D4910 transformer / looking for 1974x owners

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

Moderators: CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

Post Reply
gi097
Unrated
Posts: 3
Joined: Sun 02/27/22 11:28 am

D4910 transformer / looking for 1974x owners

Post by gi097 »

Hello,

I am working on an 1974x clone as I managed to get my hands on a pair of original Dagnall transformers. I am rebuilding/cloning the circuit from the 1974x by looking at pictures of this amplifier and schematics. It's the second amplifier I am building.

Now I started on the OT connections, but the OT is missing data about the wire colors and AFAIK there's no datasheet of it online. (It's the Dagnall D4910).

The following wire colors are on it:

- Brown (screen for V4 by looking at pictures)
- Red (screen for V5 by looking at pictures)
- White (not sure, but I think it's connected to B+ 16uf+32uf cap)

Then I am stuck with the following wire colors and they all seem to go to the output jacks/impedance selector:

- Green
- Yellow
- Black
- Orange

As I don't have my hands around an original 1974x, I am hoping somebody here has one who can take a look where the wires are supposed to go?

I am aware I can measure the transformer ratio's by connecting a low voltage source to the screen wires and measure the voltage from the remaining wires and center tap. I am a bit scared to do so, since I don't even know what wire the center tap is. Hopefully somebody can help me out, thanks!

Image
Image
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 3954
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: D4910 transformer / looking for 1974x owners

Post by JMPGuitars »

Measure the resistance of your OT primaries. Two wires connected (for example, red + white), may be the same as 2 other wires connected (for example brown + white), but will be half as much as two other wires connected (for example brown + red). My examples are an assumption based on your assumption, but may not actually reflect the correct pairs.

Whatever combination has the highest resistance are the outer wires of the primary. The 3rd wire is the center tap and goes to B+.

Thanks,
Josh
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright

Modern Ground Schemes
Soldering Technique
B+ Voltage Reduction
Amplifier Tools & Parts Info


Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: D4910 transformer / looking for 1974x owners

Post by Bieworm »

The secondaries 'might' resemble the Hammond 18W OT. They're the same colors.. maybe they're alike
1750PA.pdf
You do not have the required permissions to view the files attached to this post.
1 x
"THIS should be played at high volume..preferably in a residential area"

Post Reply