amp
> peak currents.
>
> The typical data also shows the 1500 screen tends to run much more of a
> negative current than the 1000.
>
> Other than the more negative screen current (which isn't a problem in
> the grounded screen supply situation where the "screen" supply is also
> carrying the total cathode current) it looks as if the 1500 makes a
> decent and probably more linear replacement for the 1000 and the 1500
> tolerates more grid drive without adding distortion or damaging the
> grid.
>
> I'm always concerned with plate matching and plate tank components.
> Raising the output from 1 KW to 1.5 KW raises the tank coil and loading
> capacitor currents about 50% and that raises their power dissipation
> more than double. The 30S-1 may have conservatively enough rated parts
> to handle that increase. Not all finals can stand that, and the 1.76 dB
> difference between 1 KW and 1.5 KW is far less than the second by second
> changes in propagation and not something measurable with most receiver
> S-meters. In the rare situation where propagation is steady and the 1 KW
> signal is at the noise, that 1.76 dB increase may improve received
> signal to noise ratio several more dB than the increase in power. In all
> other situations it only runs up the electric bill.
>
> If it was me, I'd run the 4CX1500B at 4CX1000A ratings and expect a very
> long tube and radio life.
> -- 
> 73, Jerry, K0CQ, Technical Advisor to the CRA
> All content copyright Dr. Gerald N. Johnson, electrical engineer
>
> ______________________________________________________________
> Collins mailing list
> Home: http://mailman.qth.net/mailman/listinfo/collins
> Help: http://mailman.qth.net/mmfaq.html
> Post: mailto:Collins at mailman.qth.net
>
>