Dumble 102 ODS

[desertmouth90]

Glad to see you got the amp working!

You mixed up the 100K OD entrance trimmer and the 10K PI balance? Or you adjusted them incorrectly?

You may want to measure and post all of your voltages too.

-Dan

They were the wrong way round, Yes I will. Also noticed I have biased it super cold at 16mV(mA) at the 1ohm Resistors... Way too low. I misinterprated my friend when he said 16 he meant Watts.

Clive

I suggest you use this very handy calculator to help you bias your amp.

https://robrobinette.com/Tube_Bias_Calculator.htm

-Dan

Yep done that fully biased at 38mV (mA).
https://www.youtube.com/shorts/7SCwSGz7bgA
https://www.youtube.com/shorts/mUQ5XUJ1pHM

[frusciante89]

I’ve checked I’ve never ordered at 12b. But what you are saying is very interesting and I’m keen to explore this further.

I have attached the 124 Layout that’s on here and the AA electronics layout for the 102 and take the outputs out of the chassis for closer photos.

Looks like the jacks are correct in the AA layout but they are labelled incorrectly (swapped).

Are you referring to the SPK1/SPK2 mislabelling? As in SPK2 is the MAIN SPK?

[desertmouth90]

I’ve checked I’ve never ordered at 12b. But what you are saying is very interesting and I’m keen to explore this further.

I have attached the 124 Layout that’s on here and the AA electronics layout for the 102 and take the outputs out of the chassis for closer photos.

Looks like the jacks are correct in the AA layout but they are labelled incorrectly (swapped).

Are you referring to the SPK1/SPK2 mislabelling? As in SPK2 is the MAIN SPK?

Yeah no biggy, got it all sorted anyways. I will be rebuilding this at some point to look better aesthetically.

Fabulous amp and sounds better than my 50w version

[desertmouth90]

First build getting a full face lift

[desertmouth90]

So the facelift has finally come through (I first completed this amp last year) once again I wired the OT up wrong and created Oscililation. this has now been corrected. I am hoping I can improve my lead dress the next build.

My main question is how do you guys drill the cabinet for the chassis bolts? I have them ready to go. I have a spare chassis that I used to house the amp before re doing the whole thing correctly. I was thinking of making a cardboard template for it. for an Architect day to day I am actually worried about this part of the build most haha!

thanks

Clive

[martin manning]

A template is a good idea. This is a tricky task, and you don't want to mess it up!

[desertmouth90]

Before that, the testing of the amp is giving me interesting results with not signal and a plate voltage of 380v

I wonder what the issue is this time!

[martin manning]

Start with the tubes out and the standby on standby. Check the AC and DC voltage at the standby switch, and the same at the power tube sockets pin 5 (bias voltage). Next, switch standby to play and measure the voltages at all the other power supply nodes (filter cap positive leads). Those should be close to the first filter (standby switch) since there is no current draw except for the FET voltage divider.

[desertmouth90]

All biased up clean channel works, but Pre amp boost and OD sends the whole thing into meltdown.

Also I tried the trick with the Return of the Fx loop and that just doesn’t seem to do much.

Tested my wiring and voltages on 12ax7s… it’s all good.

Plate voltages are spot on too.

Not sure. I’m so close and as everyone on here knows. The last 10% is the hardest!!!

[desertmouth90]

The Output transformer is oscilating when the signal is overloading, I pulled the NFB loop and the problem still persists.

Seems to oscilate when the signal from the guitar is higher... everything is correctly wired... ive checked all the grounds. I dont get it!

[desertmouth90]

Is it possible that the Primary wires have swapped around?

[didit]

Is it possible that the Primary wires have swapped around?

With no NFB in the circuit primary orientation does not cause an oscillation.

..

[erwin_ve]

Are the plate resistors on v1a en v2a: 2k2, instead of 220k?
Other things to check are tyding up your wiring fe. I see a plate wire touching the grid resistor thats a good recipe for oscillation.

[desertmouth90]

Is it possible that the Primary wires have swapped around?

With no NFB in the circuit primary orientation does not cause an oscillation.

..

okay I removed that and the problem persists

[alnight]

If it works ok with the OD switched off, I would suspect a lead dress issue.