[Heath] Recapping SB-220 - higher values OK?

[Kenneth G. Gordon]

On 6 Nov 2015 at 7:40, Alexander N. Gerli wrote:

> Hello, folks.  I have been offered a set of high-uF caps. They're 1500uF/450V,
> appear to be computer-type I guess. They would equal a 187.5uF capacity if I
> used them. That would make a really stiff supply, BUT anyone have any thoughts
> on what the inrush current stress would be? I already plan to install a
> step-start, regardless what caps I end up using.

First of all, which amp are you planning to use those in?

In any case, if you are using a step-start, I see no problem whatever.

In my SB-200s, I use up to 560 mfd at 450 VDC in place of the 150 mfd 
originals, and although I do NOT use a step-start, I have had ZERO 
problems with inrush over the past 5 years or more of almost daily use.

Of course, it is an established fact that Heathkit purposely used specially 
designed power transformers for both the SB-200 and for the SB-220 which 
have built-in surge protection in that the input CURRENT ramps up fairly 
slowly.

In addition, there is already a slight "ramp-up" from the voltage-doubling 
system anyway.

In point of fact, according to an old handbook article I chanced across once, 
the MINIMUM capacitance one should use in any voltage-doubling power 
supply is 30 MFD. Otherwise, regulation will be severely compromised.

Practically every voltage-doubling-power-supplied linear amp in the last 50 
years uses just BARELY 30 MFD total capacitance,since high-value, 
high-voltage filter caps were unknown at that time. Obviously, the designers 
were aware of the factoid I posted above.

In addition, there was a LONG article in an old GE Ham News which proved, 
on the basis of scope photos among other test data, that the greater the 
output capacitance in even a standard supply, the far better the dynamic 
regulation of that supply and thus the lower the IMD from an amp.

In your case, I would definitely say to use them, but use a good step-start 
system to prevent possible surge issues.

I am absolutely certain you will have zero problems, and in the process will 
output a better signal.

Ken W7EKB