voice of music 560a phonograph

tubeman · by **tubeman** » Sat Aug 27, 2011 5:31 pm

I have 2 vm 560a phonographs one is fully operational electronically.The other burned the 470 ohm resistor across 2 segments of the power supply filter cap.I thought the cap was defective and replaced it and the resistor.it burned again.I have the 2 6v6 power tubes out of their sockets and a brand new 5y3 rectifer tube.there is 400 volts between segments of the filter cap and obviously too much current flow.The functional one only has around 100 volts between the cap segments.Before I spend $75 on a new power trans could someone shed some light on what my problem could possibly be? I also replaced the coupling caps with orange drops.There is 600volts coming from the power trans to the 5y3 and the filament windings are fine.Any help would be greatly appreciated.I am going to sell the phonos as I am only interested in the amps at this time.

MattTech · by **MattTech** » Sun Aug 28, 2011 6:05 am

The 2nd filter, the one after the 470 ohm, only feeds the 6V6 screens.
If it's loaded down (a short/leakage) it'll burn the resistor.
If the 6V6's are out, I'd suspect a short around there.
Perhaps pin 4 of one of those sockets have burned or arcing spots ?

tubeman · by **tubeman** » Sun Aug 28, 2011 5:41 pm

Thanks for giving me a place to look.When I removed the amp from the phonograph, the volume and tone controls are located remotely so I drilled 2 holes in the chassis and mounted them.I had the volume control too close to one of the 6v6 tube socket pins hence the short.I thought I had them isolated.Now I just have to replace the 470 ohm resistor again and hopefully that will take care of it.Since you are obviously more experienced in this kind of electronics I'd like to ask another question.I want to replace the 5y3 with a 5v4ga rectifier and the 6v6's with 8417 tubes.I have tried this with the functional amp that I have with no ill effects and the sound is not only louder but more detailed and clear.I have a tube spec guide and other than the plate voltages being higher on the 8417 I don't see a problem.Any thoughts?

MattTech · by **MattTech** » Mon Aug 29, 2011 5:39 am

the tubes you want to use may work, but consider the 6V6's draw much less filament current (less than half of 8417's) and it's possible to overheat and stress the power transformer by using 8417's.

The transformer's ratings I'm not knowledgeable about, so mods as you suggest are at your own risk.