Dumble 102 ODS

[rdavy]

If for some reason you want to run an LED from the filament supply, just copy this little circuit that Fender has used for a long time across the AC heaters. D9 is just any silicon rectifier diode you have on hand. It's purpose is to shunt the reverse phase away from the LED. The reason being reverse polarity shortens the life of LED's. R56 is 150-ohms for most common type Red LED. Other colors may require a little less resistance, just depends on the color and brightness of the LED.

I've run the LED's from any handy DC supply rail, but they tend to stay on a while after the power is turned off, depending on how long the filter capacitor on that power rail takes to discharge. This particular circuit turns on and off instantly with the power mains switch.

LED-filament-power.jpg

Are you able to run more than one LED like this? I want to run a second LED and switch it with the unused half of the standby switch.

[The Quadratus]

Hoping to fire it up for the first time this weekend.

You got a current limiter?

I have a variac and a wattage/voltage/amperes readout.
Will ramp it up very, very slowly and make sure voltages etc are looking good before I go anywhere near full voltage.
But, I appreciate your concern, sir

[nuke]

Are you able to run more than one LED like this? I want to run a second LED and switch it with the unused half of the standby switch.

Yup, since the filament supply generally capable of many amps to run the heaters, and LED's are about 10-20 milliamps each (that's 0.010 amps) you can run a heck of a lot of them like that! Just duplicate the circuit in the box for each LED and send one of the legs through the unused switch section.

I've seen builds where a string of LED's wired similarly were used to light up the whole face panel.

[rdavy]

Are you able to run more than one LED like this? I want to run a second LED and switch it with the unused half of the standby switch.

Yup, since the filament supply generally capable of many amps to run the heaters, and LED's are about 10-20 milliamps each (that's 0.010 amps) you can run a heck of a lot of them like that! Just duplicate the circuit in the box for each LED and send one of the legs through the unused switch section.

I've seen builds where a string of LED's wired similarly were used to light up the whole face panel.

Great, thank you!

[The Quadratus]

Hoping to fire it up for the first time this weekend.

You got a current limiter?

So, just powered it up on the variac.
Got up to about 200v AC (we run at 240vac here in Aus).
All voltages look good, slightly concerned about the heater voltage, but, I reasoned I have an artificial centre tap with 2 100ohm resistors to ground, so they are reading 3.5ish Vac.
I am concerned that I started getting somewhat of a slight hum (nothing plugged in, no tubes, all pots at 0). Verified bias pot working fine.

Should I be concerned about the hum? Sounded like transformer hum, and maybe a hum from the relays.................. Couldn't really pinpoint where it was coming from.

[desertmouth90]

Hoping to fire it up for the first time this weekend.

You got a current limiter?

So, just powered it up on the variac.
Got up to about 200v AC (we run at 240vac here in Aus).
All voltages look good, slightly concerned about the heater voltage, but, I reasoned I have an artificial centre tap with 2 100ohm resistors to ground, so they are reading 3.5ish Vac.
I am concerned that I started getting somewhat of a slight hum (nothing plugged in, no tubes, all pots at 0). Verified bias pot working fine.

Should I be concerned about the hum? Sounded like transformer hum, and maybe a hum from the relays.................. Couldn't really pinpoint where it was coming from.

Can you post a pic around the 100/200uf Filter caps?

[The Quadratus]

You got a current limiter?

So, just powered it up on the variac.
Got up to about 200v AC (we run at 240vac here in Aus).
All voltages look good, slightly concerned about the heater voltage, but, I reasoned I have an artificial centre tap with 2 100ohm resistors to ground, so they are reading 3.5ish Vac.
I am concerned that I started getting somewhat of a slight hum (nothing plugged in, no tubes, all pots at 0). Verified bias pot working fine.

Should I be concerned about the hum? Sounded like transformer hum, and maybe a hum from the relays.................. Couldn't really pinpoint where it was coming from.

Can you post a pic around the 100/200uf Filter caps?

Can do you one better:

https://rumble.com/shorts/v7fbktu

[desertmouth90]

So, just powered it up on the variac.
Got up to about 200v AC (we run at 240vac here in Aus).
All voltages look good, slightly concerned about the heater voltage, but, I reasoned I have an artificial centre tap with 2 100ohm resistors to ground, so they are reading 3.5ish Vac.
I am concerned that I started getting somewhat of a slight hum (nothing plugged in, no tubes, all pots at 0). Verified bias pot working fine.

Should I be concerned about the hum? Sounded like transformer hum, and maybe a hum from the relays.................. Couldn't really pinpoint where it was coming from.

Can you post a pic around the 100/200uf Filter caps?

Can do you one better:

https://rumble.com/shorts/v7fbktu

C17 you have two connections to Ground?

[The Quadratus]

Can you post a pic around the 100/200uf Filter caps?

Can do you one better:

https://rumble.com/shorts/v7fbktu

C17 you have two connections to Ground?

No Sir, the thing you're seeing on the left is the jumper, and the one on the right is the actual ground wire going to ground point 2.

[desertmouth90]

So, just powered it up on the variac.
Got up to about 200v AC (we run at 240vac here in Aus).
All voltages look good, slightly concerned about the heater voltage, but, I reasoned I have an artificial centre tap with 2 100ohm resistors to ground, so they are reading 3.5ish Vac.
I am concerned that I started getting somewhat of a slight hum (nothing plugged in, no tubes, all pots at 0). Verified bias pot working fine.

Should I be concerned about the hum? Sounded like transformer hum, and maybe a hum from the relays.................. Couldn't really pinpoint where it was coming from.

Can you post a pic around the 100/200uf Filter caps?

Can do you one better:

https://rumble.com/shorts/v7fbktu

Okay, make sure you have around -50v bias voltage at the pot. Then you can fire it up with the valves in.

Are all your voltages good?

[The Quadratus]

Can you post a pic around the 100/200uf Filter caps?

Can do you one better:

https://rumble.com/shorts/v7fbktu

Okay, make sure you have around -50v bias voltage at the pot. Then you can fire it up with the valves in.

Are all your voltages good?

I am assuming none of the ones you built Vibrate/hum?

So, I only worked up to 200Vac, and the voltages at pin 6/4 on the power tubes were around 304, voltage at pin 5 was around -40.
was seeing roughly 10v at the voltage doubler section, so, voltages were correlating nicely according to the voltage I was feeding the thing.
I had nothing plugged in, no tubes, no cables. Was reading 20.5ish mAmps across the AC input, but when I noticed the hum/vibration the Amp reading was jumping a bit from mid/high 20mAmps to low 30mAmps, it was a bit erratic.
I then decided to power it down and try to think about what could be potentially causing it. I know transformers can hum/vibrate, it is a thing, but, am unsure if that is what is going on here.

Tubes arrive tomorrow. Then, have to figure out how to bias the PI

Edit: Voltages at pin 3 of the power tubes was also reading correctly for the voltage I was feeding it.

[desertmouth90]

Can do you one better:

https://rumble.com/shorts/v7fbktu

Okay, make sure you have around -50v bias voltage at the pot. Then you can fire it up with the valves in.

Are all your voltages good?

I am assuming none of the ones you built Vibrate/hum?

So, I only worked up to 200Vac, and the voltages at pin 6/4 on the power tubes were around 304, voltage at pin 5 was around -40.
was seeing roughly 10v at the voltage doubler section, so, voltages were correlating nicely according to the voltage I was feeding the thing.
I had nothing plugged in, no tubes, no cables. Was reading 20.5ish mAmps across the AC input, but when I noticed the hum/vibration the Amp reading was jumping a bit from mid/high 20mAmps to low 30mAmps, it was a bit erratic.
I then decided to power it down and try to think about what could be potentially causing it. I know transformers can hum/vibrate, it is a thing, but, am unsure if that is what is going on here.

Tubes arrive tomorrow. Then, have to figure out how to bias the PI

Edit: Voltages at pin 3 of the power tubes was also reading correctly for the voltage I was feeding it.

The 100w one I did yes, I friend 4 JJs too. Thats when I realised I wired the Bias pot wrong!

Do you have a dummy load on the OT?

Id try 240v, not much difference between 200v and 240v (I know its nerve racking).

[The Quadratus]

Okay, make sure you have around -50v bias voltage at the pot. Then you can fire it up with the valves in.

Are all your voltages good?

I am assuming none of the ones you built Vibrate/hum?

So, I only worked up to 200Vac, and the voltages at pin 6/4 on the power tubes were around 304, voltage at pin 5 was around -40.
was seeing roughly 10v at the voltage doubler section, so, voltages were correlating nicely according to the voltage I was feeding the thing.
I had nothing plugged in, no tubes, no cables. Was reading 20.5ish mAmps across the AC input, but when I noticed the hum/vibration the Amp reading was jumping a bit from mid/high 20mAmps to low 30mAmps, it was a bit erratic.
I then decided to power it down and try to think about what could be potentially causing it. I know transformers can hum/vibrate, it is a thing, but, am unsure if that is what is going on here.

Tubes arrive tomorrow. Then, have to figure out how to bias the PI

Edit: Voltages at pin 3 of the power tubes was also reading correctly for the voltage I was feeding it.

The 100w one I did yes, I friend 4 JJs too. Thats when I realised I wired the Bias pot wrong!

Do you have a dummy load on the OT?

Id try 240v, not much difference between 200v and 240v (I know its nerve racking).

I do not have a dummy load on the OT. I found out that I did not need one if no tubes are plugged in. (wired my 1975 Fender Twin and got everything up and running without tubes and no load when checking my work and only plugged in the speaker when I plugged in the tubes for power up and biasing)

And, yes, it is bloody nerve wracking. Bloody jumped at any little noise that happened, whether it came from the direction of the amp or not

Any suggestions on where/how to get a decent dummy load?

[desertmouth90]

I am assuming none of the ones you built Vibrate/hum?

So, I only worked up to 200Vac, and the voltages at pin 6/4 on the power tubes were around 304, voltage at pin 5 was around -40.
was seeing roughly 10v at the voltage doubler section, so, voltages were correlating nicely according to the voltage I was feeding the thing.
I had nothing plugged in, no tubes, no cables. Was reading 20.5ish mAmps across the AC input, but when I noticed the hum/vibration the Amp reading was jumping a bit from mid/high 20mAmps to low 30mAmps, it was a bit erratic.
I then decided to power it down and try to think about what could be potentially causing it. I know transformers can hum/vibrate, it is a thing, but, am unsure if that is what is going on here.

Tubes arrive tomorrow. Then, have to figure out how to bias the PI

Edit: Voltages at pin 3 of the power tubes was also reading correctly for the voltage I was feeding it.

The 100w one I did yes, I friend 4 JJs too. Thats when I realised I wired the Bias pot wrong!

Do you have a dummy load on the OT?

Id try 240v, not much difference between 200v and 240v (I know its nerve racking).

I do not have a dummy load on the OT. I found out that I did not need one if no tubes are plugged in. (wired my 1975 Fender Twin and got everything up and running without tubes and no load when checking my work and only plugged in the speaker when I plugged in the tubes for power up and biasing)

And, yes, it is bloody nerve wracking. Bloody jumped at any little noise that happened, whether it came from the direction of the amp or not

Any suggestions on where/how to get a decent dummy load?

Yeah you make a good point!

With your Control grid stoppers what values do you have?
I made a mistake of using 5.1ohm instead of 5.1k resistors before. Just double check that.

You can build one using 50/100w Wire wound resistors, Or use a load box, or you can use a speaker.

is the hum your power transformer?

[The Quadratus]

The 100w one I did yes, I friend 4 JJs too. Thats when I realised I wired the Bias pot wrong!

Do you have a dummy load on the OT?

Id try 240v, not much difference between 200v and 240v (I know its nerve racking).

Yeah you make a good point!

With your Control grid stoppers what values do you have?
I made a mistake of using 5.1ohm instead of 5.1k resistors before. Just double check that.

You can build one using 50/100w Wire wound resistors, Or use a load box, or you can use a speaker.

is the hum your power transformer?

My grid stoppers are 5.1kOhm. Just double checked to make certain of it.
I think it might be one of the transformers, but, can't tell. I put my ear close to the underside of the chassis, and couldn't tell if it was coming from there or from inside the chassis.

I guess we bias it up and see what happens, if anything.
Going to plug in my Fender twin reverb speakers as they are 4ohm and I have the identical fender twin Hammond OT.