Re: {Collins} (no subject)



Bill wrote:
> The right way involves isolating them (sometimes this can be done in circuit by pulling rectifiers and then pulling all the tubes (if there are no voltage dividers etc hanging on the B+ line).  There is a MIL Spec on how to do this, although you need to find the old version which I have lost track of.

Bottom line, you bring up the resulting B+ until you see capacitor leakage
coming up and stop before getting more than about 10 mA.   Then let the cap
sit until that 10 mA essentially disappears.  If the cap is reforming properly, you will see that leakage drop exponentially. 

Then, bring the voltage up some more until, again, you see about 10 mils of leakage.  Then wait until it disappears (the cap is reforming)..  You keep this up until you get to RATED voltage - not the B+ in the rig.  If you are doing it in the rig, you need to isolate things and consider other rating of caps etc. that may be on the B+ line.  Then use an external power supply to go up to rating.  

In general, as you can see it is a complicated and time consuming process - but very worth it on older valuable stuff that has been laid up.

>I write:
Considering the non-trivial time involved and the not-trivial process and pulling of rectifiers, tubes and other isolations, then putting it all back together -- I wonder if in some/many cases it might be 
faster, simpler and provide longer life to just replace the electrolytics (notice I said "might")

73 Eugene W2HX


-----Original Message-----
From: Collins [mailto:collins-bounces+w2hx=w2hx.com@xxxxxxxxxxxxx] On Behalf Of Bill Carns via Collins
Sent: Wednesday, October 25, 2017 4:22 PM
To: 'Karl Bridges'; 'RADIO N5KX'
Cc: COLLINS@xxxxxxxxxxxxx
Subject: Re: {Collins} (no subject)

 - - > That is wrong. < - -    Read my answer to him below.  Using a VARIAC
without fully understanding the process is not a good idea.  If you have reformable caps in a rig that has been in storage for long enough for them to need it, things start happening VERY MUCH at about 40 or 50 Volts AC after you get the rectifier(s) over the hump.  In this case, roaring right up to 100 volts AC will, in all likelihood, hot spot them and they will fail during, or shortly after, the VARIAC treatment.

In many cases, rigs that people bring up on a VARIAC do not need it and they think therefore that they did the right thing.....  Maybe they did the wrong thing and just got lucky.

Here is my answer I sent Denis.

" The reason you can't find it is because it does not exist. And in fact, some rigs should NOT be brought up on a VARIAC if they contain power tubes (like some high power transmitters)  because the filaments of the power tubes never come up to temperature for a long time, excessive currents flow in the filament transformer . . . and kapow.

Bringing a rig up on a VARIAC is a second choice over reforming caps the right way.  The right way involves isolating them (sometimes this can be done in circuit by pulling rectifiers and then pulling all the tubes (if there are no voltage dividers etc hanging on the B+ line).  There is a MIL Spec on how to do this, although you need to find the old version which I have lost track of.

Bottom line, you bring up the resulting B+ until you see capacitor leakage
coming up and stop before getting more than about 10 mA.   Then let the cap
sit until that 10 mA essentially disappears.  If the cap is reforming properly, you will see that leakage drop exponentially. 

Then, bring the voltage up some more until, again, you see about 10 mils of leakage.  Then wait until it disappears (the cap is reforming)..  You keep this up until you get to RATED voltage - not the B+ in the rig.  If you are doing it in the rig, you need to isolate things and consider other rating of caps etc. that may be on the B+ line.  Then use an external power supply to go up to rating.  

In general, as you can see it is a complicated and time consuming process - but very worth it on older valuable stuff that has been laid up.

So, you can see, when you are using a VARIAC, you are flying blind with no instrument panel.

How much reforming time to use is a function of many variables.  Storage time, storage conditions (temp mostly), age of the rig and history of the rig.

If your radio you are bringing up has tube rectifiers, it is best to come up to about maybe 40 or 50 volts of applied AC until you see activity in the power supply B+ line. At least try and monitor that.  Running the AC lower than that puts you in the region where the rectifier(s) is not working yet and you are accomplishing nothing.

Now all that being said, and acting as a now understood caveat, I would, on receivers, bring the AC up to about 40 volts right away.  Then start coming up in 10 volt increments and let the rig sit at each increment for an hour or so, until you get to full AC.  That means you will bring it up over about
8 to 10 hour time period.  Slower is better.  Pull all the tube while doing this, with the exception of the rectifiers.  Running tubes at very low (poor
emission) filament voltage and applying B+ (even though maybe only 60 % of the normal) can risk cathode stripping in some tubes, and then you are going from one problem to another.

How long have the rigs been in storage?"

End of quoted previous answer.

Bill

Bill Carns, N7OTQ (Trustee K0CXX)
Past President, Collins Collectors Association Founding Board, Collins Radio Heritage Group Editor, Signal Magazine (Retired) Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)




-----Original Message-----
From: Collins [mailto:collins-bounces+wcarns=austin.rr.com@xxxxxxxxxxxxx] On Behalf Of Karl Bridges via Collins
Sent: Wednesday, October 25, 2017 10:51 AM
To: RADIO N5KX <radion5kx@xxxxxxxxx>
Cc: Collins Reflector <collins@xxxxxxxxxxxxx>
Subject: Re: {Collins} (no subject)

I'd point out that, normally, most things don't start happening until you get to 100 volts -- and by then it may be too late. If you have a variac that measures current or some other ammeter that is always very useful.

On Wed, Oct 25, 2017 at 9:17 AM, RADIO N5KX via Collins < collins@xxxxxxxxxxxxx> wrote:

> Hi Bill
> I've built myself a bucking transformer that gets my excessive 125V 
> line voltage down to 114/115V. And I've also got my hands on a variac.
> For the older units, A line and S line  that have been sitting in 
> storage for a while, is there a publication that shows starting 
> voltage and how many minutes/hours at that level and any intermediate 
> voltages and times required to "bring up" the units before you run 
> them on the full 115V? I looked at the index of articles you've kindly 
> provided but could not identify this particular answer  although I'm 
> sure the question has been asked before. Thanks in advance.
> Denis N5KX
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