Debugging help: Brownface vibrolux edition

[matoni]

Sorry thats what I meant, it wasn't putting out 365VDC it was putting out 365VAC. I mistyped. Sorry!!

[sluckey]

Sorry thats what I meant, it wasn't putting out 365VDC it was putting out 365VAC. I mistyped. Sorry!!

Yes, I figured that. But my main point was "You are using a wrong transformer."

[matoni]

Ok. Will a 35V difference really make this much of a difference?

Do you have a recommendation for an output transformer? This is the one Hammond said to use, but they of course could be wrong. I will do some research and let you all know what transformer I plan on getting. Thanks again for all of your help.

EDIT: I couldn't any transformers with a 660 secondary output (330 on each tap) and the two yellow secondary wires (no clue what they're called) that would give me the ability to have a tube rectifier. I am completely fine with sacrificing this, as long as it will make the amp work, but before I shell out another $125, I want to be sure that this is where my issue is. Is the behavior I am seeing characteristic of this?


Let me recap: I currently have a 290CX power transformer installed, which is what is speced for a Fender Blackface vibrolux. What I have built is a Fender BROWNFACE vibrolux. What the difference is other than the tone stack and tremolo, I'm not completely sure (I would love it if someone could explain, again I am only 16 and am just getting into amp building). I am currently getting no sound when I plug into the effects return, but I am getting loud, gainy notes to come through when I play a note on my guitar. The volume must be up at around 50% or higher for this to occur though. I can't find any PTs other than those for Deluxe Reverbs that supply the correct amount of voltage (330 of each tap, 660 total) with a yellow secondary wire (no clue what its called, please let me know so I stop sounding like an idiot) that would allow me to put in a tube rectifier. The only problem I can forsee with putting a Deluxe reverb PT in this amp is that it may not have enough juice to supply to the output transformer and the 2 6L6GCs. Im not completely sure if this is a problem, and I'd love if someone showed me a tool to figure out how to calculate how much load is needed. I am happy to buy a new PT, but I want to be sure that its the problem before shelling out a ton of cash for a new one. If anyone needs more pictures or anything to help me, I am happy to send them along.

This is a learning experience for me, and I have found that I learn the most through the process of debugging with helpful, experienced folks like you all. Let me know if there is anything I can do for any of you in return. I love learning and am so glad I found such a constructive community to help me learn.

Thanks!!

[Stevem]

Take advantage of the excess PT voltage and add another stage of filtering and another dropping resistor to dump that 35 volts or so and then your well on the way to a very low noise floor once the amp is up and running.

All that said I don't see why your 5AR4 would be red plating, but since it did its very likely well on its way to the garbage can now.

[martin manning]

Are you following the 6G11-A Schematic and layout?
You have used pcb's, where did those come from?
What modifications have you made?
You mention an FX loop, where and how is that done?
Any other changes?

The easiest way to drop some B+ voltage is to install a 5U4GB rectifier. That should knock it down 30-40V. Your 290CX PT has the required 3A 5V rectifier heater winding.

[sluckey]

That 290CX will be fine for a 2 x 6L6 amp. You say your B+ is 500vDC instead of 365vDC. You need to qualify that by telling us what conditions you measured 500V, ie, was the STBY switch in standby mode? Or were the output tubes plugged in? Things like that.

Once this amp is working properly with no bugs the B+ will drop down from that 500V. I think you still have wiring errors in the amp. And your lead dress could be greatly improved. Find some pics of the 6G11 and try to make your wiring look like that.

Print the schematic and use a highlighter pen to trace through the amp. Start at the input jack and go to the grid of V1. Verify your amp wiring agrees with the schematic. If so, highlight that part of the circuit. Continue doing this until you get to the speaker. If you don't find any errors print another copy of the schematic and repeat. Most people find wiring errors on the first pass.

[matoni]

Hello, sorry for my absence yesterday

That 290CX will be fine for a 2 x 6L6 amp. You say your B+ is 500vDC instead of 365vDC. You need to qualify that by telling us what conditions you measured 500V, ie, was the STBY switch in standby mode? Or were the output tubes plugged in? Things like that.

Once this amp is working properly with no bugs the B+ will drop down from that 500V. I think you still have wiring errors in the amp. And your lead dress could be greatly improved. Find some pics of the 6G11 and try to make your wiring look like that.

Print the schematic and use a highlighter pen to trace through the amp. Start at the input jack and go to the grid of V1. Verify your amp wiring agrees with the schematic. If so, highlight that part of the circuit. Continue doing this until you get to the speaker. If you don't find any errors print another copy of the schematic and repeat. Most people find wiring errors on the first pass.

I like this method and will probably try this when I get time. THe power tubes, preamp tubes, speaker, etc were all plugged in. The amp doesn't have a standby switch, so it was on.

Are you following the 6G11-A Schematic and layout?
You have used pcb's, where did those come from?
What modifications have you made?
You mention an FX loop, where and how is that done?
Any other changes?

The easiest way to drop some B+ voltage is to install a 5U4GB rectifier. That should knock it down 30-40V. Your 290CX PT has the required 3A 5V rectifier heater winding.

I made my own PCBs, and ordered them from JLCPCB. once I finish the amp build and am sure it works, I will post the gerbers on my GitHub and website. I will try a new rectifier tube if Sluckey's methodic search suggestion doesn't yield any errors (which I'm sure it will). I also plan on making a post on this forum on how I make my PCBs to try to give back to this great community.

No mods were made to the circuit, other than the effects loop. THis was done directly after the 2 270K (i believe) mixing resistors. I buffered with a .1uF orange drop cap.

[martin manning]

If your power transformer is designed to go in a Blackface Vibrolux you will likely have some extra voltage wrt the levels on the Brown (vs. Black) Vibrovlux schematic (365V vs. 415V at the OT CT). No doubt it will work with higher voltages, but if you want to replicate the brown amp tone you should at minimum get the preamp voltages right (adjust the first resistor after the screen filter capacitor to do that). I think a 5U4 will get it at there, though.

[sluckey]

I will try a new rectifier tube if Suckley's methodic search suggestion doesn't yield any errors

Make a better effort to get people's names correct. Some are sensitive and may find that disrespectful or even insulting.

[matoni]

OMG I'm so sorry Sluckey. I didn't mean that. I have edited it above. I'm so sorry I legitimately thought that that's what your name was... I guess I should read more carefully.

I will trace it whenever I get time.

the screen resistors are the ones on the PCB that control how much voltage gets into pins 1 and 6 of the preamp tubes correct? (Just making sure, my terminology could still use some work. Between my other hobby and this there's so much terminology I need to learn)

[Colossal]

I will try a new rectifier tube if Suckley's methodic search suggestion doesn't yield any errors

Make a better effort to get people's names correct. Some are sensitive and may find that disrespectful or even insulting.

Since this has been edited, I can delete if desired. I figured auto-correct maligned Steve's good name and it wasn't intentional on Matoni's part. Let me know.

[matoni]

You dont have to delete my mistake, I misread his name. I apologize for this accident and will make sure to be more careful in the future.

SOrry again.

[sluckey]

the screen resistors are the ones on the PCB that control how much voltage gets into pins 1 and 6 of the preamp tubes correct? (Just making sure, my terminology could still use some work. Between my other hobby and this there's so much terminology I need to learn)

Your screen resistors are mounted on the tube sockets. They have nothing to do with voltage on the preamp tubes.

[matoni]

Oh im sorry. I still don't have the terminology completely down.my new understanding is that the The screen filter cap is the 470 ohm resistor on the tube socket lowering the voltage going into the output tubes. Let me know if this is correct. Im trying to learn all I can about this. Thanks to all of you for taking me under your wing and teaching me how to do this.

[matoni]

Just put in an extra 10k ohm 1 watt screen resistor. The A+ (With all tubes plugged in, no standby switch on because the amp doesn't have a standby switch) now reads at 358vDC, which is well within the tolerance of the 365vDC that it should be at. It sounds incredible now. Thanks everyone for your help with this, especially Sluckey for being super active and teaching me a ton about the terminology and etiquette of forums such as TAG. Thanks to all of you. until next time (when I will be building a standalone reverb unit... should be fun)

thanks again,

matoni