My First Tube Radio Restoration Log

[EpicIntelGamer]

Hello everyone!

I was able to get my hands on an old tube radio today. It's not in the original casing, I assume the original radio cabinet broke and then all of the components were transfered into this decent looking homemade box.

This is the log where I'll be showing all the steps of me restoring this radio, which is actually my first tube radio restoration project.

The first thing I did was tear it apart and clean it up. Here are some pictures of the pieces.

First, the tubes from inside the radio:

Two 6D6 Tubes


An 80 and 76 Tube


A 6A7 and 42 Tube


Maybe I'm wrong but it looks to me like all of these tubes are original!

These are the metal covers that were over 4 of the 6 tubes.


This is the homemade box for the radio.


This is the electronics chassis with the front controls and display.


A closeup on the display.


Top down of the electronics chassis.


Back view of the electronics chassis.


The plate on the back of the electronics chassis.


And finally a view of the inside of the electronics chassis.


And on that plate we can see this was a Crosley Model 635 originally. Here is what it looked like originally (not my picture)

[EpicIntelGamer]

Okay so my initial questions are:

Why is there metal cases on some of the vacuum tubes and are they actually needed?

I've heard this radio can do three ranges, police, shortwave, and "Broadcast". Does that mean AM?

What are those large rectangular cans protruding upward from the chassis. One has a wire connecting to the top of a tube. Are these capacitors?

Theres four wires going to a single speaker?

Thanks for all of your help guys!

[vk6zgo]

Why is there metal cases on some of the vacuum tubes and are they actually needed?
The metal cases are to provide RF shielding for the tubes--& yes,if they were fitted originally,they are
needed.

I've heard this radio can do three ranges, police, shortwave, and "Broadcast". Does that mean AM?
Back in the day,the Police operated on Shortwave (HF),so that is why it is marked on the dial.

"Shortwave" (HF) is nominally between around 3MHz or so to 30 MHz.
You will probably find that this radio will tune up to maybe,12MHz.

It is an AM radio,so it will receive AM stations on the Medium Wave Broadcast Band,& Short Wave AM broadcasts on the "Shortwave" bands.
Hams,& other Communications users on  HF,usually do not use Amplitude Modulation,although if you are very lucky,you might find some.

What are those large rectangular cans protruding upward from the chassis. One has a wire connecting to the top of a tube. Are these capacitors?
They are Intermediate Frequency (IF) transformers,which are tuned to the IF frequency,which is usually around 455kHz,although some old radios use 175KHz,or 221kHz.
The wire to the top of a tube is probably so the secondary of the transformer can be connected to the Control grid of the tube it is connected to----some tubes,but not all,had this configuration.

Theres four wires going to a single speaker?
Back in the day,Electrodynamic Speakers were common,as Permanent Magnets were not developed to the level they were in later years.
The HT line from the power supply was run through the magnet coil,doing two jobs--acting as a smoothing inductor for the power supply,& an electromagnet for the speaker.

[EpicIntelGamer]

Thanks for all the info.

Do you mean the output from the transformer creates a stationary electromagnet in the speaker and that is in series with the rectifier tube?

Maybe I'm mistaken but it looks like this entire radio runs off of the output of the transformer which I think is very low voltage because it looks like the little incandescent bulbs for the front display are going directly off of the output of the transformer.

I think I might disconnect the transformer and measure it'd output right after I make sure it's good and solder on a new cord.

Oh and about those metal covers, if I only want AM radio are they really nessary? Other radios don't have them and I'd prefer not too as we'll because these look very dingy and not cool like the tubes themselves. I guess if I need them then I'll use then though.  Im pretty sure I remember where they all go.

[G7PSK]

The speakers in those days were often used as a choke for the HT. So beware of the voltage on one of those pairs feeding the speaker it will be in the order of 2 to 3 hundred volts, the wire leading out of the if transformer will also be HT coming from an anode cap on one of the valves. You will quite likely find the chassis is live as well.  According to my valve data book the 6A6 uses  anode voltage of 300 volts at a max of 70mA. Heater voltage of 6.3 volts it was quite common to run the filaments in series and use a small light bulb that illuminates the dial as a fuse so the heater voltage can also be quite high I have even seen the mains fed directly across a whole string of valves.

[EpicIntelGamer]

The speakers in those days were often used as a choke for the HT. So beware of the voltage on one of those pairs feeding the speaker it will be in the order of 2 to 3 hundred volts, the wire leading out of the if transformer will also be HT coming from an anode cap on one of the valves. You will quite likely find the chassis is live as well.  According to my valve data book the 6A6 uses  anode voltage of 300 volts at a max of 70mA. Heater voltage of 6.3 volts it was quite common to run the filaments in series and use a small light bulb that illuminates the dial as a fuse so the heater voltage can also be quite high I have even seen the mains fed directly across a whole string of valves.

Oh okay. I was removing the transformer and noticed that this whole time I failed to see four other wires going into the transformer and going straight to the rectifier tube. These must be the higher voltage wires.

So is it safe to replace this stuff with some 300V wire that's like 18AWG?

I'm assuming that wire would be fine because 300v sounds like enough to handle whatever is in this and this entire radio is rated to pull only 55watts so I can't imagine the HT would have a big enough amount of amperage to be a problem for 18awg.

[EpicIntelGamer]

I got the transformer completely removed now and cleaned up.

I still need to know if some 18AWG 300v wire is good enough for the HT output of the transformer.

I'm asking because I have a lot of that wire in different colors from computer power supplies. I am also wondering if it's safe to assume the yellow wire is also rated for 300v because the red and black wires from the same psu's have it printed on them but the yellow wires have no printing at all but look the exact same.

[c4757p]

I'm assuming that wire would be fine because 300v sounds like enough to handle whatever is in this and this entire radio is rated to pull only 55watts so I can't imagine the HT would have a big enough amount of amperage to be a problem for 18awg.

1) You underestimate the insanely high voltages used in vacuum tube equipment. I have a vacuum tube function generator that can only put out up to 20V RMS and uses a 420V rail. Have you measured the voltage the transformer puts out? (Be careful doing this)

2) Amperage has nothing to do with it.

[EpicIntelGamer]

I'm assuming that wire would be fine because 300v sounds like enough to handle whatever is in this and this entire radio is rated to pull only 55watts so I can't imagine the HT would have a big enough amount of amperage to be a problem for 18awg.

1) You underestimate the insanely high voltages used in vacuum tube equipment. I have a vacuum tube function generator that can only put out up to 20V RMS and uses a 420V rail. Have you measured the voltage the transformer puts out? (Be careful doing this)

2) Amperage has nothing to do with it.

I'm not trying to underestimate it but when all I see are mostly 200v rated caps, you have to assume it can't be too much or that those caps arent subjected to the highest voltages.

I'll go measure this carefully.

And the reason why I mentioned amperage is because I thought the heaters used a good amount of amps and I wanted to make sure people didn't think I was going to put flimsy wire on the heaters.

[G7PSK]

I doubt that there is more than 200 mA from the transformers and the valves maximum operating voltage is 300 Volts so the most likely are run around 250 to 275 volts. As previously stated its not the amps that regulate the wire so much as the insulation ratings so as long as the wire is rated above the maximum voltage seen in the circuit you should be OK, and at the voltage involved with these valves I would choose a wire with insulation rated to at least 400 volts but no doubt some one will gainsay me on this.

The valve heaters are only 6.3 volts and up 800 mA each.

[EpicIntelGamer]

I doubt that there is more than 200 mA from the transformers and the valves maximum operating voltage is 300 Volts so the most likely are run around 250 to 275 volts. As previously stated its not the amps that regulate the wire so much as the insulation ratings so as long as the wire is rated above the maximum voltage seen in the circuit you should be OK, and at the voltage involved with these valves I would choose a wire with insulation rated to at least 400 volts but no doubt some one will gainsay me on this.

I'll go measure the transformer and then if it's pretty high then I'll hunt around on eBay for some cheap 400v wire.

[EpicIntelGamer]

WOW that has some real HV!

One winding gets all the way up to about 600VAC!

Another seems to have about 5VAC.

Then there is another winding which looks like it is supposed to have a center tap, however, there's a problem. This wire actually broke off VERY close to the transformer and the little bit that's left shows infinite resistance to all of the other wires coming from the transformer.

The two sides of the winding that I think is supposed to have a center tap show about 7VAC and I think its for the heaters.

I guess I'll post a picture of where that wire broke off of the transformer.

[c4757p]

One winding gets all the way up to about 600VAC!

Could be a center-tapped 300V winding, maybe another wire broke off. They're often center-tapped so you can have a full-wave rectifier with only two diodes (a tube diode is a lot more expensive than a 1N4007...). That'll give you 424V peak, probably 350-ish after the hilariously inefficient vacuum tube rectifier. Also remember that they're usually meant for 110V input, mains here is 120V nominal now and can easily run high (I've seen 130), so you could be looking at 10-18% higher voltages.

As for the broken windings - you're in for a real treat if you want to repair that transformer. Have fun!

[EpicIntelGamer]

One winding gets all the way up to about 600VAC!

Could be a center-tapped 300V winding, maybe another wire broke off. They're often center-tapped so you can have a full-wave rectifier with only two diodes (a tube diode is a lot more expensive than a 1N4007...). That'll give you 424V peak, probably 350-ish after the hilariously inefficient vacuum tube rectifier. Also remember that they're usually meant for 110V input, mains here is 120V nominal now and can easily run high (I've seen 130), so you could be looking at 10-18% higher voltages.

As for the broken windings - you're in for a real treat if you want to repair that transformer. Have fun!

See off of the one side of the transformer is 4 wires, 2 red and 2 yellow. One color makes 600V, the other color makes 5v or so.

This wire that was broken off comes from the other side of the transformer, so I thought it would have to do only with the little winding on that side, not with those 2 sets of colored wires on that other side.

I was wrong, your absolutely correct. That is the center tap for that 600v winding! And what do you know, now that I'm measuring the right wires, there is continuity and I measure from center tap to either side about 300VAC (according to my horrible DMM).

Oh and by the way, the plate on this chassis says input 100-125 so I guess it has quite a bit of tolerance and I'm also running this on a ballasted variac so I can get whatever voltage I want 

So it looks like there is just barely enough exposed wire from that broken one for me to solder on a new one and then cover it in globs of liquid electrical tape? Unless someone else has any better ideas.

It'll be tricky because there's only 1 or 2mm of wire left coming out of the transformer.

[SeanB]

The winding with 5V centre tapped is for the rectifier valve only. the heater is connected to the cathode so as to reduce voltage stress on it, as otherwise the heater cathode insulation has to withstand 400V or so at red heat, which is very difficult to do reliably in a very small space while having good heat transfer to heat the cathode. The rectifier valve has 2 anodes, you probably can look through the glass to see the 2 separate large plates around the heater with a gap in the middle.

This is to give a half bridge, while still making it easy to make a simple valve, a 4 diode full wave rectifier needs 3 separate heater supplies insulated to the peak of the AC output of the supply transformer and isolated from the AC input, output and each other by that amount.

The rectifier will have the cathode connected to a large electrolytic ( large being relative here, it might be 8uF, 16uF or go up to 47uF at 450VDC) and then it goes to the speaker energising coil to be used both as a choke to reduce noise, in conjunction with another 8uF capacitor, often a dual or triple unit in a single can, and to actively reduce hum, as the residual ripple will still be on the speaker wiring from the amplifier as it normally has a very poor supply rejection ratio. Thus if you have hum on the speaker you turn the wires on the speaker transformer the other way round so as to reverse phase, one way will have less hum.

The triple capacitors are typically 8uF, 8uF 450VDC and 50uF 20VDC in the same can, the 50uF unit being used as a cathode decoupling capacitor on the speaker amplifier. They do die after a few decades, and you probably need to replace them before turning it on as they will be dead. Use modern radial unit of 22uF 450VDC and 100uF 50VDC as replacements, just put them under the chassis and clip the leads from the original cap and leave it there. Sometimes people remove the insides of the old cap and place the 3 units inside the capacitor body and reseal it to look original.

[EpicIntelGamer]

The winding with 5V centre tapped is for the rectifier valve only. the heater is connected to the cathode so as to reduce voltage stress on it, as otherwise the heater cathode insulation has to withstand 400V or so at red heat, which is very difficult to do reliably in a very small space while having good heat transfer to heat the cathode. The rectifier valve has 2 anodes, you probably can look through the glass to see the 2 separate large plates around the heater with a gap in the middle.

This is to give a half bridge, while still making it easy to make a simple valve, a 4 diode full wave rectifier needs 3 separate heater supplies insulated to the peak of the AC output of the supply transformer and isolated from the AC input, output and each other by that amount.

The rectifier will have the cathode connected to a large electrolytic ( large being relative here, it might be 8uF, 16uF or go up to 47uF at 450VDC) and then it goes to the speaker energising coil to be used both as a choke to reduce noise, in conjunction with another 8uF capacitor, often a dual or triple unit in a single can, and to actively reduce hum, as the residual ripple will still be on the speaker wiring from the amplifier as it normally has a very poor supply rejection ratio. Thus if you have hum on the speaker you turn the wires on the speaker transformer the other way round so as to reverse phase, one way will have less hum.

The triple capacitors are typically 8uF, 8uF 450VDC and 50uF 20VDC in the same can, the 50uF unit being used as a cathode decoupling capacitor on the speaker amplifier. They do die after a few decades, and you probably need to replace them before turning it on as they will be dead. Use modern radial unit of 22uF 450VDC and 100uF 50VDC as replacements, just put them under the chassis and clip the leads from the original cap and leave it there. Sometimes people remove the insides of the old cap and place the 3 units inside the capacitor body and reseal it to look original.

There is no 5v center tapped, only a 600v center tap.

I can see two black objects on either side of the inside of the rectifier tube.

I have only one large electrolytic can, and I'm not too sure about its specs. I can see on the side a few different voltages but I don't see any MFD values and I also don't want to remove it because there appears to be no way of knowing which wire goes to which of the three terminals.

[EpicIntelGamer]

Hey guys I've got a question.

Ovbiously I need to replace all of the paper caps in this radio.

One for example, says, "CAP. .05-200V" which I guess means Capacity is .05uF and 200Volts. Most other caps have a small value as well.

I'm wondering if I can use those 250V rectangular AC capacitors that you would find on the input of computer PSU's (given that they have a similar uF).

I'm hoping that I can use those because I have pretty many and might not need to buy any caps then.

[c4757p]

In most places, yes.

[EpicIntelGamer]

In most places, yes.

Where can I not (besides the electrolytics)?

Also, how close do these need to be rated (I'm talking uF, not voltage) to the original paper caps?

I also need a bit of help with those rectangular caps. I see on there they will say something like: "0.33uF +-10%         X2"
Its that X2 that I'm wondering about. Its all the way on the right hand side but still on the same line as the other writing. These only have 2 legs so they must be a single capacitor but are they saying that that .33uF cap is actually .66uF?

[SeanB]

X2 is the insulation class, these are designed for mains filtering, so they have to be classified that they will survive spikes. This just means that they self heal on overvoltage and eventually fail as open circuit, but can short as a failure mode. The ones marked Y or Y2 are designed to fail open only. You can use them on high voltage with no problems. Rating wise in most cases if they are slightly higher in value up to about twice the value there will be no problem. Only ones that are critical are those used in tone controls ( where you will find capacitors of around 1 to 100n) and in the tuning circuits, where the value is between 1 to 1000pF and they generally are a ceramic capacitor.

[EpicIntelGamer]

X2 is the insulation class, these are designed for mains filtering, so they have to be classified that they will survive spikes. This just means that they self heal on overvoltage and eventually fail as open circuit, but can short as a failure mode. The ones marked Y or Y2 are designed to fail open only. You can use them on high voltage with no problems. Rating wise in most cases if they are slightly higher in value up to about twice the value there will be no problem. Only ones that are critical are those used in tone controls ( where you will find capacitors of around 1 to 100n) and in the tuning circuits, where the value is between 1 to 1000pF and they generally are a ceramic capacitor.

Okay then so I guess I can use these caps for most of them.

What should I use for that .05uf paper cap for example. Oh and is that actually .05uf, is that what that means? I guess I couldn't use a .33uF cap for that could I?

Would a .1uF cap work for that (I guess it should).

[EpicIntelGamer]

X2 is the insulation class, these are designed for mains filtering, so they have to be classified that they will survive spikes. This just means that they self heal on overvoltage and eventually fail as open circuit, but can short as a failure mode. The ones marked Y or Y2 are designed to fail open only. You can use them on high voltage with no problems. Rating wise in most cases if they are slightly higher in value up to about twice the value there will be no problem. Only ones that are critical are those used in tone controls ( where you will find capacitors of around 1 to 100n) and in the tuning circuits, where the value is between 1 to 1000pF and they generally are a ceramic capacitor.

Okay then so I guess I can use these caps for most of them.

What should I use for that .05uf paper cap for example. Oh and is that actually .05uf, is that what that means? I guess I couldn't use a .33uF cap for that could I?

Would a .1uF cap work for that (I guess it should).

Will that work?

[EpicIntelGamer]

Will a .1uF capacitor be a good replacement for a .05uF paper capacitor?

Will a .68 and .47 work to replace a 1uF paper capacitor?

I need to know so I can get started on this!

[c4757p]

We'll have to install a service bell for you to ring...

I'd use .047. If you don't have it, then two .1uF in series = .05uF. I don't know what this capacitor is doing so I don't know if it's OK to double it.

[EpicIntelGamer]

We'll have to install a service bell for you to ring...

I'd use .047. If you don't have it, then two .1uF in series = .05uF. I don't know what this capacitor is doing so I don't know if it's OK to double it.

I don't mean to be rude but I like to get stuff done.

I don't have a .047 but I do have two .1's!

Now I'm not sure about wiring caps in series so I'll ask, if both are rated to 275V, are those wired in series okay to replace the 200v cap?