diode rectifier mod on 5e3

[fredouille]

Hi all

i will do the mod of robinette on a 5e3 using 1n5408 , not sure of my aliexpress 1N4007, if they burn and short in diode rectifier mode, i don't want to see what can happen

point is , voltage B+ will increase around 20v as I understood , any idea for this ? voltage devider after the diodes before arriving to B+ ? value or resistor for those we already did it ?

at the end, I would love to have same B2 voltages to really compare the 2 rectifing methods

[martin manning]

You need a series resistor at the rectifier output (DC side), or a resistor on each of the PT leads (AC side) to bring the voltage back to the original level. A vacuum rectifier's voltage drop is nonlinear, so the resistor(s) will not exactly duplicate the vacuum rectifier's characteristics. Many would say it's close enough.

[fredouille]

yes this is what I'm thinking.. on the diode output , a dropping resistor.

need to calculate it, I will first don't put to calculate the current on the line fully loaded, then calculate the resistor considering the voltage dropping needed. I understood it is about 20 volts more.

[R.G.]

The 5U4 vacuum rectifier is faked reasonably well by rectifier diodes and a 100 ohm resistor. The resistor probably needs to be at least 20W, or two 51 ohm 20W resistors to keep the temps down.

[fredouille]

The 5U4 vacuum rectifier is faked reasonably well by rectifier diodes and a 100 ohm resistor. The resistor probably needs to be at least 20W, or two 51 ohm 20W resistors to keep the temps down.

I did some quick calculations.. I don't have power tubes as power transformer not here

I calculated the current and to drop 15 volt of difference I need 1,5K, I will see with power tubes

by the way it is strange, I put also the protection diodes before the tube rectifier as advised here : https://robrobinette.com/5e3_Modificati ... ier_Switch I have B+ from 420 to 380 v with the same load.. lets see with power tubes but it is strange to loose so much, i'm wondering if it is good this mod to add diodes before

[sluckey]

by the way it is strange, I put also the protection diodes before the tube rectifier as advised here : https://robrobinette.com/5e3_Modificati ... ier_Switch I have B+ from 420 to 380 v with the same load.. lets see with power tubes but it is strange to loose so much, i'm wondering if it is good this mod to add diodes before

Protection diodes connected per Rob's schematic should not cause the B+ to drop from 420 to 380. I suspect you have one of the diodes connected backwards which would effectively turn the rectifier into a half wave rectifier and that would cause a significant drop in B+.

[Stevem]

Adding those big wattage resistors will dump more heat into the chassis and PT then a recto tube will and you will get sag just from that after a while.

If you want a stiffer playing amp then you do not want 5E3 to start with!

These amps are loved for exactly what you want to change about them.

If you want Apple juice in the morning then don’t buy Orange juice!