[Collins] 30L-1 811A Tubes, Electrolytics, Diodes, Fan

[Carl]

----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: <collins at mailman.qth.net>
Sent: Thursday, January 26, 2012 2:32 PM
Subject: Re: [Collins] 30L-1 811A Tubes, Electrolytics, Diodes, Fan


> The most critical visual criteria for 811 is that the plate be up and
> down, not flat or angled when on its side in the tube sockets. RCA
> recognized horizontal usage and so put a socket orientation requirement
> in their specification. Other off shore makers have neglected that
> detail. The filament and to some extent the grid need room to sag, and
> there's not room when the plate is horizontal.
>
> Look at the temperature and ripple current ratings (in the Mouser
> catalog these days) when choosing replacement electrolytics. The Sprague
> Atoms have more surface area of the can, but a lower ripple current
> rating than some of the smaller cased capacitors. I don't know if that's
> conservatism or an indication that the guts of the modern Atom are not
> in good thermal contact with the case.


All the ATOM size indicates is a very obsolete design that has been around 
since the late 30's. They are sold for replacement use only and the price 
reflects the low volumes. Ive read that this is the last year for them.

The very low cost axial lead caps are another obsolete technology that is 
also being phased out. While I use Xicon in LV supplies and no more than 2 
in series with equalizers their ESR isnt up to general use in a very high 
ripple doubler PS. Im surprised to hear they stood up in a 30L1. My one time 
experience with 8 450V in a doubler was in an NCL-2000 many years ago and 
while they seemed OK at the CW 1800V position they soon started boiling at 
the SSB 2500V. My solution there was CDE 381LX 100uF Snap-Ins used in the 
original capacitor clips. In fact I use that series cap of many values in 
just about every overhaul and never even had one get warm


> Electrolytics do age and not always nicely, but faster when not used
> than when used. So new old stock are suspicious and once you've cleaned
> up a radio from where one has exploded you will be desirous of knowing
> the date code of new electrolytics and of not using any more than a
> couple years old. Years on the shelf hurts most.

That is certainly true of the Atom era technology but even those are fine 
for 10-12 years at least. However Ive found that the Snap-Ins are very long 
lived on the shelf and have tested leakage and capacity before/after running 
at rated voltage using commercial testers.


>
> Modern silicon diodes have controlled avalanch when the reverse voltage
> exceeds thier rating and so are somewhat self protecting and when
> several are in series they force proper voltage distribution without the
> shunt resistors and capacitors. Many a resistor capacitor network has
> used parts without adequate voltage rating (like 600 volts applied to a
> 1/2 watt resistor rated at 250 or 350 volts) and the resulting eventual
> resistor arc over inside has blown the rest of the diode string. The
> modern 1N4007 will replace any two of the original top hat diodes and if
> in the entire string there won't need to be and capacitors or resistors.


With the 1N400x family being produced in every 3rd world country that has an 
AC power plant I just dont trust them the way I used to. With 1N5408's being 
the diode de jour in every modern commercial amp and about .16 each I joined 
the 21st century for all upgrades. The cost of replacement transformers was 
the big reason for my cap and diode choices plus I, nor my customers, likes 
the smell of burning equipment (-;

Carl
KM1H