identifying leads for 220 VAC European transformer

[kneedeepinit]

I may be using some components of a Grundig 7015 radio for a tube amp build. The Grundig is a German company that sold radios in North America. On the input side to the power transformer are 3 leads - a black, a brown, and a yellow.

The schematics are not real clear so I am doing the detective work.  Between black and brown, I get 10 ohms, between black and yellow, I get34 ohms, between brown and yellow, I get 24 ohms

I am assuming that I would need two 110 VAC inputs in order to get the desired VAC output but which of the 3 input wires is neutral? My guess is that it is the black due to the other wires appearing identical in construction.

Any direction or advice would be appreciated/

[PRR]

Welcome.

I can't read the colors on that image.

The obvious intent is that you put a jumper in one or the other (not both!) of the "-( )-" marks, probably holes in a terminal board and a pin to put in.

But play safe. Apply a 12V or even 6V AC source through 10 Ohms 1/2 Watt to the supposed wall winding. Carefully! measure the secondary voltage (start with the low-volt heater winding). You expect to measure 1/10th of the nominal voltage. (1/20th if you put 6VAC into the 120V winding.) The 10 Ohms should not even be warm.

[kneedeepinit]

Ok, thank you. I was not sure if there were two 110 vac lines to make 220 like in your house.

I can read the one color as black. That is the top one. I assume the other two wires are for 110 vac input or 220 vac input. I think the middle one reads "red" which would be the brown one which has faded from red after 50 years. That would be the 110 vac

I am going to buy a 110 vac to 12 vac adapter and check.

I think this would work for a minimalist 18 watt with the bridge rectifier. The voltage of 275 vdc is low but it was based on 110 vac input. My house has 120 vac so that extra 10% gets it close to the 300 vdc i need. I might reuse the one from the radio or just spend a few dollars and buy a new one. The old one looks pretty cool as it looks like a capacitor can.

[PRR]

> the brown one which has faded from red

OK.

I found a similar model, with more primary choices, selected by fuse position.

> a minimalist 18 watt

It is already a one-EL84 amp, so you are halfway there.

It has about 39mA(!) of tuner stuff, which you don't need. Apparently the total B+ drain is 66mA-77mA. This is a hair shy of what a two-EL84 is liable to draw in 18-Watt setup. The Philips data for EL84 at 17W out is 114mA for the two EL84. Add several mA for small bottles, you are way over the intended 77mA max current. Even at 80mA idle you are one toe over the edge (and what good is an 18W that only idles?).

If you have the OT, I would just build it as a one-EL84 SE amp, a Euro-Champ. Similar 5W-6W output, which aint 18W, but is plenty for many tasks.

[DummyLoad]

found a bit more legible copy: see attached. 


- it says from top to bottom:


Primary
BLACK  - 0V
RED - 110V
GRAY - 220V


Secondary
BLUE - 0V
BLUE - 6.3V


Secondary:
PINK - BRAC1
PINK - BRAC2


--pete

[kagliostro]

I've find one other schematic that is more readable (but splitted in two parts) labeled Grundig Majestic 7000 USA

here is the PS section (I cut out)



Colors agree with Pete's schematic

Franco

[kneedeepinit]

thanks guys. I have the answer now but it was not what I hoped for. Given the limit to one EL84 SE design, this may not be a good basis. I have built a Fender Champ and a Deluxe (5E3). I was hoping to build a Marshall 18 watt because it has a different sound than the other two.

I was looking to build a low power amp (bedroom use only) that could achieve the distortion typical of 70-80's rock. I don't need 18 watts as 2 is probably sufficient but the attraction to the 18 watt was the amount of information available. It has the sound I was trying to achieve.

[shooter]

It has the sound I was trying to achieve.

so build the preamp for "the sound", and run it into a single 84 running at 110%, highish B+, you might be happy!

[kagliostro]

Not sure about the exact model you have


on the schematic I've find (Majestic 7000 USA) they say B+ 280V @ 80mA


Franco

[kneedeepinit]

It has the sound I was trying to achieve.

so build the preamp for "the sound", and run it into a single 84 running at 110%, highish B+, you might be happy!

this is an interesting concept. I wonder if this might work



link to the build at : http://chasingtone.com/dvnator/the-seplex/

[shooter]

I wonder if this might work

you might be ok with tube current, but you also gotta watch filament current, that 34 draws about 2wice an '84

[92Volts]

you might be ok with tube current, but you also gotta watch filament current, that 34 draws about 2wice an '84

You could probably get away with a 6L6 since there are fewer preamp tubes than the original design (with tuner) and it's only 0.2a more than the EL84. Another option could be dual 6V6s and you can remove one to decrease power.

[sluckey]

It will work if you replace that EL34 with an EL84.

[kneedeepinit]

I have 6L6, EL84  and El34 tubes. I think this might be a neat project.

Thank you