[Amps] Chinese 4CX1000A from Alpha

[Vic K2VCO]

According to the data sheets, they are very different. The 1500B has a special grid 
structure that produces a very low level of IMD, if you operate them according to the 
parameters on the data sheet -- which includes a screen voltage of 225 instead of the 325 
spec'd for the 1000A. The efficiency is low compared to the 1000A as it is spec'd. Maximum 
output from the 1500B at 3kV is less than 1500w per tube, even with the greater plate 
dissipation.

When I started my amp project I had some 1500B pulls that I thought about using, but since 
I wanted to use a single tube, and since I work almost entirely CW, I figured the 1000A 
was more appropriate.


On 11/15/2013 2:51 PM, Gary K9GS wrote:
> Hello Vic,
>
> I just took delivery of a new Alpha 8410 amp about 3 weeks ago.
>
> What's really interesting is that Alpha is running a promotion where you get a spare pair
> of tubes or a wattmeter.  I took the tubes. When my invoice was e-mailed, instead of
> listing 4CX1000A's, it said 4CX1500B's.  Because Alpha also sells an amp that uses the
> 4CX1500B (8406 6 M amp) I thought someone made a mistake and I called Alpha about it.
>
> Alpha said that they consider the two tubes interchangeable in their amps.  They also said
> that either tube pair is way overkill for the amp.  The power supply runs out of steam
> long before reaching what a pair of tubes is capable of.  I think I read somewhere that
> they have the screen voltage dialed down to limit the gain.
>
> Anyway, my spare pair of tubes arrived this week.  They are Penta Labs brand.
>
>
>
> On 11/15/2013 10:33 AM, Vic K2VCO wrote:
>>     I wasn't entirely happy with the behavior of 4CX1000A pulls, so I decided to
>>     bite the bullet and try a new tube. So much for my 'cheap' amplifier project
>>     (you hot rod guys understand the phenomenon of starting a project because
>>     you already have all the parts and it will cost almost nothing, and then
>>     experiencing 'mission creep')!
>>     Anyway, I decided to order one from Alpha, which sells Chinese tubes that
>>     they have tested and guarantee. There is also a guy on Ebay from Australia
>>     selling new Eimacs for close to the same price when you add the shipping.
>>     The upshot is that the screen current is more stable than with the pulls.
>>     Not surprising, since I understand that many 4CX1000A pulls were removed
>>     from BC service because of excessive secondary emission. The new tube needed
>>     slightly more bias voltage to obtain the rated ZSAC and appears to need more
>>     drive for full output.
>>     Finally, the Chinese version has an anode cooler with internal crimps for
>>     more surface area, similar to the one on the Eimac 4CX1500B.
>

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/