Greetings.
I bought a Jim kit from tubetown, I've almost finished it, and now I just realised my speaker cabinet has an impedance of 4 ohms, I don't have a lot of understanding on electronics, so I wold like to know if I can use this 4 ohms speaker with the Jim amp, by wiring the output transformer in a different way than showed in the diagram.
Thanks, and sorry for posting in English.

Hi,

Originally it is wired with yellow/black on the secondary to get 5k ist o 8R. To keep the 5k seen on the primary with 4R, you need to take the green/black wires on the secondary instead. Then you're fine.

Cheers,
Laurent

Thank you so much for your help. :topjob:
Greetings from Switzerland .

Salut!!

Just another question...
I,ve been wathing this diagram:

Hammond 125 BSE:




I was wondering if I could wire as output, all the 3  ¹/4 sockets each one with its own impedance like this:






Thanks In Advance.

Hi,

Works.

Cheers,
Laurent

Thank you ! :topjob:

Just ensure that you use only one at a time...so connecting a 8 AND a 16 Ohm Box doesn't work, it's either one

Ok, I understand that.
Thanks
Cheers.

Greetings.
I just finished the assembly of my tube town Jim amp kit.
I fired it up with my guitar hooked up and a 4 homs speaker at the output, for this I used the green /black wires from the hammond OT. and it worked.
This is my first tube amp build, I really love the way it sounds, however I steel have a few questions:

I turned all the knobs all the way up except the master, and it doesn't distort a lot, I was waiting far more distortion... Then I decided to measure all the voltages marked in the diagram for comparing and they don't match...

I need help

The red values are my readings from the spot in the diagram to the ground in the chassis, all the tubes in the sockets, my guitar at the input and a 4 homs speaker at the output:




Can anyone tell me if these values are acceptable.

Thanks in advance.

Paulo

Hi!
All these voltages are looking really low in comparison to the given values for me.
Did you measure the heater voltage with the AC function of your Multimeter? If you didn't, this would at least the reason for the over 50% to low measured heater voltage.
Maybe it could help, if you would give a picture of the power supply. Which mains voltage do you have, and which transformer primary did you connect?
Good luck,
Rattle

Hello RattleHead, thanks for your answer.
For measuring the heather, I used the AC reader.
I Live in Switzerland, main voltage here is 230 v  I think...., I used the violet and black wires from the primary of the power transformer.

Some pictures:

Power supply:





General view:





Thanks.

Hi,
it looks to me like you did not connect pin 4 and 5 (marked blue) of the preamp tubes (marked red).
This could be the problem for the heater voltage issue.
The rest is ard to check, because there is no layout PDF of the Jim online, only the schematic.
Rattle

Sorry for the huge pictures...
In fact those pins are connected, I ve bent the wire and soldered them together this way.
Thanks for your help, guess I have to debug it all starting from the power supply.
Thank you.

Greetings.

Paulo

I have to ask this: the original values in the Jim diagram were measured with the tubes plugged in, or without the tubes?

Thanks

The values only make sense with tubes plugged in. You wouldn't read anything at the cathodes without tubes ...

According to the very low heater voltage: did you measure to ground or between pins 4/5 and 9 at the tubes? The latter is the right methode.

Cheers
John