[Collins] 516F-2 Query

Sun Jan 22 10:16:34 EST 2012

I have read this topic many times on various lists with most replies agreeing 
with what is found below.

If you look at the problem from the standpoint of "heat is the enemy of 
electronic equipment" then anything you do to reduce the heat load will extend 
the life of the equipment.  If you use either resistors or voltage regulators to 
lower B+, the heat load will not change.  The power transformer will still 
provide the same power to the equipment.  For the most part, the power 
transformer is unobtainium so anything done to reduce the load on the power 
transformer is a good thing.

The only method I can think of is to go to a choke input filter with relatively 
low values of filter capacitors and put up with a little hum in the speaker. 
 Using a choke input filter should drop B+ significantly compared to 
a capacitor input filter.  The only issue with this approach is finding the room 
for the new filter inductor.  If the equipment already has a choke then 
eliminate the first filter capacitor.  Perhaps leave a .05 uF ceramic capacitor 
in place to eliminate any RF or noise from getting into the B+ from the AC line.

Converting the B+ rectifier from vacuum to solid state will eliminate the 
voltage drop of the rectifier and raise the B+ by 30 or so volts.  This, as you 
noted, frees up the filament winding on the transformer to buck the primary 
voltage.  This will also drop the filament and B+ voltages to the other tubes in 
the radio.  As long the resulting drop is less then the 10% heater voltage bogie 
number, all should be OK.

One other thing to check is that the power transformer just gets warm to the 
touch after all is said and done.  There have been issues where the chassis is 
coupled to the power transformer and causes the chassis to act as a shorted 
transformer secondary.  Spacing the transformer a bit above the chassis helps to 
decouple the chassis and reduce the effect.  The easiest way to check for this 
problem is to remove all tubes and power up the set.  The transformer should be 
only lukewarm after a few hours of operation.  If it is hotter then this, try 
spacing the power transformer above the chassis with appropriate washers. 
 Hopefully there is enough slack in the transformer leads to accommodate the 
higher mounting height.

I hope this helps,
Jim

________________________________
From: wabate <wabate at verizon.net>
To: collins at mailman.qth.net
Sent: Sat, January 21, 2012 10:50:47 PM
Subject: Re: [Collins] 516F-2 Query

Keep an eye on your filament voltage as you reduce the B+.  Filament 
voltage is the governing factor, at least that is how I feel.  Even with 
my design of the Heyboer, I went for the proper 6.3 with the primary tap 
and let the B+ go wherever.  Over voltage on the B+ is not good but even 
worse on the filament.

I used a 40V zener on the HV center tap of my R-390A supply to get it 
under control after the military replaced the expensive tube rectifiers 
with diodes.

73,

Bill, K3PGB

Dr. Gerald N. Johnson wrote:
> Yes bucking will work whether using the well insulated filament windings 
> or another transformer. Each filament winding is rated at 3 amps, not 
> much above the primary current. So you won't reduce the resistive 
> heating but will reduce the core saturation and its heat. A variac also 
> works but unless its locked in position its a tempting knob for visitors 
> to turn to see what happens and it can supply excess or two little 
> voltage. Since the power handled by the bucking windings is proportional 
> to the voltage change a 12 volt bucking transformer will handle ten 
> times its power rating. There are buck/boost transformers made with 
> 120/240 dual winding primaries and either 12/24 or 16/32 dual winding 
> secondaries that can be hooked in series or parallel.
> 
> A handy way to work out transformer connections is to use a 12 volt 
> transformer to run the primary, then when you check voltages they will 
> be 1/10th the normal and you don't get bit so bad  from the high voltage 
> leads when you accidentally hit them and you get to connect the bucking 
> windings with the wrong polarity without putting strain on the core and 
> filter capacitors.
> 
> The resistor to drop the low voltage doesn't improve the voltage 
> regulation. Though the tube drop in the rectifiers isn't a benefit to 
> regulation either.
> 
> The relay for primary power is something it should have had from the day 
> 1. Or the way I built my HP supply with power switch on the supply 
> chassis and I didn't connect to the switch in the 32S-1.
> 
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.
> 
> On 1/21/2012 12:29 PM, Byron Tatum wrote:
> 
>>Hello-
>>     I am preparing to service a pair of 516F-2 supplies, for my (newly
>>aquired) KWM-2 and 32S-3. My desires are to lower the voltages on an overall
>>basis and to lower the heat load on transformer and components.
>>     I am considering removing the tube rectifiers entirely and using diodes. 
I
>>realize this will undesirably increase my low B+ and high B+ voltages, that 
are
>>already too high to begin with. However, this of course gets rid of a lot of
>>heat and the filament load on power transformer.
>>     To bring down the voltages is it feasible to take the two 5 volt filament
>>windings and use them to "buck" the primary of power transformer? I can't 
>recall
>>hearing or seeing of this done in a 516F-2 but have heard it suggested in a
>>receiver power transformer once.
>>     I have studied the Heyboer replacement power transformer for the 516F-2 
>and
>>really like the tapped primary which allows you to counteract the higher line
>>voltages of today.
>>     If this is feasible I plan to use one rectifier spot for a relay to take 
>>the
>>current load off of the on/off switch in radio.
>>     In the past I have added the dropping resistor in the low B+ to at least
>>help there, but I am looking for a better overall solution to the voltage and
>>heat issues.
>>                                                     Thanks, Byron WA5THJ
>>
> 
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