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hugeshows hugeshows is offline
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Default Restoring a Sherwood S-5000

Hello all,


So I did in fact get my parts the other day, and I've made some nice progress. Sadly, one of the caps arrived with some damage, apparently from the factory, and I am in the process of returning it.

However, the large 40/40/20/20 filter capacitor is just fine, and it has now been installed. The results were nothing short of stunning, more on that later. All of the HV+ voltages pretty much stayed the same, actually losing a volt here and there. I suspect that either my line voltage was slightly different or perhaps even that missing volt was ripple that existed with the old cap and was fooling my DMM. Unfortunately, I'll never know because I have yet to buy a new scope since moving cross country. My old one was a TEK 535A, with Scopemobile, so it was a bit big for my current flat. So whether it was ripple or just a line fluctuation, I'll never know but overall the voltages did not change really from what I posted earlier.

The sonic situation got noticeably better immediately on first audition. There was no 'breaking in the cap' or anything like that, something I'm not really convinced of anyway... The first thing I noticed right away was that the bottom two octaves suddenly were really there. They had been there before, and I had gotten fairly used to the sound of the amp as it was. But replacing the main cap made the hum that was barely there to begin with disappear, and all of a sudden there is a quickness and depth to the lower octaves that just wasn't there before. In addition, the mids and highs seem to have really perked up as well, the highs have increased markedly, while the mids just seem clearer. The sound of the amp improved so much it was just obvious within the first 30 seconds of listening. So at least for now we can say that the cap I ordered works well in this amp. Here's how it was installed:

First off, while most of us have recapped a few amps in our day, I strongly recommend doing this the way I did, because I have done this particular amp several times and there are annoying and time consuming mistakes that are easily made and I will show you how to avoid them here. First, snap a picture of the underside of the main cap (C53 in Sherwood Scehmatics, C1 in Sams)

https://www.dropbox.com/s/u8ze7xcu7f...onnections.jpg

So once you have a record of what went where, you are good to start. First of all, you will NEED at least a 140W soldering GUN to get through this. Don't even try this with a pencil iron, there is too much metal down there and it will heat sink your little iron into uselessness. Don't use a butane iron. Those things have exhaust ports that will melt nearby wires, and you'll feel really stupid if you do that. Use a big Weller gun of at least 140W and you'll make it through. Make sure you have some desoldering wick on hand. A sucker will frustrate you on this cap.

Here's the general idea... All of the skinny rubber coated wires should just be snipped right by the terminal. Don't bother trying to desolder these, as the heat needed will make the vinyl jacket melt back even further than if you had just snipped and stripped. All of the resistor leads and cloth transformer wires should be de-soldered and removed intact. The power resistors do not have any extra length on them, so you are forced to desolder their terminals completely and unwrap and extract the leads. Use skinny needle nose pliers for that. Here is what is left after you've snipped all the little wires (except for two grounds underneath the resistor)

https://www.dropbox.com/s/ur200ncddd...53_snipped.jpg

Now you're ready to begin desoldering. Using the solder wick, carefully reclaim the 4.7K resistor, remove the 33 ohm resistor coming from the rectifier, and then all of the cloth covered transformer wires. Use desolder wick to remove as much solder from those old terminals as possible, and then with the pliers, carefully peel the lead off. The factory typically wrapped the lead around the terminal a couple times and you'll be surprised how much you can reclaim. Going slow and desoldering thoroughly is the key. Once you've gotten all those off, you can either desolder or snip the two black grounds underneath the power resistor depending on how much spare slack is available in your amp.

Once you've finished that, all that is left is the ground tab that is soldered to the chassis. Don't even attempt to desolder that. The chassis and can are such good heatsinks, you'll need 250W to do it, and as you are about to see there is utility in doing it another way. Flip the amp over, tilt the capacitor out of the clamp, and simply bend it back and forth until the tab snaps off. Trust me. Set the old cap aside. Now flip the amp over and using larger pliers, grab the tab sticking out of the solder and twist and pull it like a sadistic dentist. If you do it right, you should be left with a blob of solder and a nice clean slot in the chassis. Hmm, thought I had a pic of that but guess not.

Ok, so now you've got the old cap out and everything is just peachy. Time to take a break. Now we need to carefully compare the cap we pulled out to the new one. Here are some pics of that. Remember I told you to trust me and just rip the old cap out? Well here's where it comes in handy... We now have a perfect guide as to the orientation of the cap as it was in the chassis, and that is very critical for both alignment of the connections, but also making sure that the rectifiers first cap is 20uf and no more or less. We must align at least that section of the cap to its original position in the amp. Otherwise, we'll be making jumpers and splices to high voltage connections exposed to heat. That's not ideal.

So here are some pics comparing the caps. Sorry they're not so hot.

https://www.dropbox.com/s/0uhqs4dpen...p_Newcap_1.jpg

https://www.dropbox.com/s/efyhagz1ru...p_Newcap_2.jpg

https://www.dropbox.com/s/raq55pq9jr...p_Newcap_3.jpg

As you can see, other than the shoulder at the base, the dimensions are identical. So here's the important bit, triple check it before moving on: Stand the caps up next to each other as in the third picture. The missing tab is our key that lets us know how the cap was in the chassis in the first place. The 20uf section for the rectifier is the one to the right of the missing tab, where the red wire went. So grab the new can, read the legend on the side, and rotate the cap until the 20uf section in positioned in the same place relative to you, and mark the tab that will be going through the chassis with a sharpie. as in pic #3. Triple check this! You don't want to solder this can into the chassis and be like "oh ****" later on. That's one critical comparison out of the way.

There is one more thing you must check before installation. Look at picture #1 above. Notice anything? The ground tab on this side of the can has no hole! And, if you look at the original can, you see that this position had wires soldered to the tab. So, seeing that, the time to drill a hole is obviously before installation. The correct size in this case was 9/64". With that out of the way, it's time to stuff the cap in... But wait... If you have rust on your amp top that you plan on removing at some point, the time to remove the rust under the cap is NOW, before you stuff in the new one. So grab some scotch-brite and some CLR and you don't have to do the whole thing, but at least to the bits you won't be able to get at later. Here's the cap stuffed in place after cleaning the rust underneath:

https://www.dropbox.com/s/a4svoftuaz...Clean_Rust.jpg

As you can see, it look stock with the exception of the sticker. If you want to remove the sticker for appearance, the time to do it was before you soldered it in!

Rather than trying to remove the blob of solder on the chassis, it's better to just fold the tab over and press it into the blob as far as it will go (cold) and then use your big solder gun to melt more solder into it. This will work, you have enough heat with a gun.

https://www.dropbox.com/s/4sbo4o1lz9...%20%281%29.jpg

There's the new cap installed. As you can see, there was plenty of heat to bury the tab in that solder blob, and it made an excellent connection. So re-soldering the wires is in the reverse order of removal, and it's pretty important to do it that way. First reconnect all the grounds. After the grounds, do the all the red and orange wires but don't solder the skinny red wires, just connect them up. After that, connect the 33 ohm resistor, the two OPT leads, the 4.7K resistor, and solder it up. That terminal has a lot going on, so go carefully if you want it to be neat. After that, connect the 4.7k and the remaining wires and solder them up. The result should look stock like this:

https://www.dropbox.com/s/vi2i11spzl...%20%282%29.jpg

That's all there is to C53! The result as I said before has been night and day and this amp sounds fantastic already, and we've not finished the entire power supply yet.

Now I'd recommend stopping for a bit, coming back, double checking all the connections, and firing it up with the bottom off so you can measure all thje voltages again. Be certain before you turn it on. A good 5AR4 is not cheap to replace.

Now that we've got the old cap out, we can inspect it a bit. Bend back the tabs as I have done he

https://www.dropbox.com/s/1bd9r7wmac...53_removed.jpg

If you look carefully, you'll see that one section in particular has started to ooze the white goo from around its terminal. Interestingly, it's the 5uf@350v section, the smallest section in the can! Well, this new can now has that same section getting 20uf@500v, so that is not likely to happen again anytime soon.

Okay, so until I either get the replacement cap for that second twistlock or decide to do the bias supply, I'm done for a few days.

Cheers,


-forkinthesocket