F&Ts In A Rocket

[Blackburn]

Anyone here used a pair of the 47uf F&Ts for the reservoir in the Rocket? I know they make an 80uf, but that's one very large lytic and won't fit in the space I have allotted. I'm not worried about the paralleled value for the sake of the rectifier, just if it would be too much filtering at that point and affect the tone. F&Ts don't always read the marked value, so a pair might actually turn out to be more like 110uf or 115uf in parallel.

I do wonder what's under those top lytics in the JM build. They look like F&Ts and he'd have to be using three 47uf beneath. They're slightly shorter than the 22uf and that's kinda what I see going on there.

DK

[redshark]

If I was you I would put a 30uF and a 47uF so you don't hit too hard that GZ34!!

[Blackburn]

That seems to be the issue with hot switching. With the reservoir capacitance on the hot side of the standby there won't be the repetitive charging with each throw of the switch and won't bother the 5AR4. My issue is with the arrangement of the caps (The 30uf F&T is too large ) as well as what the added filtering might do to the tone. It's most likely negligible, but I'm still curious.

[rooster]

Use the two 47uf caps and place a 10 ohm 5 watt resistor between the two. And yes, I have done this without a problem. This is placed prior to the choke, btw.

[rp]

Use the two 47uf caps and place a 10 ohm 5 watt resistor between the two. And yes, I have done this without a problem. This is placed prior to the choke, btw.

You can do that? So, with the tiny 10ohm decoupling does it electrically perform like 47 or 100 with respect to the rectifier? I'd guess 47 or you wouldn't have done it. Sonically/feel-wise does it act like 47 or 100? Or somewhere in between?

[rooster]

Sonically and feel-wise it's good. And this addition might seem unusual but it's an old hi fi thing. The ten ohm 5 watt resistor acts as a minimal buffer between cap stages so that electrically the current flow is limited on charge up. Once the initial charge is made, the resistor becomes more 'invisible' to the current flow, yet still divides the caps. At least that is my explanation and experience. Less ripple, sure, but now there's more reserve in the power supply, too.

But also, now seeing the pic and understanding Blackburn's question better, I would say that they, JM, probably do use two 47ufs. In this case, because the GZ34 is so slow on warm up, that 80 or 100ufs reserve is created gradually. This wouldn't cause a problem with the GZ34.

[Blackburn]

Rooster, I think that resistor placement would be a good idea for any rectumfrier that one might worry about regarding reservoir capacitance and I may just try it if I come to this type of setup in the future. I agree that it would add a desirable feel to the amp.

My decision now is whether to use three 30uf underneath, or 47uf. I pulled one of my old 30uf F&Ts and checked the fit and three will work. I just didn't want to mix values on the bottom. The picture seems to show three 47uf, but often times grainy images can be deceiving... Less filtering or more? I have both values and simply need to choose.