Dumble 102 ODS testing

[desertmouth90]

Edit:

Apologies for the message i wrote, apparently you shouldnt type things out 10 mins before you sleep (Yes im obsessed).

I have Measured voltages on key areas and the voltage doubler seems the work in reverse for example the HT going into the diodes is coming out the other end at about half of what it should be instead of doulbe. Then im Getting around 10% plate voltage at the Valves (Tubes in the US)… everything else seems fine. Pics for entertainment. I have traced every connection to the schematic. I think I may try again later with fresher eyes.

Bulb limiter glows at 150v, no dead shorts from what I can see. Any Ideas? My first Amplifier build!

[desertmouth90]

Update,

All working at planned. Got a dim bulb and I’m ready to fire it up! How do I bias this thing? Can’t seem to find a guide on it.


Plugged into Speaker and there was nothing but hum... not sure whats going on

[timrobertson100]

This is a good guide on biasing
https://robrobinette.com/How_to_Bias_a_Tube_Amp.htm

[Metanoisus]

I had the same problem with AAE 102. Make sure your speaker is plugged into spk2, the 12a jack. If you plug into spk1 it will send everything to ground and suck current like a MF.

For biasing see Uncle Doug’s you tube video on grid biasing. It’s very good.

[martin manning]

There is now a one page biasing guide in the FAQ section of Amp Garage: https://ampgarage.com/forum/viewtopic.php?f=19&t=37916

[desertmouth90]

I had the same problem with AAE 102. Make sure your speaker is plugged into spk2, the 12a jack. If you plug into spk1 it will send everything to ground and suck current like a MF.

For biasing see Uncle Doug’s you tube video on grid biasing. It’s very good.

Thanks for this. Ive studied his video and its very usefully. although im still confused about where he put the negative probes for testing the Ma.

anyhow,

I am confused as to why the SPK2 is the output but there you go! should I revers them on my latest clone?

Thanks

Clive

[timrobertson100]

In the photo above (first post), is the jack plugged in to SPK1?
It looks like it might be a stereo jack, wired to short the tip to the ground when the jack is in (black wires) - if I understood the photo correctly it would be good to correct that.

Edited to add: perhaps it was intended to be a switching jack, not a stereo jack?

[desertmouth90]

In the photo above (first post), is the jack plugged in to SPK1?
It looks like it might be a stereo jack, wired to short the tip to the ground when the jack is in (black wires) - if I understood the photo correctly it would be good to correct that.

Edited to add: perhaps it was intended to be a switching jack, not a stereo jack?

On the layout and schematic this is SPK2.

Anyways im still going around the houses biasing the damn thing, I have such a small voltage drop of -0.002v and half windings resistance around 18ohm... I'm wainting on a Fender the twin coming to me to fire up fully at 100w (At Home, I may annoy alot of peope haha!).

Thanks all

Clive

[desertmouth90]

In the photo above (first post), is the jack plugged in to SPK1?
It looks like it might be a stereo jack, wired to short the tip to the ground when the jack is in (black wires) - if I understood the photo correctly it would be good to correct that.

Edited to add: perhaps it was intended to be a switching jack, not a stereo jack?

Sorry misread you, ill get photos tonight but I think I corrected it.

[desertmouth90]

So some interesting results whilst trying to bias the amp.

I have tested the amp with a current limiter I am getting a dull light. So all good there.

Without Tubes in I get around 400VDC

With Tubes in and bias pot set to max neg - crica 300VDC

not sure whats going on here, does this mean its pulling too much current?

Ta

C

[martin manning]

...not sure whats going on here, does this mean its pulling too much current?

Probably.

With no tubes installed on full line voltage in standby,
What is the voltage on the reservoir (first filter) capacitor?
What is the voltage on the power tube socket pin 5's at max and min bias trim pot settings?

With no tubes installed on full line voltage with standby on play, do you have the same voltages?

[desertmouth90]

...not sure whats going on here, does this mean its pulling too much current?

Probably.

With no tubes installed on full line voltage in standby,
What is the voltage on the reservoir (first filter) capacitor?
What is the voltage on the power tube socket pin 5's at max and min bias trim pot settings?

With no tubes installed on full line voltage with standby on play, do you have the same voltages?

Stand by
-45 Pin 5 Max Bias
-35 Pin 5 Min Bias
0 B+
0Vdc Pin 3


-45 pin 5 max
-34 pin 5 min
395 B+
390Vdc Pin 3

Seems the bias pot makes little difference in any readings! I will upload some photos too

[desertmouth90]

Here are the photos

[martin manning]

Stand by
-45 Pin 5 Max Bias
-35 Pin 5 Min Bias
0 B+
0Vdc Pin 3


-45 pin 5 max
-34 pin 5 min
395 B+
390Vdc Pin 3

Seems the bias pot makes little difference in any readings! I will upload some photos too

You should have some B+ voltage in standby, on the reservoir capacitor, and you should see that on one side of the standby switch. I want to know if the B+ voltage changes from standby to play with no tubes installed. The bias pot is working and you have negative voltage on the control grids. It won't have any effect on the B+ until you have tubes installed.

[desertmouth90]

I’ll check further tomorrow, also the pilot light isn’t working despite reversing the heater wires too… don’t understand that one!