'65 Fender Vibro Champ squel at volume 10 and 1 only

[Chuck H]

there's no excuse for NOT checking something

There! Now it's your quote too

Positively some of the best advice ever given on this forum. And thank you for ringing the bell. Loud and clear is what we do

[Justin Thomas]

I was jokingly gonna say, it only squeals at the extremes of the Volume control but nowhere in between...

Who the heck uses a Champ on "less than 10"?



Jusrin

[cjlectronics]

SOLVED!!!

Y'all were spot on with the wires on the OT backwards. I switched the red and blue wires on the OT transformer and the squeal at 10 and 1 is gone. The amp works great in all settings. I'm going to send CE Distribution an email stating the drop-in replacement transformer for the Fender Vibro Champ is wired wrong. When we buy new parts we expect those parts to be error free and fully functional. No one wants to induce a problem when repairing music gear and when you can't trust the parts to fix an issue you start not trusting the supplier as well. (My rant is over)

@Tboy, I suggest making this issue a sticky so others don't spin their wheels chasing an issue that they had nothing to do with.

Thanks again y'all!!

CJ

[Chuck H]

I suggest making this issue a sticky so others don't spin their wheels chasing an issue that they had nothing to do with.

Thanks again y'all!!

CJ

Done. I was going to put a time limit on the stick, but it wasn't offered as an option. Most here are aware of (and have dealt with) this problem before and are quick to educate others about it. But a temporary stick seems appropriate while this batch of transformers is still being sold. It's probable that the problem will be corrected in the near future.

Can you please post specifics on the OT in question. Brand, model number, etc.

[Leo_Gnardo]

I'm going to send CE Distribution an email stating the drop-in replacement transformer for the Fender Vibro Champ is wired wrong.

Thumbsup delivered for your successful repair.

About CE/Antique/AmplifiedParts, who knows they might have a thousand of those OT's in stock. Plus other parts outfits ... should they scrap them all, or change the insulation color on the ones they have (not too dam' likely), or what. Possible practical solution: maybe issue a paper advisory with every Champ OT they sell?

[Chuck H]

Possible practical solution: maybe issue a paper advisory with every Champ OT they sell?

Or deny that there's a problem and just tell people that it must be because of the amp they're using it in.

[galaxiex]

Mine was a Mojo 771

[Jazz P Bass]

A quick, down & dirty test of the OT polarity with negative feedback:
-Drive the amp to a certain level.
-Measure the output voltage.
-Now disable the feedback path (wire, resistor) while monitoring the output voltage.
-If the output voltage goes UP, then the polarity of the OT primary leads is correct.
-If the output goes DOWN, then the OT wiring is incorrect and needs to be reversed.

[cjlectronics]

This is the transformer I purchased from CE Distribution https://www.cedist.com/products/tran...put-8-w-32-ohm

Looking at the wire diagram for the transformer above, its configured as it is designed which is reversed for the Vibro Champ. So its not an exact replacement, you'll have to switch the red and blue wires if you connect the black wire from the secondary to chassis ground... Note to self, don't assume drop in replacements are true drop-in replacements. Read the datasheet

[pdf64]

But unless you’ve also got the spec for the stock OT, in regard of this issue, the spec of its replacement is of no benefit.

[Chuck H]

But unless you’ve also got the spec for the stock OT, in regard of this issue, the spec of its replacement is of no benefit.

Except that you can often SEE the unit you're replacing in the amp. Since it's typical for replacement transformers to mimic the color codes of the originals we usually assume the same color wires go to the same places if that has been done.

[g1]

Since it's typical for replacement transformers to mimic the color codes of the originals we usually assume the same color wires go to the same places if that has been done.

This went badly for me with a Hammond OT in a Garnet. I would highly recommend against it. Blue, brown, and red apparently don't have the industry standard meaning that I had assumed.
In my experience, it's the single ended OT's that usually have the colour coding phase issues. Maybe the mfgr's assume it doesn't matter because it's single ended, or it's harder to keep track of the phase, I don't know?

[Chuck H]

Oh yeah, it happens all the time. But I only know this because I read about it here. For all the transformers I've ordered, which is maybe twenty five in my life, two had incorrect wire color for their own spec. That doesn't include the blue/brown issue as it applies to OT plate leads. I just take that in stride and always leave enough lead on the first hookup that I can swap them if necessary because you really never know unless you test for phase. So that's an 8% error rate for my small experience not including the common blue/brown errors that I've learned to expect. Both were on OT secondaries. One was a green/yellow swap so the impedances were all wrong. The other was a brown lead where it should have been orange. That ones not such a big deal because there was no orange lead at all and no brown specified. Easy to figure out. But now I always ohm out the windings and scratch my head before hooking things up.