Need help finding vintage guitar amp power transformer

[nickb]

Sorry, i got a new power supply to replace the butnt one.

Thats the new supply with 3 wires, from the scematic with the supply it seems their is an option to use half the secondary coil or the full coil.

Please explain what you mean by testing the te4-tr9?
Thanks

TR4-TR9 I mean test the transistors TR4 thru TR9 - just Google how to do it.

You can use a light bulb limiter while you check it out but it won't do much good unless you use a fairly low wattage bulb, say 15W.

[52 Bill]

Hey thanks for the info. I contacted mouser and this is what they said was suitable, the amp was fine before the power supply took a crap, should i just find a correct 2 wire primary 2 wire secondary supply. I didnt realize when it was ordered this was the case I dealt with their tech support and this is wht they sent me. Do we think its just a wrong transformer, or something in the circuit causing the fuses to pop?

I am going to ASSUME that the transformer that they sent to you has a two wire primary and a three wire center tapped secondary.

It would be so much easier for all of us if you would share the facts with us, like what transformer do you have, brand, model, etc.? Which resistor is getting hot?

The original transformer probably failed due to a failure of the power amp circuit. So build a light bulb limiter or you risk damaging the new transformer as well.

[nickb]

Sorry, i got a new power supply to replace the butnt one.

Thats the new supply with 3 wires, from the scematic with the supply it seems their is an option to use half the secondary coil or the full coil.

Please explain what you mean by testing the te4-tr9?
Thanks

By 'Supply' I think you mean 'transformer'? You are going to have to be very clear or this will end in disaster. Please specify the Mouser part number. Thx.

[youredone82]

I am going to ASSUME that the transformer that they sent to you has a two wire primary and a three wire center tapped secondary.

It would be so much easier for all of us if you would share the facts with us, like what transformer do you have, brand, model, etc.? Which resistor is getting hot?

The original transformer probably failed due to a failure of the power amp circuit. So build a light bulb limiter or you risk damaging the new transformer as well.

OK the transformer is a Hammond model 166j20. Sorry I'm not down on the lingo. I figured out what had caused the original transformer failure and the resulting fuses to blow when installing the new one. The voltage regulators, not transformers, sorry my bad on the vernacular here, are not properly insulated from the case. It appears the mica insulation has degraded enough that it allowed voltage to pass from the regulators into the case, which is why it was hot in that area when it was working, and the supply burnt up. With them off the chasis, the amp works and no blow fuse, but it can only stay on for a min or so before the regulators start to smoke, I'm ordering some insulator kits and I will let you know when its all up and running. Should I use a heat conductive compound? I know anything like artic silver conducts electricity but I see they have ones that don't.

Thanks everyone for sticking with me through this. Your insights were very helpful and I appreciate all of your dedication.

[youredone82]

sorry again, upon further inspection it is 2 transistors that are mounted to the chasis, they look like the small 6 V DC voltage regulators we use on the Altec aerial line placers at work. But yea, founf out they are D526 transistors which are a NPN type. So these would short out to the cab when not insulated? or is something wrong with them?

[nickb]

sorry again, upon further inspection it is 2 transistors that are mounted to the chasis, they look like the small 6 V DC voltage regulators we use on the Altec aerial line placers at work. But yea, founf out they are D526 transistors which are a NPN type. So these would short out to the cab when not insulated? or is something wrong with them?

Look at them and read the numbers. You can then use the legend on the schematic to help you identify which ones they are.

[youredone82]

tr8 and tr9

[nickb]

tr8 and tr9

Good - now go test them see post above

BTW, I never heard of the insulation failing unless there was mechanical damage. My guess is you simply disconnected them from the circuit.

[J M Fahey]

Agree and add: those power transistors need mica insulators and thermal grease between them and the heatsink, but micas donŽt evporate into thin air so if they are missing somebody has been messing with them.

As of making a low power Lamp Bulb Limiter: I guess you can get a small "sewing machine lamp" , those are smaller than regular ones, usually around 15W, need a smaller socket but those who have such lamps might also have matching small sockets.
Small lamps are also used in bars, display cases, providing discrete illumination for Art , bedside or overhead illumination, "reading lights", etc, so they are available in many reasonably stocked electricity supply shops, they are no as unusual as some might think.
Also check microwave/fridge lamp:
http://www.ebay.co.uk/bhp/sewing-machine-bulb

[youredone82]

their connected, the amp works, its just they get so hot when they are not able to radiate the heat into the case and dissipate it, they start to smoke. The damage to the insulation must have happened when I removed the potentiometer for the bass, it was rusted up something good from this thing sitting in my dads garage for the last 10 years.

Am I way off here, should these things not get this hot?

[nickb]

their connected, the amp works, its just they get so hot when they are not able to radiate the heat into the case and dissipate it, they start to smoke. The damage to the insulation must have happened when I removed the potentiometer for the bass, it was rusted up something good from this thing sitting in my dads garage for the last 10 years.

Am I way off here, should these things not get this hot?

No, they should not get that hot. If it works and sounds OK, then the idle current is simply too high. Set the trimmer resistor "B200" to measure the lowest resistance across its terminals and then see if the transistors overheat. Ideally, the trimmer is set to get 0.032V across the emitter resistor of TR9. Let us know if you have a problem setting adjusting the trimmer to get that number.


Unrelated afterthought: Is the Reverb tank missing or it never had one?

[g1]

If those 2 transistors have been heating up enough to smoke, it is probably a good idea to replace them with new ones (once you figure out why they are overheating and correct the issue).

[J M Fahey]

Just a suggested work path:

1) get those power transistors bolted back to chassis, where they were originally.
it acts as a heatsink.

2) remember they need to be insulated (not continuity) from chassis, there should be insulating mica and thermally conductive grease between transistor body and chassis.
Maybe (depends on case type) youŽll also need some plastic (nylon type) shoulder washer,so bolt metal does not short transistor to chassis.
I bet those transistors are TO220 case o Japanese equivalent:




please post a couple gut pictures, one showing transitor mounting closeup.

asof the power trnsformer,it is fine provided it has a center tapped 20V secondary, meaning two 10V (the 11V you measured) ones in series,3 wies total.

You use the end to end wires to get needed 20V and tape 10V center tap off because you do not need it.

[youredone82]

No, they should not get that hot. If it works and sounds OK, then the idle current is simply too high. Set the trimmer resistor "B200" to measure the lowest resistance across its terminals and then see if the transistors overheat. Ideally, the trimmer is set to get 0.032V across the emitter resistor of TR9. Let us know if you have a problem setting adjusting the trimmer to get that number.


Unrelated afterthought: Is the Reverb tank missing or it never had one?

Nickb, these units come with a reverb tank but this one is missing, it has the 2 rca style connectors to plug it in, but the tank itself is missing. I want to build one myself but having a hard time sourcing a few of the components, like the actuator that would drive the springs, love some help if you guys want to embark on a project. That is if you dont think my skills are too basic for aomething like that. Im actually building my own effects pedal, and I have a MXR distortion + that was my dads that I want to copy, Its a cool pedal.

Thanks for the help, Im going to reinsulate the transistors and see if once their heatsunk, they still smoke.

[J M Fahey]

Everybody`s skils are too basic for that
Forget building the actual reverb tank itself, nobody does, not even mighty Fender/Marshall/Yamaha/Roland/whatever.

Measure the original tank dimensions, there must be screw holes. scrach marks, different colour paint or less dust, something showing that, and weŽll suggest a modern Belton tank replacement (only remaining Factory in the World, that should tell you something).

Add that area picture to the others we have asked for.