[R-390] R390 B+ Current?
jgedde at optonline.net
jgedde at optonline.net
Sun May 26 08:09:18 EDT 2019
I tested C608 and C606 using Jacques multimeter method (it's a great
method!!!.) I found the 0.22 uF to be leaky as it didn't drop to zero V at
250VDC. I was seeing about 30 nA of leakage (300 mV on my meter). Not
excessive, but more than I think a capacitor feeding a grid with only a 560k
resistor to take up the leakage should have. I replaced it with an Orange
drop. I did the same test on the 0.1 uF and it was much better (a Vitamin
Q) but I replaced it anyway. The radio still had problems though. Despite
being new and testing good on an emissions tester one 6082 didn't work at
all in the circuit. I swapped out that tube (although I think they really
want to be a matched pair). More 6082's are coming.
So the radio works, and the hum balance works, but all is still not well. I
had to chase the hum balance all over as things warm up else the hum
returns. So, there's still something going on. I wonder if it's gross tube
mismatch between the two 6082's? Or is it something else. I guess I'll
find out when the new 6082's arrive. For now, I'll just measure the voltage
drop across the four 47 ohm cathode resistors to see if they're sharing the
total load properly. I will also check the big can capacitor behind the
headphone jack.
John
-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca>
Sent: Friday, May 24, 2019 9:20 PM
To: jgedde at optonline.net
Subject: RE: [R-390] R390 B+ Current?
Importance: High
Hi John,
Good, meaning that there is no leakage elsewhere !
Attached is a picture of my own R-390 supply module.
You can see/count all the parts I changed because they were bad.
It is out of the receiver since last week because I need to test an idea to
use 6080 tubes instead of the 6082 with, but it requires that I bring the
12.6V center tap of the filament winding into the PS module.
Half done for now. More on this to come later.
And oh, yes: leakage tester.
If you have, say, a DC supply that can go up to the WVDC rating of the
capacitor you have to test, you just have to connect a digital voltmeter
(most of these equals to a 10M ohms resistance, whatever the range) in
series with the positive output of the supply, the negative side of the
meter going to the capacitor to be tested and the other side of the
capacitor to the negative of the supply.
You first adjust the supply to the testing voltage by shorting the
capacitor, then you remove that short.
The capacitor will then charge thru the 10M ohms resistance of the
voltmeter.
If there is any leakage in the capacitor, the measured voltage will never go
to zero.
In a "good" capacitor, the leakage value is so small that the voltmeter
reading will gradually decrease to ZERO, and balance across that zero value,
depending on the stability of the supply.
Say now that you test a 400WVDC capacitor: you connect it, shorted, with the
voltmeter in series to the supply, then you adjust the value read by the
meter to 400V.
You remove the short, then watch the meter reading decrease.
It should take 5 time constants to reach near zero value, right ?
Can be used as a capacitance meter that way, but...
Let say that the reading goes down to 50V and hang around that value
forever.
The capacitor leakage will then be 50/10M ohms = 5µA at 350 V across, right
?
Practically, this is too much... That capacitor is not reliable. Discard it
!
The practical limit of this measuring setup is ±1V across the meter, meaning
a leakage value of 100nA.
Not too bad for a cheap setup, isn't it ?
What I use is 700Vct, 30 mA transformer mounted in a small box with the
primary connected to the output of a variac.
The 700V winding is full wave rectified but the center tap is connected to
the GND of the case.
This way, I obtain +500V and -500V outputs max, so 1kV max. across the two
outputs.
The + and - outputs are only filtered by 2µF each, because it is enough and
there is 500k ohms resistors connected in series with each outputs as a
safety measure, so the "box" cannot supply more than a 1mA current in short
circuit.
Depending on the needed test voltage, I use only the + output against GND
(500V DC max) or from the + to the - output (1kV max at 1mA).
I tested a lot of PIO caps with this setup for years and not many were found
still good.
But any modern capacitor (mylar or polypropylene dielectric) passes the test
with flying colors.
Sorry for the long explanation.
The R-390 is a "man's radio" remember ?
Once properly restored, it will become your pride and joy.
Keep up the good work.
73, Jacques, VE2JFE
-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
part de jgedde at optonline.net Envoyé : 24 mai 2019 18:44 À : 'Jacques Fortin'
<jacques.f at videotron.ca>; 'r390a'
<r-390 at mailman.qth.net>
Objet : Re: [R-390] R390 B+ Current?
Wrong conclusion. C606 is OK. Pin 7 and 2 on the 6BH6 are shorted together
creating a path through the 18k power resistor (which was warm) and the 1k
Cathode resistor. I am considering this a normal result. R623 + R618 = 18k
+ 1k = 19k = 186 / 9.8 mA. Mystery solved. I am moving on to check
+ those
caps Jacques and Don suggested.
John
-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On
Behalf Of jgedde at optonline.net
Sent: Friday, May 24, 2019 6:33 PM
To: 'Jacques Fortin' <jacques.f at videotron.ca>; 'r390a'
<r-390 at mailman.qth.net>
Subject: Re: [R-390] R390 B+ Current?
Actually, I used the DMM and measured 9.8 mA with 186V in. R then equals
about 18k. I wonder if C606 is bad...
John
-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On
Behalf Of jgedde at optonline.net
Sent: Friday, May 24, 2019 6:23 PM
To: 'Jacques Fortin' <jacques.f at videotron.ca>; 'r390a'
<r-390 at mailman.qth.net>
Subject: Re: [R-390] R390 B+ Current?
HI Jacques,
Thank you! I used your suggestion and tested the 6082's as if they were
6080's but with setting the filament for 25.2V. The two new units test
good. But my unit is only an emissions tester... The two old ones I have,
only one tested good as an aside.
With filaments off, I see the radio drawing 15 mA from my supply no matter
what I disconnect. I had to pull the 5651's to take this measurement since
they were lit up. I can only conclude the badness in in the AF deck
somewhere.... I'm feeding the 180V into the B+ test point on the side of
the radio. 5651's and 6082's are out for this test.
John
-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca>
Sent: Friday, May 24, 2019 5:51 PM
To: jgedde at optonline.net; 'r390a' <r-390 at mailman.qth.net>
Subject: RE: [R-390] R390 B+ Current?
Importance: High
Hello John,
6082: same as 6080 for testing, but 26.5V filament you can use 25 V for
filament if available on your tester and same other settings for a 6080 if
your tester have it.
Do not rely on check for C608: You need a leakage tester to know it is good
or not. Otherwise, just shot-gun it. Any modern 0.22µF / 250V cap will do.
A leakage tester is easy to assemble if you have a variable DC supply, but
talk about that later...
Measuring leakage on the B+ 180V line.
1_ Do not power the filaments.
2_ Use a mA meter in series with your variable supply (you have one, it
seems).
3_ Connect the 180V DC supply with the mA meter in series to the 180V test
point.
4_ Power on the supply, let the current value stabilize and read the value,
if it does not balance across 0, this is not good: something draw current
and should not.
5_ Disconnect the power to every module in turn to see which one draw
current.
6_ Suspect supply decoupling capacitors first. The Sprague Vitamin Q should
still be very good for the age they have, but from experience, not all of
them....
Check that first, then came back to me please.
73, Jacques, VE2JFE
-----Message d'origine-----
De : jgedde at optonline.net <jgedde at optonline.net> Envoyé : 24 mai 2019 17:10
À : 'Jacques Fortin' <jacques.f at videotron.ca>; 'r390a'
<r-390 at mailman.qth.net>
Objet : RE: [R-390] R390 B+ Current?
Hi Jacques,
The state of the 6082's were new in box but I am suspecting they failed. My
tube tester (NRI Model 70) doesn't have a listing for the test settings for
the 6082.
I will check C608 but I think I did already. R615 is spot on. I've also
replaced the four 47 ohm resistors since they were burned, as well as R625
and R626 which were charred beyond recognition. After doing all that, the
receiver worked for a few days, B+ was normal, no hum. The resistors I
replaced are still good. Also, the resistors for the 6BH6 are good also.
I may rig up a test setup to measure the Gm of my stock on 6082's to test
them.
I'd like to measure the leakage on my B+ like you suggest. How is that
done?
Thanks!
John
-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca>
Sent: Friday, May 24, 2019 8:58 AM
To: jgedde at optonline.net; 'r390a' <r-390 at mailman.qth.net>
Subject: RE: [R-390] R390 B+ Current?
Importance: High
Hi John,
What is the state of the 6082s ?
Have you a tube tester to test those ?
Whatever the output voltage you got, the plate of the 6BH6 (V607) normally
have to be a few volts BELOW the output.
If C608 is leaky, this will reduce the output voltage for sure because it
will make the 6BH6 grid raising higher than it should.
Expect it to be leaky anyways: I do not see any original one that was
faultless.
Check also R615: I once found one that was measuring almost 1 meg. Replace
it by a 1W part.
When all is in order, you should get 180V out ± 3V and the Hum Balance
should work (provide a minimum output hum setiing).
BTW, it is easier to debug when it give you lower than expected voltage than
the reverse !
170mA is within the spec: the transformer is rated at 200mA DC !
But if there was no leakage test done on the B+ rail, to detect any leaky
cap., it can be that you draw more current than the designed value.
Any other question, just ask !
73, Jacques, VE2JFE
-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
part de jgedde at optonline.net Envoyé : 24 mai 2019 07:49 À : 'r390a'
<r-390 at mailman.qth.net> Objet : [R-390] R390 B+ Current?
I'm still having trouble with the voltage regulator. Low B+ and a hum.
There's plenty of input voltage available, but the output isn't right.
Right now I have a 180V bench supply feeding the radio through the B+ test
point and all is working but the current is seemingly high. I see about 170
mA. Does this sound right? It may well be, but I want to make sure I'm not
trying to fix the wrong thing.
John
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