Switches for 1/2 power setting and increased filtering...

[dehughes]

Hello yet again,

I'm doing two things at present on my build:

1) I'm going to install a 1/2 power switch like the DC30 where one cathode bias resistor is switched in to series after another (62ohm + 68ohm), and would like to know what type/model of switch is best suited to this function.

2) I'm going to also install a switch that, when on, brings additional electrolytic caps into the circuit, increasing filtering in either the preamp or power amp sections (haven't decided yet as to where exactly I want to kick up the filtering....probably the preamp). What type/model of switch would be ideal for this function?

THANKS SO MUCH.

[UR12]

What are you building?

[dehughes]

What are you building?

4 x EL84, two channel, AC/DC30ish amp with both EF86 and 12AX7 channels. I'm looking for two switches: one that will switch in an additional cathode resistor in series for the EL84s (a la the DC30), and one that will switch in an additional electrolytic for either the pre or power section (haven't decided yet).

[UR12]

I would use the same switch that that your using for the Standby switch. Might be a little over kill but you shouldn't have any problems as far as ratings for current and voltage (6A 250V). Radio shack has a pack of 3 toggle switches part number 275-325 with 1 DPDT(Power) and 2 SPST. I used these in my Liverpool for power standby and 1/2 power with no problems. They are about 5 - 6 bucks for the package of 3.

[dehughes]

Okay, so for clarity's sake, I'll need a normal ON/OFF switch (SP/ST) for switching an electrolytic into the circuit, and a DP/DT for switching the cathode resistor into the circuit, correct? Or, am I misunderstanding how one goes about wiring these up...

[UR12]

Yea that's pretty much it if your going with the DC 30 style arangement. You could also go with the Liverpool (Ginger) style 1/2 pwr switch and just use the SPST. If you think about the normal standby switch is actually switching 4 - 6 filtercaps, using the same style and rating switch should be able to handle the couple of caps you want to switch in/out for the preamp.


Here's Ken's 1/2 pwr switch used in His first Liverpool
http://ampgarage.com/forum/download/file.php?id=497

[gearhead]

Ahh, Dana, the 1/2 power separate biasing circuits account for most of the extra real estate on your power board! Kept looking at the forum posted one, which doesn't have the extra cap/resistor.

What I still can't figure out is the Xicon electrolytic next to them. What's it for?

Thanks,

dave

[dehughes]

Very nice. Thanks.

[UR12]

Ahh, Dana, the 1/2 power separate biasing circuits account for most of the extra real estate on your power board! Kept looking at the forum posted one, which doesn't have the extra cap/resistor.

What I still can't figure out is the Xicon electrolytic next to them. What's it for?

Thanks,

dave

It's one of the filter caps. It filters B+5 on the schematic. This was Ken's first Liverpool so he evidently did things a little differently. Yes the extra resistor and cap use up a lot of realestate. The other wierd thing Ken did was use a 25W resistor for one output pair and a 10 W for the other.


Which "forum posted one" are you refering to?

[gearhead]

Dana,

I'm talking about the one posted in the files section:
http://ampgarage.com/forum/files/liverp ... matic1.pdf

It doesn't have the half power section. Also indicates there are five filter e-caps, one at 80 uf, which is why I was only expecting to see five. You (and the express) have two 40's in parallel in place of the single 80 uf.

[UR12]

Oh I see where your coming from. Mark can probably enlighten us on where he took his schematic from. I took the Ginger pics, which was the first liverpool that Ken built in the winter of 1981 -1982, and updated Marks schematic with the 1/2 power switch. Ken included the 1/2 power switch and a line out feature on Ginger but it would seem that he dropped both features on the rest of the Liverpool amps. As far as I know the Ginger pics are the only ones in existence of a liverpool amp so this is all I had to go on having never seen any other Liverpool PS boards.Ken may have substituted a 80mfd cap for the 2 40s in the rest of his Liverpools. My layout was taken from the Ginger pics which includes the caps just like I have them on the layout.

[gearhead]

Dana,

Dredging this thread up again; got a few Ginger Qs

What value (watts) did you use for the 220uf (electrolytic?) caps?

What values did you end up with C8 and R7?

Did you use a 5k or 25k for presence?

Did you wire up the first two PS 40uf caps before or after the standby switch? Mark A. has them as after, the Express 90 kelly (and layout diagram) has them as before.

Thanks,
Dave

[UR12]

Dave

The 220uf are 100v

c8 and R7 are .002 and 150K

25k Presence control

Caps are after the switch. If you do it the other way you will have power on these caps at all times if the power switch is on and IMHO this wouldn't be good.