Bogen MO-100 increase PS capacitor

[mazur]

Hi.

I finish recapping my Bogens MO-100. They sound fine, but I was thinking of increasing the size of the 2 capacitors off the GZ-34/5AR4. Stock there are two 30uF/500V caps off the dual rectifier, which gives me 15uF on B+ (see schematic = View attachment hfe_bogen_mo-100_schematic.pdf ). How high can I safely go without compromising the GZ-34? Is it worth doing - will I see an improvement on the lower end?

Thanks
Elias

 

[azazello]

You can put 2 x 68 uF.

 

[JonSnell Electronic]

Unless you have hum from the power supply, I would leave well alone otherwise cathode stripping can occur from excess charge current.

 

[Alastair E]

As advised--Leave as the Maker intended. You'll get no real benefit--only shorten life/destruction on the GZ34--which even 30 years ago, was an expensive valve, for what it is!

 

[Tom Bavis]

At that voltage, I wouldn't increase the input cap. PSUD simulation says 1.4A peak repetitive current if the peak load is 300 mA. That's pushing the 5AR4 rating (assuming they share equally...)

The cap on V2-7 is suspiciously low - .01 uF? I'd use at least .1, though they may have been trying to limit the low-frequency response (the step network that precedes it is also a high-pass, for low-frequency stability.)

 

[mazur]

Thanks for all the replies. I'll keep the cap as is. The amp has a very faint hum, barely audible. I did add a 3-wire power cord and connected the ground wire to a ground point different from the common PS caps ground. Could this cause the hum?

Thanks
Elias

 

[azazello]

Bigger cap on first position will decrease ripples about 2 time and decrease hmmmm. /I prefer listen without hmmm and buy after 3-5 years new rect. tube, than listen with hmmm/.