[ETO_Alpha] FS: New unopened 3CPX800A7

Mon Mar 23 16:55:35 EDT 2015

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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>
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