New Tweed Vibrolux 5F11 build

[SleepLess]

Hi there everyone!
I'm currently building a 5F11. I have decided to add a bias mod. The PT is a MM (ref. FTPV/E) and it has a bias tap. Do you know what to do with it? Where would it go on the board? What changes need to be made on the board? I think I need to remove the 56K resistor, add a diode that will go from the board to the 10KL middle lug, but what about the 10K resistor and the PT bias tap?



I think I'll have other questions and of course I'll shoot you some pics when it's done!
Thanks!

[sluckey]

I would build it EXACTLY according to the original layout first. Then, when it's working properly, adding the bias mod will be very easy.

[HotBluePlates]

... The PT is a MM (ref. FTPV/E) and it has a bias tap. Do you know what to do with it? Where would it go on the board?  ...

The original amp had a bias tap, too. It's the brown wire on the layout, and connects to the 10kΩ resistor on the board.

You won't be using a selenium rectifier, so use a 1N4007 diode, with the banded end connecting to the 56kΩ resistor. (see correction below)

Build it as drawn first. You will likely then replace the 56kΩ with a 50kΩ pot and a 18k-27kΩ resistor; that is, if you wanted adjustable bias.

[SleepLess]

... The PT is a MM (ref. FTPV/E) and it has a bias tap. Do you know what to do with it? Where would it go on the board?  ...

The original amp had a bias tap, too. It's the brown wire on the layout, and connects to the 10kΩ resistor on the board.

You won't be using a selenium rectifier, so use a 1N4007 diode, with the banded end connecting to the 56kΩ resistor.

Build it as drawn first. You will likely then replace the 56kΩ with a 50kΩ pot and a 18k-27kΩ resistor; that is, if you wanted adjustable bias.

Cool about that bias tap! But damn I only have the usual 10KL bias pot... 

[SleepLess]

Well, there are some things that are absolutely puzzling to me on this original layout and that I haven't found anywhere else... For instance the heaters receive only one wire from the pilot lamp, the other green wire is grounded... What the hell is that?
Then the HT wire goes to pins 7 of the power tubes and then to pins 4/5 of the preamp tubes and pins 9 get grounded... What the hell is that?

So far I have wired it the "usual" way which is HT Voltage going to pins 7 and 2 of the power tubes and then to pins 4/5 and 9 of the preamp tubes...

Thanks Sluckey!

[sluckey]

so use a 1N4007 diode, with the banded end connecting to the 56kΩ resistor.

Banded end (cathode) must connect to the 10K.

[jjasilli]

Well, there are some things that are absolutely puzzling to me on this original layout and that I haven't found anywhere else... For instance the heaters receive only one wire from the pilot lamp, the other green wire is grounded... What the hell is that?

That is called a circuit   (sorry, haven't gotten to be a wise-ass all day!), but not a desirable heater circuit -- it may well induce 60 cycle hum in the heater circuit.  Better to build a balanced supply which is humbucking.  If your PT's heater secondary lacks a CT (or just per general preference -- see Doug's Library of Info on heaters), create a virtual CT with 2X 100R resistors.  Run twisted pair wiring to all the heater lugs.

[SleepLess]

Well, there are some things that are absolutely puzzling to me on this original layout and that I haven't found anywhere else... For instance the heaters receive only one wire from the pilot lamp, the other green wire is grounded... What the hell is that?

That is called a circuit   (sorry, haven't gotten to be a wise-ass all day!), but not a desirable heater circuit -- it may well induce 60 cycle hum in the heater circuit.  Better to build a balanced supply which is humbucking.  If your PT's heater secondary lacks a CT (or just per general preference -- see Doug's Library of Info on heaters), create a virtual CT with 2X 100R resistors.  Run twisted pair wiring to all the heater lugs.

That's what I've done yeah... The PT has a HT CT so it's grounded, no need for the 100R resistors. I wired the heaters the "usual" way, like I said.
Thanks!

[HotBluePlates]

so use a 1N4007 diode, with the banded end connecting to the 56kΩ resistor.

Banded end (cathode) must connect to the 10K.

Thanks for the correction!

I followed the markings on the selenium rectifier on the layout without thinking about the fact the banded end has to be towards the tap to get negative voltage output.

That's what I get for blindly following a layout! I never looked hard at selenium rectifiers... are they usually marked backwards of what we'd see with silicon?

[sluckey]

I never looked hard at selenium rectifiers... are they usually marked backwards of what we'd see with silicon?

It is confusing. I've always hated the way some people labeled them. The schematic symbol is correct, but putting a plus sign by the cathode has always been confusing to me. Especially when the ONLY marking is a plus sign. I get it but I hate it.

And to further complicate things... When silicon rectifiers first started appearing in the early '60s it was common to mark the cathode end with a plus sign. Maybe a carryover from the selenium days. Tophats and bullets (looked like a .22 cal bullet, not the casing) were often marked with a plus sign or a diode symbol. There wasn't a solid marking convention. Later on the banded end became popular and the confusion began to disappear.

[SleepLess]

Can someone explain or give the best input jacks wiring for the 5F11? Must I connect all the sleeves (grounds) and shunt tips together and then run the board wires to the tips? Or is there a better way?
Thanks!

[sluckey]

I'd put the resistors on the jacks and run shielded cable directly to the tube.

[SleepLess]

I'd put the resistors on the jacks and run shielded cable directly to the tube.

Awesome pic!!! Thank you sluckey! I'll do this!

[SleepLess]

Hi there!
The amp is finished and sounds great save for some oscillation noise on teh vibrato when the Depth is turned past 6. Other than that it sounds gorgeous and is quiet. I'm about to install the bias mod now. The 10KL pot is installed but I need your help about how to implement it!

To me the B+ I have is too high since I have 406V at pins 3 of the 6V6s. That's with a new Sovtek 5Y3GT. With a NOS 5Y3GT (Phillips) I have 393V. That's better but hell the schematic says 340V at the + side of the first filter cap and I have 412V there!!!! What can I do??? I suppose the sound would be a lot different with this 70V difference there!!!

I have -39V at pins 5 of the 6V6s.

Heaters are good at 3.32V.
Tell me if you need anything, and here are some gut shots.
Thanks!

[sluckey]

it sounds gorgeous and is quiet.

Then don't worry about the B+.

Here's an easy bias mod...

[SleepLess]

Thanks a lot Sluckey! What do you think about my 406V B+? Is this normal as the schematic shows 340V???
Thanks!

[SleepLess]

Bias mod is done Sluckey, thanks. I have changed the lower 10K resistor for a 1.5K and the bias range is too small, I can only go from 9mA to 19mA. So should I try a 3.3k resistor instead of the 1.5K? Or 5K maybe? I don't know if I have those...
Thanks!

[SleepLess]

I'll answer to myself... 6V6GTs have a 12w max plate dissipation. (I have new Electro-Harmonix in there). 70% of that is 8.4W.
So: 8.4 / 406 = 20mA.

So I guess I can leave the resistors as they are and stick with 19mA... Am I right?
Thanks!

[sluckey]

So should I try a 3.3k resistor instead of the 1.5K?

yes

If 20mA is your target, then I would set the bias pot to mid position and change that bottom resistor until I had 20ma. Now you will be able to adjust below or above that 20mA. As you have it now, your 20mA target is at one end of the pot.

[SleepLess]

Thanks Sluckey!

[HotBluePlates]

To me the B+ I have is too high since I have 406V at pins 3 of the 6V6s. That's with a new Sovtek 5Y3GT. With a NOS 5Y3GT (Phillips) I have 393V.

Then use an NOS 5Y3 if it makes you feel better.

All Fender schematics have a prominent notice that all voltages are +/-20%. An original 5F11 will also read higher than the old schematic/layout due to higher wall voltage.

I wouldn't worry about it.

[SleepLess]

I wouldn't worry about it.

Fine then, thanks a lot!

[SleepLess]

HI there!
I just bought a OFF/STDBY/ON switch for this 5F11 and was wondering how to install it actually, I don't really get it...
Here's the link:
http://tubedepot.com/p-dpst-3way.html

Thanks!!!

[sluckey]

Refer to this diagram... http://site.tubedepot.com/pdf/p-dpst-3way.pdf

Terminals A and C will replace your existing Standby switch.
Terminals B and D will replace your existing Power switch.

FYI, Doug sells that switch now.

[SleepLess]

Refer to this diagram... http://site.tubedepot.com/pdf/p-dpst-3way.pdf

Terminals A and C will replace your existing Standby switch.
Terminals B and D will replace your existing Power switch.

FYI, Doug sells that switch now.

Hi Sluckey!
Yeah, the thing is that the 5F11 doesn't have any standby switch, currently I just have a power switch in there... So I currently have 2 wires going to the power switch and if I install the new one I need four wires to go to this new dpst-3way switch... How do I implement that?

[sluckey]

Refer to the original Fender 5F11 layout.

1. Look at the 5Y3 socket pin 8. Disconnect the yellow wire that connects to the board and the OT red lead. Don't disconnect the yellow PT wire!

2. Connect the red and yellow wires to terminal C of the new switch.

3. Connect a new wire between the 5Y3 pin 8 and terminal A of the new switch.

That takes care of the B+ side of the switch. You got the AC power side figured out, right?

[SleepLess]

Refer to the original Fender 5F11 layout.

1. Look at the 5Y3 socket pin 8. Disconnect the yellow wire that connects to the board and the OT red lead. Don't disconnect the yellow PT wire!

2. Connect the red and yellow wires to terminal C of the new switch.

3. Connect a new wire between the 5Y3 pin 8 and terminal A of the new switch.

That takes care of the B+ side of the switch. You got the AC power side figured out, right?

OK. I hope my OT red lead is long enough to reach the switch...
On the AC power side: power cord black live wire goes to D, PT white wire goes to B?

Thanks Sluckey!

[Phil_Tre]

it sounds gorgeous and is quiet.

Then don't worry about the B+.

Here's an easy bias mod...

Hey !
I know that it's an older thread but I found it very interesting...

My question is about bias range:

So the stock bias resistors are 10k for lower resistor and 56k upper one. I put a 10k pot to adjust the
bias, in serie after the 56k (that I substituted for a 47k).   Just to be clear: 10k to diode to 47k to pot.
Problem is, the range is too small, around 6mA, so is there a way to change the bias range with only a 10k pot ?
If I read correctly, it's by lowering the 10k (lower resistor) value ?? What about the 47 k after that ? Sorry I'm a
complete newbie and if someone have the correct resistor value it would be great...

Thanks for your help...

Philippe




 

[sluckey]

If you are going to use a 10K pot then replace the 47K resistor with a 10K.

[SleepLess]

Sluckey is the right man... You can't go wrong with him. The 5F11 is a great amp!
Cheers!

[Phil_Tre]

Thanks !!

Phil.

[lego4040]

Im glad this thread is pretty current, How did the amp finish up? Im interested in using my 5F1+ Allen amp as a donor for this project. Its Power transformer is TP 25 and specs are 310-0-310 @150ma, 6.3v @ 4.5amps, 5v @ 2amps and RED/GREEN center tap is 50v(Thats the one going to 10k in place of sel. rectifier) Not sure which Ot to get yet as this is in the way beginning stages. Im in total limbo on current amp build waiting on parts. I will take all advice with open arms

[SleepLess]

Im glad this thread is pretty current, How did the amp finish up? Im interested in using my 5F1+ Allen amp as a donor for this project. Its Power transformer is TP 25 and specs are 310-0-310 @150ma, 6.3v @ 4.5amps, 5v @ 2amps and RED/GREEN center tap is 50v(Thats the one going to 10k in place of sel. rectifier) Not sure which Ot to get yet as this is in the way beginning stages. Im in total limbo on current amp build waiting on parts. I will take all advice with open arms

Hi!
The amp turned out great! The 5F11 is a really great amp, you won't be disappointed. My favourite tweed is the Tremolux 5E9A but that's bigger and more powerful.
Good luck!