Rebuild. 5e3 preamp + 5f1 output stage.

[utervo]

I don't see anything that would keep it from working as discussed.
That's a lot of switches and caps, though.

I will probably remove some, but I'm interested to hear how changing frequency response in different parts of circuit works. And hopefully have the ability to go from deep lows to a thin and high tone.

You can use a single resistor for the "phantom PI" lower half, a single 220K.

So it doesn't matter if I have the cap or not, just combine the resistance and it all leaks to groumd the same way, it doesn't affect the triodes work?

I wonder why Fender has the 1 meg go to ground through the 56k resistor.

[rdjones]

You can use a single resistor for the "phantom PI" lower half, a single 220K.

So it doesn't matter if I have the cap or not, just combine the resistance and it all leaks to groumd the same way, it doesn't affect the triodes work?

I wonder why Fender has the 1 meg go to ground through the 56k resistor.

Sorry, I should have been more clear on that.
Keep the (.1?) cap in series with a 220k to ground on the cathode to simulate the load on the cathode driving the 'missing' output tube.

The 1 Meg resistor on the cathodyne grid sets the operating point or bias for that stage by referencing the voltage below the 1.5k resistor on the cathode (instead of ground).
The grid voltage is about 2V below the cathode as is normal in a typical triode stage.
The 2x 56k resistors form the split load of the cathodyne, instead of 100k on the plate it is split half above and half below the tube.

Hope this makes sense, Merlin's cathodyne page may help.
http://www.valvewizard.co.uk/cathodyne.html

rd

[utervo]

Thanks again for input.

I made a first sketch of the layout with the reverb circuit, standard values, no extra switches, yet. Input and tips on the layout are welcome.

I am able to use the existing holes. Jacks will be at the side. I split the preamp section on the board, I am not sure if this is normally done when adding a reverb.

The reverb circuit is the green part from another schematic.

[utervo]

Here's an updated layout with wires.

I have yet again a bit of a power supply problem.

The reverb driver from 6BM8 is a triode-strapped pentode and in the 5F1 schematic it is connected to the screen node and and recovery triode is connected to the preamp node.

I simulated with Duncan's software. With 300v tranny, stock 5E3 filters, the voltages would be 362V, 320V, 236V. The preamp node is already too low and and screen node is too high for the reverb.

I am not sure how much the current draw would be, but I put extra 1.5ma on the preamp node and extra 15ma to the screen node. The voltages are now really off, 351V, 223V and 106V. Does this sound realistic, what's the best way to tackle this, dropping the filter resistors?

[rdjones]

Here's an updated layout with wires.

I have yet again a bit of a power supply problem.

The reverb driver from 6BM8 is a triode-strapped pentode and in the 5F1 schematic it is connected to the screen node and and recovery triode is connected to the preamp node.

Are you committed to the 6BM8 ? (i.e. already have the tube)
They're not the beefiest pentode/triode around, but should work for the reverb driver.
I'm not sure about the triode strapping part, but the 6BM8 screen is 300V, 1.8W max.

I am not sure how much the current draw would be, but I put extra 1.5ma on the preamp node and extra 15ma to the screen node. The voltages are now really off, 351V, 223V and 106V. Does this sound realistic, what's the best way to tackle this, dropping the filter resistors?

Yes, tweak the dropping string values to get your voltages in line.
Unless you're "blueprinting" the voltages can vary by 20% according to the schematics, 106V at the first stage is too low.

The 100k for the reverb insert is way low, the reverb will feedback and the level will not match the dry.
Unfortunately required value (3.3Meg) will reduce gain and a recovery stage may be needed.

rd

[utervo]

Thanks rd for helping me out again.

Are you committed to the 6BM8 ? (i.e. already have the tube)
They're not the beefiest pentode/triode around, but should work for the reverb driver.
I'm not sure about the triode strapping part, but the 6BM8 screen is 300V, 1.8W max.

No I haven't yet, this seemed to sound pretty good. What do you recommend? I want a proper reverb with enough drive.

Yes, tweak the dropping string values to get your voltages in line.
Unless you're "blueprinting" the voltages can vary by 20% according to the schematics, 106V at the first stage is too low.

Anything else to to do? Ripple rejection goes down too, other than that any caveats?

The 100k for the reverb insert is way low, the reverb will feedback and the level will not match the dry.
Unfortunately required value (3.3Meg) will reduce gain and a recovery stage may be needed.

I looked into the thread at music electronics forum and 470k was actually the best. Maybe I could altogether eliminate feedback problem by getting the reverb signal from the triode before the fake cathodyne and take the cathodyne signal from the cathode, the two would now bee in same phase and I could put the to 6v6gt.

[utervo]

Actually I am not sure which resistor was used... MEF is so annoying as browser keeps giving malware warnings all the time.

[utervo]

Here is the redesigned power supply with the 6BM8 reverb added. Took a bit of playing around. Current put for 6BM8 pentode is 30mA and 1.8mA for triode. Pentode (reverb driver) is connected to PS screen node (I2 at picture) and triode to PS preamp node (I3)

Added another filter section before plate with 100 Ohm resistor and 16uF cap.

With more load the voltages dropped quite much and I compensated with smaller resistors.

Estimated voltages for PS nodes are:

1st 311V (6V6-GT plate)
2nd 278V (6V6-GT screen + 6BM8 pentode plate+screen)
3rd 252V (2x12AX7 + 6BM8 triode)

Estimated ripples are:

1st 11.7V / 3.76%
2nd 1.1V / 0.39%
3rd 21.3mV /0.08%

A bit low on the 6V6-GT. Does the configuration look ok and safe?

[utervo]

Here is an alternative schematic with the reverb signal taken before the cathodyne and inserted back before the 6V6-GT grid. Cathodyne signal switched to be taken from the cathode and plate AC signal is routed back to ground with 770k load to mimic the grid input load (500k) and stock grid leak resistor. I am starting to be a bit out of my depth here but hopefully you guys can check if there are any bad mistakes there.

[utervo]

I guess the phase for reverb input doesn't matter so I switched back to plate output. Do I still need mixing resistors in this configuration?