dynaco mk 3 tx problem

Hi Maybe someone can answer this for me.

I have a MK 111 that had a burnt TX when I purchased it, I changed the power supply can cap and related selenium rectifier with diodes and new resistors and lytic caps, I also installed a new front in By Dr Peppard a Mullard Long tail phase splitter, and new bias pot, new tubes.

It worked perfectly for about two years and then the TX smoked once again. I am not sure if the second TX was just a bad one or if there is possibly something else happening here.

Any thoughts would be appreciated

Thanks
Donald

dtroise wrote:Hi Maybe someone can answer this for me.

I have a MK 111 that had a burnt TX when I purchased it, I changed the power supply can cap and related selenium rectifier with diodes and new resistors and lytic caps, I also installed a new front in By Dr  Peppard  a Mullard Long tail phase splitter, and new bias pot, new tubes.

It worked perfectly for about two years  and then the TX smoked once again. I am not sure if the second TX was just a bad one or if there is possibly something else happening here.

Any thoughts would be appreciated

Thanks
Donald

What is 'TX' ?

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That is correct, in the Electrical field TX is the symbol for a Transformer, I should have specified Power as opposed to output, sorry.


Donald

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The board from Lloyd is a point to point  not a PCB, The TX and can cap is from Dyna kit The can cap is 80/40/30/20 @ 525 V, the fuse is 2 A, it failed once and when I changed it and powered it back on it did not blow, but the TX smoked. The TX was advertised as being an exact replacement made in the USA. I made no other changes except the earth ground to the cabinet. I am thinking that it is a dead short in the windings but I can't help wondering if something else is happening, albeit it did function perfectly for over two years. I checked the choke and it was within specs.

My system is fed through a Fursman studio balanced power distribution panel which monitors the service 24/7 protected by a GFCI breaker that will trip with power swings. I have 9 amps on the panel and none of the others have or had a problem, the voltage feedback on my Neutral to ground is less than 100 mv. at the wall service. After the fursman it is 63/60 on the two conductors balanced with ZERO V on the Earth Ground.

Any thoughts

Donald

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Hi,
Allow me to thank you for taking the time to answer.

My mistake about it being a MK -3, as it is a Mark-4  the fuse is specked at 2 amps, Under load the voltage from the Fursman never gets past 119 and I always bias to the M/A load of the EL 34 per an article that I read by ( I believe ) Bob Latino,  to allow for the higher Voltage of modern day electric.

I tested the can cap and w/o power they were within specs. as far as capacitance. The rectifier tube was within a year old and tested fine on my tube tester after the fact.

I should explain more on one issue, It blew the fuse one day w/o my seeing smoke so I took it out of the rack and opened it up to see if there was anything obvious and I could find no issues, I then replaced the fuse and turned it on while on my desk and that is when it started to smoke, I unplugged it immediately and that is why the fuse probably did not blow the second time.

The smoke came from the TX and it has the smell of burnt windings so logic tells me that the TX shorted out within itself w/o obvious issues else where.??????

Is it possible for the original output TX to cause a short in the Power TX. ?

Thanks

Donald

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No, to all of your questions about changes, when I bought the amp the TX was not working so I assumed that it shorted out, that is why I changed all of the parts and the front end. It worked for over two years maybe three w/o a problem, I just checked where I purchased the TX and it was from Triode electric. I have checked the wiring for a possible intermediate short to ground but there is none, ( That is evident).

Donald

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It is the P TX as it measure a dead short to the windings and the smell is definitely coming from it . Lloyd made the front end special for me. You are correct as I can not measure any of the V w/o installing a new TX which is why I am going through this exercise, so not to just flush money down the toilet.

Donald

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This seems strange but it must have a reason.
Do check wires , especially filament connections for damaged insulation .

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That is not possible because I just checked all of the secondary windings and they are all shorted ( Closed) The primary windings appear normal . I guess that I will have to buy a TX to go forward. I looked at every connection and part through a magnifier and nothing is amiss.

Donald

How hot is the amp during use ? Is the ventilation good ?

Never got hot, the racks are open with 3 feet space behind them and a/c vent blows directly on the equipment.

Donald