[Amps] Replacing 811A with 572B

[Joe Subich, W4TV]

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 
 


> -----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
>