Tweet
Jojomanee
Hope I'm not too late to help you with your amp. I got my hands on one of those Heathkit TA-16 last month. I'm like you I can repair these things but not into the theory behind it. The amp was almost a basket case, first of all it didn't work at all. I just finished it last night and it sounds great. Right off the bat I found a burnt resistor, replaced it and got the amp working but just barely. I started checking around and found most of the resistors way out of value I know people say there is room for 10% of drift. I feel the same way 10% out is not bad but when almost all the resistors are 10, 20, 30% out of value it accumulates and then something's not going to work right. What surprised me was the capacitors were all right on the mark. By the way that amp dates back to 1966 to 1970. The schematic you have is the same one I have, there was a design change. 4 or 6 resistors were changed to a differant value. I ended up replacing all the resistors and caps, when you remove the resistors the correct value will be printed on the board, if your amp is like the schematic then its older than mine, it don't have the design change in it. If you decide to replace everything use a low wattage iron, that board is a POS and if your not careful you'll detach the copper traces from the board. Its not hard to fix I took some thin #22 solid wire from Radio Shack flattened it with a small hammer against a vise, it epoxied it to the board let it sit for a day then used a Dremel tool to make the holes. If just the end of the copper trace breaks off push the lead for the resistor all the way in bend it over until it overlaps the trace and solder it, this is a small amp and it won't make any differance, your not dealing with any RF and I won't tell. I replaced Q1 and 2, I had alot of distortion at first so I got in there with the scope and checking the voltages around the output transistors something I didn't do before and bingo Q9 was bad thats a 2N2148 or an NTE-121 you may have trouble hunting that down, its an un common number and its germainium not silicon. I found one in a junk parts box, how lucky is that. The other output Q10 is a TA2577 or NTE-130 that I bought in a local electronics parts store. Now for that cursed LDR, thats what makes the tremolo you ain't going out and buying one unless another amp maker uses one and you can con them into selling you one I didn't even try to buy one, I rolled my own. First you have to understand how that circuit works, look at the schmatic. You have a connection at Q6, a 2mfd cap, a 3.3k resistor to ground, a 2.2k resistor then the connection to the reverb section,then the line goes to the ldr, What looks like a resistor is a photocell then it goes to ground. That other symbol in the ldr a light bulb connected to Q12 and 13. when you jack up the tremolo the bulb starts to blink, this bulb shines on the photocell, when the photocell sees light the resistance drops then it shorts the input to Q6 to ground which lowers the volume. You can check that ldr, I don't have it here right now but it has 4 leads on it, 2 are spaced about 1/2" apart the other 2 are about 3/4" apart. I think the closer ones are the bulb, hook the dvm's leads to them start at the lowest setting on the dvm, if you start to see resistance at about 200 ohms thats the bulb and its good, no reading at the meters highest setting the bulbs blown. if the bulbs good put the meter on the other 2 leads you won't get a reading until you get up to about 10k or more on the meter. Now with the meter hooked up if you have a power supply connect it to the bulbs leads, don't exceed 12 volts or you will blow the bulb, you can use a 12 volt ac wall wart an incandesant bulb don't care if its ac or dc. Or you can drag the whole contraption out to the car and use the battery, be careful around a car battery its only 12 or 13 volts but 500 to 900 amps it WILL turn a test lead into a firecracker fuse lickty split. So you have the meter connected to the photocell leads as soon as the juice hits the other 2 leads the resistance should drop to about 250 ohms. So that little black box works. I made my ldr using one of those clear white super bright big ass 10mm leds, an 870ohm resistor in series with the led, a photocell from Radio Shack, they come in a package of 5 or 6, pick one of the bigger ones connect the dvm to the leads and find the brightest flashlight you can find, I used an led flashlight. Shine it into the photocell then check the resistance, pick the cell that gives you the lowest reading, mine was 240 ohms. The longer lead on the led is positive if you hook it up backwards prepare for a road trip to get another, believe me I know, the Shack had them too but your going to rebuild this amp and you get the parts from Digi-key, Mouser or any other parts supplier buy the leds from them. So I cut about 3/4" long piece of 3/8" wood dowel cut 2 grooves in it for the leads, stripped some wire covering, be sure to use red for the led pos lead and slipped over all the leads. Put the led right against the photo cell wrapped some aluminum foil around it, shiney side in. Cut up an aluminum cat food can and wrapped that around it, stuck the piece of dowel in behind the photo cell, scotch taped it together so it would stay together. Then got this very thick hard shrink wrap and covered it all up. Put liquid electric tape in behind the led and hot glue behind the cell. Then let the whole thing set up then shrunk the shrink wrap more, that works super. I had to add a 25 mfd cap to the + side of the led so it would act more like a bulb. An led is either on or off, it don't come on slowly or go out slowly like a bulb, watch a cars brake lights with leds then watch a car with bulbs you'll see a big difference. I'v read some of these posts and there right check all the solder joints, usually you have to pull the transistors to check them properly. a tip for you always attach a small alligator clip to the transistor lead close to the transistor when your soldering it, it prevents the heat from soldering from reaching the transistor and destroying it. Good luck the TA-16 I have sounds great now, better than I expected, now i have to recover the case and grille cloth, mine has 2 12'' speakers which I have 4 Ibanez rock crushers, I forgot the model but the're good ones. Keep us posted on how your doing, I'd be glad to help I know that thing inside out.
''''
'"
Hope I'm not too late to help you with your amp. I got my hands on one of those Heathkit TA-16 last month. I'm like you I can repair these things but not into the theory behind it. The amp was almost a basket case, first of all it didn't work at all. I just finished it last night and it sounds great. Right off the bat I found a burnt resistor, replaced it and got the amp working but just barely. I started checking around and found most of the resistors way out of value I know people say there is room for 10% of drift. I feel the same way 10% out is not bad but when almost all the resistors are 10, 20, 30% out of value it accumulates and then something's not going to work right. What surprised me was the capacitors were all right on the mark. By the way that amp dates back to 1966 to 1970. The schematic you have is the same one I have, there was a design change. 4 or 6 resistors were changed to a differant value. I ended up replacing all the resistors and caps, when you remove the resistors the correct value will be printed on the board, if your amp is like the schematic then its older than mine, it don't have the design change in it. If you decide to replace everything use a low wattage iron, that board is a POS and if your not careful you'll detach the copper traces from the board. Its not hard to fix I took some thin #22 solid wire from Radio Shack flattened it with a small hammer against a vise, it epoxied it to the board let it sit for a day then used a Dremel tool to make the holes. If just the end of the copper trace breaks off push the lead for the resistor all the way in bend it over until it overlaps the trace and solder it, this is a small amp and it won't make any differance, your not dealing with any RF and I won't tell. I replaced Q1 and 2, I had alot of distortion at first so I got in there with the scope and checking the voltages around the output transistors something I didn't do before and bingo Q9 was bad thats a 2N2148 or an NTE-121 you may have trouble hunting that down, its an un common number and its germainium not silicon. I found one in a junk parts box, how lucky is that. The other output Q10 is a TA2577 or NTE-130 that I bought in a local electronics parts store. Now for that cursed LDR, thats what makes the tremolo you ain't going out and buying one unless another amp maker uses one and you can con them into selling you one I didn't even try to buy one, I rolled my own. First you have to understand how that circuit works, look at the schmatic. You have a connection at Q6, a 2mfd cap, a 3.3k resistor to ground, a 2.2k resistor then the connection to the reverb section,then the line goes to the ldr, What looks like a resistor is a photocell then it goes to ground. That other symbol in the ldr a light bulb connected to Q12 and 13. when you jack up the tremolo the bulb starts to blink, this bulb shines on the photocell, when the photocell sees light the resistance drops then it shorts the input to Q6 to ground which lowers the volume. You can check that ldr, I don't have it here right now but it has 4 leads on it, 2 are spaced about 1/2" apart the other 2 are about 3/4" apart. I think the closer ones are the bulb, hook the dvm's leads to them start at the lowest setting on the dvm, if you start to see resistance at about 200 ohms thats the bulb and its good, no reading at the meters highest setting the bulbs blown. if the bulbs good put the meter on the other 2 leads you won't get a reading until you get up to about 10k or more on the meter. Now with the meter hooked up if you have a power supply connect it to the bulbs leads, don't exceed 12 volts or you will blow the bulb, you can use a 12 volt ac wall wart an incandesant bulb don't care if its ac or dc. Or you can drag the whole contraption out to the car and use the battery, be careful around a car battery its only 12 or 13 volts but 500 to 900 amps it WILL turn a test lead into a firecracker fuse lickty split. So you have the meter connected to the photocell leads as soon as the juice hits the other 2 leads the resistance should drop to about 250 ohms. So that little black box works. I made my ldr using one of those clear white super bright big ass 10mm leds, an 870ohm resistor in series with the led, a photocell from Radio Shack, they come in a package of 5 or 6, pick one of the bigger ones connect the dvm to the leads and find the brightest flashlight you can find, I used an led flashlight. Shine it into the photocell then check the resistance, pick the cell that gives you the lowest reading, mine was 240 ohms. The longer lead on the led is positive if you hook it up backwards prepare for a road trip to get another, believe me I know, the Shack had them too but your going to rebuild this amp and you get the parts from Digi-key, Mouser or any other parts supplier buy the leds from them. So I cut about 3/4" long piece of 3/8" wood dowel cut 2 grooves in it for the leads, stripped some wire covering, be sure to use red for the led pos lead and slipped over all the leads. Put the led right against the photo cell wrapped some aluminum foil around it, shiney side in. Cut up an aluminum cat food can and wrapped that around it, stuck the piece of dowel in behind the photo cell, scotch taped it together so it would stay together. Then got this very thick hard shrink wrap and covered it all up. Put liquid electric tape in behind the led and hot glue behind the cell. Then let the whole thing set up then shrunk the shrink wrap more, that works super. I had to add a 25 mfd cap to the + side of the led so it would act more like a bulb. An led is either on or off, it don't come on slowly or go out slowly like a bulb, watch a cars brake lights with leds then watch a car with bulbs you'll see a big difference. I'v read some of these posts and there right check all the solder joints, usually you have to pull the transistors to check them properly. a tip for you always attach a small alligator clip to the transistor lead close to the transistor when your soldering it, it prevents the heat from soldering from reaching the transistor and destroying it. Good luck the TA-16 I have sounds great now, better than I expected, now i have to recover the case and grille cloth, mine has 2 12'' speakers which I have 4 Ibanez rock crushers, I forgot the model but the're good ones. Keep us posted on how your doing, I'd be glad to help I know that thing inside out.
''''
'"
Comment