[ETO_Alpha] FW: FS: New unopened 3CPX800A7

[Jim Garland]

Jan,

Tnx for your info, but I'm curious where you found the data showing the d.c. plate current rating is 25-30%  than the 1A rating for a non-pulse tube. I realize the pulse-rated tubes are rated at 5.5V filament voltage, and while that might be a way to inrease cathode emission (and higher plate current), doing so significantly shortens tube life. The 3cpx1500a7 data sheet recommends backing off the filament voltage to 5.0V to inrease tube life. That suggests the filaments of the pulse-rated and non-pulse rated tubes are the same, with identical cathode construction..

 

BTW, an ordinary 8877 run at its maximum ratings of 4 kV plate and 1A plate current will routinely produce about 2500W of RF power. I have Eimac 8877s that are decades old in my homebrew amps that still show full power output. I've had some unfortunate experience in the past two years with Chinese made 8877s, however. Two of the ones I've used have died after a hundred hours or so because of internal arcing.

73,

Jim W8ZR

 

From: Jan C. Robbins [mailto:swanman at cfu.net] 
Sent: Monday, March 23, 2015 10:04 AM
To: MU 4CX250B
Subject: Re: [ETO_Alpha] FS: New unopened 3CPX800A7

 

The key difference is that the pulse-rated tubes are built to withstand plate current 25-30% higher than non-pulse--that's why they're used in medical amps, radar, and FM transmitters.  So if you are an avid contester, esp. on CW and rtty, the pulse tube is to be preferred, esp. also if you tend to run power in excess of about 1300w.  The physical difference in the tubes is about 1/4" in height, which doesn't matter, but the durability difference is substantial, and it does matter: pulse tubes last longer.  

When I was still selling tubes, many customers were international contesters, who really value the pulse difference.  For normal SSB operation or casual DXing, there is no meaningful difference, but a pulse 8877 at $595 is still a very good buy.  (Of course, the grid current requirements are just the same, pulse or no pulse.)

Tks inquiry!  73 Jan

On 3/23/2015 10:55 AM, MU 4CX250B wrote:

I was under the impression that the pulse rated tubes were identical
internally to the non-pulse-rated  tubes, except for slightly longer
ceramic insulation that increased the peak voltage rating (and added
more inductance to the internal grid wires.) I know the tubes are
specified for high peak currents, but i thought that was just an
additional specification, not a change in tube construction. If I'm
mistaken, I would welcome being corrected.
73,
Jim w8zr
 
Sent from my iPhone
 

On Mar 23, 2015, at 7:32 AM, Jan C. Robbins  <mailto:swanman at cfu.net> <swanman at cfu.net> wrote:
 
If you're running a 9500, here is your chance to get that extra tube at a REASONABLE price.
 
I have one brand new purchased 2015) Penta pulse-rated 3CPX1500A7 (8877), capable of handling much higher plate current than the standard Eimac or Penta 8877 you buy from, e.g., RF Concepts, Ameritron or RF Parts (all of which sell Pentas, which are superb tubes). I sold 3CPXs to hams for nearly 20 years, and they are THE BEST tubes for very-high-power amps.  The 3CPX1500 normally sell for $775 and up (way up), but I can ship this one anywhere lower 48, fully insured, for $595. PayPal preferred, other methods acceptable. Tks es 73 N0JR
 
 
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