The PHILCO Phorum
6X5 bypass question - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Various and Sundry Categories (https://philcoradio.com/phorum/forumdisplay.php?fid=37)
+--- Forum: Other Radios (Non-Philco) (https://philcoradio.com/phorum/forumdisplay.php?fid=12)
+--- Thread: 6X5 bypass question (/showthread.php?tid=15940)

Pages: 1 2

RE: 6X5 bypass question - TV MAN - 12-23-2016

I can see that being a problem with the grounded filament. That is a lot of voltage between the heater and cathode, and a direct B+ short to ground wouldn't be kind to the trans. I didn't see the whole schematic, but if the filament weren't grounded, wouldn't that eliminate the problem? Well, maybe, maybe not ... it could then put that across the HK of the weaker signal tubes, then one of those short, = lots of excitement. Icon_eek  I have several radios that use this tube, but they all use the GT tube, not the G tube. One did have a bad power transformer - worked ok, but just ran super hot. Gradually got worse til I replaced it. Maybe was related to a failed 6X5 at some point?? Icon_eh But, even if one of the silicon diodes shorts, that wouldn't be any too kind to the trans either.

RE: 6X5 bypass question - Mondial - 12-24-2016

I would just put a fuse in the primary lead of the power transformer and stop worrying about it. This applies either to the 6X5 tube or a replacement silicon rectifier.

Rate the fuse marginally higher than the maximum current draw of the radio under normal operation. If the rectifier should short, it will blow the fuse within a few seconds, protecting the transformer from any sustained overload.

RE: 6X5 bypass question - Arran - 12-24-2016

Kirk;
This is much ado about nothing. The 10-S-464s have 6X5 problems because the engineers over at brand Z decided to ignore the specs in the RCA or Sylvania tube manual that states that the maximum current rating of a 6X5 was 70 ma, and whatever the maximum plate voltages were (they vary based on load and what the input filter is). They thought that they could get around it if they used pairs of 6X5s with the diodes wired in parallel rather then using an #80 or a 5Z3. In something like a five or six tube radio, with a 6K6 output tube, or a wire recorder, or a record player, there was never a problem with using a 6X5/6X5G/6X5GT, but connecting them as they did in a 10 tube radio with push pull 6V6s was just asking for trouble.
Depending on the year or production run, Philco used either type 84s or 6X5s in the power supplies of their 40-180, 41-280, 42-380 series chassis with few problems, the reason being is that they kept the B+ voltage down around 180 volts and used either #41s or 6K6s for power output tubes, which incidentally were designed for car radio use as well.
Regards
Arran

RE: 6X5 bypass question - Arran - 12-24-2016

(12-23-2016, 11:05 AM)TV MAN Wrote:  I can see that being a problem with the grounded filament. That is a lot of voltage between the heater and cathode, and a direct B+ short to ground wouldn't be kind to the trans. I didn't see the whole schematic, but if the filament weren't grounded, wouldn't that eliminate the problem? Well, maybe, maybe not ... it could then put that across the HK of the weaker signal tubes, then one of those short, = lots of excitement. Icon_eek  I have several radios that use this tube, but they all use the GT tube, not the G tube. One did have a bad power transformer - worked ok, but just ran super hot. Gradually got worse til I replaced it. Maybe was related to a failed 6X5 at some point?? Icon_eh But, even if one of the silicon diodes shorts, that wouldn't be any too kind to the trans either.

 I also have several radios that use a 6X5 rectifier, and not one set that I have encountered with this tube has had a failed power transformer, but I have run into at least two or more sets equiped with a 5Y4 that had a shorted high voltage winding, shorted filter caps or a shorted tone correction cap is all it takes. I also do not trust rectifier diodes, least of all the 1N4007 cheapies many seem to use, I figure it's better to pay the extra $.10 and use at least 3 amp rated diodes connected in series.
Regards
Arran

RE: 6X5 bypass question - morzh - 12-24-2016

Arran

1N4007 is an excellent diode, I used it in many designs without any ill effects and the current that would be demanded in a radio is below its 10% rated capacity.
The reason they are cheap is because they are so good and omnipresent, and mfred in this numbers they nust have to be.

RE: 6X5 bypass question - Arran - 12-25-2016

Kirk;
  I should also add that in substituting a tube rectifier with a silicon diode or diodes that the B+ will now be full on before the tube heaters have had a chance to warm up, so in the past in things such as TV sets they used to incorporate a thermistor in line with the high voltage to keep the voltage down for a minute or so. The voltage spike can also hard on the filter caps, with no load the B+ can hit 400 volts or more before the tubes warm up, it's probably less of an issue with modern electrolytic caps but such spikes could cause the old style ones to short out.
Regards
Arran

RE: 6X5 bypass question - morzh - 12-25-2016

Add to that (for Kirk, he might not be aware of the difference ) - NTC thermistors. There are also PTC ones and they do the opposite.