Developing the DIY "Champ" for first time builders

[M Fowler]

Heck I can't even remember what model of rj's amp I just built

I think the Eagle One?


Mark

[RJ Guitars]

Heck I can't even remember what model of rj's amp I just built

I think the Eagle One?


Mark

No that's not it either, but isn't that the one that landed on the moon? You built the Eagle Premium... with the addition of a ToneStack. So that one is entirely unique and it is actually called the "Fowler Eagle".

[M Fowler]

See I told you I didn't even know what I built.

[RJ Guitars]

Will someone please direct me to the page(s) with the most up to date schematics and layouts for the basic model and the one I saw with tone controls (treble and bass)? Thanks...and I second the suggestion to put them all on the first page.

The Schematics and layouts have been moved to page one for the Eagle 100 and Premium. Neither of these has a tone stack.

The documentation on the Supre will be located in a new thread -- https://tubeamparchive.com/viewtopic.php?p=160522 this is the version with a tone stack.

rj

[mcrracer]

A great big THANKS RJ!

[xtian]

Today I added another filter cap and resistor. It dropped the hum by about half. Definitely into the tolerable range. Better, not perfect, but better.

[surfsup]

Is there any reason you didn't put it in parallel with the first cap? Having that 47R resistor in there (wasn't there before was it?) will create some noise too, wouldn't it? Interested to know why you chose to do what you did if you don't mind.

[telentubes]

I added treble and bass, ala the Triod Champ layout, to my premium kit. This lowered the gain a bunch, but the tone is still there, and now it's slightly adjustable. The amp was remarkably loud before the mod. I used 250K pots.

I also upped the 16uf cap to 20uf and that lowered the hum a little. The lower gain also lowered the hum, so now it's totally acceptable.

[xtian]

Is there any reason you didn't put it in parallel with the first cap? Having that 47R resistor in there (wasn't there before was it?) will create some noise too, wouldn't it? Interested to know why you chose to do what you did if you don't mind.

I think I'm implementing what rhinson and RJ suggested earlier. Adding an extra cap and low value resistor.

[ToneMerc]

Is there any reason you didn't put it in parallel with the first cap? Having that 47R resistor in there (wasn't there before was it?) will create some noise too, wouldn't it? Interested to know why you chose to do what you did if you don't mind.

I do this with all my SE builds while also including a small choke. The amp that I posted at the beginning of this thread(page 6) is setup like this.

tube rect>39 ohm 5W>30(35)4Hchoke>16(19)uf>resistor>16(18)uf

If you parallel that cap you aren't doing any thing to alter the circuit topology other than changing the filter capacitor value.

If you want to really control the ripple you need to add an additional filter stage. All this does is extend the filtering network on the front end by converting the first filter cap to a simple RC filter. The post rect tube 35-50 ohm resistor also serves as a soft current in rush limiter to keep the tube rectifier from being thumped so hard if you increase the first filter capacitance.

TM

[surfsup]

I understand the limiting value of the resistor, just not why it needs to be present to reduce ripple at the first stage since there is no supply node between the first and (now) third cap.

http://www.freewebs.com/valvewizard1/smoothing.html

Merlin talks only about the capacitance value here for the resevoir cap, not RC stages. So this is why i'm asking...

I guess my question is perhaps it would be better to add just the C cap instead of another resistor capacitor RC combo, because really arent both those first two caps now on the same stage so to speak, so the resistor just adds a small amount of unnecessary noise? I thought the point of RC stages was to reduce ripple due to each dropping resistor? Here, no dropping resistor is needed so what's the point of adding a small R value when it is not needed?

I'll open his book on power supply laterr today and read up more on this.

[rhinson]

here's an example of what i'm talking about. it's a very good supply style for a s.e. amp------even better if you use a choke instead of the resistor. you can also incorporate the dc heater float shown, esp. if your preamp has a cathode follower section. (although i would add a 22uf/100v cap across the 22k resistor of the voltage divider) rh

[surfsup]

I re-read the chapter and still dont see the point of the added resistor. Merlin doesnt explicitly say the smoothing cap is used to tame ripple from the resistor, but he does reference it: "a sensible design choice is to first choose the resistor, according to voltage drop, then find the necessary C value based on cutoff freq". This statement leads me to believe that smoothing is necessary due to the voltage dropping resistance.

So since no voltage drop is necessary, since there isnt another supply node added, and therefore no resistor is necessary, why add the noise?

[ToneMerc]

I re-read the chapter and still dont see the point of the added resistor. Merlin doesnt explicitly say the smoothing cap is used to tame ripple from the resistor, but he does reference it: "a sensible design choice is to first choose the resistor, according to voltage drop, then find the necessary C value based on cutoff freq". This statement leads me to believe that smoothing is necessary due to the voltage dropping resistance.

So since no voltage drop is necessary, since there isnt another supply node added, and therefore no resistor is necessary, why add the noise?

Not trying to be a wise ass here, but I think you might be better served by not relying so heavily on just Merlin's book as a single point of reference. There's ton's of abound about RC circuits.

http://www.tpub.com/neets/book6/22d.htm



TM

[M Fowler]

If you still have hum incease the filtering 20uf is low.

I have a low level SE hum I consider normal. But I will see if I can tame the hum altoghter and how much (uf) I have to go to get there without resorting to a choke.

A choke is not always the solution.

Mark