I'm overhauling my 1941 Zenith this weekend
 

I'm going to the radio club this weekend and I'm going to replace as many capacitors as I can. I'd also like to do away with the 6X5GT rectifier. I've asked how to do this before, but I guess I forgot or something. I know you can install two 1N4007 diodes, I just don't know where they go. If somebody could fill me in, that would be super helpful. The radio plays good, but the chassis does need some help. All the rubber wiring is falling apart, it needs a total recap, (I put in two and an electrolytic), and it needs a tuner belt.

Here is the inside.

Googling 6x5 tube data and searching wikipedia for diode should yield enough data for you to figure it out.
https://frank.pocnet.net/sheets/127/6/6X5.pdf
https://en.wikipedia.org/wiki/Diode

If you want to keep the original tube in and lit then remove plate and cathode leads from the socket and mount a terminal strip for those leads and the diodes.

That's what I had in mind. I want to keep an original Zenith 6X5G in there and have the diodes in the chassis. Somebody told me to remove the two plate wires and one cathode wire from the tube socket and wire them together in a Y shape. I think one lead of both diodes connects to the cathode wire and the other two leads to the plate wires.

The cathodes or the marked ends of the diodes go the cathode wire from the tube socket.
The newer GT type 6X5 is generally reliable. I, personally like a tube rectifier, but I generally only turn on my tube radios to show how well they work. :thmbsp:

Okay, I think I understand now. I've heard of people putting a resistor in the mix too. I use my tube radios almost everyday.

With the Si diodes, the B+ will come up instantly. So you need to be sure the filter caps are rated for the surge voltage.

And also, how well will the old power transformer hold up with increased peak current surges? Frankly, I would not replace the tube with ss diodes, but would add a small light bulb in series with each plate lead as a quick blow fuse. I think Zenith at the time recommended #47 bulbs.

jr

here is the old thread where that is recommended:
http://www.videokarma.org/showthread.php?t=265632

.

Well I was going to replace the filter caps with 450 volt units anyway. Unless the surge is more than that, in which case I'll go up to 600 or 1000.

You could also use one light bulb or a small fuse (say 250mA) in series with the ground connection (centre tap) of the B+ winding.

Or make a socket adapter for a 6X4 or say a 6CA4

Hi, Here is another way to solve the 6X5 problem and keep the tube. If there is room above or below the chassis add a small transformer with a 6.3 volt 1 amp secondary and wire the 6X5 heater to the new transformer, do not ground the heater of the tube. Connect the cathode to one of the heater pins, that way you do not have the break down issues of that tube. I do that with all of my old Zenith radios with transformers and 6X5 or equ. tubes. hope this helps. All the best,Tom

I'm won't be getting a new transformer. I'll probably just use a terminal strip to affix those two diodes on the underside of the chassis where you can use any old 6X5, and it will still light, but it won't be doing any rectifying.

Here's what I've come up with. Your thoughts?

I will do some research for you. I just got done restoring a Zenith radio similar to that style for titan1A on this site. His is a 7S232 chassis. He (Rick titan1A) found a place to order a solid state plug in tube to replace the 6X5, and also a belt material to use to replace the tuning belt, without having to disassemble the entire tuning mechanism. I will do some research and see if I can come up as to where I ordered this items from. I don't suggest using a 6X5, as if the tube shorts heater to cathode it most likely will take out the power transformer. Wiring diodes should work out fine also, but yes, you will need some type of resistor in series to prevent the surge and also to drop some excess voltage. Personally I don't think light bulbs are a good choice.

Yes, my No. 1 concern with this radio is getting rid of the 6X5. I don't hear any objection to my drawing, so it looks like it's going to happen. Probably next Saturday. Not tomorrow since I'm doing tubes and capacitors tomorrow.

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. :sigh:

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.

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 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

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.

****

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

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.

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

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

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. :thmbsp:

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.

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

What kind of tombstone do you have? I have a 5S127 and I use it almost everyday. It's got a great sound for a 5 tube.

I've got the same radio. Apparently I was lucky when I first turned mine on and a shorted filter cap took out the 6X5 and I was able to shut it off before the transformer went poof. I used it regularly after I replaced the filters but now not so much, been a few years since I last powered it up.

I need the general cap replacement and my dial belt slips as well, though I wonder how that belt is supposed to stay on the pulley with no groove to hold it there.

Mine is a 5R135, not nearly as expensive as yours. Its BC-only with a plain dial but a fine little set.

I'm absolutely disgusted with this radio right now. I managed to get one wire replaced before I couldn't take it anymore. Replacing those wires is a huge PITA. I can't decide if I want to keep it or get rid of it. It was my first Zenith after all.

keep the faith! You'll get there! Nice radio..