Hello! I'm powering a single ended stereo using one power supply. kt88 power tubes with two ecc83 driver tubes (one for each channel)
I currently have an old stock 5U4 rectifier installed and it seemingly runs great (decent plate voltage, bias is good, etc). Below is a screen shot of my current bias/tube dissipation.
My problem, is when I use a modern GZ34 (i wanted a little more voltage out of it) it blows a fuse every time.
Am i exceeding the GZ34 specs? Would a diode set-up make more sense?
TBH I'm getting 330v on the plates, while the schematic is calling for 370v. Any opinions would be appreciated, thank you!
I currently have an old stock 5U4 rectifier installed and it seemingly runs great (decent plate voltage, bias is good, etc). Below is a screen shot of my current bias/tube dissipation.
My problem, is when I use a modern GZ34 (i wanted a little more voltage out of it) it blows a fuse every time.
Am i exceeding the GZ34 specs? Would a diode set-up make more sense?
TBH I'm getting 330v on the plates, while the schematic is calling for 370v. Any opinions would be appreciated, thank you!
So why not just decrease the KT88 cathode resistors to increase the plate dissipation? What is it with the 5U4 rectifier?
You must be using a different power trans if the B+ is that much lower.
jeff
Maybe.
There is a large 200uF on the other side of the smoothing inductor that need a lot of current to charge up at turn on time.
Yes the inductor reduces the peak current but only by so much during the startup period when the 200uF capacitor is coming up to full voltage.
The 5U4 has a lot of series resistance that limits the peak current so will tolerate too much input capacitance better than the low resistance gZ34 in my experience.
What happens is a GZ34 at start up will source so much current into the large input capacitor that it arks over and takes out the fuse.
Each ark over event eats some of the cathode and sends junk into the vacuum degrading the tube each time.
The "yellow sheet" mod adding the diodes in series does stop the arc over in my experience.
The large 200uF capacitor would still be a concern for me with the gZ43 at start up time.
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I can not see how the designer expected to get 380V at 200mA DC from a 600v CT winding with a 5U4.
Look at the chart "operation characteristics" in attached data sheet.
The 330V DC you are getting is pretty much what the data sheet for a 5U4 says you show get for a 600 CT transformer @ 200mA DC current .
The designers numbers do not add up from what I see.
To get anywhere near 380V DC out from a 600v CT transformer solid state diodes will likely be needed.
I would plug in any proposed values into a power supply simulator before making any changes to save on time and frustration.
Solid state diodes alone can in some circuits and transformers result in unplanned 60Hz buzz noise that can be a bit hard to eliminate.
So be prepared to chase them down if it happens in your amplifier.
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