bad transformer?

[otto]

On the reverb tranformer I read on the primary 3.4k-ohm, on the secondary 120 ohm.
Primary circuit is not open because I read the same voltage at opposite sides.
Is it gone or is it ok?

http://www.drtube.com/schematics/marshall/4210.gif

[Enzo]

Not sure what you are asking here. If the primary winding has continuity, that is a good sign. If you are expecting to be able to measure the "impedance" of a transformer winding with a meter, you can't.

[otto]

ok, but reading 3.4k-ohm at the primary with a tester is ok or could it be bad?

[Twist]

It sounds bad to me. Although it may not be the exact reverb tranny, I just pulled a new fender style reverb transformer off the shelf and read 756 ohms on the primary and 0.4 ohms on the secondary. This doesn't tell you the actual primary and secondary impedance. If you have no reverb use your ohm meter to check each side of your reverb tray. Make sure the reverb tray is unhooked from the amp. Also check the continuity of the cables.

[otto]

Look at http://www.hammondmfg.com/124.htm
secondary resistance is above 1 k-ohm
could mine be ok?

[R.G.]

Look at http://www.hammondmfg.com/124.htm
secondary resistance is above 1 k-ohm
could mine be ok?

To tell if a transformer is OK:
1. Use an ohmmeter to measure for continuity of windings - that is, no open circuit windings. Open winding = bad transformer.
2. Use an ohmmeter to find any shorts to the iron or between windings. Shorts = bad transformer.
3. Use the inductive-kick test to eliminate internal shorts. Be very sure that there are no external loads - that is, all windings are open circuit. Then put a 100K resistor in series with a neon bulb (NE-2) on any winding. On another winding, momentarily connect a 6V battery across the winding and open it. If the light flashes, the transformer is not internally shorted. No light = internal short, bad transformer.

This testing only confirms that the transformer is not faulty. The turns ratio, primary inductance, frequency response, etc. may still not be correct for the application, but the tranny does what it was intended to do, whatever that was.

[otto]

thanks R.G.
I don't have the neon for test 3. I made test 1 and 2 and the only strange thing is a resistance on the primary of 3.4k-ohm, but I find similar values in data sheet http://www.hammondmfg.com/124.htm
don't you agree?