You may recall my adventure with putting Waverly tuners on my pre-war Martin 1T ukulele. The Waverlys look great, and work well, but the fit left something to be desired. To be honest, I was disappointed.
The basic problem is that the Martin's headstock is thinner than the ideal thickness for the Waverly tuners. So the washers stuck up a bit on the top of the headstock. It made me a little crazy. It just didn't look good.
My friend has a beautiful set of Gotohs on her harp ukulele. Gotoh makes very fine tuners for guitars and ukuleles, and they make a planetary set that resemble the old Grovers that came on these Martins. I checked the measurements, and found they would be a perfect fit.
Unlike the Grovers, the Gotohs have a 4:1 planetary gearing. Yes!
So I ordered some. I discovered Gotoh makes all sorts of variations - different body finishes, different knobs, etc. I wound up ordering my set from the fantastic folks at Japanese Guitar Parts. They're the Gotoh agent for North America, and can get anything that Gotoh makes. I sprung for the UPT-UB8-CW - chrome white with tortoise knobs.
And now I get to drill them out.
The Gotohs fit a 10mm hole. That's just about what the stock Martin hole is.
Probably no coincidence that the Gotoh instructions show them being installed on a Martin. Hmmmm.
This was a little tedious, but I wanted to be precise. I got the holes to the point where the new tuners would fit perfectly snug.
Obviously, if you have a stock Martin, the tuners will just drop right in. You won't have to mess with the holes as I did.
There's a locating pin on the Gotohs - again just like old Grovers. You can see the pin to the right.
You press the tuner down onto the headstock from the rear and make a small divot with the pin.
It worked perfectly. The hole can't be too big - the tuner would rotate if the pin won't sit in the hole correctly.
The locating washer is beautifully made - it has a ridge on the back to locate itself exactly in the tuner hole, thus keeping the tuner shaft perfectly upright.
I went for the white chrome because I wanted a look like old nickel - not too shiny. I think they look great and have a nice vintage vibe.
I want to put some on my other Martins, and I may go for the black ebony buttons on those. But I went a little wild on this one.
What's the verdict?
They are incredible. Smooth, very precise, and beautifully made. And having a geared tuner is very nice - much easier to use than the old direct tuners. I'm going to order up more soon. And I plan on replacing some of the tuners on my Kalas too.
I highly recommend them - frankly any Gotoh tuner for that matter. They're just fantastic.
Now that the Zenith is recapped and aligned, I can put it back in the cabinet and put it to work!
First I need to clean it up a bit.
Usually they're glass with silkscreened numbers. In this case, the dial is plastic, since it's relatively modern (1964). Either way, you need to be careful cleaning the glass. Do not use any kind of glass cleaner! It will remove the numbers from the glass!
I've found that some camera lens cleaner along with lens cleaning paper works very well. If you consider that camera lenses are something you don't want to scratch, I think you'll agree this is a good idea.
You can use a glass cleaner on the outside where numbers aren't printed, since there's no danger of removing the numbers or lettering. Even so, I generally clean the outside of the glass the same way I do car windows - hot water and clean lint-free cloths. Make the water as hot as you can stand. That way you don't get chemicals on the glass at all.
There's a screw post that supports the dial mechanism frame - top arrow in the picture. You need to get that aligned. There's a lockwasher and nut that go on the screw.
Also the two dial lights - the other arrows - have to be seated in their...seats...on the dial
If these aren't lined up, the chassis won't slide in all the way.
The support has a dimple on it that lines up with a matching dimple on the bottom of the chassis. Those clever engineers thought of everything. It's easy enough to use long tweezers to slide it into place.
Those two pins at the top are part of the AC interlock. There's a matching socket on the back panel.
You can see the other half of the AC interlock - the box near the top of the picture. The idea is the consumer can't remove the rear panel and have the radio still plugged into the wall.
I decided to leave my labels on. Why the heck not? It might save someone some time in the future.
I also put a masking tape label on the bottom of the chassis, as well as the can cap, indicating the date they were recapped.
Screw on the back panel...
I may repaint these at some point. You can see where the chrome plating has worn off over time.
It was in nice shape to start with and now it looks great. Super sensitive and it has tons of bass!
Note the "high fidelity" logo at the top - yes sir!
I bet it would be really amazing with some modern speakers....nah. I will not mod this radio! It sounds great as is.
The heritage of this set goes back to the late 1940s. I have an earlier model - from about 1950 - in the restoration queue. Zenith made thousands of these sets, and they were extremely popular. With their great performance, it's easy to understand why.
The red arrows indicate the "CD," for "Civil Defense," or "CONELRAD." These markings at 640 and 1240 kHz on the AM band indicate where you would tune in the event of an emergency.
I have a couple of sets with these markings. Here's more about CONELRAD.
With the AM alignment done, we move on to the FM alignment.
To accurately align the FM circuit, you will need an oscilloscope along with an FM sweep generator. It's possible to use an AM generator and VTVM - many old alignment instructions have directions on how to do this. But the most accurate alignment will be with a scope.
In this case, I'm using my Tektronics 453 scope. This scope was introduced in 1965 and was state of the art - two channels with a 50 mHz bandwidth. Even today, it's plenty of scope for old radios and amps. This one is ex-IBM.
But the process of connecting a signal at specified points, reading the output, and adjusting IF transformers is the same as for AM.
Here's the HP 5314A reading the output from the Hickok generator. One of the shortcomings of old tube test gear is that it takes a while to stabilize. I give the Hickok 30 minutes to warm up. At that point, it's reasonably stable, but you still need to keep an eye on it. After an hour it's pretty good.
We do this for each IF transformer in the set. Just a small turn of each slug will affect the waveform.
Another downside of old gear is that the signal isn't always 'clean.' You can see small ridges in the wave - that's DC in the output. But it's good enough for our work.
Most sets have a hard time picking up much on FM down in the dungeon. The Zenith did quite well again - it picks up a lot on just the tiny factory antenna.
And it sounds great, with plenty of volume.
I finished the recapping on the Zenith last week.
I don't know why, the caps are bad. It's really just for historic value.
For this, I'll use my trusty Hickok 288X signal generator. This generator outputs both the AM and FM signals we'll need for the alignment.
Before I go much farther, I should mention what an "alignment" is. You may have heard this term and thought "what the heck is that?"
I'm skip most of the technical detail in this post; I really just want to give an overview of the process.
The best plain-language explanation I've read is in the Bryant and Cones Zenith Transoceanic book, which I'll paraphrase.
An alignment ensures the radio is playing up to its peak performance. That means that its sensitivity, selectivity and dial tracking are all at their optimum. If you think of the tuning circuits in the radio as a number of windows in sequential order, an alignment adjusts those windows so they all line up and the signal can pass through.
In brief, what we do is inject radio signals at specified frequencies into the circuit at various points, and adjust tuning coils or slugs in the set until the signal is at its strongest. That's it in short.
The tools are plastic so they don't throw off the readings that we'll take. If they were metal, their capacitance would make the alignment inaccurate.
I'm trying to avoid a lot of radio theory here (you can find it elsewhere on the interwebs...), but this is a critical adjustment with regards to the radio's sensitivity (how it picks up weak signals), as well as its selectivity (how well it rejects adjacent signals close to the one you want to pick up).
You can see the alignment tool has a hex-shaped end - this will fit into the slugs.
I'm feeding the signal from the generator to a HP 5314A frequency counter. You may recall from my rebuild of the Hickok posts that I tapped a line from the inside of the generator to run to a counter, in addition to the RF output on the front panel. Comes in very handy since we can read the frequency at any time and keep the main output connected to the radio.
The modern method is to connect the meter to the AVC buss. You can have the volume turned all the way down and still get readings.
This is where a big meter is great. You can see the needle swing as you adjust the slugs, and see when you've peaked them up. You could use a modern DMM, but it's a lot harder to discern readings. The VTVM is the best tool for this work. Plus, it looks super cool!
In the old days, there were service manuals printed for all of these sets. In a number of cases, you'd even find the schematics and alignment instructions in the owner's manual. That material was important for the serviceman - since there were actually repair people, they would use this for troubleshooting. It's a real blessing for us modern restorers too. I have a set of CDs scanned from original manuals that have the repair information for hundreds of sets!
Next we'll do the FM alignment.
After I reconnected the filter cap can, I brought the radio up to full voltage.
This is the setup I use. On the left is my trusty General Electric variac. This is a big transformer you can vary the voltage on (as the name implies). "Variac" is actually a trade name for autotransformers (the correct technical name) made by General Radio, I believe. Much like "kleenex," it became the generic name.
In the center are two voltmeters - a more modern one and a vintage Weston model. These are wired to the variac to indicate the AC line voltage. Why two of 'em? Why not!
On the right at the top is a vintage Weston ammeter. This lets us know how much current the load (e.g. the radio or amp) we have plugged in is drawing. It's important because if something is drawing a lot of current, there is a problem.
And on the bottom right is an RCA isolation transformer. Not something I use a lot, but I'm using it on this radio because it has no power transformer - the AC voltage in goes right to the power switch. The iso transformer breaks, or isolates, the radio from the wall circuit - it's a safety measure so I don't get electrocuted if I touch the chassis, which carries AC voltage.
The isolation transformer is plugged into the variac. The radio is plugged into the isolation transformer.
I like to slowly charge new capacitors if I can - 40 or 50 AC volts overnight and then 10 volts per hour until we're at the line voltage (120). I'm of the mind that charging the caps is like charging a battery. It may not be necessary, but I do it.
The diode - the old blue selenium one as well as the small black modern one - is what converts the incoming AC to DC to run the high voltage parts of the radio.
You can see how the diode is wired using one terminal of the old rectifier, and then the positive end goes to the first filter cap. The old rectifier is now out of the circuit - nothing is connected to the tab on the red (positive) end.
The seleniums can go bad over time - and blow up making smoke and a bad smell. They look really cool, but they're unreliable.
These are the first 2 caps I'm replacing. Probably the hardest ones to do, since they're a bit buried. The red arrows indicate where they're at.
On this first one, one lead of the cap wraps around a post that's part of an antenna connector on the back of the chassis.
So I use some solder wick to get the old solder off, so I can see the lead clearly and unwrap it.
Some folks will just snip the lead, especially if it connects to a point like this. Unless it's really hard to get to, I avoid that. I just prefer doing a nice clean job.
That method of wrapping a lead around an old connection is usually called a "quig." Some restorers will wrap a lead around a terminal where there are a number of connections, flow solder on, and call it done.
I think that's a really lazy and sloppy approach. For one thing, you won't have a good mechanical connection to the joint - usually a tab or terminal. For another thing, you're soldering on top of the old potentially corroded solder, which doesn't make for a good connection.
The stuff comes in various widths and lengths. I get it inexpensively from Mouser. It's gold. Well, actually, it's copper braid!
Once I slip the loop over the post, I'll squeeze it with my needlenose pliers to make a tight joint, then solder it in place.
Solder isn't glue - I try to make a good mechanical connection always.
The old cap was rated at 200 volts. The new one is rated at 630, yet it's much smaller.
You need to replace caps with the same value and at least the same voltage rating as the old ones. Since modern caps are so much smaller, I generally keep only 600 or 630 volt caps on hand.
The modern caps also have superior electronic performance compared to the old ones.
If you have a component attached to another component which is sensitive, use a heat sink.
Here we have the old cap which connects at one end to an RF coil. These coils are a bit fragile - they're made of very fine gauge wire that's soldered to small tabs. They're generally covered with wax so they don't absorb moisture. Heating them up too much might accidentally desolder a coil wire or melt the wax too much.
So here I have some hemostats on the tab (red arrow) where I'm going to desolder. You could use an alligator clip as well. The heat sink will absorb the heat from the soldering iron and prevent it from transferring to the coil.
I soldered it (with the heat sink on it), and then snipped that excess lead you see sticking out.
I hate excess leads with a passion. I once worked on a radio that a friend had "recapped." OMG. He left all of the component leads their original length! Things were sticking up everywhere. Nothing was trimmed at all. What a mess.
He had asked me to look at the set because it wasn't working right. No wonder. Sloppy work, lots of leads everywhere. I cleaned it all up and got it going.
If you work on radios or amps like this, use the original wiring as a guide to workmanship. Or I should say workwomanship, since the vast majority of assemblers in those days were women. Smaller hands, an eye for detail, and brains. I've seen some sloppy original wiring, but most is very well done.
I think that doing good, clean work is not just the way to ensure the gear will work right, but it's also a tribute to the folks who built these things originally. It only takes a little more time to do quality work.
Now on to the rest of the caps. The fun part will be replacing all the old paper caps in the signal path with modern ones.
I'm starting to recap the Zenith H845 radio. Perhaps I should say, more accurately, I am continuing to recap the radio. You may recall in our last installment I restuffed the can filter capacitor. It's done, reconnected and installed in the radio, which now plays well with no hum.
Since this radio is known for its good tone, I'm going to replace the signal capacitors with good quality ones in an effort to make it sound really super good! Which brings me to the point of this post.
If you've read about audio (aka hi-fi) or guitar amps on the interwebs, you may have read about capacitors and their affect on tone. Tone being that mysterious, magical thing that everyone is after. I'm going to avoid hyperbole, but I did want to use this radio as an illustration of how you might approach selecting, changing, or experimenting with signal capacitors (aka 'caps').
A quick digression. In the vintage radio and amplifier world, one of the components that most often fail, or are about to fail, are capacitors. In the old days, the majority of capacitors were made of paper and a dielectric element - usually a metal foil of some sort. Because paper absorbs moisture from the atmosphere over time, and because moisture would cause a cap to short or otherwise fail, capacitor manufacturers would dip their caps in melted wax to coat them. After the wax dried, it would provide protection of sorts against moisture.
Some companies also used tar - this was commonplace through the mid-1930s. And sometimes you'll see a sealed can of some sort - recall the aluminum can I just restuffed.
Of course, 40 or 50 or 80 years later, the vast majority of these capacitors have failed simply due to age. Wax, as is turns out, is not a great way to protect capacitors. This is why modern caps are sealed in some sort of plastic.
In radio and amp restoration, we commonly replace capacitors as part of a restoration or renovation. Most capacitors are in a circuit to block DC voltage. When they fail to do that, they are referred to as "leaky." In most instances, you cannot determine if a capacitor is bad by looking at it! They must be tested at their rated voltage. While it's true that some electrolytic caps may have leaked their innards, but that's not the meaning of the term "leaky." Frequently on radio forums a novice will say "the caps look good....". Well, they may look good, but I bet they're bad!
So many of the caps you'll see in old gear are bad that it's just easier to replace all of them rather than test - although testing is a fun exercise. This wholesale replacement is called "recapping." (Or, by the spelling challenged, 'recaping.')
Now back to our Zenith. I'm going to replace all of the old wax-paper caps. Some of them are in the signal path - meaning the circuit that the actual audio signal takes.
On our Zenith, these are marked on the schematic as C27, C30 and C34. C34 in particular is the most critical cap - it passes the audio signal to the output tube. I'm going to replace the old caps with Russian K40-Y paper-in-oil caps. ("Paper-in-oil" refers to the internal construction of the caps.)
Some other notes on the caps I've highlighted. C31 and C29 are part of the tone circuit. Not as critical, but again a place where you'd want to use a quality cap (e.g. Orange Drop, etc). Another key place is C35. This is what was called the "quality capacitor." Its function is to roll off super high frequencies.
Finally, see the network of R25 and C37. If you trace the wiring from the right side to this network (it's actually a bandpass filter), you'll see it connects to the output transformer, T2. The signal actually would flow from the transformer, through the filter and back to the volume control. This circuit is a negative feedback circuit - its function is to smooth out the frequency response.
By using good capacitors (a whole other discussion, one that will start a lot of arguments) at these points, you'll ensure you're getting the most fidelity out of the circuit. I won't say it will have "killer bass" or "creamy mids" because audio is so subjective. But you will be getting the most out of the circuit as designed if you use quality parts.
Just a couple more pictures.
Here I took a shot of the radio and highlighted the caps we've been looking at above in the schematic. In this picture, I had already replaced R35, C29 and C37. But the old ones are still in place elsewhere.
You can clearly see the old paper caps. A couple of the caps are ceramic disks - C22 and C31. They typically don't fail, but their design makes them less suitable for audio, so I'll replace them as well.
It is possible to restuff the old paper caps. I've done it on special radios. Basically you take the paper caps apart, put a new cap inside the paper shell, and melt wax on them. It's tedious, but it's worth it if you want to keep the original look. In this case, I'm not going to bother since this is a fairly common set. I will however, keep the old caps in a plastic bag stashed inside the set for posterity.