Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Joe6v6 on April 08, 2018, 03:50:54 pm
-
If I wanted to use a cap can that has a shared ground for 2 - 100 UF caps is there a way to wire it that would that would work for these two separate caps?
-
Sorry, impossible.
-
Thats what I thought - but I had to ask. Thanks : Joe
-
Those two caps are in series with two 220K balancing resistors, meaning the voltage rating is now 700 watts and only 50uf. Must be an amp that has high plate voltage.
-
fwiw
some have "gutted" old metal caps and repopulated with modern small caps, probably sneak in a couple R's also. :dontknow:
-
You can use the multi section cap in the following way.
Move the cap after choke in series with one of the multi section cap.
/Leevi
-
Those two caps are in series with two 220K balancing resistors, meaning the voltage rating is now 700 watts and only 50uf. Must be an amp that has high plate voltage.
Caps get expensive past 450v, and hard to find past 500v... this makes series caps necessary (or cheaper) for as low as 500v. Once a series setup was picked, 350v might have been cheapest or most available. I haven't seen many 275v caps, even if the voltage isn't high enough to require 350v.
This brings up another issue though, if the first set of caps needs more than 450v tolerance how can the second cap, after the choke be safe? Only if the tubes are warmed up and draw power the instant it's applied to that second cap. That's the function the standby switch, which we've now decided isn't needed, serves in these older amps.
I'd encourage rethinking this design based on what's available now-- cheaper caps, to use a series pair after the choke. That lets you forget about the standby switch which can cause more trouble than good (especially if it's protecting the PS caps, and you forget to use it!)
-
Thanks for the replys - I was thinking the same thing about modifing a cap can in some way, I have attached the schematic Im going to be using. I probably wont use the fet input & also I will be using 5v taps on the power trans for the relays. If those 2 caps on the schematic add up to 50uf I dont see why I couldent just use 1 cap rated at 500v or would that not be enough? my power trans is 325-325 @ 200 ma. Thanks : Joe
-
I wouldn't even bother with stacking caps. The max B+ you can get from that PT in that circuit is 460VDC.
-
47uf @500 volts are cheap and available, would work fine in that amp, IMO. You could buy two 100uf @350 wired in series but not needed, I have a 330-0-330 PT, with SS, B+ off the diodes is 425v loaded with EL34s. I have a 32uf @500v cap, no problems.
al