need a 120vct transformer... where to look?
I am building a small guitar amplifier and need a transformer. It needs to be 120vct @ ~150ma.
As you probably guessed, its another line operated design, but I am improving on it. Aside from using a power transformer, using a FWB will give me a secondary of about 158vdc, which is better for a 50c5. That eliminates the need for a 35xx tube for the rectifier, and allows me to make a much cleaner power supply. I would like to run the 50c5 in series with a 12xx tube, and wire them from one side to the centre tap on the transformer.
This keep parts count to a minimum, and allows a better power suppply design. Since I have a lot of these tubes around, I could make a lot of amplifiers for some people that I know that are looking for the kay/harmony/silvertone sound without the dangers. I reallise there are better ways to do this, but this is what I want to do.
I don't know where to begin to look for a transformer other than tubesandmore and tubedepot, so I was wondering if any of you know of a good place I could order them from.
Also, I was wondering if using one half of the secondary to run the power hog heaters if it would mess anything up /unbalance the power supply?
I gues if I had to I could just use a low wattage iso tranny an throw a big power resistor in series with the tubes, but I don't really want to do that if I can get the right voltage utilizing the transformer centre tap. I seem to remember at least one or two of those old designs that did just this very thing.
Thanks much, ~Tsd88
I am building a small guitar amplifier and need a transformer. It needs to be 120vct @ ~150ma.
As you probably guessed, its another line operated design, but I am improving on it. Aside from using a power transformer, using a FWB will give me a secondary of about 158vdc, which is better for a 50c5. That eliminates the need for a 35xx tube for the rectifier, and allows me to make a much cleaner power supply. I would like to run the 50c5 in series with a 12xx tube, and wire them from one side to the centre tap on the transformer.
This keep parts count to a minimum, and allows a better power suppply design. Since I have a lot of these tubes around, I could make a lot of amplifiers for some people that I know that are looking for the kay/harmony/silvertone sound without the dangers. I reallise there are better ways to do this, but this is what I want to do.
I don't know where to begin to look for a transformer other than tubesandmore and tubedepot, so I was wondering if any of you know of a good place I could order them from.
Also, I was wondering if using one half of the secondary to run the power hog heaters if it would mess anything up /unbalance the power supply?
I gues if I had to I could just use a low wattage iso tranny an throw a big power resistor in series with the tubes, but I don't really want to do that if I can get the right voltage utilizing the transformer centre tap. I seem to remember at least one or two of those old designs that did just this very thing.
Thanks much, ~Tsd88
Found your transformer
Mouser Electronics www.mouser.com has a Triad N51X, Mouser Part number 553-N51X for $12.00. Its rated at 300mA. Good luck with your project.
Mouser Electronics www.mouser.com has a Triad N51X, Mouser Part number 553-N51X for $12.00. Its rated at 300mA. Good luck with your project.
If you must go center tapped
Angela Instruments has some Hammond transformers 167G120 120ct FL volts, 127.00 NL volts, 0.5 amps. EACH $17.00
www.angela.com
Angela Instruments has some Hammond transformers 167G120 120ct FL volts, 127.00 NL volts, 0.5 amps. EACH $17.00
www.angela.com
In the UK, we force our builders to use 110V tools powered from a centre-tapped supply in order to keep the voltage of each phase to 55V (making it less dangerous than 240V when they accidentally damage the cable and it touches scaffolding). I imagine that such transformers are made in sufficient quantities that they are reasonably cheap.
Hey thanks for the quick replys!
Wouldnt your drawing be for a 120-0-120 transformer? I guess I could use an iso transformer with a big resistor for the heaters. Remember I'm also using it as b+.
I guess my question is , is it ok to use a 120vct transformer like this ( see photo )
Would this cause an imbalance in the supply, or would it be ok as long as I allowed for enough current that it did not sag under load of the heaters?
Wouldnt your drawing be for a 120-0-120 transformer? I guess I could use an iso transformer with a big resistor for the heaters. Remember I'm also using it as b+.
I guess my question is , is it ok to use a 120vct transformer like this ( see photo )
Would this cause an imbalance in the supply, or would it be ok as long as I allowed for enough current that it did not sag under load of the heaters?
Attachments
ohh I see now! Its the same as mine basically, except you rectified thefiliments and added a current limiter. I asume the limiter is to keep one side of the transformer from drawing too much curent, and thus being loaded down so the voltage sags?
Also, would it be ok to just run them off AC? 82v seems a bit high for 62v worth of heaters.
Also, would it be ok to just run them off AC? 82v seems a bit high for 62v worth of heaters.
One more time
By using the 2 diodes at the top to rectify the 120 VCT you get 84.8V VDC if fed into a capacitor. Since the filiments of a 50C5 draws 0.15 Amps The equivelent resistance would be 333 ohms, the 12 Volt tube would be an 80 ohm eqivalent and the 150 ohm resistor would drop about 22.5V. The 120V on the bridge rectifier should yield 168 VDC on the output of the brige / cap.
ThSpeakerDude88 said:
By using the 2 diodes at the top to rectify the 120 VCT you get 84.8V VDC if fed into a capacitor. Since the filiments of a 50C5 draws 0.15 Amps The equivelent resistance would be 333 ohms, the 12 Volt tube would be an 80 ohm eqivalent and the 150 ohm resistor would drop about 22.5V. The 120V on the bridge rectifier should yield 168 VDC on the output of the brige / cap.
Alright well, I hooked it up like you showed. Weird thing is I was reading only 61.5vdc after the rectifier. I didnt use a filter cap because it didn't cause any hum in the amp, so thats why i didnt get 84vdc. When I tried using the 150R ( 5watt) resistor in line, it got very hot. I removed it and the bridge and the filiments warmed up quickly and worked perfect. Seems like I won't be going DC filiments after all.
I ordered the hammond 167G120 filiment transformer. Its primary is 115v, and secondary is 120vct, which explains why with todays 5v higher line voltage I got 130v under load. When I used a FWB for the B+ however, I got 180vdc under load!
Much to high for a 50c5! ( the plates were glowing!) I removed the FWB and installed a single 1n4007 , which does the same duty as a 35w4. Under load I got 140vdc, which was a lot more acceptable. I used a 47uf cap as a filter, and the amp was very quiet with no 60hz audible, which i find amazing for a single diode rectifier.
However, I am thinking about redoing my design. It seems the Harmony H303A had originally used a transformer with a 50vac tap for the heaters: 50c5 in paralell with series 35w4 and 12au6.
What I don't know is what the tap for the B+ was. I would assume it would be just 1:1 however.
My whole goal to using SS rectifier was to make things smaller by omitting the 35w4, and possibly making things a little quieter in the power supply section. The Harmony originally said 25 watts on the back, and I assume this would be at max draw.
However, 1:1 isolation transformers @ only 20-25va are scarce... at least I can't find any. The trafo that I ordered is much too large for my amp, and I would like to make it smaller if at all possible.
Also, the 125cse is overkill for my amp, but being an 8 watt ot its not a total loss as I can definatly use it in other projects.
I believe now I need to look for a 1:1 isolation transformer that doesnt take up much space, and is rated for ~30va.
I ordered the hammond 167G120 filiment transformer. Its primary is 115v, and secondary is 120vct, which explains why with todays 5v higher line voltage I got 130v under load. When I used a FWB for the B+ however, I got 180vdc under load!
Much to high for a 50c5! ( the plates were glowing!) I removed the FWB and installed a single 1n4007 , which does the same duty as a 35w4. Under load I got 140vdc, which was a lot more acceptable. I used a 47uf cap as a filter, and the amp was very quiet with no 60hz audible, which i find amazing for a single diode rectifier. However, I am thinking about redoing my design. It seems the Harmony H303A had originally used a transformer with a 50vac tap for the heaters: 50c5 in paralell with series 35w4 and 12au6.
What I don't know is what the tap for the B+ was. I would assume it would be just 1:1 however.
My whole goal to using SS rectifier was to make things smaller by omitting the 35w4, and possibly making things a little quieter in the power supply section. The Harmony originally said 25 watts on the back, and I assume this would be at max draw.
However, 1:1 isolation transformers @ only 20-25va are scarce... at least I can't find any. The trafo that I ordered is much too large for my amp, and I would like to make it smaller if at all possible.
Also, the 125cse is overkill for my amp, but being an 8 watt ot its not a total loss as I can definatly use it in other projects.
I believe now I need to look for a 1:1 isolation transformer that doesnt take up much space, and is rated for ~30va.
I bought that one, and a larger chassis.
I decided if it aint broke don't fix it, so I am going to stick with the half-wave rectifier design. Its not the best in the world, but as long as you have new filter caps and a properly layed out circuit you can't hear any hum thats noticable to any degree.
Right now I have another problem. The original circuit uses 3 tubes, 50c5, 12au6 and 35w4. The three heaters add up to 97.6v, which means I need about a 26 volt drop from line voltage. This can be achieved by means of a 150 ohm resistor ( which gives exact drop for 120v operating mains).
I calculated that since the heaters are pulling 150ma through the resistor, that it should only dissipate 3.9 watts.
I set up just the heater circuit on a breadboard and am testing it with an input of 120v, and my resistor is after the 35w4 heater and before the 50c5, just like in most schematics you see with only 3 of these tubes.
The problem I am having is that it is heating up really bad! I measured the current, and after about 10-15 seconds it finally stabilizes at the rated 150ma. The resistor that I am using is 5 watts,150 ohms. Why is it heating up so badly? Did I miss something here?
Also note that I do not know if it will stabilize after initial startup current because I am afraid to leave it on for too long without the resistor burning/bursting ( its ceramic).
I decided if it aint broke don't fix it, so I am going to stick with the half-wave rectifier design. Its not the best in the world, but as long as you have new filter caps and a properly layed out circuit you can't hear any hum thats noticable to any degree.
Right now I have another problem. The original circuit uses 3 tubes, 50c5, 12au6 and 35w4. The three heaters add up to 97.6v, which means I need about a 26 volt drop from line voltage. This can be achieved by means of a 150 ohm resistor ( which gives exact drop for 120v operating mains).
I calculated that since the heaters are pulling 150ma through the resistor, that it should only dissipate 3.9 watts.
I set up just the heater circuit on a breadboard and am testing it with an input of 120v, and my resistor is after the 35w4 heater and before the 50c5, just like in most schematics you see with only 3 of these tubes.
The problem I am having is that it is heating up really bad! I measured the current, and after about 10-15 seconds it finally stabilizes at the rated 150ma. The resistor that I am using is 5 watts,150 ohms. Why is it heating up so badly? Did I miss something here?
Also note that I do not know if it will stabilize after initial startup current because I am afraid to leave it on for too long without the resistor burning/bursting ( its ceramic).
My rectifier just failed on me! Seems its filiments were getting old and all the sudden it went flash and that was it.
Even using a single diode, a 47uf cap, a 100ohm resistor, another 47 uf cap, and then another 47 uf cap in the screen filter, I still have a noticable hum. It would not be a problem if I could use a larger filter capacitor such as a 220uf, but you can't go above 60uf with the 35w4 without hurting it.
Since I need a new power transformer ( I havent actually ordered the isolation transformer yet) and since I'm having so many problems with the current setup, and the necessity for a 15 watt resistor..
I'm thinknig about getting a Hammond262e6 and going with a 6aq5 on the output.
This will make the design a lot simpler than even the line operated setup. I eliminate the tube rectifier and use a FWB once again, making the power supply much cleaner. After rectification, my 120v tranny will give me about 180v. The 6aq5 sheet says that on 180v it gives out 2 watts @ 8% thd. Close enough to the 50c5 eh?
I am very interested to see how the 6aq5 sounds... I wanted so badly to hear what a 50c5 sounds like when pushed though, however, I may just wait untill I come across an original H303A on ebay, as they are quite common and come with a nice jensen special design too.
Seems its filiments were getting old and all the sudden it went flash and that was it. Even using a single diode, a 47uf cap, a 100ohm resistor, another 47 uf cap, and then another 47 uf cap in the screen filter, I still have a noticable hum. It would not be a problem if I could use a larger filter capacitor such as a 220uf, but you can't go above 60uf with the 35w4 without hurting it.
Since I need a new power transformer ( I havent actually ordered the isolation transformer yet) and since I'm having so many problems with the current setup, and the necessity for a 15 watt resistor..
I'm thinknig about getting a Hammond262e6 and going with a 6aq5 on the output.
This will make the design a lot simpler than even the line operated setup. I eliminate the tube rectifier and use a FWB once again, making the power supply much cleaner. After rectification, my 120v tranny will give me about 180v. The 6aq5 sheet says that on 180v it gives out 2 watts @ 8% thd. Close enough to the 50c5 eh?
I am very interested to see how the 6aq5 sounds... I wanted so badly to hear what a 50c5 sounds like when pushed though, however, I may just wait untill I come across an original H303A on ebay, as they are quite common and come with a nice jensen special design too.
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