>I wrote and asked about this tube, here is what I got back:
>
>"Thanks for your Email.
>
>I have been receiving inquiries for the past couple of days regarding this
>new product.
>
>It was an idea that languished for a period of time, the individual that
>suggested this tube was a ham I have known for many years. We promised to
>sell him a tube for his moneymaking idea, namely conversion of existing
>amplifiers such as the Drake L4B, to replace the 3-500Z that Eimac no
>longer makes. I guess I finally convinced engineering to make a tube
>sometime last January. It was just completed last month but the effort to
>check it was put off for one reason or another. Finally it was sent to the
>lab engineers to check out. RF test data indicates it is a good tube
>where 80 to 100 Watts of drive power is available. It likes to be run at
>4000 Volts (more so than 3000 V as grid current tends to drop with
>increasing plate voltage). The 3CX1500D7 is "bulletproof" compared to the
>smaller oxide cathode tubes presently being used in amplifiers made for
>the amateur radio market. I brought in an old Drake L4B and we see that it
>will work in that equipment as long as the air flow is increased by adding
>a blower to the air intake opening on the back of the linear. Also a
>gasket must be added between the OD of the plate cooler on the tube and
>the ID of the glass chimney on the existing amplifier, and the unused
>socket covered over. The gasket can be made of silicone rubber and stuck
>on with RTV or silicone rubber. Teflon might be useable if one can keep
>it from slipping down (it can't be glued to the chimney!) but no one has
>figured out how to use that material yet. Something needs to reduce the
>loss of air from the top of the chimney around the anode cooler on the
>tube. A special pyrex chimney would be nice but too costly (besides we
>don't have glass making equipment any longer). Last week my boss decided
>to send out a press release, announcing this tube. Unfortunately we have
>not built up a stocking level yet, therefore delivery is going to be
>rather lengthy, I presume it will be between 60 and 90 days. (That should
>make one available for a late summer project, right?) You may be
>delighted to know that we are introducing a new "buy-direct" plan whereby
>Hams can pay us directly (we plan to accept Visa or Mastercard sales only)
>and we ship this tube directly from the factory, thereby keeping the price
>manageable.
? - Reid - Direct sales are good news. The sole-distributorship deal
that Varian-Eimac made with Richardson Electronics was clearly a
violation of the Sherman Anti-trust Act.
>If distributors
? How many Eimac distributers are there?
>were selling this tube their normal 35% markup
>would make it much less desirable. This plan will not apply to other
>products already established as distributor items. Selling for $599 per
>tube, it is obvious that a single 3CX1500D7 will cost somewhat more than
>two 3-500ZG. But we believe the reliability will be superior to some of
>the Chinese 3-500Z that are on the market (did you ever wonder why they
>sell matched pair of 3-500Z?) Also if you take into account the extra
>headroom this tube has it starts to show virtues that are worth the
>investment. I just spoke with one individual who feels this way to the
>extent that he plans to call our customer service tomorrow and order one.
>
>... ... ...
>I have observed a 3CX1500D7 running at a plate voltage of 5500 Volts, with
>800 mA plate current, and with a drive power of 105 Watts it put out 3000
>Watts exactly. The power gain was 14.5 dB and the plate dissipation was
>1400 Watts, still within ratings. The tube is completely stable at that
>power level, but I don't recommend you try that in a linear designed to
>run at 1500 Watts or less, as component damage will certainly result!.
? Indeed, Reid, with the typical Ham bandswitch breaking down at c. 5kV.
>
>The Henry amplifiers always seemed to be an odd in some respects. I have
>seen one up close and I rather like the plate supply. Why they used
>series connected filaments is unknown to me! My hunch is that they wanted
>to keep the wire size down on the filament chokes!
? Good point. Also, winding a 30A transformer secondary is more
problematic than winding a 15A secondary.
> Maybe there was a
>desire to prevent individuals from being able to operate with a single
>tube or something, I just do not know.
? My guess is that whoever made Henry Radio's transformers was not set
up to do 30A windings.
>Ted Henry Sr. himself probably
>knows but I will leave posing him with that question to someone else.
>
>I hope this helps you decide if this tube is one you want to use in your
>"upgrade" or retrofit into an existing linear. Let me know what you think!
>
>I'll mail you a copy of the data sheet as soon as they are available.
>
>Best 73,
>
>Reid Brandon W6MTF
>
>Applications engineer
>
>CPI Eimac division
>
>301 Industrial Rd.
>
>San Carlos CA 94070
>
>Tel. 650-594-4175 or 1-800-414-TUBE(8823) press 1 at the prompt and ask
>for me."
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>
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