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| Power supply Filter cap solutions - method one | |
| There is more helpful info on this page | |
| Click on the small images to see the full sized photo. | |
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This is the standard 5F6A Bassman cap can arrangement
like you would find on the original amps. I will be
using 5 - 20uf/500v Sprague atom filter caps. The
negatives of all the caps are soldered to the can
itself and then the can must be screwed down tight
to the back of the chassis so that the four corners
of the can make good contact with the chassis. That
way you will get a good ground contact between the
can and the chassis. The positive ends of the caps
are clipped short. There will be four positive wires
that are soldered to the filter caps and then exit
out of the can through a rubber grommet. The four
wires go to each of the four filtration stages you
find on the Bassman circuit. You can secure the caps
to the metal can with double stick tape, glue or RTV
silicon.
All of these parts can be found in my on line parts catalog. See the link at the bottom of this page. The cap can and the grommet are on the Hardware/Handles page. The 20uf/500v caps are on the capacitors page. |
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Here you can see that I have taken a small Fender re-issue cap can and drilled 5 holes for each negative/ground connection. |
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Twist the first two capacitors positive leads together to make two 20uf capacitors in parallel. This is the first stage of filtration downstream from the rectifier. 20uf + 20uf = 40uf total filtration on stage one. Stages 1 through 4 are numbered in the photo. |
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Push the negative leads of each cap through the drilled holes, bend them at a 90 degree angle and then clip them to about 10cm or roughly 3/8". Solder all the negative leads to the filter can. You may need a 50 watt or more soldering iron to be able to solder the leads properly. The can will suck the heat right out of a small solder iron. |
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Here you can see that I took one of the 1/2" grommets that I sell and cut out a small wedge so that it would fit into the cap can hole. The four positive wires exit through this grommet and go inside the amp to the circuit board. |
| Power supply Filter cap solutions - method two | |
| Click on the small images to see the full sized photo. | |
| Here is another way to do the filter caps without a cap can. All the filter caps are inside the chassis going point to point. The stage one filter caps are between the power transformer and the circuit board on an 8 lug terminal strip. The remaining three stages are along the front edge of the chassis, under the pot harness. | |
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Here you can see the whole chassis and all five filter caps. |
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These are the two main stage one filter caps mounted
to an 8 lug terminal strip. I have done a series arrangement
here of two 100uf/350v caps. You could do a parallel
arrangement here also. The bottom lug (#1), and the
top lug (#8), of the 8 lug terminal strip are bolted
to the choke holes in the chassis. The choke is on
the other side of the chassis bolted to the same holes.
The resistors are bleeder resistors. You can see more
info about parallel and series cap arrangements on
this page. The bottom lug #1 acts as the chassis ground for the filter caps. You can also run a wire from this lug to the main power transformer ground lug. Lug #2 is the main B+ connection. Lug #7 is where the two caps and two resistors are all soldered. Lugs 3, 4, 5, 6 and 8 are not used. Note that the top lug, #8 of the terminal strip is not connected to anything except the chassis. |
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Here you can see the last 3 stages of filtration. The positive ends of the caps go right to the lug on the circuit board. The negative ends are all soldered to the buss wire that runs down the back of the pot harness. I have put some #18 gauge red wire jacket on the positive ends of the cap leads as a safety feature. The caps are all tucked neatly under the pots and out of the way. |
| Power supply Filter cap solutions - method three |
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Another way is to make an insulated filter cap circuit
board. All the capacitors are mounted on the circuit
board and a filter cap can covers the whole arrangement.
The filter cap circuit board must be insulated from
the chassis. All the positive and negative wires must
go to the filter cap circuit board from the main circuit
board. This is the way Fender did many of their combo amps. This method is way more work than is necessary. The two above methods are way easier and work great. |
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