[morzh]

In a radio from Kirk (a GM Delco I thinkl, a typical AA5 with curtain burner dropout cord, the output tube is the 43, a pentode with 25V filament.

After some of the changes I made (the radio is a disaster with bunch of missing stuff plus discrepancies with the sch which I am not sure are factory or rework) radio briefly worked, then ceased to. There are some things I am not sure I understand, but as a result I pulled the 43 and found it has a short between the heater and Cathode.
That is my Hickok 600 shows the glow on the switch position #3.
It only occurs when the heater is on for a few secs.

I ordered another tube on eBay, says it is good and since it was no name i was sold cheap. Came today. And when I put it in my Hickok, it showed the same short in the same position. Then after pulling it out and putting back in, I saw this: instead of solid glow in the position #3 it would persist fo 1-2 seconfs and then extinguish.
Again only when filament was hot.
Eventually this also disappeared, and now it tests as all other positions, that is short flicker of the neon lamp and no glow afterward. That is it tests good. But it wasn't first!

Anything I should know about 43 pentodes?

[Phlogiston]

H/K short? Relatively high(er) voltage on the heater. Probably OK. If it makes noise, throw it out.

[morzh]

Russ

It would be fine if they were isolated but this is an AA5 so the HK short can affect things as they are referenced to tne same neutral line as 0V for filament string and comon.

Now what I want to know - I have two tubes with the same problem, though in one it gradually disappeared.
Coincidence or ...?

[Arran]

Mike;
  There is no way of knowing without having more #43 tubes to sample but it may just be an idiosyncrasy of the Hickok 600 tube tester to set off the short light in that position. I have an old Precision tester that was giving me similar readings on some loctal tubes I was testing, I can't remember the type, but three of them read as shorted on the same pins.
   In any even the #43 tube is unrelated to the set not playing, usually a heater to cathode short in a power output tube will create a load 60 cycle hum in the audio but will not stop the radio from working. If it is a G.E, even a U.S model, I probably have the service info for it if you can find out what model it is, if it's a cheap TRF AC/DC set then it probably isn't a G.E.
Regards
Arran

[morzh]

Arran

I will be able to tell you what radio it is (it is a superhet with 6A7 pentagrid, as I said classic AA5) when come home this evening. Yes while receiving stations it was humming very loudly.

I will need to ask Kirk if he has a 43, he says he sent it to me but it is a 42 which would be the same were it nt for 6.3V filament


As for the idiosyncrasies of the 600, well, in the past when I first saw many of the same tube diagnosed as bad by it when restoring 37-116 and it was suggested that it might be the 600....no, it turned out to be the tubes.
Plus so far it never gave me a short indication on a tube that would not disappear on the same type good tube when tested.

In this case, again, one tube shows it solid when heater is on, another no longer shows it but did first. This tells me the 600 is not misbehaving but the second tube might have something intermittent. Obviously a third tube would be the charm

[Phlogiston]

I have a 600A and some 43s. All I have to do is remember to test some. I'll try them on the 533 and TV7 too.  If shorts are found I can try them on a Superior 612 (different brand tester, not Hickok circuit). I know I have at least 1 NIB.

I vaguely remember seeing this while testing tubes for my Spartons, 61, 62, 59 so on---

[Phlogiston]

OK. I tested 6 tubes on my Hickok 533 that I calibrated last year. Two were NOS both tested near 2300, neither showed any signs of shorts. Of the 4 used tubes one was like new, no shorts. Two had the #3 position show flickering shortlamp after warm up lasting about 10 - 30 sec. One that tests near new had the #3 position remain flickering until I removed the tube.

Maybe your tubes are used. They will probably still work.

[morzh]

Russ

They are indeed used, after all why would I buy a new tube for a really screwed up chassis that is also somewhat miswired?
It seems to me used 43s are prone to pos 3 (HK) short.

The radio is DELCO 4052 ACDC.

Now you tell me looking at the sch if you have it, if the filament of the 43 is essentially the Line (hot) after the dropout resistor and the Cathode is Common Negative (GND isolated from Chassis) which is 50 Ohms from Neutral, if the short is low ohms will it work?

[Phlogiston]

Russ

They are indeed used, after all why would I buy a new tube for a really screwed up chassis that is also somewhat miswired?
It seems to me used 43s are prone to pos 3 (HK) short.

The radio is DELCO 4052 ACDC.

Now you tell me looking at the sch if you have it, if the filament of the 43 is essentially the Line (hot) after the dropout resistor and the Cathode is Common Negative (GND isolated from Chassis) which is 50 Ohms from Neutral, if the short is low ohms will it work?

As I recall from the cal., the flickering lamp short is going to be several thousands of ohms but I can't seem to find that test value now. It is a little arbitrary to say flickering is better than solid on (bright) but it is somewhat true but open to interpretation. If you want to be really safe don't use the tube. It is more likely to get worse than better. Low ohms short=bad.


BTW, the noise test on many tube testers is just a sub function of the shorts test. You can listen to the noise that the short could cause.

[morzh]

Well...I decided not to do the reconstruction to bring the chassis in full agreement with the sch, considering some discrepancies seem to come from factory.

There are some problems after I soldered all that was not and weeded out tubes that were plain bad.

1. Voltages rise VERY slow. The voltage at the output xfmr first gets negative (!!! ) -10-12V or so, and only then starts going back. It lags the voltage for the field coil quite a bit though evntually becomes the same, 110V or so. It gakes 3 minutes maybe for the radio to get to hum.
I first thought of the diode that is dual one and creates two separately rectified voltages for the output and for the field coil, and indeed one half did not work so I replaced it.

2. Potential problem with the output 43 tube, though seems to work.

3. I am receiving a station, pretty loud, though at lower than max volume reception cuts out. Need to clean the volume pot.
4. But while the radio is quiet while not receiving it hums and distorts when is.
I suspect the radio is misaligned. Need to find the alignment procedure (don't remember if it is in the manual I have from the Radiomuseum.

Oh...and I am using a cap to lower the voltage, 8.2uF.

[OldRestorer]

I dont know what is going on but good work!

Me

[morzh]

I am not sure I understand something.


http://www.nostalgiaair.org/pagesbymodel...022404.pdf


In the voltage chart (page 2) it lists pin1 of the 25Z5 rectifier at -20V measured relative to the B- (tuning cap frame is what they use for convenience).
This is the voltage separately rectified for the Field coil. How can it be negative?
Granted the voltage used is between the Neutral AC pin and the Pin1 (the 25Z5's Cathode) and there will be some bias between the B- and the Neutral (due to the big choke between them with some 500 Ohm DC resistance) but then the voltage developed from the rectifying is quite large (100V or so) and even with some negative bias the voltage measured relative to the B- should be positive.

Another thing is, unlike the rest of the heater voltages (6.3V and 25V) between pins 3 and 4 for the rest of the tubes, the 25Z5 heater voltage is listed as -20V. Which is 1) implies DC, 2) should be 25V.

I am puzzled a bit.

PS. A negative voltage does indeed develops first across C19 which is unnerving. It reaches to about -12V , then starts dropping and eventually goes to +100V when measured relative to the Neutral (which is totally weird).
PPS. again, warming up takes very long time, 2 minutes or so. Weak rectifier might be the culprit but it is not totally weak, it is in fact OK or close to it.

[Radioroslyn]

Strap a couple of 1N5408's across that 25Z5. We need to rename Kirk to Kurtan Burner Kirk! He seems to have a strange magnetizum for these types of sets! Hope you are not using those pin # on the diagram, there all wrong.

Terry

[morzh]

yes I know, that was the first thing I realized. But then it actually shows the pins themselves in correct arrangement when looking down inside the chassis.
There are discrepancies - in one tube the heater is crisscrossed, and in the 25Z5 the rectifiers are crisscrossed (the two halves): no biggie but makes the tracing a bit tougher than it needs to be, as if it is not tough enough already with this cobweb inside plus the Kirk's recapping job .


>>>>>>>Strap a couple of 1N5408's across that 25Z5.

You mean - replace it altogether? Possible, would have to decrease the cap to catch extra 25V of the filament voltage. Or disconnect the Cathode and Anode and keep the tube in place......messy....

Or did you mean "across the load" to clamp the negative voltage?

[Radioroslyn]

Plate to cathode.

Terry