Low Output Help

[jpet4387]

I'm out of ideas on this one. my 18watt build has at best bedroom volume. I have checked and rechecked all my connections, caps and resister values. Replaced tubes, tried other speakers
and so on. I have attached the voltage test sheet ( JJ and GT are tubes I swapped when readings appeared off on originals.)
Anyone have any suggestion?

Voltages.pdf

[Bieworm]

Please post your schematic and some detailed pictures. Complete the voltage chart , including the mV of the control grids of the power tubes. It happened to me once too and it turned out I forgot to connect the wiring to the plates of the power tubes, but that's not your problem.

[jpet4387]

Here is the completed voltage chart and schematic with pictures.
Thanks

[Bieworm]

It's hard to tell from those pictures, but the grounding method is imho not failsafe. You should look into the docs from Josh. They're in his signature. He'll chime in soon I think. He's an excellent expert on these amps and will definitely help you find the problem. But he'll ask for more clearer pics and certain details. Don't give up.
I rebuilt my classic 18W to his layout advice AKA modern classic. It's in the downloads area.

[jpet4387]

I know the pictures are not great...cheap camara!
The grounding might not be up to par but it all has continuity for now. I got the idea for it from the original 18 watt layout on this site and it's similar to my 5e3 build. Hopefully Josh will check in.

Thanks for the replies too.

[jpet4387]

I know the pictures are not great...I'll retry in better light.
The grounding might not be up to par but it all has continuity for now. I got the idea for it from the original 18 watt layout on this site and it's similar to my 5e3 build. Hopefully Josh will check in.

Thanks for the replies too.

[geoff 1965]

is that a 250 ohm resistor biasing the el84’s? the schematic shows 2 in parallel which gives you 125 ohms.

[JMPGuitars]

Take a look at the links in my signature, and I'll look stuff over when I have a chance.

Thanks,
Josh

[jpet4387]

Yes there are two 250 ohm resisters. Hard to see in the picture.

[crgfrench]

Is it possible that you have wired the two 250 Ohm bias resistors in series rather than in parallel? That would cause issues.

[Daviedawg]

My first approach would be to check the area of the Phase Inverter. The voltages are strange and that would affect both channels with low drive. So a proper detailed examination and recording of the built circuit around the PI is my suggestion.
V1 and the power valves look enough in line to produce proper signals. So that adds to my feeling. But more information is always useful.

Dd

[jpet4387]

After doing some reading I will first try revamping my grounding and see what the results bring....Stay tuned!

[JMPGuitars]

After doing some reading I will first try revamping my grounding and see what the results bring....Stay tuned!

You also need to do a highlighter test. You can use the schematic you posted, but also compare it to the Modern Classic in the downloads section. Highlighter testing is checking every component value and connection on the schematic, only highlighting after verifying in the live build.

[jpet4387]

Will do. I had went over the layout several times but not the schematic. Not real good at following one yet. It will be good practice. I will update when finished....Thanks.

[Bieworm]

Will do. I had went over the layout several times but not the schematic. Not real good at following one yet. It will be good practice. I will update when finished....Thanks.

Once you can read them adequately it's all more simple and clear. I used to be the kayout reader too

[jpet4387]

Well I went thru and did the highlighter test(twice) and only found a miss labelling of V2 and V3 on the schematic. Confirmed all cap and resister values. Revamped the grounding.
FINDINGS...no change.
Suggestions on where to go next before I chuck it in the garbage can(lol)...

[Bieworm]

The problem probably is narrowed down to the PI, power section or the output section. Since both channels have the same result...

Could you post sound clips to see if it sounds at least normal? How many guitars and cables did you try?

[JMPGuitars]

Post a new / fully completed voltage chart along with a sound sample of your amp.

Inspect your amp very closely for frayed wires or anything that might be grounding out that shouldn't be.

EDIT: Please also post clearer updated photos of your build.

Thanks,
Josh

[jpet4387]

I will do all the above . It may be a couple days before I get it done. Got some other things to do .
Thanks again to all...

[jpet4387]

Here are the items you requested. I hope they are satisfactory.
The amps volume is at best around 90 db per my decibel meter. The sound clip is a les paul with the amp wide open.
today when I turned it on to record the clip I had no output (first time for that) I now may have a tube or a socket that is bad. Got it to work by chopsticking. Geeeee!
Thanks
John
PS. I will get the grounds off the transformer screws but I need to make a trip to the hardware store first.