I'll try swapping some tubes and see what happens. The sound was in both channels last night, but was definitely louder on the left. There was another sound too that's hard to describe. This probably sounds odd, but the best way I can describe it is it sounds like a mouse or chipmunk nibbling on something. It's faint, but it's there behind the hum or the static when my ear is close to the speakers. I searched for a sound clip of something similar and found this clip of a mouse eating a cracker that is pretty close, lol. The irregular pace or rhythm is definitely similar. https://pixabay.com/sound-effects/mouse-eating-cracker-35523/
I still have a lot of parts to replace on this amp, so I'm probably jumping the gun again trying to track down something like this, but if anyone has an idea about the source of a sound like that, please let me know.
Cheers.
I still have a lot of parts to replace on this amp, so I'm probably jumping the gun again trying to track down something like this, but if anyone has an idea about the source of a sound like that, please let me know.
Cheers.
I started working on the first can capacitor. This one is the 4x100uF 100v with the common positive. Here's a few pics before I put the can back together.
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I'm looking for some photos of how I've done restuffing. I found the easiest way is to use a hacksaw to cut the can at the "shoulder," leaving the larger circular portion as a base. Sand down the edges, and rout around the inside of the base so that the top part slips into the base. It makes the cut pretty much invisible, the fit is usually tight enough that you don't need to use glue or anything.
I used a hole cutting drill bit to make a circular jig that's cut in half down the middle so it can be clamped.
At right note the "trough" around the inside of the base. I leave the stubs of the terminals, drilling holes next to them and inserting the leads, you can then solder a wire directly to the leads. the aluminum terminals don't seem to take solder easily.
Nicely polished and shiny, the finished products at the rear.
At right note the "trough" around the inside of the base. I leave the stubs of the terminals, drilling holes next to them and inserting the leads, you can then solder a wire directly to the leads. the aluminum terminals don't seem to take solder easily.
Nicely polished and shiny, the finished products at the rear.
Thanks for the tips. That looks like a pretty good way of doing it. I'll give it some thought.
I used the method at the link below and used wire cutters to pry up the rolled over edge on bottom of can. I'll hammer the edge back over when I reassemble everything tomorrow. I did a test on an old can first and it worked pretty good.
https://antiquetvguy.com/WebPages/M...Can Restuffing/ElectrolyticCanRestuffing.html
I used the method at the link below and used wire cutters to pry up the rolled over edge on bottom of can. I'll hammer the edge back over when I reassemble everything tomorrow. I did a test on an old can first and it worked pretty good.
https://antiquetvguy.com/WebPages/M...Can Restuffing/ElectrolyticCanRestuffing.html
I used that method on my 222C. Then I had to recap Scott 299B which has five cans. I found that sawing off the top was quicker. It also leaves the bases in better shape to mount the new capacitors.
I use a hot glue gun to firmly attach the caps. Morgan Jones' book Valve Amplifiers, recommends doing that so they aren't as susceptible to harmonics. A lot less messy (and smelly) than the tar-like epoxy they used to use.
You would think they could have just used four caps per can instead of two for the first two cans (C201, C202) but it's possible it was simply because they could only get 30uF/20uF cans with just the two caps, or get them at a better price. Or two separate cans provided better isolation? Unfortunately, all the engineers from those days aren't around anymore to answer such questions.
I use a hot glue gun to firmly attach the caps. Morgan Jones' book Valve Amplifiers, recommends doing that so they aren't as susceptible to harmonics. A lot less messy (and smelly) than the tar-like epoxy they used to use.
You would think they could have just used four caps per can instead of two for the first two cans (C201, C202) but it's possible it was simply because they could only get 30uF/20uF cans with just the two caps, or get them at a better price. Or two separate cans provided better isolation? Unfortunately, all the engineers from those days aren't around anymore to answer such questions.
Thanks for the hot glue tip. I was wondering if I should do something to make them more secure.
How did you cut the "trough" around the inside of the base... a dremel tool or something?
Also wondering how you deal with the common leads? I twisted the four leads together, then struggled a bit to figure out how to pass that bundle of wire through the wafer. So I soldered an insulated extension wire on to that, then added heat shrink, and looped it over the caps and back down through wafer. I don't see anything like that on yours and they seem much cleaner looking.
Thanks again.
How did you cut the "trough" around the inside of the base... a dremel tool or something?
Also wondering how you deal with the common leads? I twisted the four leads together, then struggled a bit to figure out how to pass that bundle of wire through the wafer. So I soldered an insulated extension wire on to that, then added heat shrink, and looped it over the caps and back down through wafer. I don't see anything like that on yours and they seem much cleaner looking.
Thanks again.
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I put the can back together tonight and I'm pretty happy with results. The process is a bit tedious, but it was my first attempt as well. Hopefully the rest will go a bit quicker.
The three 18ohm resistors attached to this can tested 19-20ohms. So I ordered some 18ohm, 1w, 5% replacements, but they are tiny compared to originals. Is there any concerns using resistors like this, or is it just a matter of appearance?
I ordered these: https://www.digikey.ca/en/products/detail/yageo/FMP100JT-52-18R/9107412
Here's some pics.
The three 18ohm resistors attached to this can tested 19-20ohms. So I ordered some 18ohm, 1w, 5% replacements, but they are tiny compared to originals. Is there any concerns using resistors like this, or is it just a matter of appearance?
I ordered these: https://www.digikey.ca/en/products/detail/yageo/FMP100JT-52-18R/9107412
Here's some pics.
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Looks pretty good.
I used a Dremel tool with a round bit to rout out the "trough" around the inside of the base. Go in the direction the tool wants to go, otherwise it wants to hop out and make some nasty marks on that soft aluminum. Ask me how I know.
Re: resistors. Those are metal film types you have. Modern resistors use much more efficient materials than the old carbon comp resistors, they're less noisy, and usually closer to the stated value. It doesn't cost much more to get 1% tolerance for that kind of component but 5% is just fine for that application.
I used a Dremel tool with a round bit to rout out the "trough" around the inside of the base. Go in the direction the tool wants to go, otherwise it wants to hop out and make some nasty marks on that soft aluminum. Ask me how I know.
Re: resistors. Those are metal film types you have. Modern resistors use much more efficient materials than the old carbon comp resistors, they're less noisy, and usually closer to the stated value. It doesn't cost much more to get 1% tolerance for that kind of component but 5% is just fine for that application.
With the capacitors, I usually put the wire going to the cap through the hole in the terminal and then wrap the capacitor leads around the wire if the leads are long enough.
Thanks for the info. I wanted to order 1% resistors, but Digikey and Mouser only had wirewound in 18ohm 1W 1%. I wasn't sure if wirewound was good for this.
I reinstalled the can last night, along with the new 18Ω resistors, and the amp sounds good. One down and three to go. 🙂
I also discovered that it was the CL-80 Thermistor Inrush Current Limiter I installed that was causing the hum I described earlier. I thought it started after that, but I wasn't sure and was second guessing my memory. Then I did some searching about Scotts and Hum, and found this thread on AudioKarma that got me thinking. So I removed the thermistor and the amp is quiet again. I think my mistake was attaching it to the back of the power switch at the front of the amp. I will see if I can fit it at the back where the AC wiring comes in instead.
Here's an excerpt from that AK thread:
I also discovered that it was the CL-80 Thermistor Inrush Current Limiter I installed that was causing the hum I described earlier. I thought it started after that, but I wasn't sure and was second guessing my memory. Then I did some searching about Scotts and Hum, and found this thread on AudioKarma that got me thinking. So I removed the thermistor and the amp is quiet again. I think my mistake was attaching it to the back of the power switch at the front of the amp. I will see if I can fit it at the back where the AC wiring comes in instead.
Here's an excerpt from that AK thread:
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I've disconnected the switch on the volume control on my 222C and my 299B. I have them plugged into an old computer power station that was made to sit between the computer and the monitor, it has multiple switched outlets. I mounted a Corcom RFI filter from Ebay inside the box to help keep crud out of the AC supply.
The shielded wire Scott used wasn't the greatest but there were probably fewer home noise makers back in those days. I've replaced that with some better coax shielded wire, you can get short lengths about 10' long in various colors on Ebay.
Scott's engineers did a pretty good job of star grounding with the main ground point under the phono preamp tubes which are most susceptible to noise. That's why it's important to keep the insulating wafers under the can caps so that the ground is only connected at that one point.
The LK series were sold in kit form, so it's a good idea to check over the wiring carefully for bad solder joints or misplaced ground wires. You can find assembly manuals online to check that whoever made that kit did it correctly. Although I've heard that some were built at the factory.
One problem I've seen is that the AC heater wiring isn't adequately twisted to reject noise. The preamp tube heaters use DC, they used the bias supply for those to keep the noise lower, but the power amp tubes are AC from the transformer.
The shielded wire Scott used wasn't the greatest but there were probably fewer home noise makers back in those days. I've replaced that with some better coax shielded wire, you can get short lengths about 10' long in various colors on Ebay.
Scott's engineers did a pretty good job of star grounding with the main ground point under the phono preamp tubes which are most susceptible to noise. That's why it's important to keep the insulating wafers under the can caps so that the ground is only connected at that one point.
The LK series were sold in kit form, so it's a good idea to check over the wiring carefully for bad solder joints or misplaced ground wires. You can find assembly manuals online to check that whoever made that kit did it correctly. Although I've heard that some were built at the factory.
One problem I've seen is that the AC heater wiring isn't adequately twisted to reject noise. The preamp tube heaters use DC, they used the bias supply for those to keep the noise lower, but the power amp tubes are AC from the transformer.
I breathed a big sigh of relief last night when I finished restuffing the last can capacitor. It was a long tedious process, but I'm glad I was able to reuse the old cans and maintain the original appearance. All the old caps have been replaced now and the amp is looking and sounding good.
I may try replacing the 33ohm 5W resistor in the bias circuit with a 40ohm as suggested earlier. Also debating whether I should remove the 220K grid resistors I installed earlier and go back to original value of 330K. I do have some new 5% metal film for replacements. I also have 1% replacements for some of the plate resistors as recommended in the website therling shared earlier.
If there is anything else I should be considering, please let me know. Also wondering if there are any tests I could do with my oscilloscope to determine how well the amp is operating. I used the scope to identify the foil side of the new caps, but would like to learn other ways to use it.
Suggestions are always welcome.
I may try replacing the 33ohm 5W resistor in the bias circuit with a 40ohm as suggested earlier. Also debating whether I should remove the 220K grid resistors I installed earlier and go back to original value of 330K. I do have some new 5% metal film for replacements. I also have 1% replacements for some of the plate resistors as recommended in the website therling shared earlier.
If there is anything else I should be considering, please let me know. Also wondering if there are any tests I could do with my oscilloscope to determine how well the amp is operating. I used the scope to identify the foil side of the new caps, but would like to learn other ways to use it.
Suggestions are always welcome.
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I've been enjoying the Scott and my Altec speakers, but I'm in the midst of some renovations in the livingroom. So today I moved the Scott into some shelving built into the wall in another room. See pics below.
I'm not sure if this will be permanent, but I kind of like this setup. However, I'm a bit worried about things getting too hot. Is this a concern? Right now there is about 3 inches above the amp and the tuner, and about 2 inches on either side, but I do have some flexibility to move the shelves. If I decided to make this permanent I will probably make some new shelves that are more sturdy.
Is it ok to have the tuner above the amp? It needs some works and isn't hooked up at the moment, but I seem to recall reading somewhere that this was not a good idea due to interference from amp below, but I can't remember where I read that.
Thanks for any feedback.
I'm not sure if this will be permanent, but I kind of like this setup. However, I'm a bit worried about things getting too hot. Is this a concern? Right now there is about 3 inches above the amp and the tuner, and about 2 inches on either side, but I do have some flexibility to move the shelves. If I decided to make this permanent I will probably make some new shelves that are more sturdy.
Is it ok to have the tuner above the amp? It needs some works and isn't hooked up at the moment, but I seem to recall reading somewhere that this was not a good idea due to interference from amp below, but I can't remember where I read that.
Thanks for any feedback.
No problem at all. Scott amplifiers were originally in wooden cases with much less ventilation than in your setup.
Modern resistors have much higher power ratings for their size but they do this by running HOT. It's an immutable Law of Nature.
This does not matter if they don't dissipate much power. But if they do (eg Cathode resistors on the final output), I would use several resistors in parallel to make up the original value in about the same size package ... or a modern resistor of about the same physical size even if its power rating is much higher.
There's also where and how they are mounted and if the higher temperature might affect nearby stuff adversely. A common case is if the Cathode Resistor is decoupled by an Electrolytic.