FDR new build - needs drain down resistor

[Petedub]

Hello again, My FDR head is near completion.

It is all wired up but not yet working. I am fairly sure it will work soon, voltages are coming up about right.

Unfortunately my V1 socket is not accepting a valve so that looks like it might need to be replaced (and I have not got a spare base).

Anyway all this aside, I have tried to build a replica of the AB763 Deluxe Reverb, however I would like to add a drain down resistor, can anyone please recommend the best location and value resistor for this particular model.

I have attached some photos, I am a musician more than an electrician and I've tried really hard but it's not as good as other ones one this site.  Any constructive advice would be welcome.

[acheld]

the best location and value resistor

I would put a 470K 1 watt resistor in parallel with your 16uF caps in the doghouse.   If you don't want to go back to the doghouse, you could wire it up at your standby switch to the connection where your B+ comes in.  To me, the doghouse will keep it out of the way and will be neater.

Truth is, it doesn't matter where you place this along the power rail for it to work as a drain, so long as the standby switch is closed.  Personally I'd want it "before" the standby switch so that someone doesn't place the amp in standby, turn it off, and assume that the caps have been drained.   

Of course, anyone with any technical knowledge would approach an open amp as if the caps are charged, no matter the circuit . . .

Assuming B+ of 450V, a 470K resistor will drain about 1mA, at less than 1/2 watt power dissipation.   Any modern resistor type would be ok.     

And, your pictures and build are great.   

[HotBluePlates]

Unfortunately my V1 socket is not accepting a valve so that looks like it might need to be replaced (and I have not got a spare base).

Tech Tip:
   Soldering socket contacts can sometimes allow solder to flow down into the space where the tube pin is supposed to go, preventing tube insertion.  Other times, the socket contacts can be held in a position by the solder that doesn't provide proper spacing to allow tube insertion.

   To fix either case, insert a tube into the socket before/while soldering.  This will hold the contacts in the proper orientation, and act as an obstructive heatsink to prevent solder from going where it shouldn't.  I haven't experienced damage to the tube used, but you might use a worn out or broken tube to insure there's no impact.


   You might even use desoldering braid to remove all the solder from your present V1 socket, then re-solder using the method above.  Of course if a poorly-made ceramic socket has the wrong pin spacing or too-narrow holes for pins then this method won't resolve the issue.

[tubeswell]

Any value between 100k* to 500k will work. 100k will drain slightly faster on power off but will want to be higher wattage than a 500k.

(*e.g., a Marshall 1959 Super Lead uses 50k 5W in parallel with each reservoir cap - with the pair of filter caps in series).

Calculate the resistor’s power-handling requirement (using Ohms law solving for power) and rate the resistor for the nearest commonly  available value above 2x the peak power the resistor will dissipate.

If your amp has a standby switch in series with the B+ rail, the location of the standby switch relative to the location of the bleeder resistor can affect whether you need to leave the standby switch on after powering off the amp, in order for the resistor to drain all the filter caps.