[Amps] Replacing 811A with 572B

[Roger (K8RI)]

Joe Subich, W4TV wrote:
> Why waste the money ... four 572Bs are half again to twice the 
>   

Waste?  When compared to most tubes in the 1KW to legal limit either the 
811 or 572s are down right inexpensive.  OTOH the 572s are much more 
rugged and tolerant.   They should run until they die of old age. So, 
when I look at  it that way the 572s are less expensive over time than 
the 811s.  Of course you can't get that cherry glow as quickly out of 
the 572s as with the 811s<:-))

To me it's a good choice (IF they'll fit)

73

Roger (K8RI)
> 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 
>  
>
>
>   
>> -----Original Message-----
>> From: amps-bounces at contesting.com 
>> [mailto:amps-bounces at contesting.com] On Behalf Of Bert Almemo
>> Sent: Wednesday, April 09, 2008 7:37 PM
>> To: amps at contesting.com
>> Subject: [Amps] Replacing 811A with 572B
>>
>>
>> Hi guys,
>>
>> I have a friend who wants to replace 4x811A with 4x572B in an 
>> Ameritron amp. I don't think it's a good idea but he insists 
>> a lot of hams do it. What do you think?
>>
>> 73 Bert, VE3OBU
>>
>>     
>
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