One thing I forgot to say to test the diodes a valid way, you have to lift one end from where they are attached. If the diode is connected to a transformer, you'll read the transformer both ways, not the diode.
Okay, if the diode that reads funny is okay with one end lifted, reattach it. If not replace it. After it is okay, put your meter on 600 VDC scale and clip lead the black probe to chassis, like a can tab or something. Take off all jewelry, chains etc. Put the wrong hand in your pocket, because HV electricity that crosses your heart can kill you. Take the red plus meter probe, put on the inner leg of the can attached to the line of the diodes, read the reading. Should also pop in your loudspeaker if it is above 100 (should be 400+) Going down through the resistors, the other 3 legs should read like 350, 275, 225 or something like that. They might not be in order around the cap, just depends on how they wired it.
Signing off for rack time. Have fun, don't kill yourself. Make sure somebody is watching you to call the EMS if you do knock yourself out, for the first few times taking HV measurements. The rule is all the time, but I have people in my house here about once a month- but I'm very meticulous. Oh, don't talk on the phone or anything while you have your hands in there with the power on, just concentrate. Like walking a tightrope, it's just as dangerous.
Okay, if the diode that reads funny is okay with one end lifted, reattach it. If not replace it. After it is okay, put your meter on 600 VDC scale and clip lead the black probe to chassis, like a can tab or something. Take off all jewelry, chains etc. Put the wrong hand in your pocket, because HV electricity that crosses your heart can kill you. Take the red plus meter probe, put on the inner leg of the can attached to the line of the diodes, read the reading. Should also pop in your loudspeaker if it is above 100 (should be 400+) Going down through the resistors, the other 3 legs should read like 350, 275, 225 or something like that. They might not be in order around the cap, just depends on how they wired it.
Signing off for rack time. Have fun, don't kill yourself. Make sure somebody is watching you to call the EMS if you do knock yourself out, for the first few times taking HV measurements. The rule is all the time, but I have people in my house here about once a month- but I'm very meticulous. Oh, don't talk on the phone or anything while you have your hands in there with the power on, just concentrate. Like walking a tightrope, it's just as dangerous.
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750 VDC scale is more than the 450 you expect, that would be fine to measure B+ voltage.
Clip leads are essential for working one hand at a time with the power on. The last bag of Radio Shack ones I got were okay. They also rarely have them in the automotive section or the boat section of discount stores. Also in big farming areas, the tractor electrical supply area of farm stores. Sears tool dept and Fluke official clip leads at Home Depot are way too expensive. Be sure to set the clip lead on the negative to frame before you turn the amp on.
If your amp is not making music, forget the standby and set up the way you want the controls when you try to make music. You can buy a mini phone plug to 1/4 phone jack adapter to plug a transistor radio (mono) in the guitar input for some noise. If you don't have a mono radio, you'll have to buy a stereo mini phone plug (the cheapest ones are on ear buds at the dollar store) and a 1/4" phone jack and some kind of a little box or ball of electrical tape to cover the jack tabs. Also a little wire to connect them. Connect plug tip to center of jack, back of plug to ring of jack.
Clip leads are essential for working one hand at a time with the power on. The last bag of Radio Shack ones I got were okay. They also rarely have them in the automotive section or the boat section of discount stores. Also in big farming areas, the tractor electrical supply area of farm stores. Sears tool dept and Fluke official clip leads at Home Depot are way too expensive. Be sure to set the clip lead on the negative to frame before you turn the amp on.
If your amp is not making music, forget the standby and set up the way you want the controls when you try to make music. You can buy a mini phone plug to 1/4 phone jack adapter to plug a transistor radio (mono) in the guitar input for some noise. If you don't have a mono radio, you'll have to buy a stereo mini phone plug (the cheapest ones are on ear buds at the dollar store) and a 1/4" phone jack and some kind of a little box or ball of electrical tape to cover the jack tabs. Also a little wire to connect them. Connect plug tip to center of jack, back of plug to ring of jack.
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OKay, so I tested the voltages on the filter cap that I replaced. (only three sections of the 20/20/20/20 @450 were supposed to be hooked up). Two of the tabs, square and triangle, read 385v, but the third section, the - section, read nothing whatsoever. it's hooked up to the triangle section with a janky looking 8.2 ohm @ 5.5watt resistor. I outlined a path on this picture to hopefully help you follow it. Alsp, I noticed that when I touched my positive lead to it, the amp started buzzing a little louder, until I took the lead off.
I don't know which wire is the one that is low, I can't see that well. There are 6 posibilities:1 the solder joint on the previous section to the resistor is not good. 2. the resistor is open, not 8 ohm. 3. The solder joint on the dead end of the resistor is open. 4. the capacitor section is shorted 5. The wire leading away to the load has nicked or burned insulation somewhere. 6. the load tube is shorted or the tube socket has a bridge to ground. If the resistor is not directly on the cap but over on a terminal strip somewhere. that is two more solder joints you have to inspect by wiggling, and two more wires you have to inspect that they are not burned or nicked somewhere, touching the frame. Be sure to measure below 25 V before getting in there and wiggling and looking closely. Lots of light and reading glasses are helpful.
So, just start inspecting wires and connections, then measure the resistors with an ohm meter, then test the cap with an ohm meter. If I find anything wrong, replace it, or if that section of the cap is dead, move it to the section not being used. I also have a 20uf @450 spare cap, so I could always mount it on a terminal strip if I had to.
Affirmative. You won't get a proper ohms reading on the resistor with it connected, so check for cold joints and nicked or burned wires first. Steel tabs are hard to get solder to stick to- I try to get the two wires to touch before the solder goes on because tin to tin sticks better. Same with the cap, you can't check it with the wire on. Caps should charge up on 20000 ohms scale, to 1999, then flip to 2V DC scale and watch it discharge - with nothing connected should be slow. Discharge the caps to frame with the resistor and clip leads before measuring anything on ohms scale- any leftover voltage would make the meter read wrong or maybe burn it out on ohms.
out till noon tomorrow EDT.
out till noon tomorrow EDT.
Okay, so I inspected the wire, and I found a little burn on the insulation, right near the end. No exposed wires, I must have just touched it with my iron lightly. I then de soldered the 8k2 @5.5w resistor and tested it, and got no readings either way. I guess I need to buy a new resistor. I also noticed some of the insulation on the resistor was stripped, showing a little bit of bare steel.
Cool, dead resistor probably burned out by the old cap. Buy a couple, a little bigger in wattage than the old one, in case a tube is shorted downstream and you take out another one before you find it. 25 watters are about $1.50 ea. You can wrap the burned wire with Scotch 33 electrical tape, 600V rated and available at electrical supply houses. Stays stuck, too, doesn't fall off like lumberyard tape. I burn too many wires. I have started using surplus teflon insulated wire for new intallations, but there is a lot of PVC wire in my old devices that will burn.
I'm not sure you checked that 1n4007 that read the same both ways yet. They are about $.20 if you have to mail order anything and pay $6 freight from vancouver or toronto.
I'm not sure you checked that 1n4007 that read the same both ways yet. They are about $.20 if you have to mail order anything and pay $6 freight from vancouver or toronto.
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So, now I need a list of parts to order. I'll order the resistor value I need, plus a couple other ones of different values. Also, a couple of those diodes would be nice as well. Newark/ Fernell Canada were great the last time I ordered, $12 for shipping seemed outrageous, until I got my parts the next day delivered to the middle of nowhere that I live.
If you click on shipping options somewhere, I think you can save a few dollars by shipping Royal Mail. I'm getting shipping for $6 for 600 miles but my house (garage) used to be a body shop, so I get UPS business rate.
I just made a howler of a mistake. Don't connect anything but grounds to the grounded leg of the terminal strip. I replaced my "dangerous" selenium rectifier with a 1n4003, on a terminal strip. The mistake was putting the transformer lead and the diode leg on the grounded terminal. I had the 6CA7 tubes drawing 400 ma each before the line fuse blew! They are supposed to draw 100 ma.
Newark has great "multicomp" metal film resistors in 2 & 3 W sizes suitable for tubes for about $.10 each. They are way smaller than the carbon comp resistors put in Western equipment before 1970. When I need one, I buy a dozen, because the shipping is so much more. Needed a 22k 2W night before last, had 11 left- cool. Of course if you're young and going to move around a lot it might not help you. I'm a packrat, pulling bits out of boxes I bought at Radio Shack 40 years ago & stuff.
I just made a howler of a mistake. Don't connect anything but grounds to the grounded leg of the terminal strip. I replaced my "dangerous" selenium rectifier with a 1n4003, on a terminal strip. The mistake was putting the transformer lead and the diode leg on the grounded terminal. I had the 6CA7 tubes drawing 400 ma each before the line fuse blew! They are supposed to draw 100 ma.
Newark has great "multicomp" metal film resistors in 2 & 3 W sizes suitable for tubes for about $.10 each. They are way smaller than the carbon comp resistors put in Western equipment before 1970. When I need one, I buy a dozen, because the shipping is so much more. Needed a 22k 2W night before last, had 11 left- cool. Of course if you're young and going to move around a lot it might not help you. I'm a packrat, pulling bits out of boxes I bought at Radio Shack 40 years ago & stuff.
Hope I dont make any mistakes like that! I checked that section of the cap that wasn't working when plugged in, and it actually does take a charge, leading me to think that the resistor is infinite right now. But it need to be replaced none the less! I'm going to make a list of mixed values soon, plus some diodes and order them.
Got the resistors in the mail, I could only use the $12 shipping option, and I replaced that resistor, plus a couple more, changed the rest of the lytic caps and made that last filter cap. Sounds great! With the 15 inch speaker, not a piece of glass in the house won't rattle with the volume at 4. I also noticed that the volume goes to 12 instead of 10, so if I felt like it, I could turn it up to eleven!
I also remember someone mentioning that I could test the tubes using a multi-meter?
I also remember someone mentioning that I could test the tubes using a multi-meter?
Congratulations. Loud & proud.
On the tubes. Old signal tubes like 12A*7 sometimes get leaky and draw too much current idling. Also, the dropping resistors that make the B+ voltage get blistered and high value. Next time you feel like tinkering, check the B+ to the various signal tubes. It should be lower in the first ones and higher in the later ones, but the last one before the power tubes should be up near the maximum plate voltage for those tubes. The datasheets for the tubes are at triodeelectronics.com, or other places.
As far as measuring the dropping resistors, discharge your caps and measure them after they reach 0V with the ohms scale of your meter. Blistered looking ones are suspect. If they are brown body (carbon composition) about 1/2" long they are quarter watt, or 1" long, 1/2 watt. Farnell has some nice Multicomp brand metal film resistors (hiss less) in the 2 & 3 watt sizes that are the same size as an old AB brand 1/2 watt, and are rated for 500 VDC or higher for tubes. Modern 1/2 and 1/4 watt resistors are too short to use for tubes, they arc over at the high voltages.
You can check the power tubes for their idling current using the two clipleads across the cathode resistor and dividing out V=IR where v is the measured voltage and R is the resistor value. My 6CA7's draw 100 ma idling (0.1 amp) and your 6L6 somethings should draw even more than that. If your power tube b+ is low, that would affect it, but old tired tubes also get where they can't boil off the electrons anymore and won't have enough idling current. The cathode is the pin of the tube that connects to a pointy thing, or on really old schematics, a curlicue. There are two wires that go to the transformer, those are the 6VAC filiment current, then there one of those pins goes to a resistor and maybe a potentiometer that has the other end connected to ground. (minus) That is the cathode resistor that you can measure the idle current across. One hand at a time using clip leads, you remember.
I would suspect your 6l6's as being tired if your amp has as many as 8 years playing time on it (not closet time). The caps, closet time wore them out, but tubes sit in closets just fine without deteriorating.
Have fun.
On the tubes. Old signal tubes like 12A*7 sometimes get leaky and draw too much current idling. Also, the dropping resistors that make the B+ voltage get blistered and high value. Next time you feel like tinkering, check the B+ to the various signal tubes. It should be lower in the first ones and higher in the later ones, but the last one before the power tubes should be up near the maximum plate voltage for those tubes. The datasheets for the tubes are at triodeelectronics.com, or other places.
As far as measuring the dropping resistors, discharge your caps and measure them after they reach 0V with the ohms scale of your meter. Blistered looking ones are suspect. If they are brown body (carbon composition) about 1/2" long they are quarter watt, or 1" long, 1/2 watt. Farnell has some nice Multicomp brand metal film resistors (hiss less) in the 2 & 3 watt sizes that are the same size as an old AB brand 1/2 watt, and are rated for 500 VDC or higher for tubes. Modern 1/2 and 1/4 watt resistors are too short to use for tubes, they arc over at the high voltages.
You can check the power tubes for their idling current using the two clipleads across the cathode resistor and dividing out V=IR where v is the measured voltage and R is the resistor value. My 6CA7's draw 100 ma idling (0.1 amp) and your 6L6 somethings should draw even more than that. If your power tube b+ is low, that would affect it, but old tired tubes also get where they can't boil off the electrons anymore and won't have enough idling current. The cathode is the pin of the tube that connects to a pointy thing, or on really old schematics, a curlicue. There are two wires that go to the transformer, those are the 6VAC filiment current, then there one of those pins goes to a resistor and maybe a potentiometer that has the other end connected to ground. (minus) That is the cathode resistor that you can measure the idle current across. One hand at a time using clip leads, you remember.
I would suspect your 6l6's as being tired if your amp has as many as 8 years playing time on it (not closet time). The caps, closet time wore them out, but tubes sit in closets just fine without deteriorating.
Have fun.
Life is good.
Did a search on 6L6 idle current. Some guy with the handle of ginger is setting his Fender amp to 60 ma idle current. (.06 A) So I guess 6L6 is not as powerful as 6CA7. Do check this fairly soon. If your control grid (the first one in the drawing nearest the cathode) is not negative compared to the cathode, the current will be 5X too high (like my ST70 with the bias voltage grounded, mistake detailed above) and , while sounding great, will burn holes in the tube plates in a couple of weeks. When your amp had bad capacitors, it didn't have enough power on the tubes to burn anything.
Fenders have a test point for the output tube bias current. I don't know about your amp. It would be from the cathode resistor to ground.
Did a search on 6L6 idle current. Some guy with the handle of ginger is setting his Fender amp to 60 ma idle current. (.06 A) So I guess 6L6 is not as powerful as 6CA7. Do check this fairly soon. If your control grid (the first one in the drawing nearest the cathode) is not negative compared to the cathode, the current will be 5X too high (like my ST70 with the bias voltage grounded, mistake detailed above) and , while sounding great, will burn holes in the tube plates in a couple of weeks. When your amp had bad capacitors, it didn't have enough power on the tubes to burn anything.
Fenders have a test point for the output tube bias current. I don't know about your amp. It would be from the cathode resistor to ground.
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