From Scratch Amp Building Chronicle - 6/13/10 UPDATED!!

[sah5150]

I didnt see, but thats a really cool option. last night I added a 15v zener and a 1n4007 to a non cathode following MV. it has 4 gain stages, regular MV with that diode config on a switch.. sounded really good really open and clear.

Cool! Here's a couple closeups of my Jose Master. Pull brings the zeners in:




Steve

[jerrydyer]

some people have all the best toys. I see it now sir. I see you have a ccv. Mark called mis morn. were finally going to hook up and get this crap rockin. I didnt even know you were on the list. sweeeet !

[sah5150]

some people have all the best toys. I see it now sir. I see you have a ccv. Mark called mis morn. were finally going to hook up and get this crap rockin. I didnt even know you were on the list. sweeeet !

I actually got my CCV used, not directly from Mark...

If you go visit Mark lemme know - he invited me to come up and bring my CCV for him to check out and I'd be happy to ride up together...

Tubes should be here tomorrow and then it's time to fire up my creation! Whoohoo!

Steve

[jerrydyer]

he says hes coming to my house today around 2..

I might be going up there next week if I get these two done.

[sah5150]

he says hes coming to my house today around 2..

I might be going up there next week if I get these two done.

He's supposed to call me - he said he'd make me a deal on a cab and I'm interested!

Steve

[jerrydyer]

call me 714 313 5603

[sah5150]

Alright... got my tubes and started testing...

Throughout the below process, I found some mistakes and fixed them.

First I put in the preamp tubes and plugged in the amp. Measured 120.4 VAC at the live terminal of the IEC socket and the power switch. Good...

Flipped on the power switch... Preamp tubes light up... Measured between 6.1-6.2 V DC heater voltage on the preamp tubes measured from pin 4 to pin 9. Seeing 3.3-3.4 VAC on pin 2 and 3.5-3.6 VAC on pins 7 of the EL34s... A bit high, but ok...

Checked Pin 5 of each EL34 and found -51V... Ok...

Turn the amp off, drain the filter caps. Put in the EL34s... Threw the power and standby switch on... Starting taking measurements...

V5 EL34 Pin 2 - 3.315 AC, Pin 3 - 460.5, Pin 4 - 458.8, Pin 5 - -40, Pin 6 - 458.6, Pin 7 - 3.485
V6 EL34 Pin 2 - 3.336 AC, Pin 3 - 460.5, Pin 4 - 458.8, Pin 5 - -40, Pin 6 - 459.6, Pin 7 - 3.52
V7 EL34 Pin 2 - 3.364 AC, Pin 3 - 460.3, Pin 4 - 458.6, Pin 5 - -40, Pin 6 - 460, Pin 7 - 3.562
V8 EL34 Pin 2 - 3.388 AC, Pin 3 - 460.6, Pin 4 - 458.7, Pin 5 - -40, Pin 6 - 459.5, Pin 7 - 3.625

Ok, time to bias the EL34s... I've got 1 Ohm 5 Watt resistors from pin 8 to pin 1 to ground. Check V5 and pin 1 and adjust the bias pot, mess with it a bit and I get:

V5 EL34 34.8 mV
V6 EL34 33.1 mV
V7 EL34 36.6 mV
V8 EL34 37.5 mV

Ok, good enough...

My relay power supply is measuring 6.085 VDC and I get the same reading at the coil of each relay, so it looks like the relay supply is working...

None of my switching LEDs is lit though... Flipping the manual switches doesn't light any of them... Hmmmm.... Start checking some of the manual switches - definitely something wrong with the switching...

Troubleshooting continues...

Steve

[erigm]

Sounds good so far (other than the LED's). Great job taking it nice and slow and methodically.

[sah5150]

Sounds good so far (other than the LED's). Great job taking it nice and slow and methodically.

Thanks, man - Of course, lotsa stuff could still be wrong... but I'm encouraged by the things that look ok... Ya just gotta take it one section at a time...

It is more than the LEDs, it's the whole switching thing... I'm thinking about it though... I'm seeing some strange stuff, but I think I can get it figured out...

Steve

[paolojm]

Sounds good so far (other than the LED's). Great job taking it nice and slow and methodically.

Thanks, man - Of course, lotsa stuff could still be wrong... but I'm encouraged by the things that look ok... Ya just gotta take it one section at a time...

It is more than the LEDs, it's the whole switching thing... I'm thinking about it though... I'm seeing some strange stuff, but I think I can get it figured out...

Steve

Hey man, I have some trouble shooting experience with channel/function switching and LEDs using relays.
Took me a while to get mine working right/at all.

For peace of mind the diode test function on your meter will provide enough juice to light each LED.
The first step I would take is, with power off, test each LED with the diode test to eunsure that they are actually working.
If using 6Vdc a 200-400 ohm resistor is about right brightness wise.
Assuming the - side is grounded you can jump a 6Vdc source onto the + from the resistor side to test the diode circuit.
After that it's a matter of finding where your 6V potential is gone when switching happens.

[jerrydyer]

on that push pull it looks like in the non pulled position youre shorting the input to ground. is that a wire.

[sah5150]

on that push pull it looks like in the non pulled position youre shorting the input to ground. is that a wire.

Yup, that is another mistake. I'll snip that...

Steve

[sah5150]

Sounds good so far (other than the LED's). Great job taking it nice and slow and methodically.

Thanks, man - Of course, lotsa stuff could still be wrong... but I'm encouraged by the things that look ok... Ya just gotta take it one section at a time...

It is more than the LEDs, it's the whole switching thing... I'm thinking about it though... I'm seeing some strange stuff, but I think I can get it figured out...

Steve

Hey man, I have some trouble shooting experience with channel/function switching and LEDs using relays.
Took me a while to get mine working right/at all.

For peace of mind the diode test function on your meter will provide enough juice to light each LED.
The first step I would take is, with power off, test each LED with the diode test to eunsure that they are actually working.
If using 6Vdc a 200-400 ohm resistor is about right brightness wise.
Assuming the - side is grounded you can jump a 6Vdc source onto the + from the resistor side to test the diode circuit.
After that it's a matter of finding where your 6V potential is gone when switching happens.

Cool - thanks for the ideas!

Steve

[sah5150]

I continued my troubleshooting last night... I tried the guitar into the loop return to bypass the switching and as I expected that didn't work. I then decided to just check the voltages on the PI since the power amp looks ok and got:

Pin 1 333.3
Pin 2 280.8
Pin 3 315.7
Pin 6 332.5
Pin 7 281.2
Pin 8 315.8

Obviously something crazy wrong here! I then tracked down two problems:

1.) I missed an under-board connection I was supposed to wire from the PI 10K/.1uF junction to the NFB circuit. I found this by continuity checking. I just wired this above board. (Good thing I had pictures of the underside of the board as well as a good layout diagram from documenting this!)
2.) I had not grounded the Presence pot! Fixed that as well...

Re-measured with these fixes in place and got:

Pin 1 206.7
Pin 2 21.99
Pin 3 34.57
Pin 6 200.7
Pin 7 23.21
Pin 8 34.56

That looks much better...

I also think I know what is wrong with the switching. My manual switches are all wired wrong (I found this with continuity checking as well), so I'm going to fix that and try the guitar into loop return thing again (I believe the loop is always off now). If that doesn't work, I'll try wiring a jack into the PI and checking the guitar into it, but I think that will actually work now... Oh - I also fixed the mistake Jerry caught with my Push/Pull Master...

My troubleshooting continues after work tonight - this is fun actually, although I wish it just worked when I turned it on!

Steve

[jerrydyer]

cool. you wouldnt beleive some of the bonehead mistakes ive made. In fact just recently Mark Cameron found a big mistake I had on my vactrols that were switching MV's .. once he pointed it out, I couldnt beleive I could get that twisted around. When you look at switches too long, you end up overthinking it.