Output transformer question (Valveking head)

[razaretcha]

Hello,

to improve the tone of my Peavey Valveking head, I read that changing the output transformer can make quite a difference.
The valveking mod site suggests that the original OT could be replaced with one of these:
-Weber WOT100HHR
-Weber WOT100LHR
-Heyboer HYOT100
Now, since I live in Germany, shipping would cost me crazy $100+, thats more than the transformer itself. I'm obviously not going to pay for that.
So I just bought one I could find on ebay, and as usual, I tend to act first and think second.
I bought the Hammond 1750U (which usually goes in JCM 800 amps).

Those three output transformers I listed up there all have a primary resistance of 1900 Ohms. The Hammond 1750U has only 1700 Ohms, so my question is: does it work anyway or did I buy the wrong thing?

And if anyone of you could possibly help me understand what this primary resistance actually does, I would be forever grateful

Oh, and I know the cap isn't self-draining and it could kill me, so you don't have to warn me here

Thank you very much in advance!

Best wishes,
razaretcha

[ScottMarlowe]

That's a 10% mismatch, which shouldn't cause a lot of problems. Just keep it at 8/10 maybe on master volume and you should be OK.

[Enzo]

And that is a primary IMPEDANCE, not resistance.

[razaretcha]

Yeah, I wrote impedance at first, but then thought it was wrong
Anyway, I don't usually turn up the volume that much anyway so if you say it'll be fine, then that's great!
I just hope the transformer is worth the effort
Thanks a lot!

[Enzo]

Before you do that, try connecting the amp chassis to other speakers. A speaker swap is by far the single most effective way to change the tone of an amp.

[KTB]

The transformer will likely sound close to the same until you get to power-tube distortion then it could have some mojo. The two main things that alter tone is the preamp section including the voicing and the quality or combination of preamp tubes and the speaker type and wattage rating then the OT and power tubes then the power transformer and the design of the power supply and voltages distribution circuit.

[razaretcha]

Alright, so the transformer arrived. I had to file it a bit because the mounting brackets wouldn't fit, but now it works.
So, I figured out which color goes where using this little guide:
https://ultimate-guitar-valveking.wikis ... nformation

Green 16 Ohms - Orange pin (inside the amp)
Yellow 8 Ohms - White pin
Orange 4 Ohms - Green pin
Violet - black

Now, the transformer has a blue, a red and a white wire for the primary winding. The old one had red, blue and brown. So, if I'm not mistaken, my white cable must be plugged into the brown connector, right?

Oh, and one more thing: the transformer has the cables on different sides. I could stuff them inside the iron core (is this correct?) and pull them out on the other side so that I can push them through the amp's hole. Would this affect the magnetic field of the transformer negatively?
I uploaded a picture.

Thanks in advance!

[Enzo]

Didn't your new transformer come with a data sheet that included its wiring?

You have three primary wires? Verify they are all connected together with your ohm meter, just to be sure. Now with three wires, there are three combinations of two. SO measure resistance between each pair of wires - that is three readings. I have no idea what resistance you will find, but you should find two lower readings and one larger that adds up to the other two. The two lower resistance ones might or might not be the same, but assuming they are, you will get three results like 50-50-100 or 25-25-50 or 100-100-200. See the pattern? The two with the highest resistance are the two plate leads - what is now blue and brown on your amp. The third wire will go to B+ power supply, and is red on the present transformer.

[razaretcha]

Allright, I got it working. Thank you very much for your help!
The amp sounds awesome now, but I have a really loud hum through my speaker. Removing the speaker cable eliminates the noise, so it can't be the transformer's coils. Anything I can do to change this? Is it the bad, thin speaker cable from my amp?
I know the amp had some hum before, but I don't remember it to be this loud.

[Enzo]

Removing the speaker cable eliminates the noise, so it can't be the transformer's coils.

WHAT??? First NEVER run a tube amp without a speaker connected. You can destroy your new transformer that way. Unplugging the speaker of course makes noises stop - they come out the speaker after all.

Is your loud hum now exactly the same type hum as say touching the tip of a guitar cord? because if you get the transformer primary wires backwards, the amp will howl. By backwards, I mean the two wires going to power tube plate pins might need to swap places.

[KTB]

Check all the connectors and grounds especially speaker jack and make sure they wired right. Big difference between a squeal and a hum. If it's hum it's either ground related or possible mismatched power tubes or reverb wire placement .