Replacement Transformers

[hywelg]

YEs it is possible, but they would have had to wire the red/yellow and red/blue incorrectly. Heres what I measured

Red-red 21.7 ohms Spec sheet says 20.15 +- 20% so Ok there
Red 10.2 red/yellow 11.2 red
Red/yellow 2.2 red/blue
Red 12.5 red/blue 9.2 red

So it seems red-red/yellow-red is better balanced than red-red/blue-red so that makes me question whether they have mis-wired it or not. I think not. But then why the voltages ????

[rp]

I think not.

It's unlikely, especially with a big shop like Hammond, but not impossible. I would take a break come back in the morning and quadruple check, then call the supplier.

http://audiokarma.org/forums/index.php? ... er.536576/

[JazzGuitarGimp]

YEs it is possible, but they would have had to wire the red/yellow and red/blue incorrectly. Heres what I measured

Red-red 21.7 ohms Spec sheet says 20.15 +- 20% so Ok there
Red 10.2 red/yellow 11.2 red
Red/yellow 2.2 red/blue
Red 12.5 red/blue 9.2 red

So it seems red-red/yellow-red is better balanced than red-red/blue-red so that makes me question whether they have mis-wired it or not. I think not. But then why the voltages ????

At face value, I agree. But, and I probably should have iterated this in my original post, unless you are using a high-dollar meter, AC Voltage measurements will always be more accurate than low-ohms resistance measurements.

[hywelg]

Tomorrow I'll swap Red/yellow for red/blue and see what I get.

[hywelg]

I swapped the red/yellow CT for the red/blue Bias and I get very little difference in the voltages 257-0-315, 28v tap against 256-0-314 , 22v tap. This is unloaded, wires disconnected from rectifier, CT connecting through fuse to ground.

[martin manning]

That seems to leave little doubt that the transformer is defective.

[hywelg]

Dohhh.

Since I had checked it a while back (whilst troubleshooting the old PT) I made an incorrect assumption. I was double checking everything to try and prevent me looking an utter fool, and I found the fuse on the CT had blown.

Replaced it and now my unloaded voltages are bang on. Unconnected to the rectifier though so I might yet find a problem there thats causing the fuse to blow, but we'll see.

[martin manning]

Well, progress, anyway... The CT fuse might have been taken out by a shorted rectifier, so be prepared for that, or just replace the rectifiers. Cheap insurance.

[rp]

Told you to try fresh in the morning. BTW if this is a Hammond and it has a CT for the 5V - don't connect that.

[hywelg]

Update.

Getting 337 at both HT connections. 61.7v Bias. But going off standby blows the CT fuse. This is different to first run after fitting the PT, then the fuse held up long enough to allow me to set the bias to 38mV, flip the amp over to start checking voltages, and by then the fuse had blown giving me the weird unbalanced voltages.

This is getting a bit beyond my knowledge level so its off to a tech tomorrow who'll probably find the problem inside 10 mins!

[rp]

I've had a Ceriatone OTS 50w for about 8 years now and the PT has gone bad. Continually blowing fuses.

quickly looking back, didn't you replace the pt as you were blowing fuses with the original? maybe problem was never the pt??

why does everyone always think they have a blown transformer? when their car breaks down do they think they blew the engine?

[martin manning]

If you can power it up and the fuse holds on standby then the rectifiers are ok. After switching to play it previously held long enough for you to set the bias, right? It's possible that the HT fuse was a random failure, or it is just too small, implying it was barely adequate before the PT swap. What amperage is (was) the one that blew?

[hywelg]

I've had a Ceriatone OTS 50w for about 8 years now and the PT has gone bad. Continually blowing fuses.

quickly looking back, didn't you replace the pt as you were blowing fuses with the original? maybe problem was never the pt??

why does everyone always think they have a blown transformer? when their car breaks down do they think they blew the engine?

No it was defintely the transformer. Absolutely nothing connected to the secondaries would blow a fuse or light up my bulb limiter with vigour. No question it was bad. And they do have a bit of a reputation aparently.

[hywelg]

If you can power it up and the fuse holds on standby then the rectifiers are ok. After switching to play it previously held long enough for you to set the bias, right? It's possible that the HT fuse was a random failure, or it is just too small, implying it was barely adequate before the PT swap. What amperage is (was) the one that blew?

Previously Martin it would blow the 2a/240V SloBlo mains fuse very rapidly simply by turning the mains on.

This time it is blowing the Secondary CT 0.5A FastBlo fuse and only when I go off standby. But as I said it didn't blow on first power up I was off standby for 3-4 minutes letting it warm up and setting the bias. Then I powered down, flipped the amp over, powered up amd started testing the dropping string. At this point I found the mismatched voltages and never even thought to check the CT fuse.

[martin manning]

If it was running off standby for several minutes and there was no smoke, then I would be inclined to put a bigger fuse in, or at least 0.5A slow.