GZ34 with 50uf filter cap???? (Marshall Lead 20)

[greg]

I have built a clone of a Marshall Lead and Bass 20 which specifies 50uf + 50uf for the first two filter caps. I built this into an existing chassis which had a tube rectifier and I used a Groove Tubes solid state rectifier plug-in adapter in the slot. I didn't care for the sound and have since been using a GZ43 rectifier to smooth it out. Then I came across some information about the danger of using too high of a capacitance after a tube rectifier.

In short, is what I am doing safe or must I reduce the value of the first capacitor??

Thanks

Greg

[MWJB]

You'll be fine with 50uf as your 1st filter with a GZ34 (it will take 100uf). This is what any GZ34 equipped 5F6A reissues/Kendrick 2410s have, as well as any large BF Fenders that have been serviced and had the 1st stage filters replaced with 2x100uf in series (very common practice).

If you have a standby switch that breaks the B+ rail after the rectifier, it would be a good idea to move the 1st stage filter "+" connection (this wire ONLY) to the hot side of the switch, rather than the cold side, if it doesn't connect there already.

[greg]

Good news, then. Thanks for the reply.
Greg

[KevinOConnor]

Hi Guys

You can also retain the solid-state rectifiers and add a series resistance feeding the first filter. This will mimic the tube's internal resistance.

Note that two 100uFs in series equals 50uF. They have to be in parallel to add together as 200uF.

Remember to add a bleeder across the first or second filter cap - 330k-1W - so the caps will be drained upon power-down.

Have fun