64 Revererocket Mercury OT upgrade

[64verberocket98]

Hello. First thank you for any help you can provide. I am posting first. Searching second. I am so bummed right now it's not good

Recently I decided to upgrade my 64 R12-R OT with a shiny new Mercury OT-151 (i believe) verified with them. They're super nice btw. Recommend them. But things went wrong.

I followed the schematics and compared it to the Amps original schematic for the secondary side. It shouldn't matter which of the green and black leads go to the speaker and chassis. The original had an outside black and inside green running to the speaker and vice versa going to the chassis. Merury's schematic places both outside green and black leads to the speaker. Which is what I did do. I have continuity through the new OT to the chassis ground and on the positive side respectively.

I also clipped my original leads inside the chassis with a touch of sheath left behind before removing the old one from the circuit. Thus to be certain I re-connected in the proper places. I then replaced wiring one by one. This is just a sanity check but should keep you from making a mistake on something simple.

For the primary side the red wire goes to the diode network fed from the PT and the brown and blue go to pin nine on the output stage respectively.

I have double checked it and tried again.. When I turn on the amp the tubes warm properly and do not blue or red plate. Things look good. But after about 30 seconds. It begins to make this horrible low frequency noise and I pull the power.

At this point I have tried three times. I am afraid to move forward as I don't want to fry anything else. Is this a common issue? If not.. I will call my tech (but I am a tech...) Or could I have a bad OT?

Also for piece of mind, I have thoroughly inspected the chassis to ensure I didn't fold over a component or break another connection several times to no avail. I even tried a different set of pre-amp tubes (that third and last time). Super bummed.. I had the amp playing last night pre install no problems with the tube compliment I used today.

[Liquids]

Bummer man. A fairly amatuer suggestion here - did you try flipping the primary or secondary transformer leads around...? Or disconnect any negative feedback temporarily to see how that affects things? Keep a REAL careful eye on it for sure if you DO flip and fire it up. Ideally use some older tubes you care little about--or get some, for troubleshooting, if possible.

It sounds like oscillations or 'motorboating' of some kind develops, though the symptoms are a little weird for it to be just reversed transformer leads I think, despite my suggestion. So even if that doesn't fix it, you'll be more certain that the transformer is wired properly, if you give that a try, if nothing else. It seems logical to start with stuff surrounding the transformer given that it's what you replaced...rule it out or otherwise.

Steve/Hangman or others will likely have better input though.

[Hangman]

Liquids is right on.

The feedback is only negative feedback if connected to the proper side of the transformer. otherwise its positive feedback, which is a good way to have an oscillator, but not helpful for a guitar amplifier.

your intuition that it "doesn't matter" what the polarity of the speaker is, is not unfounded, the ear won't hear a difference, but if you didn't hook up the feedback wire to the right side... then it does make a difference to your amp.

Bummer man. A fairly amatuer suggestion here - did you try flipping the primary or secondary transformer leads around...? Or disconnect any negative feedback temporarily to see how that affects things? Keep a REAL careful eye on it for sure if you DO flip and fire it up. Ideally use some older tubes you care little about--or get some, for troubleshooting, if possible.

It sounds like oscillations or 'motorboating' of some kind develops, though the symptoms are a little weird for it to be just reversed transformer leads I think, despite my suggestion. So even if that doesn't fix it, you'll be more certain that the transformer is wired properly, if you give that a try, if nothing else. It seems logical to start with stuff surrounding the transformer given that it's what you replaced...rule it out or otherwise.

Steve/Hangman or others will likely have better input though.

[Liquids]

64verberocket98 - did you get it working or make any progress?

[Hangman]

Yes, I am also curious how this one ended up. Let us know what happened.