Output transformer for 18watt

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bagudan

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Joined 2010
#1
Hi. I´m building my third amp. An 18 watt clone, based on the layout from ceriatone:

http://ceriatone.com/images/layoutPic/marshallLayout/18Wceriatone.jpg

The OT wires on the layout are blue, red and brown! The blue and brown wires goes to the powertubes, and the red one goes to the big cap.

Well, My OT has brown, red and white wires? (IGOT-M18R)

The brown is B+ according to the datasheet, and the red and white are anodes?

My guess is that I´m supposed to solder the brown wire to the cap, and the two anodes to the powertubes.

But the colours have me a bit bit confused, and the technology og the output transformer in apparantly a bit out of my league?

Can anyone point me in the right direction?

Thanks in advance
-Kasper
 
#4
Where did you buy the transformer? Can you direct us to the data sheet?. I would not guess the same as you, in fact I would assume that the red was still the center tap of the primary of the output transformer and therefore should go to the cap. If you have an ohmeter you should be able to measure the transformer primary and at least decide which is the center tap. This could be be kind exciting if you get it wrong. If you get the two other wires on the wrong tube it will not go boom, so you need to find the center tap.
Also Ceriatone does not provide schematics which is I believe a busness decision. A very good learning assignment for you would be to sit down and draw the schematic from the layout. Or perhaps someone else has it posted online.
 
#7
#9
Set to ohms. This is going to be very low resistance so just clip the leads together and make note of how close your meter reads to zero ohms. Most of the time it will be like a couple of ohms because of the lead resistance. Then go between any two of the primary leads. The resistance between the center tap and either of the two outside leads should be 1/2 of the resistance between the two outside leads. Does that make sence?
 
#11
resistance between brown/White: 133 ohms
resistance between brown/red: 136 ohms
resistance between red/white: 268 ohms

This means that the brown wire is centertap, right, and it is supposed to be soldered to the cap, and not one of the powertubes?
 
#15
hey-Hey!!!,
Twist two of the secondaries together. The primary inductance will likely give your meter fits when it applies voltage for the Ohms test. Shorting the secondary means all it will have to deal with is the *MUCH* smaller leakage inductance and the reading won't be jumping around all over the place.
cheers,
Douglas
 
#17
bagudan said:
Ok, I´m a bit confused now. Are you saying that my readings are done the wrong way? Should I twist two wires and then measure from them to where? Sorry I´m such a beginner at this 😉
Click to expand...

You want to measure the primary to confirm where the center tap really is. The primary's inductance will likely mess with the meter, so you short the secondary to eliminate this issue.
cheers,
Douglas
 
#19
Bandersnatch said:
You want to measure the primary to confirm where the center tap really is. The primary's inductance will likely mess with the meter, so you short the secondary to eliminate this issue.
cheers,
Douglas
Click to expand...

I'm not sure I follow? 😕

All we're looking to figure out is the DC resistance of the primary,which he did. From there we can deduce the winding ends and center-tap.

The primary's inductance may be an issue in an impedance measurement,but he was only checking resistance..whether the secondary is shorted or not should make no difference on the primary's DC resistance.

Or am I missing something? 🙁
 
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