I'm overhauling my 1941 Zenith this weekend

[TUD1]

I numbered the tubes out of my Radio Amateur's Handbook. What does NC mean on pin one of the 6X5?

[dieseljeep]

Originally Posted by TUD1

I numbered the tubes out of my Radio Amateur's Handbook. What does NC mean on pin one of the 6X5?

NC, means no connection. Ages ago, they made a metal 6X5, where the pin one went to the metal envelope. That was another trouble prone 6X5.

[Titan1a]

I don't recommend attempting to directly replace the 6X5 with 1N4007 diodes. Tubes usually provide some sort of inrush limiting that might damage other components. I use a solid-state replacement from tedweber.com on my Zenith 7S363 radio. An inrush limiter is included in the copper-colored tube form. Also, no soldering! Plug and play for years providing energy savings and protection. I had Walter Beers procure mine and he was very satisfied as am I.

[dtvmcdonald]

A lot of what has been said is hooey ... except, of course, the bad reputation
of the 6x5.

There is nothing in a recapped radio that is going to be hurt by 2N1007 replacing
a 6X5 if the power supply caps are high enough voltage rated, as are the replaced
paper caps. I looked at Zenith schematics from 1941 using 6x5 rectifiers and they had
250 v B+ voltages. With 450 V electrolytics and 630 (or even 400)V film caps,
you don't even need additional series resistance, as the transformer resistance will be
safe for 1N4007s.

To be picky, I usually start with a 500 ohm resistor in series with the diodes,
get the radio running, set the line voltage so the heaters are at 6.3 volts,
and adjust that resistor to get the rated B+. I might also add a thermistor startup
slower-downer in the AC line, but only after that was done.

BUT ... at a 250 or even 375 volt B+, none of that matters except if your line voltage
is high enough to endanger the heaters. Now at 400 or 450 V B+ on the schematic
I do always worry about the resistor and thermistor.

[walterbeers]

I mentioned I would get back with you, and Rick (titan1a) sort of beat me to it, but yes I would use a solid state replacement tube for the 6X5. Must easier than adding diodes and resistors to limit the inrush of current, and to me using bulbs would be out of the question. The inrush would cause the bulbs to flash bright when first turned on, probably in time, if not right away burning them out. Also the belt kit is available through radiodaze, and using this you don't have to disassemble the entire tuning shaft. I used this on Ricks radio, and it has worked fine for over 8 months or more. Just cut the belt to the right size, so that it has some stretch to it, and glue (with the provided super glue) it and once dry, slip the belt on. Yes, It will hold. Link for belt kit below. Also below is a link for the solid state plug in rectifier. Simple and easy, just pull out the old tube and plug in the new solid state one. No wiring, no messing with resistor values, diodes, etc. Links below. Hope this helps you. Rick has had absolutely no problems with using the 6X5 solid state replacement or the belt. Yes, it might cost a bit more, but it's worth it

http://www.radiodaze.com/dial-belt-kit-6-foot/

http://www.tedweber.com/wx5

[dieseljeep]

Originally Posted by dtvmcdonald

A lot of what has been said is hooey ... except, of course, the bad reputation
of the 6x5.

There is nothing in a recapped radio that is going to be hurt by 2N1007 replacing
a 6X5 if the power supply caps are high enough voltage rated, as are the replaced
paper caps. I looked at Zenith schematics from 1941 using 6x5 rectifiers and they had
250 v B+ voltages. With 450 V electrolytics and 630 (or even 400)V film caps,
you don't even need additional series resistance, as the transformer resistance will be
safe for 1N4007s.

To be picky, I usually start with a 500 ohm resistor in series with the diodes,
get the radio running, set the line voltage so the heaters are at 6.3 volts,
and adjust that resistor to get the rated B+. I might also add a thermistor startup
slower-downer in the AC line, but only after that was done.

BUT ... at a 250 or even 375 volt B+, none of that matters except if your line voltage
is high enough to endanger the heaters. Now at 400 or 450 V B+ on the schematic
I do always worry about the resistor and thermistor.

I have a Zenith chairside with the same chassis. It's one of the few radios in my collection that uses a triode output.
When I restore a radio or a TV, I first plug it into a Variac and operate it at a lower voltage.
The AC tubes, used in the radio have rugged heaters. A classic example of that is the tubes used in the old six volt cars. Many times the generator put out close to eight volts.
The prevailing line voltages today are 120-122 volts, to compensate for periods of heavy use.

[old_coot88]

****

[jr_tech]

Originally Posted by dtvmcdonald

A lot of what has been said is hooey ... except, of course, the bad reputation
of the 6x5.

There is nothing in a recapped radio that is going to be hurt by 2N1007 replacing
a 6X5 if the power supply caps are high enough voltage rated, as are the replaced
paper caps. I looked at Zenith schematics from 1941 using 6x5 rectifiers and they had
250 v B+ voltages. With 450 V electrolytics and 630 (or even 400)V film caps,
you don't even need additional series resistance, as the transformer resistance will be
safe for 1N4007s.

How about the transformer itself? While I agree that in general, power transformers can tolerate overload conditions and in-rush surges, pre-war transformers *may* be a special case. These may just be "old wives tales", but several old-time collectors that I know treat these transformers very gently, arguing that the paper insulation in these transformers contains sulfides (from bleaching) which may attack the copper wire if the insulation is comprimised, leading to unintended internal "fuses" in the transformer. These weak spots can be perhaps blown out by high in-rush currents. They usually are careful to use close to the same value input filter cap (not too much higher) to limit peak currents that might strain the (perhaps) compromised transformer.

jr

[TUD1]

Okay guys, I've got good news and bad news. First the good news - I got all the new capacitors in the Zenith except for two. Bad news - in doing so, I caused another problem and now it motorboats really bad. I talked to a few of the guys there, and they said they would help me replace all the old rotten rubber wire. One guy who was restored many Zenith radios said he felt the problem was in the tone control switches. It did play for a few minutes after the recap, but when I went to reassemble it, that's when the problems started.

[Titan1a]

I hope you get it fixed. I love my Zenith!

[TUD1]

Yeah, I love Zeniths too. I really want a 12S266 or 12S267 right now.

[dieseljeep]

Originally Posted by jr_tech

How about the transformer itself? While I agree that in general, power transformers can tolerate overload conditions and in-rush surges, pre-war transformers *may* be a special case. These may just be "old wives tales", but several old-time collectors that I know treat these transformers very gently, arguing that the paper insulation in these transformers contains sulfides (from bleaching) which may attack the copper wire if the insulation is comprimised, leading to unintended internal "fuses" in the transformer. These weak spots can be perhaps blown out by high in-rush currents. They usually are careful to use close to the same value input filter cap (not too much higher) to limit peak currents that might strain the (perhaps) compromised transformer.

jr

I have the same chassis, an 8A02 in my chairside. It has a potted transformer, instead of the kind, we're used to seeing. I also see a late issue 6X5GT tube. I didn't repair or restore it, I bought it that way.
I also have a Zenith table radio from the same era, that also has a potted transformer. It probably was an improvement.

[jr_tech]

Originally Posted by dieseljeep

It has a potted transformer. It probably was an improvement.

Potting would likely would reduce the level of the copper sulfate problem... do you know when Zenith started potting their transformers?

jr

[dieseljeep]

Originally Posted by jr_tech

Potting would likely would reduce the level of the copper sulfate problem... do you know when Zenith started potting their transformers?

jr

It's really hard to say. Zenith seemed to use both types, depending on size and supplier.

[DavGoodlin]

Check your resistors if you have the schematic. My 1937 Zenith tombstone is used daily and it needed about 8 resistors in addition to the caps.
This site can be helpful http://www.oldradios.com/reference/zenith.htm