Output transformer issue

[blindboybenton]

Hi

I did post this yesterday, I think the title is not getting the interest. so ive posted another

Im new to valve guitar amp repair., but not new to electronics. Have decided that i would like to learn. I am aware of the high voltages I do have some test equipment inc a scope and a sig gen
I have been given a old british carlsbro cs40-60 mk1 with valve rectifier to learn on. The amp had been gutted to be rewired and never done
Ive started to rebuild and i have come to a stop point. Unable to find a schematic online. not for this model with the valve rectifier
The output tx primary has 2 x red wires soldered together ( ct ??)
and 2 white wires and 1 brown and 1 blue
Multi meter on the reds
white wire = 20ohm
white wire = 47ohm
Blue wire = 41ohm
Brown = 18ohm
If i disconnect the reds and measure interdependently one red is connected to the 2 whites and the other red is connected to brown and blue
with the same resistance than above. All the wires look like they have been soldered on to something. This amp was working before my friend gutted it
The secondary has 3 wires Ground/4ohm/8ohm

All the schematics i look at have 3 wires for the primary?? Right

can anyone help

[pdf64]

A good course of action is to feed a test signal into the secondary and then map out what appears on the primary; polarity (with in respect to the input signal) and voltage, between all points
After a while, in conjunction with the resistance measurements, it will become clear how the winding is arranged.
It may be simpler to separate the connection between the 'reds' and approach it as 2 independent windings.
It may be an ultra linear type transformer; there may be some marker / trace to differentiate the 2 white wires. Examine them very closely, the marking may have faded.
See p4 http://www.mif.pg.gda.pl/homepages/f...k/KT66_GEC.pdf
Pete

[eschertron]

Just a SWAG, but it seems that the primary side has ultralinear taps, not uncommon in PA amps. Measure all the wire-to-wire resistances and chart them out. There aught to be identifying marks on the two white wires (stripes or etc) to keep them apart, otherwise you're bound for confusion! Since 20 ohms is 43% of 47 Ohms, and 18 ohms is 43% of 41 ohms, I'm hypothesizing that the taps are 43% of the way from red (CT, you are correct) and the terminal white or blue wires. Measure to be sure of your readings. If you are building a guitar amp and starting from scratch, you might want to ignore (tape off) the 43% taps since guitar amps generally are NOT designed for ultralinear operation. Then you will have the 3 primary wire taps that you'd expect on a guitar amp OT.

edit: Pete beat me to it!

[Mick Bailey]

Is yours like this;

Servicing a Carlsbro CS40-60 PA Amplifier

[blindboybenton]

Is yours like this;

Servicing a Carlsbro CS40-60 PA Amplifier

Hi mick

yes it is, But no schematic on his site?

bassman1965

[Jazz P Bass]

Carlsboro schematics: Carlsbro Amplifier Vintage Wiring Diagrams

[blindboybenton]

many thanks jazz bass. But this site has no schematic for this model on this site
Ive checked them all and all have 3 wire primary side output tx. He has some pictures of this amp but none any clear wiring.
My friend has emailed him as he use to work at carlsbro,

bassman1965

[blindboybenton]

Just a SWAG, but it seems that the primary side has ultralinear taps, not uncommon in PA amps. Measure all the wire-to-wire resistances and chart them out. There aught to be identifying marks on the two white wires (stripes or etc) to keep them apart, otherwise you're bound for confusion! Since 20 ohms is 43% of 47 Ohms, and 18 ohms is 43% of 41 ohms, I'm hypothesizing that the taps are 43% of the way from red (CT, you are correct) and the terminal white or blue wires. Measure to be sure of your readings. If you are building a guitar amp and starting from scratch, you might want to ignore (tape off) the 43% taps since guitar amps generally are NOT designed for ultralinear operation. Then you will have the 3 primary wire taps that you'd expect on a guitar amp OT.

edit: Pete beat me to it!

Hi There

Thanks for the reply Sounds like Ill use the 2 x reds as CT and one white ( 47ohm) and one blue wire ( 41ohm) I had a feeling thats what i needed to do
Im going to see if a conversion to guitar amp. instead of pa

[blindboybenton]

Many thanks for the info

There are no more marking on the white wire. looking at the pdf ill try it using the 3 wire standard wiring
2 x red as CT and one white (47ohm) and blue wire ( 41ohm). Should this work ok in your opinion

bassman1965

[eschertron]

Many thanks for the info

There are no more marking on the white wire. looking at the pdf ill try it using the 3 wire standard wiring
2 x red as CT and one white (47ohm) and blue wire ( 41ohm). Should this work ok in your opinion

bassman1965

For a push-pull pentode circuit, the ultralinear taps connect to the tube's control grid (screen). Without taps, as in guitar amps, the screens are connected to B+. In modern designs (and for many rebuilds and clone circuits) a dropping resistor is added in series with the screen for overcurrent protection. from an electrical standpoint, this "mod" is easy to do and bulletproof. Don't sweat the OT connections.

You've said that you don't have a schematic for this amp, and that it's been gutted. Do you have a drawing to use for your project? Do you have any info on the PT voltages and current capacity? Power tube complement, etc? This could be a very exciting project... be sure to start out armed with the info you need to finish! And good luck

edit: I see the drawings from the website, using 1k Ohm 2W resistors on the screens. That'll be what you can do.

[eschertron]

On the Carlsboro page there's a link to this Ultralinear Bass Amp with the 2xEL34 power tubes and a tranny like yours. Similar to what you have?

[blindboybenton]

Well the plan is to turn it into a carlsbro 50 top. i use to own one years ago it was a good amp. I have made the Tag board and was busy assembling when i came across this problem
the only thing that i want to keep is the valve rectifier. once done i may fit a line out

The schematic below for any thoughts and changes you may recmd

Carlsbro 50 Top Amp Schematic

Bassman1965

[blindboybenton]

Hi All

Ok the story of this amp continues

In short im converting a carlsbro cs60 mk1 to a carlsbro 50 top. as i use to own one years ago and i loved it

Im trying to get it working without too much help so i can learn more ... make sense too me

I have the board in the chassis all wired up and its sort of working

1 have a few questions
1. My tx only has 4ohm and 8 ohm tap. Does it make a different where i connect the negative feedback too ? If not connected whats sort of issue will i get?
2 I have not brought the tone circuit parts yet so i have bypassed them for a bit until all working.

This is how ive done this V1 has a 0.047uf connected too it then a 100k. Ive connected the 100k directly to one side of the volume pot

Whenever im testing the volume control is working!!

Carlsbro 50 Top Amp Schematic

I will post some more info tomorrow if not sorted

Bassman1965