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

[Dr. Gerald N. Johnson]

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.

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.

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.

You can check the fan bearings, just grab the fan blade and try to 
wiggle the fan shaft sideways and up and down. If you can fell motion, 
the bearings are worn. There may also be a thrust washer that's worn 
allowing the field to try to center the armature along the axis of the 
shaft while the thrust from the blade tries to push it off center.

I suspect the bearings are bronze bushings that probably can be replaced 
though it may require removing a couple rivets to get the motor apart. 
McMaster-Carr is a decent place to shop for such bronze (oillite) 
bushings. It may be that oversize bearings will need the outsides turned 
in a lathe to fit the motor.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 1/26/2012 8:38 AM, whitebear1122 at comcast.net wrote:
>
>
> Hey Byron et al, long time no chat.   I can share my experience with
> my 30L-1 tubes.  After buying my 30L-1, one 811 shorted out after
> maybe 6 months.  I replaced it with some used hamfest purchase .  A
> few months later another original one crapped out.  That's enough so
> I bought two full sets of 811A's from Frank Krize K5SVC I think is
> his call.  I figured I'd put in one set now and have one set for
> standby for the future.   They were NOS Cetron's and the price was
> good.   I put the set in and it's been running just fine for all
> these years.  Gosh those may have been in for 12 years or more.  I
> bought mine from him direct but  I don't have his email anymore.  I
> see he does sell 'Bayside'.  I don't think it has to be complicated
> with hunting for particular branded old tubes.
>
>
>
> I am aware of the Chinese 811 discussions where those are not
> recommended for the 30L-1 because tube element sag from the horizonal
> positioning.   Don't know if my Cetrons are Chinese tubes or not.
> All I know is that they've been running for 12 years without any
> problems.  So you might check out Frank Krize.
>
>
>
> Since we're on the 30L-1, I would also recommend that every owner who
> is running with original electrolytics take a look at them at a
> minimum.  On mine, while the amplifier worked, nearly all of the high
> voltage electrolytics had a ruptured gas vent.  I had looked at the
> Sprague Vishay Atoms and the cheaper Xicons.  I believe that the
> Atoms would have been a drop in replacement and probably should have
> gone with them although they were something like 5x the price at the
> time.   I chose the Xicons.  They had a smaller body and the leads
> wouldn't reach the original connect points.  I had to stub them in .
> It looks fine, and has been working fine for 12 years.  Just a heads
> up on the electrolytic thing.  I am fond to say that there is no such
> thing as a 'good ole electrolytic capacitor, just bad ones and ones
> going bad'.  hi hi
>
>
>
> Oh yeah, a couple of the tophat diodes went out too and I pressed the
> "Easy Button" and  bought a K1ROD board.  The thought was to drop it
> in temporarily while I update the original board.  12  years later
> the original board is still sitting on the shelf. hi hi  I know there
> are newer options out there with the HV caps built in.   Point is I
> had tube problems, electrolytic cap problems, and diode problems.
> Replaced all of 'em and the amp has been work fabulously all these
> years.
>
>
>
> My 30L-1 fan is noisy, too noisy, so I'd like to hear what people are
> doing for that.  It's well oiled, so I don't know if it's a balance
> problem or just worn out bearings.  I haven't seen any direct
> replacements.
>
>
>
> I really like the 30L-1 as it's been a solid performer.  I use it
> with the KWM-2A station and the S-line.
>
>
>
> 73, Scott WA9WFA
>
>