Power transformer wire grouping help

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Re: Power transformer wire grouping help

Post by davemojo »

geoff 1965 wrote:
Sat 03/06/21 5:48 pm
Yeah the 2 red are your HT to the rectifier and the 2 green are the heater filaments,which schematic/layout are you using?
Could you please confirm

Are the 2 red wires going to the same Ez81 where you are going to also attach the pink and the grey?

According to my instructions the 2 reds are going to Ez81 lug 1 and 7 and the pink and the grey (in my instructions are yellow and white) are going to lug 4 and 5

See also portion of my guide instructions
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Re: Power transformer wire grouping help

Post by geoff 1965 »

yeah just use pink & grey to 4 & 5 and the 2 red HT to 1 & 7
note; if this was my amp i would put the fuse between the mains positive and power switch.
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Re: Power transformer wire grouping help

Post by davemojo »

Great thank you done just now the reds

So pink to 4 and Grey to 5?
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Re: Power transformer wire grouping help

Post by geoff 1965 »

either way is okay 4 & 5 are connected internally
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Re: Power transformer wire grouping help

Post by davemojo »

geoff 1965 wrote:
Fri 03/12/21 10:50 am
either way is okay 4 & 5 are connected internally
Done should be fine , hehe it is getting challenging but I love to do it.
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Re: Power transformer wire grouping help

Post by geoff 1965 »

get a 2W 220K metal film resistor so you can add a bleed to the dual can capacitor,for safety this bleeds the voltage from the capacitors to ground when you switch the amp off.
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Fri 03/12/21 3:23 pm
get a 2W 220K metal film resistor so you can add a bleed to the dual can capacitor,for safety this bleeds the voltage from the capacitors to ground when you switch the amp off.
ahah ok here I need to understand what do you exactly mean by adding 2w 220k metal film resistor.

Where do I exactly need to put it :-) ? Please? As you may understand my knowledge with electronics is limited and I am learning while doing it.

Could you further clarify ?
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Re: Power transformer wire grouping help

Post by davemojo »

davemojo wrote:
Fri 03/12/21 5:05 pm
geoff 1965 wrote:
Fri 03/12/21 3:23 pm
get a 2W 220K metal film resistor so you can add a bleed to the dual can capacitor,for safety this bleeds the voltage from the capacitors to ground when you switch the amp off.
ahah ok here I need to understand what do you exactly mean by adding 2w 220k metal film resistor.

Where do I exactly need to put it :-) ? Please? As you may understand my knowledge with electronics is limited and I am learning while doing it.

Could you further clarify ?
I have used so far in general in this build carbon composite resistors, but other mentioned that it means noise. However the original was built with carbon composite, so question is how true and how bad is the noise you get?

I am sure it depends also on how well is the amp built and what specific technique are used to reduce the noise.

It seems that film resistors are better choice, maybe on my next build I'm going to use metal resistors.
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Re: Power transformer wire grouping help

Post by geoff 1965 »

https://18watt.com/files/JMPGuitars_18_ ... Layout.pdf
have a look at this layout,the 220K goes between the first positive and negative lugs of the 32/32uf capacitor.negative goes to ground so when you switch off the voltage stored in the capacitor bleeds off.
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Re: Power transformer wire grouping help

Post by davemojo »

geoff 1965 wrote:
Fri 03/12/21 5:48 pm
https://18watt.com/files/JMPGuitars_18_ ... Layout.pdf
have a look at this layout,the 220K goes between the first positive and negative lugs of the 32/32uf capacitor.negative goes to ground so when you switch off the voltage stored in the capacitor bleeds off.
Very easy cool got it. In other words is going to discharge that capacitor off to the ground, got it ! Thanks
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Fri 03/12/21 5:48 pm
https://18watt.com/files/JMPGuitars_18_ ... Layout.pdf
have a look at this layout,the 220K goes between the first positive and negative lugs of the 32/32uf capacitor.negative goes to ground so when you switch off the voltage stored in the capacitor bleeds off.
Would this kind work? Metal Oxide 220 kOhm that is what I found at Tonefactory?
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Re: Power transformer wire grouping help

Post by geoff 1965 »

metal oxide will be okay,you want 2 watt rating.
looking at the layout did you notice the difference with the grounds in the mains/power section to the stewmac layout?
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/06/21 2:00 pm
The instructions don’t match the schematic,
The blue & orange wires are’nt used so either cut them short and seal the ends with heatshrink or solder to an unused isolated tag.
Black is mains negative and white is mains positive “240V”
Ez81 rectifier filament are grey & pink,
The yellow and green/yellow are your centre taps for the heater filament and HT so they are soldered to ground at your star ground point.
Sorry more questions, since I fee unsure:

In my case now I must run the black wire to the mains switch and the white toward the fuse holder which is than bridged to the power inlet, correct?

See picture to check what I exactly mean since the power transformer leads are not matching what I am following as a guide
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/13/21 8:30 am
metal oxide will be okay,you want 2 watt rating.
looking at the layout did you notice the difference with the grounds in the mains/power section to the stewmac layout?
The resistor is 2 watt. In stewmac the ground is on the 3 lugs ground attached on the corner of the power transformer and this is how I did it, so I guess I should run the wire from the capacitor can to this 3 lugs ground, or shall I attach a ground on the V6 pot on the screw nut?
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Re: Power transformer wire grouping help

Post by geoff 1965 »

add a pic of your mains socket & fuse,first you need to determine the orientation of the mains lugs i.e. which is positive and negative,also if you have a solder lug i would ground the mains socket seperately close to its mounting.
been trying to find any feedback on this stewmac with no success,i don't have the tremolo circuit in either of my amps but i know from watching other builds you have to be very careful with both grounding and lead dress or you will have problems.
transformers can vibrate so the mounting bolts are not ideal grounding points,as a rule the preamp & pots ground seperately close to the input jacks,the power section/transformer centre taps/dual capacitor have a star ground point and the mains input has a seperate grounding point.
you have to be careful working from layouts
Last edited by geoff 1965 on Sat 03/13/21 10:56 am, edited 1 time in total.
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/13/21 10:38 am
add a pic of your mains socket & fuse,first you need to determine the orientation of the mains lugs i.e. which is positive and negative,also if you have a solder lug i would ground the mains socket seperately close to its mounting.
been trying to find any feedback on this stewmac with no success,i don't have the tremolo circuit in either of my amps but i know from watching other builds you have to be very careful with both grounding and lead dress or you will have problems.
As you can see the black and the white are the mains one is positive one is negative. Not sure which one is which.
at this point looks like the black goes to mains switch and the white goes to fuse holder and from there with a jumper to power inlet.

I also ran the yellow from stand-by switch to pin 3 of V6. In addition one more wire a jumper from lug left on mains switch down to the other lug of the power inlet.
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Re: Power transformer wire grouping help

Post by geoff 1965 »

i would run a wire from the negative mains lug to the tag pointed out on pic,then you wire one of the pilot light leads and the black transformer wire to the same tag. if you move the other tag strip to the cap mounting bolt "see pic" you can use that as your star ground point.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/13/21 11:36 am
i would run a wire from the negative mains lug to the tag pointed out on pic,then you wire one of the pilot light leads and the black transformer wire to the same tag. if you move the other tag strip to the cap mounting bolt "see pic" you can use that as your star ground point.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
Thank you, I am getting a little lost :-( I didn't realize that the power transform wire were different , I thought they would be all the same color for all power transformer versions.

Now I can do what you said but this will change everything else and will not allow me to continue on my own.

I need to understand the black and the white on my transformer to what stewmac color do match? In order to try to continue using that same schematic.

I noticed that all USA schematic have the power transfer colors do not match the power transformer I bought here at Tonefactory

Is the way you proposed better technically speaking?
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/13/21 11:36 am
i would run a wire from the negative mains lug to the tag pointed out on pic,then you wire one of the pilot light leads and the black transformer wire to the same tag. if you move the other tag strip to the cap mounting bolt "see pic" you can use that as your star ground point.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
Ok I understood the way you proposed is actually a different method to achieve the same.

However the white wire on my PT is the 240v which is basically what stewmac has in black/white 120v which basically is not matching or they have the black/red which is the 240V, so in other words the white is the match for the black/white or red/black in stewmac, so based on that I can follow that schematic.

I understand your point, for you it may be very easy for me isn't strugling a lot, so... let's hope I can make something working fine :-)
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Re: Power transformer wire grouping help

Post by geoff 1965 »

the confusion is just different wire colours on the PT, if you wire the negative like shown it will be good.then you can wire the positive lug to the fuse holder lug as shown "in red" then from other fuse lug to the power on/off switch,when you run lengths of ac wire push it into the corner of the chassis tight around then up to the switch.then you can wire the white transformer lead and second pilot light wire to the second switch lug.
the unused blue & orange wires can be cut short and soldered to the isolated tag "see pic" and you can earth the mains with a lug at point shown "green"
this is just helping you with mains/PT wiring and relocating the ground points is good practice,it won't affect the rest of the build but it's up to you to decide.
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