----- Original Message -----
From: "Scott Manthe" <n9aa@arrl.net>
To: "Joe Subich, W4TV" <w4tv@subich.com>; <Amps@contesting.com>
Sent: Wednesday, April 09, 2008 10:07 PM
Subject: Re: [Amps] Replacing 811A with 572B
> The AL-811H runs about 1600-1800 volts HV, not 1400, which is why it's
> not a bad idea to run the 572Bs in that amp.
It certainly makes sense when the user takes forever to tune up or doesnt
have a clue what he is doing. This is often the case with entry level amps
and entry level or senile citizen hams. (Im in that age bracket...)
The 572B has a substantially higher plate dissipation and can take a lot of
abuse. Ive had zero problems with Chinese versions in years, just dont buy
RF Parts. I buy Penta or direct from China off Ebay.
>
> While the cost difference seems substantial, you'll probably never have
> to replace a 572B, imported or otherwise, when run in an AL-811H. RF
> Parts lists the Marshall 811A at $29.45 each and Chinese 572Bs at $39
> each, so the price difference at this point is substantial, but not so
> much so, if you consider the increased life expectancy.
I wouldnt call that substantial, simply common sense investing.
Carl
KM1H
>
> The size difference between the two tubes does not present a problem in
> the AL-811H amp.
>
> 73,
> Scott, N9AA
>
>
> Joe Subich, W4TV wrote:
>> Why waste the money ... four 572Bs are half again to twice the
>> price of four 811s. The 572B will not provide any more gain or
>> power output than the 811 unless you modify the power supply for
>> about 40% more voltage (2 KV vs. 1400 V).
>>
>> The 572B is taller and wider which might represent a problem
>> (moving the plate caps too close to the metal case or overly
>> restricting air flow between the tubes).
>>
>> If you are really concerned about reliability pick one of the
>> better 811 suppliers - perhaps Marshall (made in the USA) -
>> but I would not waste the money and effort on imported 572Bs.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>>
>>>
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