Using a 1070 transformer on a 1040

[ocdecio]

There is a person on FB that has a fried 1040 transformer and I was trying to help troubleshoot. I found a 1070 transformer online, but the voltages are slighgtly higher on the 1070, mainly on the secondary that feeds the power amp boards. The 1040 reads +-32V and the 1070 +-36V.

I think the power supply design should be able to still give the 34V the preamp section needs.

I wonder if there is a safe way of stepping down slightly the amp boards voltage, and if anyone ever heard or did this type of conversion.

 

[mbz]

Voltages shown in schematics are subject to change, better to get input from someone with actual voltages, I've assumed you
got the +/-32, +/-36V from the schematic (since the 1040 is dead). I would expect the VA rating of the 1070 unit to cover the
needs of the 1040. Keep in mind that these voltages are for the unregulated supply, need to keep an eye on the main cap
rating(35V). Maybe consider dropping a volt or two using diodes or resistors as last resort.

 

[ocdecio]

Voltages shown in schematics are subject to change, better to get input from someone with actual voltages, I've assumed you
got the +/-32, +/-36V from the schematic (since the 1040 is dead). I would expect the VA rating of the 1070 unit to cover the
needs of the 1040. Keep in mind that these voltages are for the unregulated supply, need to keep an eye on the main cap
rating(35V). Maybe consider dropping a volt or two using diodes or resistors as last resort.

Thank you! How much of a problem would it be to allow say 4 volts more going to the amp board? They look so similar. It seems quite simple to replace the caps with higher voltage, but I wonder if it is a must to actually get some diodes in series to take it down a notch as you suggested.
The preamp should be OK because there is a pot to adjust the voltage.

 

[mbz]

Yeah, I agree with your point that an extra 4V on the unregulated supply is not a big deal, keeping in mind that the mains AC
is bouncing around. Problem might arise if it's +4V at 120Vac then it may be +8V at 126Vac? Still like the idea of some of
the marantz guys chiming in with actual voltages from their units.

 

[ocdecio]

Yeah, I agree with your point that an extra 4V on the unregulated supply is not a big deal, keeping in mind that the mains AC
is bouncing around. Problem might arise if it's +4V at 120Vac then it may be +8V at 126Vac? Still like the idea of some of
the marantz guys chiming in with actual voltages from their units.

I have both but my 1070 is waiting for a relay replacement. You are correct, there is no substitute to reading the values off the units. I will do that and see what I get on the AC side.

 

[rBuckner]

The reported AC voltages of the secondaries for the power amp seem to not jive with the voltage to get 20 watts and 38 watts, so yes indeed, check them out as you have the actual units. How handy! I'd check the voltage ratings on the amp's transistors to be sure they aren't marginal for the higher voltages that would be coming in.

I would also suggest upping the dropping resistor R801 on the regulated supply to 22 or 33 ohms and be sure that the wattage rating is enough on whatever is used. I'd also use something beefier for the pass transistor, possibly something that could fit a heatsink. If so, the 10 ohm resistor (R801) could just stay that value.

 

[ocdecio]

Thank you so much @rBuckner !