aa764 champ. can i use the extra node on the cap can?

[Jimmybjj]

...since it's not being used can i just add a extra stage of filtration? Would this improve anything? Would it cause any negative affects? Any affect at all?

if there is an advantage to using the node how would i wire it in? a resistor (what size and why) off the node before the first stage?

thanks for any input

[Enzo]

The schematic shows three 20uf/450v sections, and the wiring layout the same. Since I don;t have your amp to look at, what are the ratings of the unused section? is it an original cap or is it a cap that has been installed since the amp was made? In other words how old is the cap?

[ThermionicScott]

I'm a big fan of using 4x20uF cap cans in Champs for extra filtering. You can double up for the first stage (giving 40uF), which goes a long way toward killing that single-ended hum, or you can wire a power resistor between them to drop the B+, which is often super-high in BF Champs and really cooks the 6V6.

Some caveats:

* 40uF is beyond the max spec for 5Y3's, but they seem to tolerate it in Champ-style amps.
* The power resistor will generate heat, so don't locate it really close to the capacitor tabs.

- Scott

[Jimmybjj]

The schematic shows three 20uf/450v sections, and the wiring layout the same. Since I don;t have your amp to look at, what are the ratings of the unused section? is it an original cap or is it a cap that has been installed since the amp was made? In other words how old is the cap?

I have a new "ce manufacturing" 40/20/20/20 rates at 525v per section. currently using 40/20/20 with 40 being the first in line.

I'm a big fan of using 4x20uF cap cans in Champs for extra filtering. You can double up for the first stage (giving 40uF), which goes a long way toward killing that single-ended hum, or you can wire a power resistor between them to drop the B+, which is often super-high in BF Champs and really cooks the 6V6.

Some caveats:

* 40uF is beyond the max spec for 5Y3's, but they seem to tolerate it in Champ-style amps.
* The power resistor will generate heat, so don't locate it really close to the capacitor tabs.

- Scott

How do you determine which power resistor (plate is @390v) to use other than trial and error, i'm not opposed to this, just wondering if there is an easier way. Where would you use the 40 since it is not a 20x4?

[Jimmybjj]

Is the resistor between the first and second stages just a small as possible resistor to maintain the b+, or should i use a specific value for some reason i am unaware of.

[ThermionicScott]

How do you determine which power resistor (plate is @390v) to use other than trial and error, i'm not opposed to this, just wondering if there is an easier way. Where would you use the 40 since it is not a 20x4?

I just use trial-and-error, but you can guesstimate based on the current draw of the amp. If your cathode voltage is 20V and the cathode resistor has drifted up to 500 ohms , then that's 40mA. Figure 2mA more for the preamp tube, and you've got 42mA. If you want to drop your 390V down to 360V, then 30V / 0.042A = 714.3 ohms. Use a $1 750-ohm/5W and you're done.

Here's a gut-shot of a '66 Champ where I did this mod. Bear in mind, the B+ was nearly 440V, so it needed extra resistance to get the voltage down. I would use the bare minimum, so as to minimize the heat generated by the resistor.



The 1K/1W between the first and second stages (of the stock circuit) is to get an adequate amount of filtering for the 6V6 screen and preamp without incurring too much voltage drop. You can bump it up to 1.5K if you're one of those folks who gets uneasy looking at an idle screen voltage that's higher than the plate.

- Scott