From: SMTP@VPGXTNCA1@Servers[] To: "reid.brandon" Cc: Subject: Pulsed tubes in continuous service. Date: Tuesday, August 19, 1997 4:48PM Hi Reid, I wonder if I could trouble you a minute with a tube question ? Are there are problems associated with running tubes intended for high peak power, pulsed use (ie 3CPX800A7, 3CPX1500A7, 3CPX5000A7, YC156 etc) at high duty-cycle (near continuous) service ? I could guess that you might damage the cathode of a standard tube if you tried pulsing the tube to very high peak output powers, but the reverse, seems on the face of it quite harmless, as long as you stay with the ratings. However, is it harmless ? Would a 3CPX5000A7 work okay if you fed it with SSB and tried to extract the same sort of powers as you would reasonably expect from a 3CX5000A7 ? I've been offered a YC156, which appears mechanically identical and not too different electrically from my 3CX5000A7. It might do as a spare, as I've so far been unable to find a second used 3CX5000A7. However, I was wondering if there are in general problems running pulsed tubes like the YC156, 3CPX5000A7 etc at high duty cycle, lower peak power. I appreciate the YC156 is not in your catalogue, so you might be restricted about what you can/can't say about that particular device. I am more interested in the general principles, rather than of that specific tube. I've still not finished the 3CX5000A7 amp, but nearly so. I'm still waiting on the anode line to be machined, which one of the mechanical technicians here said he would do on a computer controlled milling machine. I've told him this week that unless its done within the next two weeks, I'll make it myself with hand tools - he has had the design nearly a year! I have all the parts now for the amp, and the most of its been assembled. Still need to make a directional coupler to sample the drive power and wire up the meters etc. Someone from the USA kindly sent me a few 10-24 machine screws for the cathode and heater rings. Those screws were missing from my tube are very difficult to find here in the UK. I've just got a sample of a very nice high power cable from Andrews (HST4-50). Its the same size as LDF4-50 (1/2" diameter), but capable of handling 7.5 kW on 2m, and is very flexable too. The Y799 amp has not really been started, but I received the correct base (SK660A) from Richardsons. I've ordered a huge heatsink (0.2 deg C/Watt) from Germany, but not got that yet. I think I have all the other major bits, but not enough time to do much on it yet. G8WRB From reid.brandon@eimac.cpii.com Tue Aug 19 18:25:11 1997 Return-Path: Received: from mail-b.bcc.ac.uk by medphys.ucl.ac.uk (4.1/SMI-4.1) id AA20087; Tue, 19 Aug 97 18:25:09 BST Received: from pgtp1.eimac.cpii.com (actually host 206.99.149.66) by mail-b.bcc.ac.uk with SMTP (XT-PP); Tue, 19 Aug 1997 18:25:01 +0100 Received: by pgtp1.eimac.cpii.com; Tue, 19 Aug 97 10:24:32 PDT Date: Tue, 19 Aug 97 10:24:31  Message-Id: X-Priority: 3 (Normal) To: davek From: "reid.brandon" Subject: RE: Pulsed tubes in continuous service. Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Status: R Hello, Dave. The pulse ratings are put on a standard product to define how it can be used in low duty pulsed service. In reverse, one can simply find the standard product that a specific pulse tube is derived from, and use the ratings established for it (SSB/CW typical operation). The YC156 is a version of the 3CPX5000A7, which is a version of the 3CX15,000B7. All these triodes use the same grid and same cathode. The only difference (besides special electrical tests) is the plate dissipation. The plate diss. rating of YC156 is 5000 W, and as long as you do not exceed this rating, it should be simple to use in amateur service. Do you need a copy of the 3CX15,000B7 data sheet? I'll be glad to send you a copy and we have your snail mail address on file here. Incidentally, there are YC156 starting to surface lately, one ham bought a couple and plans to use them in a SSB HF linear. They like to run at a plate voltage of 4500 - 6000 volts. Gain is good (provided the tube is good in the first place!) Regards, Reid Brandon. ---------