HiFi Haven Group Project - Building The "World's Best Tube Phono Preamp"

Wntrmute2

Junior Member
Paul's point about the voltage running high is right. What you are doing when you run the PS without the audio circuitry is just confirming that things are wired correctly and working. The B+ without any load might easily run 30 to 50 volts higher than with the load connected. It's totally safe but don't be surprised if you see something in the 260-275v range with no load. Likewise the voltage on the DC heater supply is going to run higher than you expect, perhaps in the 7.5 to 9.0v range. These are just guesstimates.
Tested the PS last night. No smoke so that's a step in the right direction! B+ is 264V and the heaters seem to be running quite high at 10.3V. That is with no load.

IMG_20200126_174720.jpgIMG_20200126_174727.jpg
 
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Salectric

Senior Member
Very pretty! You are going to end up with one really nice preamp. The voltages seem to be in the ballpark so you’re all set with the PS.
 
I'm always impressed when people put together projects like this that are going to be finished at the end. The thought that goes into the process eludes me hence the admiration. Looks fantastic!

This thread has caused me to re-look at rectification in mine as I can't keep using mercury (too rare) if I'm to maintain a stock to feed it going forwards so I have a bunch of different DH rectifiers, 5U4G, 5R4GY and DW4-350 and 6AX4 dampers coming soon to play with :)
 

Salectric

Senior Member
I have a bunch of different DH rectifiers, 5U4G, 5R4GY and DW4-350 and 6AX4 dampers coming soon to play with :)
I will be curious what you conclude about the different rectifiers. I definitely favor DH rectifiers over indirectly heated like 5AR4, but it’s been a long time since I tried something other than a 5R4GY.
 

Salectric

Senior Member
Are you sure you have those .33 resistors wired correctly? I thought they were meant to be in series on just one end of the heater wiring. The other end goes to ground.
Either way should be fine as far as heater voltage is concerned. Since the resistors are in series with the tube heater windings, the heaters will see the same voltage regardless of which leg the resistors are in.

From the perspective of noise and RFI, it also shouldn’t make any difference. The only ground reference for the heater supply should be after the resistors, I.e. between the resistors and the tubes, so it shouldn’t matter which leg has the resistors.

However, keep in mind that you may have to change the value of those resistors to get the correct heater voltage. I like to run heaters at around 5% below rated voltage, so 6.0-6.1v for this circuit. If you are using an outboard PS the wiring will have some losses which will vary depending on gauge of wire and length. The wire losses are in addition to normal component tolerances. So for any given preamp you could easily need more or less resistance than the .66 ohms I used. In my case I happened to have several Mills .33R in my parts box so when I measured the heater voltage and found it was high I just added resistors until I got the voltage I wanted.
 

jmathers

Junior Member
Either way should be fine as far as heater voltage is concerned. Since the resistors are in series with the tube heater windings, the heaters will see the same voltage regardless of which leg the resistors are in.

From the perspective of noise and RFI, it also shouldn’t make any difference. The only ground reference for the heater supply should be after the resistors, I.e. between the resistors and the tubes, so it shouldn’t matter which leg has the resistors.

However, keep in mind that you may have to change the value of those resistors to get the correct heater voltage. I like to run heaters at around 5% below rated voltage, so 6.0-6.1v for this circuit. If you are using an outboard PS the wiring will have some losses which will vary depending on gauge of wire and length. The wire losses are in addition to normal component tolerances. So for any given preamp you could easily need more or less resistance than the .66 ohms I used. In my case I happened to have several Mills .33R in my parts box so when I measured the heater voltage and found it was high I just added resistors until I got the voltage I wanted.
Not sure mine is wired up correctly then, especially the ground. Here's basically what I have (ground bus is red line and resistors do not connect to it):

heaters.jpg

@Salectric I guess I'm wondering about that ground connection now. Any thoughts?
 
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Salectric

Senior Member
I can’t tell which of your 6.3v leads is positive and which is negative. The negative side should go to ground. It will work either way but that orientation elevates the heater voltage slightly above ground vs slightly below.
 

jmathers

Junior Member
I can’t tell which of your 6.3v leads is positive and which is negative. The negative side should go to ground. It will work either way but that orientation elevates the heater voltage slightly above ground vs slightly below.
6.3v Negative lead is the lead going first to ground and then on to the negative side of the Panasonic cap.

I'm not sure where else to place the negative 6.3v lead to get the heater voltage slightly below ground?
 

Salectric

Senior Member
6.3v Negative lead is the lead going first to ground and then on to the negative side of the Panasonic cap.

I'm not sure where else to place the negative 6.3v lead to get the heater voltage slightly below ground?
That’s fine then. That’s just how mine is wired.
 

paulbottlehead

Active Member
It can be hard to hear/measure the need for snubber caps. Typically what you hear is a very glassy sound when you have a really high frequency oscillation taking over.
 

Wntrmute2

Junior Member
Trying to wrap things up in the signal chassis. There are three places that look like they tie to the chassis.
Bus bar to chassis - Green circle
B+/_ umbilical as it enters the chassis - red circle
Heater negative as it enters the chassis - red circle
Is this correct? I know we've had this question come up before but I cant seem to locate the answer. TIA

I know the blue circles connect to the bus so i'm good there.

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