2nd Gen Build Started (that didn’t take long…)

[Raoul Duke]

In either man or Ped I have ~21v going in to pin 1 of the regulator and 12v coming out of pin 3.
When I measure at the bottom of the 1k where it meets the DC+ line, it drops to 2.5 in Manual.

[Raoul Duke]

I think I might have found the problem. Stand by.

[martin manning]

Relay coil connected to the 1k? Its should go to the reg output.

[Raoul Duke]

Yup, I’m a complete idiot…

It all works now; and it’s fantastic! Quiet, different character than 102 - kind of raunchy and loose (less filtering?) - really cool!

But I’m still a dumbass… lol.

And I’ll even prove it - I’ll be wiring up the foot switch soon - then we’ll see what low ASVAB scores really look like

[Raoul Duke]

Ok, first hour of playing voltages:

B+1: 452
B+2: 450
B+3: 425
B+4: 307
B+5: 298

Tubes biased at ~63%

V1A: 202
B: 199
V2A: 222
B: 217
V3A: 286
B: 282

FET Rd top: 3.0
bottom: 9.9

Preamp voltages seem a little high? I’ve read here that keeping them about 10v lower is the key to the 2nd gen sound? Actually, it all seems high. I’ll try a couple of different values and see what I get.

[martin manning]

There were some odd relay voltage measurements at the first smoke test, but I thought you measured differently and resolved that. More rigorous confirmation of the relay operation at that point would have saved a lot of time tracking it down later. Anyway, all good now.

Yes, I would increase the first dropping resistor (2k2) to get the V1 voltages down ~10V, try a 3k3 and see what that does. You could bias the FET a bit cooler by increasing the source resistor a couple of hundred ohms. Try to get the drain resistor voltage ratio just under 3, it's 9.9/3 = 3.3 now. Do that last, after you get the V1 voltages down.

[Raoul Duke]

Understood and agreed Martin. All my relay work from the past couple of days was likely not needed had I been more attentive to drilling into those test readings and the simple routing of those two wires. I’ll take it as part of the “tuition” of my electronics education. It wasn’t wasted time in my eyes (however embarrassing it was, lol) - I reworked a lot things and improved some routing, connections, and co-ax heat shrink. Much tidier now.

Based on a ton of reading I’ve done here regarding the 2nd gen FET, I replaced the 1.6k Rs with a 3k a couple of days ago. I’ll take new readings once I get the 3k3 dropping resistor in and see.

I’ll put up the results

[martin manning]

I’ll take it as part of the “tuition” of my electronics education. It wasn’t wasted time in my eyes (however embarrassing it was, lol) - I reworked a lot things and improved some routing, connections, and co-ax heat shrink. Much tidier now.

IMO, although it didn't quite work in this case, it's an example of the value in the test-as-you-go approach. If work proceeds with an unknown or unexplained fault, the effort required to resolve it increases because the number of possible explanations increases.

Based on a ton of reading I’ve done here regarding the 2nd gen FET, I replaced the 1.6k Rs with a 3k a couple of days ago.

FETs vary quite a bit, so you will have to find the right value for the one you have in the circuit.

[Raoul Duke]

I certainly see the value in “test as you go” first hand - especially for new builders with limited troubleshooting experience/ability.

Here’s the voltages with the 3k3 dropper and another hour plus of run/playing time:

B+1: 447
2: 445
3: 410
4: 296
5: 289

FET is getting 287 with 2.8 at the top and 9.5 at the bottom of Rd.

Everything sounds great! The clean channel really gained some dimension once I got the voltage down. The FET has a unique “fuzz” like quality to it, and OD is very 70’s sounding - which is what I hoped for.

All the controls certainly add something as well. Accent gives pick attack more bite, J/R does what we expect, Bright increases treble, Deep really adds some thump, and the pull pot idea definitely changes the overall bass response (two useful versions IMO), Treble is pretty standard and Mid is as expected - subtle; but still there.

Really interesting amp so far

[martin manning]

Voltages are looking good. What's V1a plate now?
I'd try a 3k3 Rs for the FET.

[Raoul Duke]

V1A plate is 193.4

I’ll pop that 3k3 in next; then on to the foot switch. Built out of scrap from the cut off bin - front and back are 1/2” clear pine, sides are 1/2” hard maple, top is 1/4” red oak - all stained to match. Probably make the bottom out of an old pick guard or something.

IMG_0361.jpeg

[Raoul Duke]

With the 3k3 and the FET getting 291v Rs is 3.4 top, 9.8 bottom and has a good range of adjustment on the trim for both boost and some distortion.

[martin manning]

With the 3k3 and the FET getting 291v Rs is 3.4 top, 9.8 bottom and has a good range of adjustment on the trim for both boost and some distortion.

Perfect.

[Raoul Duke]

Thanks for your help again Martin! I’m really liking what this amp does. I figured it would be like a stripped down 4th gen, but it’s got its’ own bag of tricks for sure.

I feel like selling all my other amps now (except this one and 102).

Actually that’s not true - I have one of Paul Vogel’s first Trainwreck Express builds and it’s pretty special; but the old Fenders, JMI Vox, and vintage Boogies might be on their way out, lol.

Oh; I actually wired my footswitch correctly the first time without bugging anyone with my inane questions, lol. I feel quite triumphant

[martin manning]

Nice. How's the pull switch on the bass pot working out? which way sounds better?