Cathode Switching

[J Rindt]

In the bottom right schem, can I add a resistor on the positive side of that 4.7 cap.? Would that create a parallel resistance (with the switch closed) and give a lower value cat resistor.?
I only have a SPST switch available, so that is why I chose that schem.
Thank You

[jojokeo]

there's no schematic?

[J Rindt]

Do you think that would help maybe.?
OK.....my original is fixed (I hope).
Thanks

there's no schematic?

[kagliostro]

Are you talking about a pre tube or a final tube ? I'm not sure about

if you intend a pre tube you can consider also a simply way to obtain lot of intermediate cap values

put the bigger cap you intend to use and lift it from ground using a pot wired as rheostat

turning the pot you'll have a lot of variations

something like V2 cathode bypass in the attached schematic

Kagliostro

[Fresh_Start]

If your goal is to be able to switch from a 2.7K cathode resistor to a 1.5K cathode resistor, for example, then use the upper-right example and replace the 20uf cap with the appropriate resistor.  The 82K "anti-pop" resistor probably isn't necessary.

If we call the 2.7K resistor R1 and the resistor on the switch R2, we calculate the value of R2 to get the lower net cathode resistor value "RC" of 1.5K like this:

R2 = 1 / [1/RC - 1/R1] = 3.375K

Hope that helps,

Chip

[J Rindt]

Fresh_Start......
Thanks for the post. I am trying to have 2 cap values and 2 resistor values from a SPST switch. Maybe I am trying to get too much out of an On-Off switch.?
Thanks
 

[jojokeo]

Just use a spdt switch for what you want to do.

[J Rindt]

Is that available as a slide that will take the place of a deep switch on a BF Fender Bassman.?
Is it possible to just have 2 different values of cap/resistor, common at the V1 grid, and then run the ground side from the SPST deep switch.? Switching the ground connection between the 2 cap/resistor sets.?
Thanks

[Fresh_Start]

What exactly are the two cap/resistor combinations that you want?

Also, is a Bassman "slide" the same as a typical Blackface "Bright" switch?

Chip

[J Rindt]

Not sure about exact values, but in round numbers.....
800-5uf
1500-.68uf

Yes, we are talking about the same as a BF Fender bright switch.
Thank You

[Fresh_Start]

You can get what you want with a SP/ST switch.

Resistors: 1.5K || 1.5K = 750 ohms

Caps: .68 || 4.7 = 5.4uf

FYI Hoffman's Bright switch is a DP/DT switch.

Chip

[J Rindt]

F_S ......
Thank You So Much for the schem.
It was the switching, at the bottom, with the pop resistor that I could not get a rope around.
Also, I did not know Doug sold a switch like that. Guess I could have looked, but I assumed.....
Is there an advantage to using a SPST vs DPDT. Assuming I get the values I need, do you think one switch would be "better" or quieter than another.?
Thank You

[Fresh_Start]

Well... a single-pole/single-throw switch can only do one thing.  A double-pole/double-throw switch can do all sorts of things.  Is there a chance you might want to switch something else in (or out) at the same time you're changing this cathode network?  Maybe a bright cap bypassing a volume pot?  Maybe a "raw" resistor under the tone stack (extra mids) or changing the slope resistor?  Who knows?

I used one of Doug's dp/dt switches as a guitar/harp switch in one build.  It gave me a lot of options to experiment with. 

Chip

[J Rindt]

When I saw those DPDT slide switches, I figured I would just use the whole switch to go between two sets of cathode cap/resistors. Not sure what the raw control is. I have seen the phrase used a lot, but I am not sure what part of the circuit you modify to have a raw control (or a fixed raw resistor for that matter).
But it would be nice to have as many options as reasonably possible.
Switchable slope
Switchable plate
etc. etc.
My problem is I am limited by what I can make work with an existing AB165 eyelet board. If I use both sides of the DPDT, I can fit 2 cathode cap/resistor sets, along with the pop resistor.
Not sure I could put all of that on one half of the switch, use the other half for switchable slope resistors, and still be able to fit it all on the board. I think at my current level of amp "building" ability, I should probably just be satisfied with the switchable cathode.
After I get that configured, I am still going to have to figure out how to implement a cat follower, so I can take advantage of that one unused triode.
I may be back for advice on that later.
Thank You Very Much

[HotBluePlates]

I think your original idea is pretty slick. One position with "little more gain, full range" and a second with "full gain, bass shaved."

[Fresh_Start]

J - Sorry I muddied the water.  Your original 2-way idea is slick and very useful as HBP says.

You can leave the .68uf/1.5K network on your tag board.  The attached sketch shows just one way to wire up the switch.  The "extra" poles provide handy mounting points. (apologies for the scratched out connection for the 100K resistor - you want that hard-wired to ground, not subject to switching)

HTH

Chip

[sluckey]

This drawing is electrically the same as Chip's drawing, but it 'may' give more room for installing the components directly on the switch.

[Fresh_Start]

This drawing is electrically the same as Chip's drawing, but it 'may' give more room for installing the components directly on the switch.

sluckey's approach is better because it gives you more room for the components and your soldering iron. (It's also more professional looking). 

Sometimes I find it easier to solder components onto those switches before mounting them in the chassis.

Cheers,

Chip

[J Rindt]

Hey........
Nobody "muddied" anything. It can be difficult to explain things via the Internet. Especially if it is knowledge that is pretty basic to you, and you are trying to "dumb down" the explanation for a guy that is just struggling with the basics.
I did not really understand, until now, that I am not really dead switching between two separate circuits. One circuit is always in play, and you are just adding or subtracting the other circuit to suit your needs. And the pop resistor is always "on" so to speak.
Tube, guitar amp, technology might be 70 years old, and low tech by todays standards, but it is not "simple". There is A Lot going on, electronically in these amps. Always a lot to consider when moving components around.
Thank You