Question about Marshall 82 WTS LITHIUM BATTERY, 3 LED POWER INDICATOR => Model IDX-E80S Car Audio Amplifier

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A Marshall 100w amp that lacks heater voltage on all tubes

This amp is a 1969. It has worked flawlessly until the other day; now it is dead. I have voltage on power caps but the tubes are not glowing. Has the power transformer failed? I am not sure if the 6.3v supply is present off of the transformer. I discharged a power cap with my body and have not invetigated much further since this rather ugly episode.

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It would be worth just checking a little further before doing anything too radical (and expensive). First remove all the valves carefully and then with the chassis out of the case and upside down plug in the amp and switch on the power but not the standby. This should put the bias and heater voltages to the amp but not the HT. Now with a volt meter set on 10v AC range check pins 4 to 9 on one of the ECC83 valve bases. If you get nothing then the transformer is most likely damaged but if you get 6.3v it may just be a valve with a short holding the heater voltage down. Admittedly its a bit of a long shot but I have seen this happen once and its better to check than to go spending on an unnecessary replacement transformer.

The other thing to consider is if its only the 6.3V supply that has failed you could get the amp running for less than the price of a replacement transformer if you were to put in a simple mains to 6.3V auxilliary heater supply transformer to run alongside the existing mains transformer which could supply the HT and bias voltages. The 1969 required 8A at 6.3V for its heaters if you decide to look at this option

Posted on Jul 18, 2009

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Yes, it is the power transformer that has failed. If you are comfortable with replacing it then do so just be careful. If you could though I would be careful and check to see what power you are getting at the transformer just to make sure

Posted on Feb 06, 2009


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Be vvery careful as there are lethal voltages present in these.

If the fuse blew, replace it and try just once as there could be other problems and more damage could be done.

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