Sunday, December 29, 2024

A New Bike: Priority 600X

Note: I wrote most of this post back in April, but never got around to posting it. I believe Priority no longer sells this specific model of bike, though they sell others using the Pinion gearbox.


I've been commuting back and forth to work on my Priority Continuum Onyx (referred to as PCO from here on) for about 3 years and it has been wonderful! The sealed Enviolo CVT in the rear hub and the Gates belt drive have been absolutely perfect. But time marches on... I retired in September last year and no longer need to commute daily, though I still ride the bike around town, even through most of the winter.

The mean streets of Milwaukee are cracked and potholed a lot like I remember Tijuana in the 80s. I decided to get myself a bike with some suspension and fatter tires to make the ride more comfortable. I started watching youtube videos of some of the Priority bikes and was really impressed with the Pinion gearbox bikes. 

The Priority 600X has a Pinion C1.12 gearbox at the cranks instead of the PCOs CVT in the rear wheel. I have always been a bike geek and love to try different transmissions. I saw the Pinion gearbox a few years ago and found it interesting, but most bikes with that gearbox cost $4-5k, often more, and that was a bit too rich for my blood. $3k has always been the far upper limit of what I could see ever spending on a bike.

I don't know if it was coincidence or the result of some artificially intelligent Google surveillance of my viewing habits and interests, but I got an email from Priority Bikes promoting a spring sale. Among others, they were offering an incredible deal on the 600X. The bike normally sells for $3500, but it was $250 off and there was an ordering code that knocked it down another 25%. I couldn't resist! I don't know how they can sell that bike at that price and stay in business. I'm guessing they were getting rid of inventory of this bike prior to selling the newer models.

The Priority 600X is an incredible machine. It has a 110 mm travel Wren suspension fork that is owner-serviceable (unlike the Cannondale headshock in my old MTB). It also has a very low maintenance (oil change every 10k km or once a year) Pinion C1.12 gearbox, a maintenance-free Gates CDX belt drive like the Onyx (CDN), four piston hydraulic brakes, tubeless capable WTB rims and tires. You can see all the details at Priority's site, and a bunch of youtube reviews here.

The bikes 2.4" wide tires and suspension fork mean it will be great on the pot-holed streets and good for off-road riding, as well. The frame is built to have bags and carriers, so it's super versatile.

I also ordered a trailer hitch and bike rack to fit my car. I didn't order a roof rack because the bike is relatively heavy (~32 lbs) and I don't like the idea of having to lift it that high. I also figured that if the bike gets muddy I don't want to try to carry it inside the car, where it will be hard to fit anyway, due to the 29" wheels.

A few people liked my review of the PCO, so after I get through all the other stuff, I'll go into some detail about the bike that you might not find in other reviews. You can skip down to the Bike Details section below if you prefer to skip the other stuff.


Arrival!


The bike arrived 4 days after ordering and within minutes I had it out of the box, preserving it for future shipment via airlines. As usual, the packing was perfect and the bike came out of the box without any damage whatsoever. I took pictures of the way it was packed so that if I ever want to ship the bike via an airline, I will know how to pack it up so it arrives undamaged.


It's here!  It's here!



This is how it gets packed for shipping. No damage at all!




The usual goodies: pedals, shock pump, touchup paint, bash guards for shock, tools, and manuals.


Here it is, about a 1/2 hour later, fully assembled!

My bike came equipped with Tektro Orion 4P brakes, Goodyear Peak 29 x 2.4" TC tires on WTB KOM Tough i35 rims, WTB Volt saddle, and Wellgo B087 platform pedals. Note: the tires and rims are tubeless capable, but the bike ships with tubes installed.

When I separated the front wheel from the rest of the bike after taking it out of the box, I was impressed by the size of the wheel and tire. It looks like something that should be very heavy but it was surprisingly light.

Assembly was pretty easy- unwrap everything, mount the pedals, turn the stem around 180 degrees, mount the handlebars, and install the seat. I also checked belt tension, tightness of screws all over the bike, headset tightness, brake caliper to disc alignment, etc.

Next I studied the shock manual and gave it some air as suggested, then took it outside to bed-in the brakes. That involves getting up to speed and then squeezing one of the brake levers until the bike slows to walking speed. At first is squeaks and vibrates, but you speed up and do it again, and again, and again, and eventually the brake starts slowing the bike smoothly and quietly. Then you repeat the whole process for the other brake. Fortunately, I live on a relatively steep hill and the getting up to speed part was super easy.


The Pinion C1.12 Transmission

The ride back up the hill gave me a chance to test the low end gears of the of the Pinion transmission. I was impressed! The lowest gear seems like you could ride the bike up a tree if you wanted to. I was used to shifting the Enviolo CVT on the Onyx, and shifting the Pinion gearbox was similar. I found that shifting required a little more muscle than I had expected, but I was wearing heavy winter gloves, so maybe the gloves were forcing me to grip the shifter harder. It may also be the tension on the shift cables is a bit higher than it needs to be. That can be adjusted, but I'll wait until I've ridden the bike a while to give the cables time to stretch. 

Gear shifts were instant, but you have to time your pedaling pressure a bit when shifting so you're not putting too much of a load on the gearbox during the shift (like the Enviolo hub in the Onyx). You don't have to stop pedaling, just reduce pressure momentarily. The shifter clicks at each gear position, so as soon as you feel /hear the click you can start mashing the pedals hard again. To me it seems like it's easier to shift down than up because you don't have to time the shift to your pedal stroke as much- the gearbox seems to tolerate more pedal pressure when downshifting. Rotating the shifter forward increases the gear ratio, rotating back reduces it for climbing. You can shift through the entire gear range while stopped.

I remember the old Sturmey-Archer 3-speed hubs I rode as a kid. If you worked the shifter carefully, you could put the thing between gears and the pedals would just turn without moving the bike. I tried to do the same thing with the Pinion gearbox and could not get it to do it, so you probably don't have to worry about shifting and having the pedals suddenly go limp while you're barreling down single track on rocks or roots, or worse, while pedaling a heavy load up a steep hill.


Wren Inverted Shock Fork

I played with the shock settings a bit and found it very responsive. There are so many adjustments you can make it will take me a while and some off-road riding to set it up just right. My old Cannondale with a headshock, and the only adjustments were the air pressure and damping. The Wren shock has a lockout for street riding, though with the potholes we have in Milwaukee, I may leave the shock active most of the time.

I've been riding it for months now, and find that I have to top-up the pressure in the shock every couple weeks to keep it working consistently.


Lights and Reflectors

Since I'll be riding around town on the bike, and frequently at night, I did my usual thing and put reflective tape on the wheel rims after I peeled off all the WTB stickers and wiped the rims with IPA. I used blue, fluorescent yellow, red, and white reflective tape randomly arranged between the spokes on the rims. I'll probably add more reflective tape to the cranks and head tube.




I also bought a bright headlight that has a large battery and a "smart" taillight that senses when you're braking and lights up at maximum brightness like a car's brake lights.


Headlight and Wahoo GPS/computer. I made the headlight mount from a piece of aluminum angle stock.


Here's The Hitch

I want to be able to transport the bike easily so I shopped for hitch receivers that would fit my car. Draw-Tite and Curt seem to be the most popular brands on amazon.com, both getting many good reviews. I don't want the bike and rack bouncing and swaying around so I chose the Curt 11473 over the Draw-Tite 24944 after studying pictures of the two. The Curt hitch seemed to be the more sturdily built of the two. I also bought a hitch tightener. 

The hitch arrived on the same day as the bike and I took it to the Milwaukee Makerspace to install it. Three hours later it was finished, with most of that time spent dealing with the little plastic fasteners used to hold all the splash guards and the lower bumper cover (the black part) in place. I managed to put it all back together without any leftover parts, and the sensors on the rear bumper still work!

The hitch is solid as a rock!


Bike Carrier

I ordered a bike carrier, too, and went cheap. Big mistake. The carrier I ordered hangs two bikes by their top tubes. It can tilt back to allow access to the back of the car, which seemed like a good idea. There are two main problems with this rack. First, the top tube on my bike is tilted which means the bike hangs on the carrier tilted, putting the front wheel about 7" off the ground. That's a bit too close for comfort. Second, the hinged joint that allows the rack to tilt out of the way of the hatch wobbles. There's no easy way to stabilize it. Ugh. It turns out the rear hatch clears the bike carrier and bike without tilting, so maybe that feature wasn't that important.


The wrong bike carrier. Maybe it would have worked OK if I had hung the front end of the bike by the fork/downtube joint, but it was a bit too wobbly, even with a hitch tightener in place.

I returned the carrier and ordered another- a Swagman "platform" type that holds the bike's wheels and has a clamp that comes down over the top tube. Much better! It can hold two bikes, and I set it up so my bike goes on the back side of the carrier. That leaves enough room to open the car's hatch, even when the bike is on the carrier. If there's a second bike on the carrier, that may not work so well.


The bike and Swagman XTC 2 platform carrier on the car. Both wheels are now about 14" off the ground. The bike is 75" long and the car is 69" wide, so the wheels stick out a bit on either side of the car. The center clamp that comes down on the top tube is supposed to be located at the top-tube/seat-tube junction, but that would require shifting the bike about a foot to the left and leave the front wheel sticking out, far beyond the side of the car, just waiting to bang into something. The bike is completely constrained as shown, so it's not going anywhere.



The Swagman platform carrier folded up. 




Another view of the bike carrier mounted on the car. The central post can be folded down so it doesn't block the back-up camera when there are no bikes on the carrier, but then you have to leave the wheel trays down as shown.



I added a hitch tightener to minimize wobble and sway- but there wasn't much to start with, so maybe this isn't really needed. The bolt at the left is the hitch pin that comes with the bike carrier and threads into an insert in the carrier that holds it tightly- the hitch tightener might not be necessary. I'll probably use it anyway because it will be one more thing that a potential thief will have to deal with and it might slow them down a little.


Another view of the hitch tightener. That's a 1/2" stainless U bolt. One 19mm or 3/4" wrench can be used to tighten bolts on the hitch and the tightener. You can also see the cotter pin that comes with the bike carrier.

I have a bunch of tools, but didn't have a socket deep enough for the bolts on the hitch tightener, so I ordered a ratcheting wrench specifically for the purpose. I'll just keep it in the car with other loose parts for the bike carrier so I'll always know where it is when I need it.

When you travel with a bike on a car carrier, you're going to have to stop to eat now and then. How do you ensure the security of the bike(s)? I ordered a locking hitch pin that comes with a steel cable. No, it isn't super high security, but it will stop someone from simply walking up and taking a bike off the carrier. When you put the bike(s) on the carrier, you loop the steel cable through the wheels and frame(s) and anchor the end of the cable on the hitch pin. It's a little difficult to get at, but it's better than no security at all. My bike only has to be a little more difficult to take than the one on that other car, over there. Of course, if someone is prepared to cut the cable they will make quick work of stealing the bike.


New Bike, New Other Stuff


Sometimes, the best part about getting a new bike is getting all the other stuff to go with it.


Top tube junk carrier. It's big enough to fit my Pixel 7 Pro phone, still in its case. There's plenty of room for glasses, ear buds, wallet, keys, snacks, etc.- you know, all the stuff you need to carry that they don't put pockets in bike clothes for. Over the several months I've been using it, the velcro that holds the phone in place has become very weak. I don't recommend this bag.


The Enfitnix Cube tail light, with auto on/off and brake light functions, mounted on the seat post. It also comes with a mount for the seat rails, but I didn't have room for it there. The light twists on and off the mount, so it's easy to take inside to charge (or to steal!). The battery is supposed to last between 4 and 14 hours, depending on how you set it. The button that turns it on and sets operating mode is a little too easy to push. I paid about $22 via amazon.com, but you can buy similar lights via aliexpress for about $5.
 

Fenders


I'm going to be riding the 600X around town (I sold my beloved PCO via Craig's List) in addition to off-road, regardless of the weather, within reasonable limits. That means fenders are a must. The problem is fenders made for MTBs are mostly intended to protect shocks, bearings, and the rider's face from mud thrown up off the trail and tend to be very short so they won't get caught on branches.

The 600X's inverted Wren fork makes it difficult to fit a front fender. Most forks have a bridge just above the wheel that moves up and down with the wheel and makes a great attachment point for a fender that follows the motion of the wheel as the shock compresses. MTB fenders are usually designed to attach to the fork's bridge. The Wren fork on the 600X has no such bridge, so the only attachment points for a fender are the upper stanchions. If you want the fender close to the tire, it has to attach to the lowers that move up and down with the wheel as the fork compresses. The problem with that is the fender has to be about 15" away from the axle and you need something that long to support it. You can mount a fender using the upper stanchions but it won't follow vertical motion of the wheel. OTOH, if you're riding on streets, you can lock out the fork and mount the fender low enough on the upper stanchions to put the fender close to the wheel.

A fender for the 600X rear wheel isn't too big a problem because unlike the front wheel, nothing moves up and down, so attaching it to the seat stays should be fine.

After a lot of searching, I found the Mucky Nutz fenders to be the most likely to provide most of the coverage I wanted to keep my clothes clean when riding on wet streets. I ordered them via ebay.


Mucky Nutz rear fender on the bike. It's plenty long at the back, but a bit short at the front end. I may have to figure out how to add an extension to get more coverage toward the front. The fender is held in place with velcro straps that come with it, so it's easy to put the fender on in wet weather and take it off in drier weather.




Mucky Nutz fender on the front wheel. I wish it were longer at the back- I may need to figure out how to extend it. Velcro straps secure it to the upper stanchions. I can keep it close to the tire as long as I lock out the fork so the wheel doesn't move up and down. 


The fork has no bridge to secure the front fender and it seemed a little too wobbly just strapped to the stanchions, so I designed and printed a bridge specifically to hold the fender. It friction fits over the upper stanchions, gripping them tightly, and Velcro tape secures the fender to the bridge. It greatly increases the stability of the fender.


Mucky Nutz fender mounted on the front wheel with 3D printed bridge. I printed it with black TPU filament. It grips the two stanchions tightly without any retaining straps, and improves stability of the fender. We'll see how it holds up when exposed to weather. 




Closeup of the 3D printed bridge. The fender has slots for the Velcro straps that secure it to my printed bridge.


CAD render of the bridge. The holes for Velcro straps match the holes in the fender. It took about 20 minutes to design it and I only had to print two versions to get the dimensions right. Printing with a 1mm nozzle in 0.5mm layers at 30 mm/sec took about 1 1/2 hours. Everything you see is 5mm thick.



It takes just a minute or two to attach the fenders, so when the weather is bad I'll put them on and when the weather is nice they're coming off.


Tubeless? Tubes?


I watched a lot of YouTube videos about running tubeless tires on MTBs. Under some circumstances it seems like a really good idea, (riding in areas with lots of thorns, etc.) but otherwise the maintenance seems troublesome. I'll probably use tubes for the foreseeable future.

I picked up a couple spare tubes - I got TPU tubes that are super thin and light. You can buy a 2-pack of 29" Cyclami tubes via amazon.com for $26, or buy the same package via aliexpress for $10. Guess which I did. On-line reviews indicate that they are lighter, harder to puncture, retain air better than butyl tubes, and are difficult to patch reliably. I chose the Cyclami tubes because they have threaded metal stems- a lot of the TPU tubes have plastic stems that can break, and won't work with screw-on pump connectors.


One of two Cyclami TPU tubes ordered for $10 from AliExpress. That's a 29" tube and only 62 g! Very small and easy to carry on the bike. I bought two tubes and they came with some cleaning wipes and a couple patches (regular bike tube patches won't work with TPU tubes). I chose these tubes for their threaded metal stems- most TPU tubes have plastic stems to reduce weight, but that makes them incompatible with a screw-on pumps, and plastic stems can break. Note: the valve cores of these tubes are not removable, so I probably won't be putting any sealer in these tubes.


One of the butyl rubber tube that came in the wheels. 4X heavier than the TPU tube! That's almost an extra half pound in each wheel that you have to spin. Yikes!



Size comparison. Which would you rather carry as a spare? You can carry 4 of the TPU spares in the space (and weight) of one butyl tube.


When I received the TPU tubes, I immediately set about replacing the butyl rubber tubes that came on the bike. That presented a new problem: how do you get the tires off the rims? Tubeless capable wheels and tires require a very tight fit and I found that I couldn't get a tire lever between the tire and rim no matter how hard I tried. Back to YouTube to search for the answer. The trick is to lay the wheel down with the tire deflated, then step on the tire with your shoes to force it in toward the center of the rim. Once you get it started, it's pretty easy to get the rest of it to go. Once the bead is all pushed into the center of the rim, you can grab it in one spot and pull it over the rim. Then you can pull the tube out and stuff the new one in. 

I started this post in April, and now it's December. I've had one flat tire caused by a piece of glass. I patched the TPU tube per the instructions and found that it was flat again a day later. I opened the wheel up and inspected the patch and found it wasn't entirely stuck to the tube. I applied some localized pressure to it for a couple minutes and put it back and it's been holding air for about 3 months now.

One claim about TPU tubes is that they leak less air than butyl tubes. I haven't found that to be the case. They seem about the same to me and I find myself topping up the tire pressure every few days. I typically run the tires at 40 psi on the streets.


Pump


I got a small pump to carry on the bike for just-in-case. It's a Crank Bros Klic HV pump. It's a great design that includes a flexible hose, valve adapter, pressure gauge, and CO2 cartridge fitting in case I don't feel like pumping (but don't use CO2 with TPU tubes!).


The Crank Bros Klic HV pump. It's 260mm long and about 30 mm in diameter. It comes with a mount that bolts on the bike. When it's closed up like this everything is sort-of protected from mud and dirt. It contains a flexible hose with screw-on adapter for Presta and Shrader valves, a pressure gauge, and a CO2 adapter so you can inflate your tires that way (don't use CO2 with TPU tubes!). It takes 300 strokes (I counted!) to fill a 29x2.4" tire to 35 psi with this type of pump, so I hope I don't get many flat tires.


Pedals


The bike came with Wellgo B087 pedals as did the PCO. I took one of the Wellgo pedals off the bike and tried to open it to see what the bearings and seals are like, and found that I didn't have a socket that could get inside the pedal to unscrew the lock nut. Hmmm. 

I bought some very slightly used, large size Crank Bros Stamp 7 pedals via eBay for the 600X. The advantage is that they fit my big feet better, are easily serviceable, and the traction pins are adjustable and replaceable. The one's I got happen to be a metallic blue color that matches some of the parts on the Wren fork. 


Stamp 7 pedal in metallic blue.


The new pedals match the fork air cap and lockout lever!


Rack/Bag


When I ordered the bike I ordered the same Axiom rack I had on the PCO. I also did some research on pannier bags and found one I liked- a Rhinowalk knock-off of an expensive Ortlieb bag. It is water tight (well, rain proof- not sure about getting it wetter than that) and can carry a lot of stuff. It goes on and off the rack quickly and easily.


Heavy duty rack, the same one I used on the PCO, fits over the rear fender, no problem.



Bag on the rack. I have tested this bag in pouring rain. Not a drop got inside.

I had one small problem with the bag. It uses a similar clamp system to the Ortilieb bag it copies, that has clamps that slide along a rail to allow you to space the clamps to fit your rack. I found that the clamps moved easily when I pulled up on the strap that releases them to take the bag off the bike. I fixed that with a couple drops of super glue.


Bike Details


The bike's frame has internal cable routing for a dropper seat-post. It also has a quick release seat post clamp that I'll probably replace with one that requires a tool so my seat is less likely to get stolen. The seat post diameter is 30.8 mm.

The large frame that I ordered has cranks that are 170 mm long. The ground clearance to the pedals is 130 mm, quite high off the ground compared to a street type bike, meaning that when you're riding on the street you can pedal through turns without worrying about the pedals hitting the ground.


The bike comes with a heavy-duty kick stand that is set far back on the frame. It's far enough back that you can roll the bike backwards while the kick stand is down without the pedals hitting it. I haven't noticed any heel-strike while pedaling. 


The belt drive is Gates CDX type rated for a very wide temperature range. Both the front and rear belt pulleys have 32 teeth. Both are made of stainless steel, and since the tooth counts are the same, I'd expect the two to wear at about the same rate. The 32 tooth crank pulley is pretty small, giving it lots of ground clearance when riding off-road.

The wheels are quick release, with 15 mm through-axles. It appears that the rear hub has a standard freewheel (is that what it's called these days?) so the wheel is dished to make room for it. I would have thought that with the belt drive and a single cog, and a disc brake rotor on the opposite side, there would be no need to dish the wheel, but I guess it doesn't work that way.


More New Stuff


I don't like to wear padded bike shorts (what a ridiculous concept!). The Volt seat that came on the bike is pretty good, but after riding the bike for a few months I wanted to see if I could find something more comfortable. I did some digging and found recommendations for something called an "Infinity" seat. I looked them up. Yikes! $400 for a bike seat! These things are made in LA by a company started by a chiropractor, and used by almost all the Race Across America riders because of the comfort. I checked to see if I could pick one up on eBay and and yes, you can, for about $300, but they go fast. I got an email from Infinity offering 15% off, so I ordered a seat figuring that if I didn't like it, I could always sell it on eBay and only lose $50 in the process.

Most of the infinity seats have a leather cover, but I didn't want to have to worry about taking care of leather if I'm out in rain and snow, so I bought the seat with the "marine vinyl" cover. I am pleased to say that it is every bit as comfortable as the reviews said. So far the longest ride I've done is 25 miles in a day, but the seat is no longer a comfort issue.


Infinity seat and Suntour suspension seat post. There is a neoprene cover over the mechanical bits of the seat post to help keep them dry.

One thing I discovered early on is that you'd better not pick up the rear of the bike by the Infinity seat- it will distort enough for the rails to pop out of the back of seat frame and then you have to use a screw driver to release the front end of the rails, get the back end inserted back into the seat frame, then screw the front down again. I've trained myself to grab the rack when I want to lift the back of the bike instead of the seat, so it's no problem.

The suspension fork does a great job soaking up bumps and potholes on the streets, but rear end of the bike (and my butt) take a bit of abuse when the rear wheel goes over the same bump or into the same pothole. I decided to look into suspension seat posts. After reviewing several YouTube videos about them, I bought a Suntour post for about $100. There are more expensive posts out there, but the reviews didn't really find the extra money worth spending. There are also cheaper seat posts out there from unknown Chinese manufacturers. I didn't want to gamble on one of those.

I'm pleased to report that the Suntour seat post is "all that and a bag of chips!" It is not a shock absorber, just a spring that compresses on the bumps and takes out the bone-jarring that accompanies them. There is a preload adjustment screw that you can set to compensate for your weight. I set it so it doesn't compress when I'm riding normally- it only compresses when I hit a big bump. I weigh 197 lbs and the spring that comes with the seat post is fine. If you weigh much more than that, you can get a stiffer spring (for added $, of course). 

Riding is getting very comfortable between the Infinity seat and the Suntour seat post. Now I have to work on hand/arm comfort a bit...



Friday, December 27, 2024

More recapping projects: Rotel RA-840BX3 integrated amplifier and RT830 Tuner


Basic, early 90s, very black, audio gear by Rotel. Does it sound as dark as it looks?


I couldn't resist another Craig's List deal (after looking for and finding the service manuals online), and picked up working Rotel components from the early 90s. When I went to check them out, they were connected to speakers so I could twist all the knobs and switches. They both sounded fine, and seemed to be working properly, and I didn't hear any scratchy noises or pops from the speakers when I turned any of the controls, so I took them home.

After I got them home, I discovered that these things were made to be serviced. There are hatch covers on the bottom of both the amp and the tuner to allow easy access to the bottom sides of the PCBs. Component designators and polarities are marked on both sides of the PCBs!  The bottom side metal pattern is printed on the top side of the PCB to allow easy circuit tracing. How sweet is that?

There are different "philosophies" about the order in which to troubleshoot and restore audio gear like this. Some argue that you should fix specific problems first, then replace bad caps as needed. Others say fix specific problems first, then recap completely. My idea is to recap completely first, then assess other problems and fix them. If the caps are bad, the circuits can't work properly, and I'm going to end up recapping the whole thing no matter what (any gear 20+ YO needs complete recap as far as I am concerned), so recap first, then hunt for other problems knowing the caps aren't the cause of any other problems I may find.


RA-840BX3 amplifier


The amp is a relatively small box rated for 50W/ch at 8 Ohms and 80W/ch at 4 Ohms. It has a phono preamp that can be switched for either moving coil or moving magnet cartridges, tone controls, and an odd speaker/headphone switching arrangement. Pretty basic stuff. There are several NE5532 and 5534 op-amps used in the phono preamp and tone control circuits. The owner's manual is here, and the service manual is here

As soon as I got it home I removed the top cover to assess the recap job. I found a bunch of dead bugs, some dust, a couple apparently leaking electrolytic caps, and some resistors that look like they've been running too close to or maybe a little beyond their power limit. The whole interior of the thing had a greasy film on it, like someone was using this amp in their kitchen, near the stove, for a long time.

Before recapping, I vacuumed out the dead bugs and sprayed the PCB with IPA and let it drain a few times to get rid of most of the greasy film that was all over it. I couldn't get in and scrub it as there are a lot of polystyrene caps stood up on their leads that are pretty delicate. There were a few dark areas on the PCB that turned out to be from glue that was used to hold some of the electrolytic caps in place. I scraped some of it off when I recapped.


The amp with the top cover removed. The PCB is single sided and marked with component designators and polarities, and even the metal traces on the bottom of the board so you can trace connections just by looking at the top side of the board. Nice! Is that a toroidal transformer, or a round can covering an EI transformer so that it looks like a toroid?


Some of the dead bugs, circled, and lots of dust stuck to an oily film...


Two of the four toasted resistors- note the cracks in the covering. These are 2W rated parts. I'll replace them with 3W parts.



The PCB looks toasted in this area, but it might be discoloration caused by adhesive or leaking caps. Note the jumper wire looks green, suggesting corrosion. This is a voltage regulator part of the circuit, so maybe the transistors need some small heatsinks. 




The chassis has a hatch to access the bottom side of the PCB!  There's no need to remove the board to recap! Part numbers are marked on this side of the PCB, too, making it easy to find the solder pads for the parts being replaced.



Underside of the amp PCB. Lots of solder flux residue everywhere. There are a few resistors tacked across some solder pads, too.




The service manual is very nice- it includes voltage levels at critical nodes in the circuits. Unfortunately, it doesn't include a complete parts list, so I made a list of all the electrolytic caps on the board that I could see, then checked them against the schematic and found no discrepancies.


Page 1 of schematic with electrolytic caps highlighted in yellow. It seems left channel caps are given even number designators and odd numbers are for the right channel, and not shown in the schematic.  



Second page of the schematic. Note- no electrolytic caps in the power amplifier circuits. The resistors circled in red are two of the four 1k 2W 5% carbon film parts that showed evidence of running too hot. 


Some of the caps on the board were Elna and Nichicon audio rated caps. I replaced those with audio rated caps by Nichicon and Rubycon. C403 and C404 were 4.7uF 10V tantalum caps used as coupling caps in the phono preamp stage. The consensus among audiophiles is that tantalum caps are not good for audio coupling (capacitance changes slightly with applied voltage), and when they fail, they tend to short. I ordered WIMA PP film caps to replace them, but they were much too large to fit in the available space. So I left them alone temporarily.


RT830 tuner


The tuner doesn't need/have the ventilation holes that the amp needs, so there weren't any bugs, dust, or grease inside the box. Just lots and lots of electrolytic caps. I didn't find any toasted parts anywhere, so this one should be just a recap job. I did find one cap that had only one lead soldered and the other wasn't even in its hole in the PCB. The owner's manual is here and the service manual is here

This one is a lot like the amp- there's a single large PCB with component designations and polarities and even the bottom side metal marked on the top side of the board. They put a hatch cover on the bottom of the tuner so it wasn't necessary to remove the PCB to replace the caps. That meant I didn't have to mess around with the dial cord. Nice!

A strange thing about the tuner design is that they put a red LED on the dial indicator, but there are no lights lighting up the dial, so you can't see the frequency unless the room is pretty brightly lit.


RT830 tuner, one PCB, lots of caps, and old-school dial-cord to move the pointer on the frequency dial.


They put a hatch on the bottom to access the PCB without having to unstring the dial cord. Nice!


Hatch open.


Oops! Someone missed a hole with that cap lead... C126



Tuner schematic, electrolytic caps marked in yellow.



The rest of the schematic and caps.



Parts parts parts


I selected the replacement caps based on their function in the circuit and availability. When the originals were Nichicon or other "audio grade" caps, I used audio grade caps. Others were chosen for long life, low leakage, low ESR, etc., depending on what they were doing in the circuits.

In the amp, C652 is 220uF, not 22 uF shown on schematic. 

The new C909 and 910 are a little taller than the original caps, but fit under the amp's cover. 

C403 and C404 were originally tantalum parts. I replaced them with audio grade electrolytics after ordering the PP film caps and discovering they were much too big to fit.

R641-644 were originally 1k 2W 5% carbon film parts. I replaced them with 1k 3W 2% metal film parts.

Total order cost was actually $47.13 plus $7.99 shipping. In many cases, I ordered 10 parts instead of the specific number used in the equipment because of steep price breaks for larger quantities. Why buy 2 parts for $0.80 when you can get 10 for $2.00 and have them in stock for the next project? The prices shown in the list are based on the actual quantity I ordered, not the exact quantity of parts required. If you order the exact quantities needed, the total cost will be a bit lower.

Here's the complete replacement parts list for both the amp and tuner:

C uFV
4.763PP film505-MKP4D044706DKB$3.99C403amp
4.763PP film505-MKP4D044706DKB$3.99C404amp
1050232-50ZL10MEFC5X7$0.20C411amp
1050232-50ZL10MEFC5X7$0.20C412amp
10050647-UKW1H101MPD1TD$0.39C415amp
10050647-UKW1H101MPD1TD$0.39C416amp
1050232-50ZL10MEFC5X7$0.20C601amp
1050232-50ZL10MEFC5X7$0.20C602amp
10050647-UKW1H101MPD1TD$0.39C615amp
10050647-UKW1H101MPD1TD$0.39C616amp
22016232-16TWL220MEFC8X15$0.47C652amp
1050232-50ZL10MEFC5X7$0.20C653amp
1050232-50ZL10MEFC5X7$0.20C701amp
1050232-50ZL10MEFC5X7$0.20C702amp
1050232-50ZL10MEFC5X7$0.20C709amp
1050232-50ZL10MEFC5X7$0.20C710amp
10050647-UKW1H101MPD1TD$0.39C713amp
10050647-UKW1H101MPD1TD$0.39C714amp
10050647-UKW1H101MPD1TD$0.39C903amp
10050647-UKW1H101MPD1TD$0.39C904amp
1000050647-UFW1H103MRD$5.06C909amp
1000050647-UFW1H103MRD$5.06C910amp
4702580-ESK477M025AH1EA$0.20C911amp
4702580-ESK477M025AH1EA$0.20C912amp
10050647-UKW1H101MPD1TD$0.39C118tuner
2.250232-50YXJ2R2M5X11$0.12C126tuner
150232-50YXJ1M5X11$0.07C127tuner
150232-50YXJ1M5X11$0.07C128tuner
4.725232-25TWL4R7MEFC5X11$0.22C130tuner
10050647-UKW1H101MPD1TD$0.39C134tuner
1025232-25ZLG10MEFC4X7$0.18C148tuner
150232-50YXJ1M5X11$0.07C153tuner
4.725232-25TWL4R7MEFC5X11$0.22C154tuner
3.350232-50YXM3R3MEFR5X11$0.21C155tuner
10050647-UKW1H101MPD1TD$0.39C158tuner
1025232-25ZLG10MEFC4X7$0.18C164tuner
1025232-25ZLG10MEFC4X7$0.18C165tuner
4725667-EEU-FC1E470H$0.17C166tuner
10050647-UKW1H101MPD1TD$0.39C168tuner
10050647-UKW1H101MPD1TD$0.39C169tuner
1025232-25ZLG10MEFC4X7$0.18C170tuner
3.350232-50YXM3R3MEFR5X11$0.21C171tuner
1025232-25ZLG10MEFC4X7$0.18C174tuner
4.725232-25TWL4R7MEFC5X11$0.22C177tuner
4702580-ESK477M025AH1EA$0.20C178tuner
4.725232-25TWL4R7MEFC5X11$0.22C186tuner
4.725232-25TWL4R7MEFC5X11$0.22C187tuner
10050647-UKW1H101MPD1TD$0.39C189tuner
4702580-ESK477M025AH1EA$0.20C190tuner
220025598-228CKS025M$0.83C191tuner
1025232-25ZLG10MEFC4X7$0.18C197tuner
2.250232-50YXJ2R2M5X11$0.12C198tuner
1k3W 2%metal film71-CPF3-G-1K$2.07R641amp
1k3W 2%metal film71-CPF3-G-1K$2.07R642amp
1k3W 2%metal film71-CPF3-G-1K$2.07R643amp
1k3W 2%metal film71-CPF3-G-1K$2.07R644amp

Notes: I ordered qty 10 of most of the caps because it was either cheaper or cost only slightly more than ordering the actual required number of caps. Prices shown are based on the actual number of parts I ordered. I will have left-overs for the next recapping job. Note: the PP film caps at the top of the list were too big to fit and I didn't end up using them. I used some Rubycon electrolytics.


Recapping the amp


It was very straightforward, just pull the old caps and replace them one by one. All the polarity  markings on the PCBs were accurate, except two caps were not polarity marked on the board, so I put the new ones in the way the old ones were. A couple of them were located at far edges/corners of the board a little under the chassis with the hatch cover removed. I was able to get at them without removing the PCB.

Once the recapping was done, I adjusted bias and DC offset, hooked up speakers, then applied signals to all the inputs and checked them out. The phono preamp was very noisy and there was some motorboating in the left channel. I replaced the tantalum coupling caps with some Elna audio grade, low-leakage 4.7 uF electrolytics and the noise level dropped and the motorboating stopped. Everything worked as it should, and the amp sounded great. 


Recapping the tuner


As above, just a couple caps near the edges of the PCBs that were a little hard to reach, but no big deal. 

When I finished, I checked power supply voltages- all good. The tuner works perfectly and sounds great. I don't have test equipment to tune the radio, IF amp, and stereo demodulator, so all I could do was replace capacitors. Fortunately, the parts used to do the tuning are all stable over time, so it really shouldn't be necessary to retune those circuits.



Now what am I going to do with another amp and tuner? Hmmm.