Rectifier mods

[AdamK]

Hi Guys!

Regular reader, first time poster. Hope I can gain some of your wisdom and expertise.

Built a KT66SE few years back, had issues with the 5U4G and would like to put some diodes in series with the plates, as attached sketch.

Seems to be that 1N4007 are the optimum choice for these protection diodes, I do have some, but also BY255 which are better rated. Will these be OK to use?

I would also like to consider replacing the 5U4G with SS rectifier, again either 1N4007 or the BY255, this time 2, or 3, in series with 10nf Parrallel caps.

I will have to account for not having 45v or so of voltage drop (from not using the 5U4G) and this would mean, refering to my  ropey power supply schematic, that the series dropper resistor would need to increase from 100R to 400R, dissapating close to 10W.

So, a couple of questions:

1) Will the load on the Mains TX differ now that the 5U4G is omitted? B+ needs to be 430v or so, and my unrectified ac voltage unloaded is 530v and loaded voltage around 495v. 495v - 45v (5U4G) = 450v as measured. So I suppose I'm asking do you think the loaded ac voltage, before rectification and omitting the 5U4G will still be 495v.

(Load is 2 x SE KT66's and 61mA each, 6n1P at 6.5mA per channel = 135mA total)

Finally, Is there anything I could do with the then redundant 5U4G? e.g. keep the heaters wired. Would like to keep it installed and have, at least, a little glow.

[SEL49]

There is no benefit for replacing the 5U4 with diodes in a SE amp. Save some headaches and just add the diodes to the 5U4 plates.

[mresistor]

[AdamK]

That's great guys thanks, could I just double check the BY255 are OK?

Just being extra cautious as 1N4007 are the norm.

Thanks in advance.

[SEL49]

BY255 is fine. 1300V_piv and 3A.

[kagliostro]

To me things are like this

SE amp don't need a Vacuum Rectifier, current consumption don't vary much from no signal to max signal so also with Vacuum rectifier no SAG is to be expected

Using a pair of Solid States diodes on an SE amp (but also in a PP amp) has the effect that if the PS used a Vacuum Tube rectifier and you swap it for Solid State diodes B+ level will increase (because of the miss of the internal resistance of a Vacuum Tube), so a difference in sound may happen (pay attention, B+ can increase too much for the circuit, verify)

Adding a pair of diodes in series of a Vacuum Tube rectifier has the effect to protect the circuit if one of the diofes in the Vacuum Rectifier shorts, the more, the Voltage that can be afforded increases, if your Vacuum Rectifier can afford 350V of B+, putting in series Solid State diodes will increase those 350+ of the voltage that can be afford by the Solid State diode you are using (1000V if you use 1N4007), so ig you have a good Tube Rectifier that can afford the current of your circuit but it can't afford the Voltage because it is too high for it, simply add a Solid State (1N4007 as an example) in series with the tube

Franco