Hi,
I bought a Reisong A10 and I convert it on Reisong A12 with following the Stephe's mods (Skunkie Designs).
I plan to replace the tube rectifier to solid state rectifier.
I've a little of 100Hz on the output with 5AR4 tube rectifier from TungSol ...
I want to replace it with solid state rectifier like this (https://www.thomann.de/fr/tad_solid...MIlOmyxLWh_gIVy49oCR2yKgLBEAQYASABEgLzN_D_BwE)
Should I modify the wiring / remove the diodes under the tube socket to swap tube rectifier to solid state rectifier ?
Thank you !
Best regards
Schematic
Tube Rectifier Socket
I bought a Reisong A10 and I convert it on Reisong A12 with following the Stephe's mods (Skunkie Designs).
I plan to replace the tube rectifier to solid state rectifier.
I've a little of 100Hz on the output with 5AR4 tube rectifier from TungSol ...
I want to replace it with solid state rectifier like this (https://www.thomann.de/fr/tad_solid...MIlOmyxLWh_gIVy49oCR2yKgLBEAQYASABEgLzN_D_BwE)
Should I modify the wiring / remove the diodes under the tube socket to swap tube rectifier to solid state rectifier ?
Thank you !
Best regards
Schematic
Tube Rectifier Socket
Why replace the 5AR4 with solid state diodes?
(yes, I use solid state diodes on my amplifiers, but I know the tradeoffs and design considerations).
Please name the advantages.
Please name the disadvantages.
Or else research all those factors before making that modification.
A general rule is to make an amplifier work properly, before you modify it.
Solid state diodes instead of a 5AR4 will not reduce the hum at the first cap, "22uF 400V".
And if you take the 5AR4 out, you still have to use the original 2 diodes, and connect the 2 new diodes as if they are the 5AR4 (the original diodes and 5AR4 together are a Bridge Rectifier).
Caution: When you turn on the amplifier, before the EL34 tubes warm up, you will have 410V across the 22uF 400V rated capacitor.
1.414 x 290V = 410V peak. There is no safety margin for the 22uF 400V cap.
As you can see, a small change can have large implications and problems to solve.
(yes, I use solid state diodes on my amplifiers, but I know the tradeoffs and design considerations).
Please name the advantages.
Please name the disadvantages.
Or else research all those factors before making that modification.
A general rule is to make an amplifier work properly, before you modify it.
Solid state diodes instead of a 5AR4 will not reduce the hum at the first cap, "22uF 400V".
And if you take the 5AR4 out, you still have to use the original 2 diodes, and connect the 2 new diodes as if they are the 5AR4 (the original diodes and 5AR4 together are a Bridge Rectifier).
Caution: When you turn on the amplifier, before the EL34 tubes warm up, you will have 410V across the 22uF 400V rated capacitor.
1.414 x 290V = 410V peak. There is no safety margin for the 22uF 400V cap.
As you can see, a small change can have large implications and problems to solve.
According to the schematic, the 12AX7 heater and EL34 heaters are floating.
Each 6.3V pair of heater wires should have a pair of 100 Ohm resistors to ground (one from each 6.3V wire to ground).
That is the recommended Pseudo Center Tap.
The 5AR4 heater is at about +370V.
Do not ground that, except through the Missing Bleeder Resistor.
Safety First!
Use a bleeder resistor.
"Prevent the Surviving Spouse Syndrome"
Each 6.3V pair of heater wires should have a pair of 100 Ohm resistors to ground (one from each 6.3V wire to ground).
That is the recommended Pseudo Center Tap.
The 5AR4 heater is at about +370V.
Do not ground that, except through the Missing Bleeder Resistor.
Safety First!
Use a bleeder resistor.
"Prevent the Surviving Spouse Syndrome"
Thanks for your feedback!
To be more precise, I mainly have a 100hz problem on the left channel.
I tried to reverse the preamp and power tubes, the noise remains on the left channel.
I also checked the placement of wires, components, without success.
The 100hz noise doesn't vary with the position of the volume pot.
Do you have an idea ?
Thank you Community !
More Pics ...
Global___
Left Channel___
Right Channel ___
Power Supply __
To be more precise, I mainly have a 100hz problem on the left channel.
I tried to reverse the preamp and power tubes, the noise remains on the left channel.
I also checked the placement of wires, components, without success.
The 100hz noise doesn't vary with the position of the volume pot.
Do you have an idea ?
Thank you Community !
More Pics ...
Global___
Left Channel___
Right Channel ___
Power Supply __
First, I would do what @6A3sUMMER recommended in #4. 12AX7 and EL34 heaters must not be floating. Then check for ground loops, it looks from the photos that there are multiple ground connections to the chassis.
Power off, remove the 12AX7, power on. Is the hum still there? Do the same with the EL34.
About the 100Hz hum, how did you measure it? Are you sure it is 100Hz? If yes, that points to power supply noise.
Look at transformer orientation (output transformer vs power transformer), measure ripple at B+ (careful with that!),
I have also seen something like this, basically injecting part of the ripple to the cathode for hum cancellation (don't remember the rule of thumb for the cap value, either 1/3 or 1/10 of the cathode to ground cap, max voltage 1.5*B+):
Power off, remove the 12AX7, power on. Is the hum still there? Do the same with the EL34.
About the 100Hz hum, how did you measure it? Are you sure it is 100Hz? If yes, that points to power supply noise.
Look at transformer orientation (output transformer vs power transformer), measure ripple at B+ (careful with that!),
I have also seen something like this, basically injecting part of the ripple to the cathode for hum cancellation (don't remember the rule of thumb for the cap value, either 1/3 or 1/10 of the cathode to ground cap, max voltage 1.5*B+):
If I understand correctly, I insert two resistors of 100R in place of the wire which currently makes the connection between the 6.3v and ground?
Like this ? (It's not my amp, but the view is clear here 😉)
100 Hz hum causes:
B+ ripple
B+ electrical ground loop
B+ secondary (all 3 leads), diode rectifiers, tube rectifier, or first capacitor + or - wire (all of these leads). They have a very high transient current;
It is runs parallel to any signal wire, it induces interference (A parallel air core transformer).
Power transformer and Choke magnetic fields that are near to a tube (steel plates).
Steel Chassis.
A lower resistance B+ rectifier chain (like a 4 diode bridge, versus a bridge with 2 diodes and 1 rectifier (more resistance of a tube rectifier). That will cause higher B+ voltage, and much harsher and larger transient currents to the first filter cap.
And a few others that I can not think of now.
B+ ripple
B+ electrical ground loop
B+ secondary (all 3 leads), diode rectifiers, tube rectifier, or first capacitor + or - wire (all of these leads). They have a very high transient current;
It is runs parallel to any signal wire, it induces interference (A parallel air core transformer).
Power transformer and Choke magnetic fields that are near to a tube (steel plates).
Steel Chassis.
A lower resistance B+ rectifier chain (like a 4 diode bridge, versus a bridge with 2 diodes and 1 rectifier (more resistance of a tube rectifier). That will cause higher B+ voltage, and much harsher and larger transient currents to the first filter cap.
And a few others that I can not think of now.
I tested removing the 12ax7 tube from the left channel, and turned on the amplifier, no noise in the speakers, the left channel is as quiet as the right one (I kept the 12ax7 in place on the right channel)
As a reminder, the right channel is absolutely silent (Hum & hiss Free), which makes me say that there is not a problem with the power supply of the amplifier.
After observation, the two pairs of 6.3v heater wires have one ground connection per pair; Like this :
I tried to reverse the 12AX7 tubes between the two channels, the noise remains on the left channel, no improvement
Is that the noisy one? The yellow wire looks like a shielded cable, can you double check that the shield is properly
soldered? Does anything change if you touch/move the yellow cable?
The grid and cathode resistors (pins 2 and 3), are they connected to ground at the same point as the other channel?
soldered? Does anything change if you touch/move the yellow cable?
The grid and cathode resistors (pins 2 and 3), are they connected to ground at the same point as the other channel?
WDECHO,
I already have a wire that connects two 6.3v to ground.
Adding the 100 Ohm resistor to ground does what?
Yes it's the noisy.
The yellow wire that brings the signal is indeed well shielded and its end on the potentiometer side is well connected to ground.
I tried to move the yellow wire, and even completely unplugged it from pin2, no improvement in the noise level...
The grid and cathode resistors are well connected to the same ground point, same reference as the other channel, like this
I noticed that the heaters are grounded, we though it was floating based on the schematic. It is not ideal but I do not think it is the reason for the hum.
If I add the 100R resistors instead of the wire that connects to ground, possible reduction of the noise level? No risk ?
Worth a try. The schematic did not show the heaters being ground, reason for previous post. I've installed a virtual ground on a number of my builds that were noisy. A couple of those cheap Chinese kits you can buy comes to mind that were noisy. I think the hum is more at 120hz if in USA which means PS problem if that helps any. Be sure and use proper wattage rated resistors because they will generate some heat.
I don't understand why it would be a PS problem, the two chanels share the same PS, and the other channel (right) is completely silent ...
I live in France (240V/50Hz)
What kind of resistor can i use for the 100R resistors ? 2W or more ?
Does the hum go if you unplug the right channel. Its much better to put the left and right input tubes in the same place rather than having them at each corner. The latter can lead to ground hum loops. In your case building both inputs around a single 12ax7 is better and not using the other tube.