[Amps] 3CX1500D7

[R.Measures]

>The development of a new power amp tube always creates a lot of interest and
>excitement in the ham community. It's too bad Eimac
>pulled the info from their website. Their development and marketing people 
>might benefit from the discussions about the new tube.
>
•  Perhaps there was an error in the anode-cathode (feedback)-C ?  It 
doesn't make sense that the 3cx1500D7 would have 4-times as much 
feedback-C as a 3cx1500A7.  

>The actual spec sheet is still available. Just go to the Amp Archives for 
>March
>16 "3CX1500D7 Spec Sheet" The compressed file is 1.24 mb and consists of 4 
>gif's.
>
>
>IMO, this tube will have limited appeal for the ham market. The
>type acceptance process discourages new amplifier dessigns. As for retrofits,
>how many hams are willing to cut the sheet metal in their commercial amps to
>install the air socket, required chimney, and blower? The TL-922 has its 
>3-500z's
>in series and
>would require an additional 5 volt transformer. Finally, the plate voltage 
>available
>in most 3-500Z amps run from about 2700 to 3300 volts which as Eimac has 
>already
>said is low for good
>performance of the new tube.

•  Good points, Dennis.  The rub with jacking up the anode-supply 
potential is that most Ham-amp bandswitches are not going to be very 
happy with a >3500vdc anode PS.  
>
>As far as instant on is concerned, it's not that big of an
>advantage. Two of my four amps (all Eimac powered) have at least 3 minute 
>wait times. How many hams really turn the amp on and off between QSO's? 

•  I turn the amp on when needed to communicate.  With instant-on tubes,  
warmup is c. 1-second.


>Planning ahead takes care of the wait requirement.
>
•  I've seen 80m West-Coast to Europe openings into that were over within 
3-minutes after I turned on my transceiver.

>Page 4 of the 3CX1500D7 spec sheet states "This tube is designed for 
>commercial service, with no more than one normal off/on filament cycle per 
day." I 
>wonder if the warranty will be
>voided if the amp does not have filament soft-start circuit.
>
•  It is hardly  good engineering practice to build an amplifier without 
step-start.

>Eimac should be commended for the effort to develop new tube designs. 
>Unfortunately,
>economics dictate high volume sales and raise the question of whether the 
>3CX1200A series will soon be discontined.
>
•  With the 3cx1200Z7 now svailable, why settle for the obsolete _A7 
version?

cheerz, Dennis