[ETO_Alpha] FS: New unopened 3CPX800A7

Mon Mar 23 17:16:07 EDT 2015

Jan  my intention was not to slam or knock you in any respect.  what i 
offered was intended to cast the CPX tube in a more correct light, i 
truly while not defending you,  thought you were in a hurry and just 
confused Current and Volts with respect to the tube when you listed 
it..  oddly i was not intending or trying for some sort of pissing 
match, i see you list these type tubes and have for years..all i ever 
intended was support for the tube and a wake up information for guys who 
value the 8877's performance ...If you have construed or inferred 
something else, that is you,  but not intended from me..

mac/mc  w5mc

On 3/23/2015 3:59 PM, Jan C. Robbins wrote:
> 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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