[Amps] Chinese 4CX1000A from Alpha

[Roger (K8RI)]

On 11/16/2013 11:15 AM, Vic, K2VCO wrote:
> I didn't intend to criticize Alpha. Alpha said they were
> "interchangeable in these amplifiers" which is reasonable if they are
> running lower screen voltage. Since they are using two tubes, the lower
> efficiency and output from the 4CX1500B is not a problem. I just wanted
> to note that they are different in more than plate dissipation.

True. Anytime Tubes are listed as interchangeable it often comes with 
unstated caveats that are only in the spec sheets.  My amp lists the 
4CX1500B and the Chinese FU728F as interchangeable. The transformer 
supplies the different filament voltage required, but I believe (without 
looking) that the screen voltage is higher than best for the 4CX1500B 
As it's capable of a peak output of 2500 PEP, but will run 2 KW key 
down, and the legal limit all day long. However it's going to kick into 
high blower on ling  digital transmissions at 1500 watts out.
The output appears very clean if properly tuned (max screen current 
within ratings) and there are no spikes from the driver running reduced 
power.  I'm pretty sure I'd not want to drive it that way with a 
4CX1500B in there.

There are 30S-1s running 4CX1500Bs in place of the 4CX1000s but they run 
no where near the tubes max ratings. That and I doubt the tank 
circuit/band switch would take it.  They were after all designed under 
the old rules.

73

Roger (K8RI)

>
> On 11/16/13 1:01 AM, Roger (K8RI) wrote:
>> On 11/15/2013 7:27 PM, Vic K2VCO wrote:
>>> 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.
>>
>> Doesn't the Alpha run the lower screen voltage?
>> If it does there shouldn't be a problem.
>> In past amps, I've used the interchangeably although I never measured
>> IM, I never had a bad report.  OTOH that was quite a while ago.
>>
>> 73
>>
>> Roger (K8RI)
>>
>> 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.
>> <snip>
>>
>>
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