Can someone point me in a direction to identify this amp. It uses a 5y3 rectifier 12ax7 pre and 6L6GC output.
Power transformer #s 12580-3 and 549833
Output transformer #s TO-10-11 and GA6235
The black connectors on the side appear to break the connection to B+ and the 6l6 control grid.
This is the first tube amp or project I've had, and I don't know much about sketching a schematic by tracing it, but I'll give it a try, and post it. (Ive made a couple of very messy attempts...)
I don't know much about tubes, but I figured what better way to learn that to jump right in feet first.
I would like to use it as a guitar amp if I get it figured out.
I appreciate any info and direction.
(I'm a lineman by trade, so I'm well aware of the dangers of high voltage) [emoji88]
Thanks in advance!
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Power transformer #s 12580-3 and 549833
Output transformer #s TO-10-11 and GA6235
The black connectors on the side appear to break the connection to B+ and the 6l6 control grid.
This is the first tube amp or project I've had, and I don't know much about sketching a schematic by tracing it, but I'll give it a try, and post it. (Ive made a couple of very messy attempts...)
I don't know much about tubes, but I figured what better way to learn that to jump right in feet first.
I would like to use it as a guitar amp if I get it figured out.
I appreciate any info and direction.
(I'm a lineman by trade, so I'm well aware of the dangers of high voltage) [emoji88]
Thanks in advance!
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I have seen similar (not identical) used by Muzak for background music. Also anonymous amps for grocery store "cleanup in aisle 4!" announcement.
5Y3, one 6L6, and a 12A_7. This is a Fender Champ, except the 9-pin mini's circuits are designed for clean sound from line inputs instead of colored sound from small inputs. AND a 6L6 circuit is liable to be twice the Watts Out of a Champ. Almost tavern-worthy.
As a linesman, you can trace it. The rect-6L6 end will be very much like a Champ. May have an extra resistor here or there. All of this should NOT be tampered. The Power section and the Output section, tubes and transformers, were all engineered to work WITH each other. Guitar use hardly changes that. We know the small tube heaters are correctly wired, forget them. This leaves the 6 "active" pins on the small tube to see what goes to what.
At a glance, the input goes to the Volume pot. Correct if input is already at line level. For guitar you usually want one stage of gain before the volume pot. So you will be tinkering.
5Y3, one 6L6, and a 12A_7. This is a Fender Champ, except the 9-pin mini's circuits are designed for clean sound from line inputs instead of colored sound from small inputs. AND a 6L6 circuit is liable to be twice the Watts Out of a Champ. Almost tavern-worthy.
As a linesman, you can trace it. The rect-6L6 end will be very much like a Champ. May have an extra resistor here or there. All of this should NOT be tampered. The Power section and the Output section, tubes and transformers, were all engineered to work WITH each other. Guitar use hardly changes that. We know the small tube heaters are correctly wired, forget them. This leaves the 6 "active" pins on the small tube to see what goes to what.
At a glance, the input goes to the Volume pot. Correct if input is already at line level. For guitar you usually want one stage of gain before the volume pot. So you will be tinkering.
Thanks PRR!
I'll get it traced asap. I'll compare with a champ like you mentioned. I was wondering about a gain stage.
I thought about putting a jumper on the amphenol connector so it powers up and checking voltage as it. It looks clean enough, and all the wiring is intact. I'll do this also and post my finding.
Thanks again for your help!!
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I'll get it traced asap. I'll compare with a champ like you mentioned. I was wondering about a gain stage.
I thought about putting a jumper on the amphenol connector so it powers up and checking voltage as it. It looks clean enough, and all the wiring is intact. I'll do this also and post my finding.
Thanks again for your help!!
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A bigger question is IDing the output taps.
Little rigs use a single 4/8/16 Ohm speaker.
A supermarket, school, or factory has LONG lines and maybe dozens of speakers.
You know when you want to bring power a mile, you want to do it at 600V if not 13KV, to get copper-losses down. The general rule is you want nearer 100 Ohms (with wide variations). You also want to change volume on individual speakers as easy (or easier) as changing lamps on 120V lines. In large many-speaker systems the lines are nominal 25V or 70V (at max nominal output) and the speakers are transformed-up to present a load which will suck 1W 2W 8W etc from that voltage. Without markings this becomes measurements and guesswork.
Little rigs use a single 4/8/16 Ohm speaker.
A supermarket, school, or factory has LONG lines and maybe dozens of speakers.
You know when you want to bring power a mile, you want to do it at 600V if not 13KV, to get copper-losses down. The general rule is you want nearer 100 Ohms (with wide variations). You also want to change volume on individual speakers as easy (or easier) as changing lamps on 120V lines. In large many-speaker systems the lines are nominal 25V or 70V (at max nominal output) and the speakers are transformed-up to present a load which will suck 1W 2W 8W etc from that voltage. Without markings this becomes measurements and guesswork.
Powering up a 40+ year old bit of tube gear takes some thought, it's not too likely the original electrolytic is still good and if shorted could take the rectifier and transformer with it. You can try reforming the supply capacitor using a variac, but it would be better to simply replace it and any other electrolytic cap as well. The coupling capacitor(s) should also be regarded with some suspicion.
If nothing else google "dim bulb tester" here and build yourself one to plug the amp into before powering it. It will save the power transformer.
If the goal is to make this a guitar amplifier this thread is posted to the wrong forum. Let me know and I will move it to Instruments & Amps.
If nothing else google "dim bulb tester" here and build yourself one to plug the amp into before powering it. It will save the power transformer.
If the goal is to make this a guitar amplifier this thread is posted to the wrong forum. Let me know and I will move it to Instruments & Amps.
Please read the Safety and Newbie stickies that are part of this forum if you haven't already. Plenty of information on staying safe and not breaking things. 😀
Thanks for the info!! I'll build a dim bulb tester today, and see how it goes.
The goal is a guitar amplifier, so moving the post is probably a good idea.
I appreciate your help
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The goal is a guitar amplifier, so moving the post is probably a good idea.
I appreciate your help
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I built a dim bulb tester, but Halloween has taken priority for tonight.
I got a 200 watt bulb, so as soon as I can jumper out the amphenol I'll pull the tubes and take voltage to get an idea of what's possible.
What is a good source for a 3 section capacitor? I find plenty of dual section, but no 3 section.
I'll look a little harder, and also study on how to reform them with a variac.
Thanks again for all the help!
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I got a 200 watt bulb, so as soon as I can jumper out the amphenol I'll pull the tubes and take voltage to get an idea of what's possible.
What is a good source for a 3 section capacitor? I find plenty of dual section, but no 3 section.
I'll look a little harder, and also study on how to reform them with a variac.
Thanks again for all the help!
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I fired it up with the dim bulb tester late last night. Everything went well, no short circuit. I tried a 200 watt and a 90 watt bulb.
I downloaded a fender champ 5F1 schematic as it uses the same rectifier and pre, and I'm going to trace it out and overlay it to see how similar they are.
I plugged in an 8ohm speaker (all I have) and used a rca to 1/8" adapter, and it gave VERY low volume and had quite high distortion anything past 1/2 volume. Is this a bad capacitor type issue, or an effect of a severely unmatched load?
I read conflicting info on replacing and reforming capacitors. Some sites say do it as a matter of course, others say only as needed. I don't mind replacing parts at all, but I would like to know why I'm doing something before I do it, so I will be better able to troubleshoot in the future.
Thanks!
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I downloaded a fender champ 5F1 schematic as it uses the same rectifier and pre, and I'm going to trace it out and overlay it to see how similar they are.
I plugged in an 8ohm speaker (all I have) and used a rca to 1/8" adapter, and it gave VERY low volume and had quite high distortion anything past 1/2 volume. Is this a bad capacitor type issue, or an effect of a severely unmatched load?
I read conflicting info on replacing and reforming capacitors. Some sites say do it as a matter of course, others say only as needed. I don't mind replacing parts at all, but I would like to know why I'm doing something before I do it, so I will be better able to troubleshoot in the future.
Thanks!
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Ok...... So after using a champ schematic my amp is very similar. The rectifier and output are wires identical just different resistors.
What I thought was the output of the amp is not. There's a resistor that has been jumpers out and it's actually the 6l6 grid. I effectively wired my speaker from the 6L6 control grid resistor to ground, so I was just getting the output of the 12ax7. The very low, heavily distorted output makes sense now!
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What I thought was the output of the amp is not. There's a resistor that has been jumpers out and it's actually the 6l6 grid. I effectively wired my speaker from the 6L6 control grid resistor to ground, so I was just getting the output of the 12ax7. The very low, heavily distorted output makes sense now!
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The output of the amp is that mess of wires from the output transformer.
Look for a pair that reads about 0.8 Ohms, more or less. A 50r DC winding is liable to be a 500 Ohm Audio winding and a poor match to an 8r load. Most ohm-meters get goofy near or below 1 Ohm so don't take it too literally.
Look for a pair that reads about 0.8 Ohms, more or less. A 50r DC winding is liable to be a 500 Ohm Audio winding and a poor match to an 8r load. Most ohm-meters get goofy near or below 1 Ohm so don't take it too literally.
It works!!
I used the green from the OP transformer that it was originally wired to and sent it to an 8ohm speaker and it's LOUD. Then I made a patch cable and played guitar through it, and it's super clean for 3/4 of the volume knob, then it gets dirtier and dirtier till full distortion at 100%
I'm still leary of the capacitors though, so I'm still running the dim bulb tester.
Thanks PRR and KEVINKR!! I really appreciate your help.
This is my first tube amp, so I still have a long way to go towards understanding what's really going on, and all the how's and whys, but this is a great way to start.
Thanks again!!!
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I used the green from the OP transformer that it was originally wired to and sent it to an 8ohm speaker and it's LOUD. Then I made a patch cable and played guitar through it, and it's super clean for 3/4 of the volume knob, then it gets dirtier and dirtier till full distortion at 100%
I'm still leary of the capacitors though, so I'm still running the dim bulb tester.
Thanks PRR and KEVINKR!! I really appreciate your help.
This is my first tube amp, so I still have a long way to go towards understanding what's really going on, and all the how's and whys, but this is a great way to start.
Thanks again!!!
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Here is a hand copied schematic of the amp. PRR you were definitely correct about it being a Champ! I used the champ schematic, and just overlaid any changes and then traced it on paper with a ruler
I'll be working on a computer drawing, but that's a whole learning process in and of itself.
If you look close, I added voltages that I took without the dim bulb tester.
Appears to be at about 20W.
Does the feedback look strange going back to the control grid?
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Delighted you got it to work!
Since it is clearly destined to be a guitar amp I will move the thread to I&A where you will get lots of additional assistance.
Since it is clearly destined to be a guitar amp I will move the thread to I&A where you will get lots of additional assistance.
> Does the feedback look strange going back to the control grid?
That was very common for other designers, not for Leo Fender.
I don't see a problem with doing it that way. (Tucking it into my bag of Champ tricks.)
Ah, 0.01uFd feeding nearly 100K is a rather high bass-cut. While shaving bass at the power tube grid is an old tweak, I'd start with 0.1uFd there and trim to taste.
The input stage, no cathode cap, is something Fender moved away from mid-1950s. It works up to a point. Hot pickups and other changes tended to overload it. This form is still favored as a specialty sound. For general playing, most folks prefer the 1Meg, 1.5K biasing. Near radio sources you do want the 2*68K or one 33K series resistor.
That was very common for other designers, not for Leo Fender.
I don't see a problem with doing it that way. (Tucking it into my bag of Champ tricks.)
Ah, 0.01uFd feeding nearly 100K is a rather high bass-cut. While shaving bass at the power tube grid is an old tweak, I'd start with 0.1uFd there and trim to taste.
The input stage, no cathode cap, is something Fender moved away from mid-1950s. It works up to a point. Hot pickups and other changes tended to overload it. This form is still favored as a specialty sound. For general playing, most folks prefer the 1Meg, 1.5K biasing. Near radio sources you do want the 2*68K or one 33K series resistor.
E-Caps
Just a friendly reminder- You should replace the capacitors before the amp blows something. I had a Magnavox stereo power amp I used for some time and then one day the power transformer started running hot and dripping potting tar out the bottom. I don't think anything is permanently damaged, but I shoulda replaced the caps first off.
As I'm sure you know, one of the caps is in a tall cylinder on the topside of the chassis and contains two or more caps internal. It will be well worth it to perform these upgrades in the beginning. You may either purchase a direct replacement, (most likely), for the can cap or use a terminal strip and substitute two external caps for the can model. It will be much cheaper to do it that way.
colorcat.
Just a friendly reminder- You should replace the capacitors before the amp blows something. I had a Magnavox stereo power amp I used for some time and then one day the power transformer started running hot and dripping potting tar out the bottom. I don't think anything is permanently damaged, but I shoulda replaced the caps first off.
As I'm sure you know, one of the caps is in a tall cylinder on the topside of the chassis and contains two or more caps internal. It will be well worth it to perform these upgrades in the beginning. You may either purchase a direct replacement, (most likely), for the can cap or use a terminal strip and substitute two external caps for the can model. It will be much cheaper to do it that way.
colorcat.
PRR
Thanks for the info the the 0.01/200k acting as a filter. I should ha e recognized that.... I have a .1uf-400v I'll stick in there tonight. What about the .01 in the 12ax7? Should I increase that to the same as the grid capacitor, or are they identical by coincidence?
Colorcat
I see that the champ schematic uses less capacitance than this amp. Is more better? I've heard that tube rectifiers cannot use as much capacitance. I believe this is a homemade amp, so I'm not too worried about keeping things original, so I'm not opposed to using 4 single capacitors in place of the can, I'm just unsure of what's best for the amp. If I remember correctly the can is a 50uf-400v, 40uf-350v, 30uf-350v, 40-125v unit. Or is the extra capacitance needed because it's a 6L6 as opposed to a 6V6 and the increase in output would result in more ripple?
I added a .1uf cap to the volume pot, and it sounds much better. It was a bit dull before. What about the .047mfd input cap. Keep it or cut it out? I'm interested in trying a single 33k as recommended.
Thanks!!
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Thanks for the info the the 0.01/200k acting as a filter. I should ha e recognized that.... I have a .1uf-400v I'll stick in there tonight. What about the .01 in the 12ax7? Should I increase that to the same as the grid capacitor, or are they identical by coincidence?
Colorcat
I see that the champ schematic uses less capacitance than this amp. Is more better? I've heard that tube rectifiers cannot use as much capacitance. I believe this is a homemade amp, so I'm not too worried about keeping things original, so I'm not opposed to using 4 single capacitors in place of the can, I'm just unsure of what's best for the amp. If I remember correctly the can is a 50uf-400v, 40uf-350v, 30uf-350v, 40-125v unit. Or is the extra capacitance needed because it's a 6L6 as opposed to a 6V6 and the increase in output would result in more ripple?
I added a .1uf cap to the volume pot, and it sounds much better. It was a bit dull before. What about the .047mfd input cap. Keep it or cut it out? I'm interested in trying a single 33k as recommended.
Thanks!!
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Colorcat
I see that the champ schematic uses less capacitance than this amp. Is more better? I've heard that tube rectifiers cannot use as much capacitance.
... I'm just unsure of what's best for the amp. If I remember correctly the can is a 50uf-400v, 40uf-350v, 30uf-350v, 40-125v unit. Or is the extra capacitance needed because it's a 6L6 as opposed to a 6V6 and the increase in output would result in more ripple?
As I recall the limit for that rectifier tube is 60 uf. I'd just leave the existing values as they are. I'm guessing the design was made to handle low frequency range well, the output is oriented towards the 70 volt output, or it was just a vanilla power supply design.
I added a .1uf cap to the volume pot, and it sounds much better. It was a bit dull before. What about the .047mfd input cap. Keep it or cut it out? I'm interested in trying a single 33k as recommended.
The Champ used a .022 in that position. The purpose of that particular cap is to block the high voltage from the input tube, and pass a particular range of frequencies onto the next stage. The .1 uf value will allow lower frequencies than the previous .047 value, to pass to the next stage. It's looking more like this was, as PRR mentioned, some sort of lowish-Fi audio amp. Not a bad project chassis for your purpose and a great start to a, for some, obsessive hobby. Check the chassis for some stamped numbers, ink, that when typed into an Internet search engine bring back results like Magnavox or RCA schematics. The caps look too old to be a home build and the wiring and chassis looks familiar to an age gone by... 58-61. As it turns out I've got a Single Ended EL84 version of a stereo power amp, pulled from a Magi that awaits the proper moment to rejuvenate. This is in addition to my PP Magi that awaits the proper moment to recap. both sound fantastic and the bass response is very good.
colorcat.
I see that the champ schematic uses less capacitance than this amp. Is more better? I've heard that tube rectifiers cannot use as much capacitance.
... I'm just unsure of what's best for the amp. If I remember correctly the can is a 50uf-400v, 40uf-350v, 30uf-350v, 40-125v unit. Or is the extra capacitance needed because it's a 6L6 as opposed to a 6V6 and the increase in output would result in more ripple?
As I recall the limit for that rectifier tube is 60 uf. I'd just leave the existing values as they are. I'm guessing the design was made to handle low frequency range well, the output is oriented towards the 70 volt output, or it was just a vanilla power supply design.
I added a .1uf cap to the volume pot, and it sounds much better. It was a bit dull before. What about the .047mfd input cap. Keep it or cut it out? I'm interested in trying a single 33k as recommended.
The Champ used a .022 in that position. The purpose of that particular cap is to block the high voltage from the input tube, and pass a particular range of frequencies onto the next stage. The .1 uf value will allow lower frequencies than the previous .047 value, to pass to the next stage. It's looking more like this was, as PRR mentioned, some sort of lowish-Fi audio amp. Not a bad project chassis for your purpose and a great start to a, for some, obsessive hobby. Check the chassis for some stamped numbers, ink, that when typed into an Internet search engine bring back results like Magnavox or RCA schematics. The caps look too old to be a home build and the wiring and chassis looks familiar to an age gone by... 58-61. As it turns out I've got a Single Ended EL84 version of a stereo power amp, pulled from a Magi that awaits the proper moment to rejuvenate. This is in addition to my PP Magi that awaits the proper moment to recap. both sound fantastic and the bass response is very good.
colorcat.
Interesting what you find inside a capacitor. The lead to the 6l6 plate supply section was rotted off. The coils inside were damp in some spots, dry in others, and there were dark corrosion looking spots also. I can see why a recap is important!
I can't find a direct replacement can, so for the moment I re-stuffed the can with 4 individual 47uF 400V caps I had laying around till I figure out what the next best cap would be. I'm afraid 47 is too much for the 5y3 though. The data sheet says 20.
It is however much quieter! And I'm not worried about ruining it now.
Thanks again for the help!!!
http://cloud.tapatalk.com/s/581cdbff2fde4/20161104_100756.jpg?
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I can't find a direct replacement can, so for the moment I re-stuffed the can with 4 individual 47uF 400V caps I had laying around till I figure out what the next best cap would be. I'm afraid 47 is too much for the 5y3 though. The data sheet says 20.
It is however much quieter! And I'm not worried about ruining it now.
Thanks again for the help!!!
http://cloud.tapatalk.com/s/581cdbff2fde4/20161104_100756.jpg?
Sent from my SAMSUNG-SM-G900A using Tapatalk
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