Tube Radio Capacitor Can Replacement

Intro: Tube Radio Capacitor Can Replacement

You know that "hum" noise that comes out of old electronics, especially tube powered radios and amplifiers/ This is usually caused by failed electrolytic capacitors in the power stage from the transformer. Replacing these old parts will usually resurrect a dead tube set or eliminate a constant hum in a functioning set.

This is a method for replacing failed multi stage capacitor cans to get old radios working again. These things only last about 25 years so most of them have failed at this point. New ones are not generally available and are expensive if you can get one at all. Follow along as I show a quick and dirty way to replace these pesky caps. Some people will re-stuff the cans with new parts to preserve the look but I don't and I don't care how it looks, my amps are not for showing to people, they are for making music!

STEP 1: Cut Off the Old Can!

Using a hacksaw blade and taking care to not damage the tubes, cut off the can right above the crimp line, saw right through the sucker and you are left with a stump. Remove tubes if you need to in order to get a clean shot at the can. Be sure not to damage the info stamped into the side of the can, it will tell you what value to get for the replacement parts and what terminal to use.

STEP 2: Take Note of What You Need to Buy , Get Shopping

For this one I need

60 MFD at 350 volt

40MFD at 350 volt

30 MFD at 350 volt

10MFD at 350 volt

I can go up in voltage, substituting a 10 MFD at 450 volt for instance but I can't change the MFD by very much-10% is the furthest I'd push the specs. If I had no time to wait for a new part and I had a 42MFD on hand I'd try it, but be prepared to pull it off if the amp sounds funny.

I buy mine from Justradios.com but you can get caps just about anywhere on the internet. I'm not a proponent of buying super expensive caps for old tube radios. My ear does not hear a difference and I'm not shelling out $20 for a cap in a blue wrapper that functions the same to my ear as a $4 black capacitor.

STEP 3: Note Where the Caps Go

See those little symbols next to the value designation? the triangle, box, half circle and "nothing" are etched into the bottom of the cap, we are looking at the same chassis here, but from the bottom, you can just make out the square symbol and half circle in the pic. Now CAREFULLY transfer that to the top of the chassis, be sure not to mix up the position while flipping the amp over

STEP 4: Drill Next to the Cut Stubs of the Old Cap, Install the New Caps

Yep, drill right next to them, this will allow you to pass the replacements down to the stubs and solder them on! and you wrote down which position was what so if you destroy the symbol drilling through it, no problem! See how the new caps fit right in? Be sure to observe polarity, most cans are wired negative to ground against the case but there are exceptions. this one is can ground so I'm passing the positive leads through the holes I drilled. BE SURE the positive leads don't touch the rim of the can you cut off.

STEP 5: Finishing Up the Electrical

Solder the Positive leads. connect all the ground leads together and solder a bit of wire to them, run it though another hole , drill if you need another hole, and connect to ground. there is usually a leftover tab from mounting the can into the chassis you can use. Don't try to connect to the original solder point on the chassis, your iron probably won't be able to get the metal chassis hot enough fast enough, just find a new ground nearby. Now you can test it out!

STEP 6: Glue!

Use hot glue to stick all the caps together up top and then squirt some glue into the gab between the cap and base, this will insulate and physically support the caps so they don't bend over and ground out. YOU ARE DONE!

Please note in the pics there are only two, I've yet to install the other two caps.

Comments

[Justin A]

what if my electrolytic can is paper? how do i get this paper can off? where do I scolder my common negative wires to? chassis ground?

[2nup350]

sometimes the can is paper, they cut just like the aluminum ones. ONLY solder the negative to ground if that's the way it was wired to begin with, having a floating negative isn't all that uncommon. You are going to have to spend some time with the wiring diagram to determine what's best.

[Justin A]

Oh u rock.....I was thinking that's the case...floating ground as my ohm meter told me that he chassis is not connected to the lugs that are showing ground in the schematic....still learning....the phenolic wafer is isolating it from the chassis. so I drill a hole and pass the negatives to that lug at 3 o'clock?

[tryb01]

I was just about to remove the entire can but desoldering the large tabs with multiple resistors involved it was going to be a lot more work than I anticipated. This makes so much more sense eliminating a ton of work. I have a number of vintage amps I need to fix so this is a huge help. Thanks for producing such a clear presentation.

[SteveA182]

Best thing I have seen all year! I restore stereo consoles and can caps are the worst to replace.....this is now my go to solution!

[sataraid1]

Thanks for posting this with all the nice clear pictures. Used this technique to replace a Mallory can cap almost identical to the one shown in a Regency Monitoradio.

LOTS easier than trying to get in there and desolder the can and all the leads.

[Mtixe72]

When replacing 2 electrolytic capacitors with different uF. Ratings but the same voltage can you replace them with one single cap?

[2nup350]

Not even a little bit. The UF rating can be thought of as the "Frequency" of the noise you are eliminating. You need all those different values. You can use caps with higher voltage ratings, even different UF ratings as long as they are close. In the power circuit they won't change much but in the signal path they will change the sound. but you need something close to each value in the circuit minimum.

[wb0snf]

Hi. I've been using this process for years and it works great. Many old can capacitors have a paper tube over them that You can twist off. I save and reuse them by shoving them onto the stub left from the above process. Two caps fit side by side but if there's three I stack one above and use spaghetti. Looks very tidy. Nice article, and thanks for putting it out.

[BeachsideHank]

This looks like a good way to keep the old girl working far beyond retirement age. ☺

Just a note for audiophiles who prefer tubes, at the time when the sun set on tubes and transistors began to dominate, it was discovered that by varying the filament voltage with a high wattage rheostat, hum could be noticeably diminished, since excess heat also caused distortion.

[2nup350]

I've found that most really old sets, those from before 1960, are designed for 110 volt AC not the more common today 120 volt, my house has 122 volts. Rebalancing the circuit for this increased voltage really helps boost reception and kill signal noise

[gm280]

Nice repair. I think I would remove the multi-cap from the chassis and open it up from the end for replacements. That way when reinstalling it again, it looks like it never was changed. But that is just me. Any repair for these old tube radios and amps is a good thing in my opinion. Thumbs Up!.

[2nup350]

I don't re-stuff cans, every time I see one I want to rip it out immediately. it's a visual red flag for me.

[DIY Hacks and How Tos]

Cool. I love old radio restoration projects. It is like bringing a dinosaur back to life.