The Eagle Supre - Big SE Amp

[surfsup]

Okay I solved the no sound problem. FX loop is working.

New Problem now that I can hear it, the amp plays like it is a 2 watt amp. I know it's louder than this. I am wondering if the place where I pulled the signal was the right place? Or V1 tube is pulling a lot of current for some reason (191V node with 100kR and 11V on the plate means 180V drop = 1.8mA). I swapped it but no change. I wonder if I need to reduce the plate Ra to get the voltage higher to make it louder?

I pulled the signal between the wiper of Vol pot and pin 2 of V1b

[img877]http://chicagocadcam.com/ChrisHahn/supre/ESupre.jpg[/img]

Voltages:
B+Rail:
VAC, 121.5, 122
HT, 253, 315
B+, 283, 352
C2, 233, 288
C3, 152.2, 187

Tube Recto:
5Y3-GT, Low, High
Pin2, 283, 353
Pin4, 141, 180
Pin6, 114, 143
Pin8, 283, 353

12ax7
Pin 1, 93, 117
Pin 2, 0, 0
Pin 3, 0.9, 1.04
Pin 6, 10.2, 11.5 (seems really low)
Pin 7, 5.34, 6.6 (coupled to return stage plate @ FX)
Pin 8, 4.4, 5.4

FX Loop 12ax7:
Pin 1, 5.34, 6.6
Pin 2 mV, -366, -342
Pin 3 mV, 127, 131
Pin 6, 146, 175
Pin 7, 3.37, 5.2
Pin 8, 8.72, 13.8

EL34:
Pin 1, 16.07, 20.1
Pin 2, 16.07, 20.1
Pin 3, 280.6, 348
Pin 4, 230.5, 285
Pin 5 mV, 5.3, 7.4
Pin 6, 232, 288
Pin 7, 16.11, 20.1
Pin 8, 16.07, 20.1

[ToneMerc]

Okay I solved the no sound problem. FX loop is working.

New Problem now that I can hear it, the amp plays like it is a 2 watt amp. I know it's louder than this. I am wondering if the place where I pulled the signal was the right place? Or V1 tube is pulling a lot of current for some reason (191V node with 100kR and 11V on the plate means 180V drop = 1.8mA). I swapped it but no change. I wonder if I need to reduce the plate Ra to get the voltage higher to make it louder?

I pulled the signal between the wiper of Vol pot and pin 2 of V1b

[img877]http://chicagocadcam.com/ChrisHahn/supre/ESupre.jpg[/img]

Voltages:
B+Rail:
VAC, 121.5, 122
HT, 253, 315
B+, 283, 352
C2, 233, 288
C3, 152.2, 187

Tube Recto:
5Y3-GT, Low, High
Pin2, 283, 353
Pin4, 141, 180
Pin6, 114, 143
Pin8, 283, 353

12ax7
Pin 1, 93, 117
Pin 2, 0, 0
Pin 3, 0.9, 1.04
Pin 6, 10.2, 11.5 (seems really low)
Pin 7, 5.34, 6.6 (coupled to return stage plate @ FX)
Pin 8, 4.4, 5.4

FX Loop 12ax7:
Pin 1, 5.34, 6.6
Pin 2 mV, -366, -342
Pin 3 mV, 127, 131
Pin 6, 146, 175
Pin 7, 3.37, 5.2
Pin 8, 8.72, 13.8

EL34:
Pin 1, 16.07, 20.1
Pin 2, 16.07, 20.1
Pin 3, 280.6, 348
Pin 4, 230.5, 285
Pin 5 mV, 5.3, 7.4
Pin 6, 232, 288
Pin 7, 16.11, 20.1
Pin 8, 16.07, 20.1

[img1216]http://chicagocadcam.com/ChrisHahn/supre/loop2.jpg[/img]

Off the top my head, the loop is in the wrong place. Also, "seems to be low" is an understandment, what do you think it should be?

TM

[surfsup]

Well it "should" be about the same as v1a because they both tap the same node and have 100ks. I didn't do the math.

The loop seems to be affecting this. I basically took merlin's loop (the last one) from his book. He says it should work with any amp. Guess not, or I screwed up, but I went over it 10 times today. Can't find an error anywhere.

Where should I put the loop! After v1b?

[M Fowler]

The only other place I can see the loop going is the wiper of the treble pot and pin 2 then.

Mark

[surfsup]

Mark, thinking about this, theoretically it should "work" wherever it is placed and not run the amp volume down to bedroom levels (or lower), right?

Perhaps I misunderstood how to insert a FX loop...Should the wiper of the volume still be directly coupled to the screen of V1b? Currently I have the wiper going to the screen of the send stage, and the plate of the return stage to screen of v1b. I basically broke the connection from the wiper to v1b and "inserted" the loop there.

I also noticed when I fire up the amp fresh, as the caps charge, the volume of the amp initially jumps and gets loud, for a split second, then falls to soft levels.

[M Fowler]

Is that your loop circuit in this last picture? What is that based off? I was referring to an interrupt type loop. I don't know what you built? Looks like it would require to be tube driven.

Mark

[breakfastbuddy]

try a 220k pot

[breakfastbuddy]

change the treblepot with a 220k pot

[rogb]

Hi mate, couldn't you use a simple loop like the ones used in the Mini D amps?

Mine works perfectly.

http://ampgarage.com/forum/download/file.php?id=17598

[surfsup]

Mark, yes that is my loop circuit, the black eyelet board, two jacks, pot, and white ceramic noval. Figure 11.22 Last FX Loop schemo in merlin's preamp book is the schemo. Better pic below:

try a 220k pot

-I clipped in a 330k resistor on each the MV and T pots and no difference. The 330k effectively gave me 248k resistance.

-I put in a cap between the plate of the return stage and the screen of next stage. No change. But when I probed the plate side, the amp jumped to life and immediately started into what seemed like an endless feedback loop.

-I paralleled a 56k with the 100k to bring the total R down to 35k to increase the voltage at the plate and following screen. Interestingly, (to me), this actually made the amp quieter.

I should re-iterate as the amp fires up, if I'm plugged in and strumming, the sound initially gets loud for a split second, then farts out and comes back softly. The three white caps are 10n. the two black electrolytics are 100u

[img800]http://chicagocadcam.com/ChrisHahn/supre/loop3.jpg[/img]

[martin manning]

I know this place is often about discovering secrets, but posting Merlin's loop schematic is definitely a copyright violation. Better to just cite the book and figure.

[xtian]

I know this place is often about discovering secrets, but posting Merlin's loop schematic is definitely a copyright violation. Better to just cite the book and figure.

Copyright can protect against reuse in a commercial situation, but copyright law also gives protection to fair use for editorial and educational discussion, like here!

[surfsup]

Man, I've exhausted my very limited knowledge... For the send stage I get a Zout of 950R which is low, per Merlin this is what I want. I ran through the voltages, after moving the HT supply to the second cap to get it a bit higher. The last two stages seem to be drawing a lot of current. Voltages (plate, screen, cathode):

Input gain stage (V1a):
140v
0.001 mV
1.1v

FX Loop stage 1 (send) (V2a):
248v (33k Ra)
10.4v
33.8v (33k Rk)

FX Loop stage 2 (return) (V2b):
9.4v (100k Ra, plate coupled to next stage screen)
-260 mV
124 mV (1.5k Rk)

Last gain stage (V1b):
9.25v
9.4v (coupled to plate of V2b)
7.22v

[Zippy]

Have you considered disconnecting the "extra" parts of the circuit and just checking to see that the basic functions are working?

It's frustrating to sit and watch this since the Supre is such a basic and great sounding amp.

There's nothing wrong with "just a Champ"...

[Cliff Schecht]

Zippy you are so grumpy sometimes..

I agree though, get the basics working first then start tacking in the extra stuff. You may have another issue that you're not even seeing because you're focusing only on the unnecessary extra circuitry.