My First Tube Radio Restoration Log

[c4757p]

Yep.

Ideally voltage ratings would add, so two 275V = one 550V. In real life you really need to put high-value balancing resistors across them (1Meg or so), which could ruin the performance depending on what they're being used for. But you don't lose voltage rating.

[c4757p]

Oh, by the way, the decimal point was invented to make engineers miserable when it's hard to see. It's 47nF and 100nF.

Damn font designers making it so small it's a single pixel at GUI sizes.... I can hardly make them out on my laptop display!

[EpicIntelGamer]

Oh, by the way, the decimal point was invented to make engineers miserable when it's hard to see. It's 47nF and 100nF.

Damn font designers making it so small it's a single pixel at GUI sizes.... I can hardly make them out on my laptop display!

Alrighty, I'll write it out next time (its the least I can do in exchange for all of this information).

Now I know that there is voltages that are way over 200V in this chassis but if all of these caps are rated at 200V then wouldn't it be fine to use some 300V wire just for the wire connecting directly to the caps?

[c4757p]

I know I repeat this over and over here, but remember that voltage is differential. You don't have "200V", you have 200V between two points. The capacitor's voltage rating is for the voltage between its pins. The wire's voltage rating is between the wire and anything it could ever possibly touch. That capacitor will be perfectly happy stuck between +400V and +200V but the wire will not.

Now..... (*looks around cautiously*) now that nobody is listening..... in my experience decent quality 300V-rated wire can usually handle 400V in a pinch. But I didn't tell you that, you reckless jackass! Why would you think to do that? And certainly don't if it happens to say "Wun Hung Lo" on it. Or if it's entirely unlabeled.

I really wish you'd track down some 600V wire, it's not hard to find.

[xrunner]

Now..... (*looks around cautiously*) now that nobody is listening..... in my experience decent quality 300V-rated wire can usually handle 400V in a pinch. But I didn't tell you that, you reckless jackass!

I saw what you did there. 

[EpicIntelGamer]

I know I repeat this over and over here, but remember that voltage is differential. You don't have "200V", you have 200V between two points. The capacitor's voltage rating is for the voltage between its pins. The wire's voltage rating is between the wire and anything it could ever possibly touch. That capacitor will be perfectly happy stuck between +400V and +200V but the wire will not.

Now..... (*looks around cautiously*) now that nobody is listening..... in my experience decent quality 300V-rated wire can usually handle 400V in a pinch. But I didn't tell you that, you reckless jackass! Why would you think to do that? And certainly don't if it happens to say "Wun Hung Lo" on it. Or if it's entirely unlabeled.

I really wish you'd track down some 600V wire, it's not hard to find.

LOL

I already soldered in a capacitor with 300v wire, but I guess I'll have to dismantle it and put in some 600v wire. I did find some cheap and available in different colors on eBay: http://www.ebay.com/itm/10ft-18-AWG-Black-Appliance-Stranded-Wire-105C-600V-/111010425643?pt=LH_DefaultDomain_0&hash=item19d8bcab2b

Unfortunately this wire I was using was probably not decent quality, and even if it was I'd like to keep everything safe if it only costs like $4 for enough 600v wire for the whole radio.

So I guess I'll just fix whatever else I can while I wait for that 600v wire to come.

Now..... (*looks around cautiously*) now that nobody is listening..... in my experience decent quality 300V-rated wire can usually handle 400V in a pinch. But I didn't tell you that, you reckless jackass!

I saw what you did there. 

SSSSHH! You'll attract attention from the Safety Police!!!

[EpicIntelGamer]

So is http://www.ebay.com/itm/10ft-18-AWG-Black-Appliance-Stranded-Wire-105C-600V-/111010425643?pt=LH_DefaultDomain_0&hash=item19d8bcab2b good?

[Chryseus]

I've never actually seen a wire rated for 200V fail even on several hundred volts, maybe if you're putting a lot of current through it but I'm still skeptical.
Anyway I'll give you a few tips that might help.

Pick the nearest value for capacitors particularly if they are in the RF stage, avoid using series or parallel combinations as that will just result in more mess and confusion if you should sell it later.
Any capacitor directly across the mains should be replaced with a safety type, elsewhere it does not really matter, I suggest adding a fuse in any case at some point.
Check that the tube filaments glow and there are no shorts, if any tube appears to be white rather than silver it's junk.
Replace all the wax paper caps as these are most certainly bad, if you want to keep to the original look consider restuffing them, other caps such as mica are generally good so hold off replacing them.
The case of the electrolytic cap is usually the negative side, this may not be true if there is an insulator between it and the chassis, the output may be marked on the can if not refer to to the schematic.

Which brings me to getting the schematic, I've had a brief look around but cannot find a free source, so unless it's in the case you may have to buy it as distasteful as that is, don't forget to redistribute it afterwards, seriously selling schematics and service manuals makes my blood boil. 

Repairing tube equipment is a lot of effort but also very fun and educational, good luck! 

[c4757p]

So is http://www.ebay.com/itm/10ft-18-AWG-Black-Appliance-Stranded-Wire-105C-600V-/111010425643?pt=LH_DefaultDomain_0&hash=item19d8bcab2b good?

Looks OK to me.

[EpicIntelGamer]

I've never actually seen a wire rated for 200V fail even on several hundred volts, maybe if you're putting a lot of current through it but I'm still skeptical.
Anyway I'll give you a few tips that might help.

Pick the nearest value for capacitors particularly if they are in the RF stage, avoid using series or parallel combinations as that will just result in more mess and confusion if you should sell it later.
Any capacitor directly across the mains should be replaced with a safety type, elsewhere it does not really matter, I suggest adding a fuse in any case at some point.
Check that the tube filaments glow and there are no shorts, if any tube appears to be white rather than silver it's junk.
Replace all the wax paper caps as these are most certainly bad, if you want to keep to the original look consider restuffing them, other caps such as mica are generally good so hold off replacing them.
The case of the electrolytic cap is usually the negative side, this may not be true if there is an insulator between it and the chassis, the output may be marked on the can if not refer to to the schematic.

Which brings me to getting the schematic, I've had a brief look around but cannot find a free source, so unless it's in the case you may have to buy it as distasteful as that is, don't forget to redistribute it afterwards, seriously selling schematics and service manuals makes my blood boil. 

Repairing tube equipment is a lot of effort but also very fun and educational, good luck!

Yeah I imagine it takes quite a bit to break down the average piece of insulation, but then again, 600v is quite a bit.

I have no idea where the RF stage is (please don't hurt me, I'm not too good at electronics  ) I'm also not going to be selling this so I'm not going to worry too much about confusion, other than the confusion that I'm already experiencing lol.

There is no caps across the mains. A fuse will be added as well.

It's going to be at least a week before I get to turn this on for the first time and see if any filaments fire up. I can tell you that I think all of the tubes are original and that they all have that shiny spot intact (the one that is supposed to go away as it absorbs contaminants and gasses).

I'm replacing all of the caps right off of the bat just to be safe.

I'm not sure what's up with that large can cap. I also think its a shame you can't buy a new one of those, you have to just use normal modern electrolytics and then leave the can there "for show". I hate leaving stuff "for show" but not so much that I'd remove it. I just wish it could look good and work you know?

I did manage to find a schematic for the radio on some other site for free.

Yeah this is going to be quite an in depth thing to do.

Thanks for all of your information   

So is http://www.ebay.com/itm/10ft-18-AWG-Black-Appliance-Stranded-Wire-105C-600V-/111010425643?pt=LH_DefaultDomain_0&hash=item19d8bcab2b good?

Looks OK to me.

Good, I'll order some of that tomorrow then, along with some heat shrink, caps, and a fuse holder.

[ElectroIrradiator]

I wouldn't bother with the cap across the mains, it won't do anything meaningful to an old tube radio, though the fuse would be a good idea.

The reason why you cannot buy a replacement filter cap, is that back then each model from each brand frequently had its own, custom type. So you would need to fabricate a gazillion different type for a vanishingly small market, to be able to supply everyone. The usual way of getting around this, is to disconnect the original cap, leaving it in place, and discretely mount modern electrolytic caps below the chassis. I wouldn't even bother testing it, it doesn't work.

Depending on how much time you wish to spend on this, then I may be able to provide a few tips and tricks. The usual way of restoring radios of this age, is to do so very, very slowly and methodically. You cannot rely on *anything* working, so frequently you'd proceed methodically in a set order. The intent of doing so is to reduce the chance of letting the blue smoke out of something, which you will need later.

Any chance you could post or link the schematic, please?

[Rascal]

Im always reluctant to replace original components in a restoration project - but you usually find some need replacing

Paper caps should be replaced. Electrolytic caps I will try to reform (usually successfully). Mica caps should be okay.

Resistors I leave alone if they are within 20% of value.

Cloudy tubes are no good.

Use a variac.

 

[EpicIntelGamer]

I wouldn't bother with the cap across the mains, it won't do anything meaningful to an old tube radio, though the fuse would be a good idea.

The reason why you cannot buy a replacement filter cap, is that back then each model from each brand frequently had its own, custom type. So you would need to fabricate a gazillion different type for a vanishingly small market, to be able to supply everyone. The usual way of getting around this, is to disconnect the original cap, leaving it in place, and discretely mount modern electrolytic caps below the chassis. I wouldn't even bother testing it, it doesn't work.

Depending on how much time you wish to spend on this, then I may be able to provide a few tips and tricks. The usual way of restoring radios of this age, is to do so very, very slowly and methodically. You cannot rely on *anything* working, so frequently you'd proceed methodically in a set order. The intent of doing so is to reduce the chance of letting the blue smoke out of something, which you will need later.

Any chance you could post or link the schematic, please?

Yeah I'm just going to replace the old huge cap but leave it there for looks.

I agree, I don't want to take any chances and end up blowing up any tubes so I'm going to replace all of the caps and any wiring I feel is too degraded.

The schematic was found on http://www.nostalgiaair.org/Resources/ If you look for crosley and then for the model 635.

Im always reluctant to replace original components in a restoration project - but you usually find some need replacing

Paper caps should be replaced. Electrolytic caps I will try to reform (usually successfully). Mica caps should be okay.

Resistors I leave alone if they are within 20% of value.

Cloudy tubes are no good.

Use a variac.

I'm just going to replace all of the caps just to be safe.

No tubes are cloudy.

I will use a variac, with a ballast.

Thanks guys for the info!

[ElectroIrradiator]

I agree, I don't want to take any chances and end up blowing up any tubes so I'm going to replace all of the caps and any wiring I feel is too degraded.

The schematic was found on http://www.nostalgiaair.org/Resources/ If you look for crosley and then for the model 635.

Got the schematic.

There are some additional, simple things you might consider doing, in addition to replacing the caps, to try and maximize your chance of success under full power.

It is a bit hard to judge the condition of the radio from over here, but I don't mind writing up a few additional suggestions to check. They might come in handy later, if you think you might want to restore more radios in the future. All of them can be done without AC mains power, so you could do them while waiting for parts/wire.

[Chryseus]

If you want to you can remove the contents of the electrolytic can quite easily and put the new caps inside, just uncrimp the end or cut the can, apply some heat to melt the tar blob at the top of the can and the guts should slide right out.
Referring to the schematic 16 is the safety cap that you can either leave out or replace, 10Z, 10Y and 10X are the electrolytics in the main can with the negative side going to the can.

[fpliuzzi]

The following ebook can be useful for an antique radio restoration project. Richard McWhorter wrote a 212 page book entitled "The Vacuum Tube Shortwave Radio (understanding and troubleshooting)" and has generously made this ebook available as a free pdf download...

www.richardmcwhorter.com/vacuumtuberadio/

The pdf does ask for a password when opened (password is allamericanfiveradio). The ebook is fully indexed so it's easy to jump right to the sections needed.

The pdf's intro states that the RCA 8Q2 radio was chosen as the example radio for the book because all the vacuum tube circuits of the 8Q2 are representative of a very popular architectural design dating from the late 1930's through the early 1960's.

Regards,
Frank

[EpicIntelGamer]

Today I was cleaning up a bit and I guess one of the tubes got stuck under my chair and when I sat down, CRUNCH!!!

Looks like I'm going to have to buy a "76" tube now. It also looks like since I broke this, this radio no longer has all original tubes.

 

[c4757p]

They're not quite like transistors, are they?

Damn things. I've broken a few too, and nice ones at that

[EpicIntelGamer]

They're not quite like transistors, are they?

Damn things. I've broken a few too, and nice ones at that

Unfortunately not.

This is the cheapest listing on eBay for 76 tubes. Which brand should I get (they have a drop down menu of different brands for the same price)?

http://www.ebay.com/itm/231018533109?var=530178370454&ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

[c4757p]

Damned if I know...  Eeny-meeny-miney-moe?

[ElectroIrradiator]

Which brand should I get (they have a drop down menu of different brands for the same price)?

Doesn't really matter from a technical point of view. They either work, or they don't. Back then it wasn't unusual for one manufacturer to sell 'raw' tubes in quantity to another brand, who would then sell the tubes with their own branding stamps printed on the glass. You may see minor, mechanical variations between tubes made in different factories, and the amount of the silvery gettering may also vary, that is about it.

The tubes in the auction are all 'ST' shape, meaning coke bottle as seen in the photo. So if possible you may want to just match the brand to that of the other ones in your radio, perhaps?

[EpicIntelGamer]

Which brand should I get (they have a drop down menu of different brands for the same price)?

Doesn't really matter from a technical point of view. They either work, or they don't. Back then it wasn't unusual for one manufacturer to sell 'raw' tubes in quantity to another brand, who would then sell the tubes with their own branding stamps printed on the glass. You may see minor, mechanical variations between tubes made in different factories, and the amount of the silvery gettering may also vary, that is about it.

The tubes in the auction are all 'ST' shape, meaning coke bottle as seen in the photo. So if possible you may want to just match the brand to that of the other ones in your radio, perhaps?

All of the other tubes in the radio are the original Crosley branded tubes. I guess I'll just choose a brand at random.

[EpicIntelGamer]

I did not order a tube yet but I did receive my 10Ft of 600v 18awg wire. I notice it actually has two different layers of insulation and proudly states it is 600v on the wire so I feel pretty good about this purchase.

The only thing I've done is to solder on a piece to the little stub of wire where the one broke off of the transformer (it's the center tap of the 600v winding) and covered it in heaps of liquid electrical tape that I let soak into the windings to make sure it doesn't have any possibility of arcing.

I'm also going to put heat shrink over the joint and another layer of liquid electrical tape just to make sure everything is good and safe. I'll also heat shrink any rough looking parts of the existing transformer wires that I want to keep.

I'm also using electrolysis to clean off those metal covers that cover up 4 of the 6 tubes, it's slow but its working quite nicely!

[ElectroIrradiator]

There is no particular reason to insulate the center tap on the transformer. It is connected to ground, giving you two 300V phases for the rectifier. All you need is a good mechanical and electrical connection.

If you get grief from the transformer, then it will probably be due to shorted internal windings, or internal arching due to broken down insulation. If moisture has been able to build up in the insulation, it may have swollen up and/or partially lost some of its insulating properties.

[EpicIntelGamer]

There is no particular reason to insulate the center tap on the transformer. It is connected to ground, giving you two 300V phases for the rectifier. All you need is a good mechanical and electrical connection.

If you get grief from the transformer, then it will probably be due to shorted internal windings, or internal arching due to broken down insulation. If moisture has been able to build up in the insulation, it may have swollen up and/or partially lost some of its insulating properties.

I already tested the transformer with no load and it didn't pull any current from my 30watt ballast that I was using so I assume we're good.

The only problem is that the wires coming from the transformer were crammed in really tightly to the actual frame that mounts to the electronics chassis and now if I move the wires they just break off so I guess I need to break them off and replace them.

More work for me.....