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 Post subject: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Fri 04, 2021 1:38 am 
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Location: Northeast Florida
Obviously I will have to change from a loktal to octal socket, but are they interchangeable electrically? I see they are both directly heated (no cathodes). For what it's worth, it's for a late 40's Westinghouse H161 table radio, schematic here http://www.nostalgiaair.org/pagesbymode ... 024114.pdf

Someone was kind enough to 'pre-break' the socket before I got it, and I really don't want to go with another loktal.

Thanks for any help you can give

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Fri 04, 2021 2:12 am 
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According to my RCA tube manual, RC30, under 5AZ4 it says "For ratings and characteristics, refer to type 5Y3"


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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Fri 04, 2021 2:15 am 
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I'd consider that a definite upgrade, given all the issues people report with loktal tubes and sockets. The two are electrically identical, physically different.

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Fri 04, 2021 2:43 am 
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That's good news, thanks for the help, guys

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Fri 04, 2021 3:38 am 
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Also buy some bolts that have smaller nuts, one time that smaller is better. There is very little clearance on the new socket for a nut, designed for rivets. Could use pop rivets, maybe, but the tool is impossible to use from below, and now that I think about it, too many obstructions topside as well.

I collected jars of nuts and bolts over the years, and a good-looking vintage radio bolt is a thing of beauty. :D

Label every wire and take pictures of all terminals, draw diagrams, etc. I cut short pieces of food bag twisters and write numbers on them for markers.

FYI, trivia for the lurkers, Sylvania made Loktals, Philco bought boxcar loads, named them Loktals.
Zenith also used alot of Loktals, and they are good in the portables.

To pop them loose safely, rock towards the keyway, most bases have a dimple to mark it, back and forth, and sometimes slide the tip of a screwdriver under an edge while rocking. Pulling or prying straight up while the pin is locked is what damages the socket.

*I needed a Loctal rectifier and had no time to wait for a tube order, grand kids were coming and I wanted the radio playing. So I swapped in a 7-pin socket for a 35W4. Four insulated, single strand wires just fit thru the hole for the center pin. This mod is reversible. Good luck with the Westy.


Attachments:
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7-pin scktr.jpg [ 47.5 KiB | Viewed 907 times ]
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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 12, 2021 5:57 pm 
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Hey guys, I have a follow up question; I know it sounds crazy, but will a tube rectifier put out any B+ at all it's wired backwards (ie; heater wires going to plates, plates to heaters)? I don't think I miswired, but I want to be sure.

The reason I ask; I powered up the radio with a variac, and also a 100w bulb in series to check for shorts. Bulb never got bright and nothing seems to be burning up, but at 100v on the variac, I'm only getting around 85v B+ measured at the rectifier (supposed to be 320v). I didn't take the variac any higher, because I was afraid I'd damage something.

Thanks for any help you can give

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 12, 2021 8:46 pm 
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If you connected the filament pins where the plate pins were supposed to be connected you would likely burn out the power transformer.

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 12, 2021 9:14 pm 
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Jim Mueller wrote:
If you connected the filament pins where the plate pins were supposed to be connected you would likely burn out the power transformer.


Thanks, Jim. So the fact that I'm getting even 83 volts B+ would indicate that it's probably wired properly, and that the trouble lies elsewhere, correct? Like maybe another problem loading down B+ via a short to ground?

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 12, 2021 9:36 pm 
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I just had a similar issue with a Philco, and it was a faulty grid bias resistor on the power tube socket. You have a big resistor on your 6AT6 grid.
You can bring the voltage up briefly with a DMM set to DCV clipped to the grid and B-, the negative end of a filter cap. There should be a healthy negative voltage there and on the 6L6.

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 12, 2021 11:14 pm 
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Thanks, John. It seems to me that there is something pretty badly shorted to ground, I need to do more digging

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sun 13, 2021 10:45 pm 
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Defective or miswired filter capacitors can also cause low B+ but that frequently also causes bad hum or a capacitor explosion.

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sun 13, 2021 11:46 pm 
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Jim Mueller wrote:
Defective or miswired filter capacitors can also cause low B+ but that frequently also causes bad hum or a capacitor explosion.


Thanks, Jim. This one still has the original filters, and there is black rubber oozing out of the various slots underneath. There was no hum, but then again it only got up to 83v coming out of the rectifier (supposed to be 320v) @ 100v ac input---didn't take it up any higher, because it was obvious something is wrong. I have replaced the filters, haven't tried it out yet

But I am noticing there are many split plastic/paper capacitors in this set (the square ones that look like micas but aren't), and the papers are looking pretty poor as well (melted, cracked ends). I'm wondering if the effects of all of these damaged capacitors is resulting in a collective short to ground?

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Mon 14, 2021 9:28 pm 
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Could be. They could also be biasing tubes into drawing excessive current. Lots of possibilities.

There really isn't any point in trying to troubleshoot a set full of known bad parts. Just replace them. But do it carefully so that you don't create wiring errors, inadvertent shorts, or other new issues.

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Tue 15, 2021 2:40 am 
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Last night I replaced the electrolytics, and the paper caps in the power/preamp stages (that's all I had time to do last night), and pulled all of the receiving tubes leaving just the rectifier, output and preamp tubes. Powered it up tonight---at 120v in, I got 200v dc at the rectifier. It's still not right (supposed to be 320v), but it's better than my original 83v.

Another positive sign--when I'd power it up before, the lamp on my dim bulb tester was linear to voltage in, which isn't right. This time the bulb went dim while the filaments were warming up, and gradually brightened once B+ came up (but not too bright).

But the B+ is still being loaded down by something---time to replace the rest of those pesky caps.

Thanks to everyone for all of the help, and hopefully I'll have a better update next time

EDIT; I'm using a 100 watt bulb in my tester, and the unit is supposed to draw around 100 watts---could the dim bulb tester account for the missing 100v?

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Wed 16, 2021 3:02 am 
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What's the voltage going into the radio? Not what the Variac is putting out. The DBT can drop considerable voltage. If you pull all the tubes except the rectifier, the B+ should be MUCH higher than what the schematic shows. If the schematic show 320 volts during normal operation, I would say 450 to 500 volts would be about right without any tubes. Watch out for the voltage ratings of your capacitors!

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Wed 16, 2021 3:06 am 
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Thanks, Jim. When I tried it yesterday, I had the output tube and preamp tube in it as well, so it loaded it down a bit. I finished recapping tonight, I will try it out tomorrow, monitoring the voltage going into the radio

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 19, 2021 1:51 am 
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I recapped the radio and tried it out tonight---interesting results. Using a meter on the dim bulb tester, I took it up to 90v, where the phono and FM started working (AM is stone dead), and noticed that volume is much lower than it should be. Took it up to 110v, and the entire radio goes dead, like someone flipped a switch inside of it. No bad smells, nothing's getting hot, just dead.

I replicated it multiple times. Something is going open once I get near full line voltage. It's not a short---bulb is not getting bright, instead it goes out (as does all of the pilot lights on the radio) when the radio dies, indicating open circuit. I replaced the cord/plug before....just hoping this isn't a bad primary winding in the power transformer...

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 19, 2021 1:54 am 
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If it's an open circuit, a voltmeter will find it pretty quickly. If all the voltages are normal, it becomes more fun.

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 19, 2021 2:29 am 
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Jim Mueller wrote:
If it's an open circuit, a voltmeter will find it pretty quickly. If all the voltages are normal, it becomes more fun.


Now that the weekend is here, I will have much more time to delve into it. I was thinking I would pull the rectifier tube and check plate voltages and heater voltage next to see what happens at full line voltage. I'll report back what I find

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 Post subject: Re: Can I use a 5Y3 in place of a 5AZ4?
PostPosted: Jun Sat 19, 2021 8:32 pm 
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You won't find much if you pull the rectifier. The only voltages you will see are the AC voltages on the rectifier, the AC line voltage, and the heater voltage on the other tubes. Everything else will be close to zero.

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