[ETO_Alpha] FS: New unopened 3CPX800A7
Jan C. Robbins
swanman at cfu.net
Mon Mar 23 17:42:37 EDT 2015
I understood that entirely, Mac, and I agreed with what you said. Sorry
you thought otherwise; that's my fault.
Your tale reminded me of some others from the 90's and early 2000s.
Bil Edwards built his LK-800 mods to run 5000 watts. He wanted my 3CPXs
for them, so they wouldn't burn out tubes.
Pat Stein bought my 3CPXs for his exceptionally high-powered amps, also
to prevent burn out.
Dick Byrd used only 3CPXs in his Alpha 76 conversions as long as I could
get him tubes.
But my favorite story, from the 90s, was an international contester
(i.e., from another country) who called me to ask if I could get him 6 or 8
3CPX tubes. I asked him what he was running, and it turned out he had
an Alpha 77SX and a couple of the monster Henrys--8K or whatever
they were. He said he couldn't keep tubes in them. It turns out that
he ran them at 5kw,+ in contests, which was perfectly legal in his
situation (and EVERYBODY in conesting knew his call!!). He was forever
grateful that ON4UN or one of his other DX friends put him on to pulse
tubes. He had lots of dough, but a healthy chunk of
it had been going to 3CX tubes!
Just backs up your point, Mac, and I appreciate your kind support.
vy 73 to all! Jan
On 3/23/2015 4:16 PM, Mac McCullough wrote:
> 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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