Need help sorting out new build (5E7) Success! Clip Added...

[ER]

I'll check again tonight, but I'm pretty sure it's around 440 volts on the 6l6's, around 320v on the cathode follower and PI, 190's on all the gain stage plates, 1.6 volts on the gain stage cathodes...

I'm stumped, this thing should be a very healthy 35 watts.

My 40 watt 6l6 amp was rattling the back panel on the 4-12 test cabinet turned up to about 3, this thing is even quieter that the single ended 6AQ5 amp I built.

No smoke, no crackles or buzzes, everything seems right. Don't know what else to try or check out...I'll scan the layout and get some voltage readings tonight.

[Phil_S]

Couple of thoughts...

Are you getting a good loud pop when you probe the plate of each preamp tube? Listen for the one that's not loud enough.

Look for misconnect -- something is grounded that shouldn't be or is shunting the signal. These can be hard to spot. Time for the yellow marker and a schematic. Trace and verify the whole circuit.

When you are doing that look for wrong value resistors, like 1K where you need 100K or vice versa. This sort of thing can happen to anyone.

It seems your B+ rail is operating OK, so I'd give the tonestack a very close inspection.

Check the wiring on your input jacks. It is easy enough to botch this, even if you have lot's of experience. Are you using Chinese knock offs of the Cliffs jack? If so, the switch may be on the "wrong" side.

[rfgordon]

Regarding my earlier post about cathode followers eating tubes...I just had a client's amp come in that sounded, maxxed out, like a 2 watt amp. It was the EH 12AX7 on the cathode follower. I replaced it with a vintage 12AX7 and returned the amp to its former glory.

Try swapping out that tube and see what happens.

[ER]

SUCCESS!!!! We have Rock and Roll! O.K. I'm exited and Amp Garage is THE BEST.

Thanks everybody! I've learned a ton about trouble shooting, not electrocuting myself, tracing schematics to layout to build and back again, feedback loops, and cathode followers.

So the moral of the story is DON"T think that everything is fine with the final stage and power section just because you get a good thump on the plates. Turns out when I drew up my original schematic I omited the 100K plate resistor on the final gain stage (V3a) because I was thinking PI and not typical gain stage, that error continued on throught the layout and then the build, I couldn't find the error because everything looked like it was SUPPOSED too. It wasn't until I systematicly checked voltages on the WHOLE amp (not just where I thought the problem was) that I found a final gain stage plate with a voltage of 319v! (which was fine for a PI but not a gain stage, thanks Phil for spelling things out stage by stage, and to RF Gordon; luckily the tubes survived this abuse!).

The amp sounds great! Now I'm tweaking out all that gain that I tweaked in trying to get the thing working, starting with putting all the presence loop back in and putting a 12ay7 in the first position. All the controls and gain stages work perfectly now, totaly transformed, amazing what a difference a missing 3cent part can make. I still need to add the local NFB loop back in, as it is now it's so gainy that the OD is really redundant, with the 4x12 cabinet you can really hear the herritage of the tweed amp to Marshall thing. No problems playing with a drummer now!

Thanks again for the help everyone, I've learned more from your feedback and the hands on trouble shooting than anything else so far!

-ER

[tubeswell]

Yep voltages are the first things to check with a new build (or with any problem for that matter). Glad you found the gremlin and shared in the enjoyment of your journey of discovery

[Structo]

Cool glad you got it sorted.

Another Amp Garage success story.

[ER]

Update-Thanks for the help everybody!

Check it out here; http://www.youtube.com/watch?v=_G0g7P9CzCw

Now to finish those cabinets.

-ER

[oatz]

Very cool man.