First Amp Build.. 5e3

[Caparris]

Welp, just thought I'd share a few pictures of my build of the mission amps kit.. I am missing the pots so I haven't turned it on yet but it sure looks good

[Tom Phillips]

Look good. Nice work.
But...missing the pots? Don't they come with the kit?

[Caparris]

Small mistake--they were left out of the kit when it shipped on accident. Bruce shipped them as quickly as possible but the bad weather here has fedex delayed at best...

[Chuck H]

Who finished the cabinet? Did you age it or did it ship that way? Looks great.

[Caparris]

I got the "aged" tweed option for $25 from mission amps. I agree, the darker look is awesome and def worth it. And the job of putting on the tweed is second to none in my opinion.

Sorry but I mis-spoke here. All of the mission amps kits look like this. Some other vendors have an "aged" option to give this look and I got them mixed up.

[Chuck H]

Who ever Bruce has making and finishing these cabs is good. No doubt. Nice.

Wiring looks good too.

[ThermionicScott]

That does look nice. Make sure the 6V6's cathode resistor has some room to "breathe" -- the nearby capacitor won't last if it gets too hot.

- Scott

[Caparris]

That does look nice. Make sure the 6V6's cathode resistor has some room to "breathe" -- the nearby capacitor won't last if it gets too hot.

- Scott

Thanks--I made the adjustment last night and moved it out 3/4" or so away from that capacitor.

[Caparris]

Well, it's alive!

Think I may have an issue though.. It's not nearly as loud as expected which I'm not sure is from a build issue, my inability to play hard right now bc it's late or just a wrong expectation.. With volume on 12 though I can strum reasonably without thinking the neighbors are going to kill me (in an apartment bedroom)

Any suggestions on what I should take a look at first? Heaters are working fine and B+ was just below 400V if I remember correctly. That's about all I know how to check

[Tom Phillips]

With a new build don't assume that anything is correct. Try another set of tubes, etc.
Since you have already turned it on and it made no smoke I would start by measuring all the plate and cathode voltages for each tube and compare your readings to the schematic. If a voltage is off by more than 20% then you have a clue about where to investigate.

Another plan would be to re-check all the wiring per the layout. Highlight the drawing as you go. It won't take much time for that amp.
Tip: Turn the chassis around so you are tracing the wiring from a different perspective with respect to how you built it.
Also verify the parts values as you check. Maybe you will find a 15k cathode resistor where you need a 1500 Ohm or something like that.

Cheers,
Tom

[Caparris]

Rechecked everything.. Found one wire that was suspect that i replaced but no change. Very little volume until 8 or so then a jump up in volume around 10. Turning both volume knobs up yields a much lower volume than turning the knob down for the channel I'm not plugged into. I know the knobs interact but wasn't sure if this is normal.

V1:
1: 134v
3: 2.0v
6: 125v

V2:
1: 162v
3: 1.35v
6: 206v
8: 49.5v

V3:
3: 395v
4: 351v
8: 23v

V4:
3: 396v
4: 351v
8: 23v

16uF caps:
400v
342v
250v

Pilot light: 6.6v
Yellow wires from transformer: 5v

[Caparris]

should the bridge rectifier have this coloration around the bottom?



the two 6v6's have similar markings but less

[ThermionicScott]

should the bridge rectifier have this coloration around the bottom?

[ATTACH=CONFIG]12365[/ATTACH]

the two 6v6's have similar markings but less

Weird, never seen a "5C4S" before -- looks like it's a Russian 5Z4 equivalent. The fact that it's directly-heated is contributing to your high voltages.

The "coloration" you see is the getter, which helps absorb stray gas molecules when the tube is in use.

- Scott

[Caparris]

Alrighty,

Now that I'm on a computer where I can actually type and not an iPad I'll explain everything I can in hopes something will help.

First: The first time I flipped from 'standby' to 'on' I blew a fuse. After some digging around I found that I had wired the bridge rectifier wrong. The wires that were supposed to be on 4/6 were on 5/7 if I remember correctly. Fixed that, replaced fuse, turned standby switch to on, everything was fine. Heaters came on (well, were on when on stand by of course).. you could see them on (is this normal?). Has sound, but not a lot of of it. I did some measurements on the output and it was a fraction of what it should have been. I wish I had written the numbers down but can update later on. It was something like 1/10th what is listed on the drawing, though.

After that I have not been able to find another wiring issue that's wrong. I do have an oscilloscope now. Any suggestions on how/where to check? I'm really starting to think there is actually something wrong and it's not just a simple newbie error. Maybe I fried something with the bridge rectifier wired wrong? I don't know what else to do.

Any tips? I pulled the board back out yesterday and re-flowed solder on every point, checked values of every resistor and checked continuity with every wire that was connected to the board. Everything checks out that I know how to check..

[Bruce / Mission Amps]

Where is that red/yellow wire going in the picture of the eyelet board? It should be connected right to ground or the negative lead of the first main filter cap.
All those voltages look OK, relative to each other, but the actual plate voltages are a little high... that would not make the amp quieter.
That is a Russian GZ30 type tube and the only ones I can find anymore that are close to 5Y3GT but not an over priced SOVTEK 5Y3GT which is also a 5U4C.
It is not a bridge rectifier... just a simple full wave rectifier.
You can lower the B+ voltages a bit with some 5 watt zener diodes but this is not the problem you are running into.
Shoot me/us some other pictures and email them or post them here, and I'm sure we'll spot what is/are the issue(s).
Also, as mentioned in our private email messages, try to measure some of the AC signal voltages coming out of the coupling caps while strumming too. It could be that there is not enough drive from the preamp to turn the power tubes on all the way, due to a bad part or a very simple miswiring.