[ETO_Alpha] FS: New unopened 3CPX800A7

Mon Mar 23 16:59:54 EDT 2015

About 100 of the top contesters in the world bought 3CPX1500s from me, 
and a bunch more the 3CPX800s.   So far as I know, they're all still 
using those tubes, some of them 20 years later. Obviously, none of them 
knew what they were doing, eh Mac? Just why, I wonder, do some people 
think engineers designed DIFFERENT tubes for medical, pulse and radar 
use if the 3CX versions did the same thing. Interesting.

73 to all, and thanks again for the legitimate inquiries.  Jan

On 3/23/2015 3:55 PM, Mac McCullough wrote:
> WE ARE talking here about the 3CPX1500A-7 tube  and NOT the 3cpx800a7  
> .. sri didn't catch what tube number Jim had listed,  i was keying off 
> what i had seen as Jan's listing for the 3CPX1500 tube
>
> On 3/23/2015 3:51 PM, Mac McCullough wrote:
>> At the first reading I also noticed what Jan had said about higher 
>> CURRENT  values for the tube,  but i dismissed it as his push to get 
>> something listed and not to hopefully overstated the value or 
>> features of the CPX tube..
>>
>> Beginning in May of last year I went on a  "update" of my Alpha 77Sx  
>> Soon like most things, the project went big or more. Followed by a 
>> new HV filter cap and a slight increase in capacitance as well 
>> operating voltage. Then came the main Xformer followed by a new HV 
>> rectifier board that has been totally redesigned and updated. All the 
>> while the moment of effort and truth was fast approaching.
>>
>> I was yellow, and punted to Eimac for help.  In two separate calls 
>> with direct application engineers for the 8877/3CX1500A-7 tube they 
>> never budged on the HV top rating of 5000 vdc.. My amp was now making 
>> 4950 idle plate voltage, yes sure they tested it higher, but would 
>> not move even for idle voltage. Finally we discussed real operating 
>> conditions and characteristics of the amp proper. This is a 
>> conversation in it's own self.
>>
>> As an off hand comment it was proffered, had i considered the 3CPX 
>> version of the 3CX tube  I said no never heard of it.  Soon enough as 
>> much data as they would release was here on my computer for review. 
>> Yes the outward tube design for the CPX gives the white ceramic area 
>> about a 3/16-1/4" taller profile than the 8877/3CX model.  Outwardly 
>> that is it. No more.
>> I was struggling within myself about and even though it was at idle 
>> the higher right at 5Kv voltage where before the amp had run like 
>> 3.8Kv at idle, looking at the Plate meter "pegged" or very damn near 
>> left me no room for comfort and seriously questioning my effort and 
>> how i had lost the original objective and was now lost in the forest 
>> of higher Plate Voltage..
>>
>> I like the 77Sx  and was just not warming to the idea of the 8877 and 
>> 5kv and operating right at or on the edge..
>>
>> The operating and performance spec's for the CPX tube had immediate 
>> appeal and the 10kv plate voltage spec I was in love with and as Jim 
>> states it was only for the HIGHER plate VOLTAGE pulse and as it was 
>> explained to me indeed only the Ceramic body length was increased to 
>> allow for a slightly higher grid inductance and plate voltage.
>> I bought into the CPX version and went on the hunt for a pair of the 
>> damn things.  Soon enough that was accomplished and at what I thought 
>> was a decent enough price of $375 per tube and while not new did come 
>> from a medical application and checked almost identical to new tube 
>> testing numbers.
>> As for operation is was text book if not easier and quicker in the 
>> Loading and Tuning to get the amp up and performing, an absolute 
>> breeze, I had total confidence from the outset and that was not 
>> misplaced. I have had the 77 since it was new in 85' . It has always 
>> loaded and tuned well, but now the SWEET spots are or seem very sure 
>> and easy to walk into and rock back and forth between tune and load 
>> and just feel and know you are at the best efficiency of all the 
>> design parameters ...
>>
>> Soon after I had the thought of spare tubes and that i wanted a set,  
>> none were showing up in the usual haunts, only ebay, United RF seems 
>> to have as I recall at the time 56 of the CPX tubes listed.  I wanted 
>> the personal attention and knowledge of the tube so i called and soon 
>> enough we had agreed on $380.00 per tube incl shipping and test 
>> results, so i have a set of spare tubes now as well..
>>
>> closing notes:  my 77 had the original Eimac 8877 tubes as supplied 
>> when delivered new and had become weak and not holding the same 
>> numbers of recorded settings i have recorded for various band freq 
>> and antennas SWR points .. so that is what started the whole circus 
>> and $2,400 later not including the spare set of tubes.  If the amp 
>> last me the rest of my operating life, that i have over invested in 
>> the amp will be of small concern, reflecting back to 85'  i had to 
>> hock my ass to buy the thing in the first place.
>>
>> Final thought:  I like using the CPX version tube and i don't drive 
>> the amp any more or harder than i previously did..
>>
>> The fellow who is offering the replacement HV boards did a splendid 
>> job and that was the second 'goal' to replace or just assure the 
>> performance of the HV rectifier board. over time i had already 
>> replaced and upgraded the other smaller ckt boards.
>>
>> HV board: John Stanford, email is wb8svn at gmail.com
>> Xformer:   Hammond using the Peter Dahl design  using DigiKey
>> HV Filter Cap:   Condenser Products
>> other small nuances and tricks i had to use upon request
>>
>> Warm regards:  mac/mc  w5mc
>>
>> 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 <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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