Hi! Who Want's Help Install MMs In My AC15HWH?

[Structo]

Why wouldn't he be able to measure the primary resistance?

His measurements of two of the wires are in the low hundreds of ohms so the blue brown wires should measure around 350-380 ohms.

The Red is the B+ center tap so it should be fairly close to half of the resistance between the Blue and Brown.


You could rig up a low voltageg experiment with a wall wart that puts out AC voltage.

Hook it up then measure the voltage out of the other side.

Be careful though because depending which way you go, you can have high voltage.

[power chord hack]

Email from MM support:

You have to have a circuit to measure the secondary.
Blue to red should measure approximately 194 and brown to red 193 etc.
Have you tried installing it?
My guess is that it is fine.
Thanks.

I like the wall wart idea.
Ha! What about a 9v battery

I will for sure do a light bulb limiter for the initial power up.

Tom - I don't get why there has to be a circuit, either...

[Bob-I]

Email from MM support:

You have to have a circuit to measure the secondary.
Blue to red should measure approximately 194 and brown to red 193 etc.
Have you tried installing it?
My guess is that it is fine.
Thanks.

I like the wall wart idea.
Ha! What about a 9v battery

I will for sure do a light bulb limiter for the initial power up.

Tom - I don't get why there has to be a circuit, either...

A battery won't work, transformers only work on AC. Use an AC wall wart like Alesis uses, or a filament xformer.

There needs to be continuity to complete the circuit.

[KT66]

It doesn't make any sense that there is no continuity between the blue and brown wires if you have it between the red/brown and red/blue, I think you must have made a mistake in your measurement and the unit is fine.

Realizing that you are kind of green, I should have spelled out in more detail how to determine which wires are which with a meter. First, you need to understand what a transformer is - 2 pieces of wire wound around a magnetic core and when an AC current is applied to the primary winding it creates a magnetic field that induces a current to appear on the secondary winding. Connections made somewhere in the middle of the windings are known as taps. SO, you can use an Ohmmeter to determine 1) which wires are part of each main winding by testing for continuity between them and 2) Which wires that connect to each winding are the main winding and which are the taps - you do this by measuring the resistance and the 2 wires that have the highest resistance are the main winding because the longer a piece of wire is, the higher the resistance is going to be. So, the actual "ohms" readings that you get are used to compare to each other to figure out the lengths of the windings parts, but are meaningless otherwise. Hope that makes sense.

Learning about and working on amps is fun, but you really should take the time to learn about what you are doing. Here is a little article on transformers to aid in your education : http://www.radioremembered.org/outimp.htm There is also a lot of good reading here about everything amp : https://tubeamparchive.com/viewtopic.php?t=9023

Also, I hope you are making sure to unplug the amp and properly drain the filter capacitors before attempting any work.

After you complete the swap I would be interested in hearing your thoughts on how it sounds compared to with the stock units.

[power chord hack]

So, the actual "ohms" readings that you get are used to compare to each other to figure out the lengths of the windings parts, but are meaningless otherwise. Hope that makes sense.

OK, I get what a xformer is & does on a rudimentary level but what I don't get, then, is why the taps are called 8 & 16 ohm since... they're not


I guess I should have paid attention in electric shop back in high school

[mlp-mx6]

OK, I get what a xformer is & does but what I don't get, then, is why the taps are called 8 & 16 ohm since... they're not

No offense intended, but your question proves that you do *not* "get what a xformer is & does."

You cannot directly compare DC resistance with AC impedance. Also the purpose (well, *one* purpose) of the xfmr is to reflect the load of the speakers correctly to the power tubes. There is a LOT going on w/r/t the transformer. Transformer science is very complicated. (BTW, I'm not representing myself as an expert either. I think I just have a better grasp of how much I do not understand. )

[Structo]

Impedance is kind of like a moving target.

It is a reactive property having to do with the frequency, voltage and current.

For instance, the primary of a 2 x 6L6 output transformer doesn't measure 4K ohms, but the tubes see that when in operation.

Some call it a reflected impedance.

An output transformer has no impedance by itself (ignoring primary inductance/resistance for the moment, which is a different subject). It simply reflects the impedance load on the secondary back to the primary.

Here is a great article about output transformers.

http://www.aikenamps.com/OutputTransformers.html

[power chord hack]

You cannot directly compare DC resistance with AC impedance.

Where am I doing that?

I'm just trying to figure out why the 8 & 16 ohm taps are called 8 & 16 ohm?

And more to the point, whether the ohm readings I get on my MM unit mean it's OK to install.

For instance, the primary of a 2 x 6L6 output transformer doesn't measure 4K ohms, but the tubes see that when in operation.

An output transformer has no impedance by itself (ignoring primary inductance/resistance for the moment, which is a different subject). It simply reflects the impedance load on the secondary back to the primary.

Ohhhhhhhhh.
OK... the fog is beginning to lift - a bit.