[Amps] More information for "What NOT to buy"..

[Joe Subich, W4TV]

Clint, 

You have gotten good advice ... but a couple more thoughts 

Almost any amplifier is a good starting amp but be prepared to make 
some changes and learn from the experience.  

1) The MLA-2500 is to be avoided - as others have said - because of 
   the fragile and out of production 8875.  Yes, it can be converted 
   to other tubes but the small chassis is a significant handicap to 
   a clean conversion. 

2) home built amplifiers using ex-USSR tubes are probably not a good 
   vehicle for learning.  Replacing the ex-USSR tubes can be a problem 
   as many are not being made and surplus sources are not reliable. 

3) External anode tubes (8874/3CX400, 3CX800, 8877/3CX1500) are 
   expensive and have fragile grids.  The 3CX800 and 3CX1500 are 
   great tubes in the hands of an experienced designer but are 
   probably not a good place for the beginner to start. 

Recommendations: 

A solidly built single 3-500Z or pair of 3-500Z amplifier ... 
SB-1000, AL-80, SB-220, L4B, L7, AL-82, etc.  You can learn 
much but be prepared to eliminate the "floating grids", add 
the proper glitch resistor, improve the cooling of any external 
power supply, fix the bias and metering circuits, and convert 
the T/R switching to low voltage and (possibly vacuum relays).  
Converting any of the 3-500Z amplifiers to one of GM3SEK's 
"triode board" controllers would be worthwhile from both a 
reliability and learning prospect. 

A clean amplifier with FOUR 572Bs is not to be avoided.  With 
the proper voltage 4 x 572B will produce nearly the legal 
limit and the tube cost will not break the bank.  Again, be 
prepared to fix many of the "floating grid," bias and T/R 
switching issues.  I would avoid the two tube 572B amps if 
only because they are generally too small, undercooled have 
poor layout are difficult to service and cost as much or more 
than a single 3-500Z amplifier. 

73, 

   ... Joe, W4TV