[Amps] Chinese 4CX1000A from Alpha

[Gary K9GS]

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.

-- 


73,

Gary K9GS

Greater Milwaukee DX Association: http://www.gmdxa.org
Society of Midwest Contesters: http://www.w9smc.com
CW Ops #1032   http://www.cwops.org

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