Tube Preamp Project: advise and discussion

[rankot]

If you talk about diode in SMPS, right after the IRF740, then answer is NO, 1N400x series are a lot slower than UF400x, so it will not work as expected. It will oscillate more in basic frequency and have some parasitic oscillations, so I wouldn't suggest you to do that.

[johngovan1234]

thank you so much sir Rankot. A very big help indeed.

[MJ_Sound_Cubed]

The 1N is really slow the UF is ultra fast, you will need at 30kHz.

[johngovan1234]

here is my current layout for the power supply. im just waiting for the inductor. Thank you for all your help. My build is so slow because of the availability of the components.

credits to sir vigilante397 circuit.

[johngovan1234]

Currently waiting for the components. Thanks for the help.

[vigilante397]

credits to sir vigilante397 circuit.

As much as I enjoy taking credit for things, that circuit has been around for a looooooonnnnggg time even before I started building. Layout looks good though!

[MJ_Sound_Cubed]

Well done This seems to going well 

[johngovan1234]

Please correct me if i am wrong. I will connect the pins 4 and 5 together and put a 6.3v positive and the pin 9 to the ground?

[bluebunny]

Yep.  Merlin has a neat picture on his website:

[johngovan1234]

Thank you bluebunny. that helps a lot

[MJ_Sound_Cubed]

Cant belive this thread has 4 pages already. 

[bluebunny]

Cant belive this thread has 4 pages already. 

Just wait for Rob (deadastronaut) to post a new thread, like "I just had an idea for a new project..."

Before you know it - twenty-six pages! 

[johngovan1234]

Let's make it 10 pages. Hahaha.

I hooked up everything and it makes a decent sound. But i dont know why the regulator for the 6.3v heater gets hot and i hear some squeals when there no guitar plugged in. I replace the 12ax7 but the high pitch squeal is still there. I also have grid stopper resistor on the first and second stage.

[rankot]

If you use only one tube, then regulator will dissipate 0.3*dV, so if you have 9V DC at the input and regulate down to 6.3, it will be 0.3*2.7=0.81W of power. It will require 15K/W or less declared heat sink. If you use two tubes, it will be 9K/W. However, it also depend on your input voltage, so take this only as a hint.

[anotherjim]

For the squealing with nothing plugged in - I would always used a switched input jack socket. The tip will be grounded without a cable plugged in it by the built-in socket switch. Almost every guitar amplifier does this. It stops the amp picking up stray noise as the high input impedance of the tube grid is highly sensitive.

In this photo, you can see...
Screened cable used. If the tube and socket are not mounted on a pcb, I would use screened cable for the input if practical.
1M grid resistor mounted immediately on the socket. More for convenience in wired assembly, it doesn't have to be put right there.
Wire link across from tip contact switch to ground. So the input grounds with no plug in.

[PRR]

> i dont know why the regulator for the 6.3v heater gets hot

You got 9V. You need 6V. Where does the other 3V go?

When I cut 9 foot lumber to 6 foot I get a heap of 3 foot scraps in my way.

Here, the excess 3V doesn't lay on the floor to trip over, thank goodness. Instead it "goes away" as heat.

3V at 0.3A is nearly a Watt. 1 Watt in a TO-220 package may be safe but sure is HOT. Normally we'd bolt the regulator to a heat spreader at about this point. But it may live forever, naked, if it gets good air.

[rankot]

If you have stuck to your first post and use one tube, then you need 15°C/W or better declared heat sink for your heater voltage regulator. Or you may simply use 9.1 ohm 2W resistor in series with heater, connected directly to 9V, and omit whole heater regulator circuit. I vote for this option.

[johngovan1234]

You are awesome guys. Your responses are very helpful and i learn a lot.

This is what i did. I remove all the bits and pieces of my project. Rewire everything and it seems that the sqeals comes from the gain wire and thr input wire which i use sheilded. And i follow anotjerjtm advice to groind the input using a switch jack. And it do the trick but i think i see the biggest source of the squeal. It comes from the ceramic treble cap in the tonestack. Then i bend the leads and push it down kinda right angle. The squel becomes so little.

I also make the chassis my heatsink as of now. I'll post pic when i finish this.

[johngovan1234]

So far. This things goes. I have 2 boards made. 1 with cathode follower and one is the typical  1st stage tone stack 2nd stage design.

What i've learned is the conventional design sounds weak, i think because it needs a 3rd stage to compensate for the loss of the tone stack.

My other question is, how can i modify the smps supply to receive 19v (laptop psu) i' just trying out some posibilities here. Thank you for all your help. Please have patience with me.

[thermionix]

For fewer problems with instability (squeals) and noise, pop the grid wires up in the air, and keep them as short as possible.  Keep the plate and cathode wires pushed down against the chassis.  The wires to the tone controls might like to be pushed against the chassis as well.