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Planet Audio amp

P

potto

New Member
Hi Guys,
I just purchased a HVT754 planet audio hybrid tube amp for my car. I have started it up to test it and it was draining 2.6 amps on idle, which I thought was high even with 4 x 12ax7 tubes in it (they should use approx 600mA for the heaters) I took off the case and checked all the outputs with a multimeter and they seemed fine, but when I power it up there is a 1 ohm resister before the speaker connection that is getting hot. Its only on one channel and the corresponding output transistor doesn't get warm. Note that there is nothing connected to the amp while I was testing. Does anyone have an insight of what could be happening, any help is greatly appreciated.
 
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2.6 amps might be a bit high, but remember that not only do you have the tube heaters, but the switching power supply. Couldn't find a schematic online, do you have one you could post? At least pictures would help. Dose that one ohm resistor go from speaker output to a cap that is connected to ground? Also check for DC output voltage on the speaker outputs.
 
You do have the heaters as stated, and the switcher and the amp section after the tubes all drawing current. There is most likely higher voltages going to the plates and grids of the tubes also. Although current would be low for the B+ voltage connections going to the tubes. I have seen a few tube preamps using 12AX7's in a 12v circuit though. A schematic and pictures of the inside would be helpful. I have an all tube headphone amp that has a switching power supply that has a step up transformer to power the tubes.
The fuse is maybe 1amp? But the output tubes only produce about 1.2wpc into 16 ohm. Selecting higher impedances like 60 ohm and higher lowers that output. It sounds like you have a tube driver section driving a SS output section? If you have a schematic it may show the amp rating for the fuse.
 
Hi Guys,


Thanks for the replies, I am searching for the schematic, but its not looking good.
I have attached a couple of photos below,
Would I check for DC voltage on the outputs with a signal running or just on idle .

IMG_6886.jpegIMG_6885.jpeg
 
stillspin'n said:
2.6 amps might be a bit high, but remember that not only do you have the tube heaters, but the switching power supply. Couldn't find a schematic online, do you have one you could post? At least pictures would help. Dose that one ohm resistor go from speaker output to a cap that is connected to ground? Also check for DC output voltage on the speaker outputs.
Click to expand...
yep it has 0.1uF cap on it
 
So the channel with the burning resistor if probably oscillating. So you will need a scope to see if it's the power amp section or in the tube preamp section and maybe trace down cause of the problem.
 
Stephen Mantz of Zed Audio is still alive and well. He designed it. Contact him after the holidays.
 
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