DSL 401

[Valvehead]

The dreaded jcm 2000 ..... This is the 401 with el84s. Have a big short or current draw . Not the tubes...but only does it with the el84s in (new ones and the old set) , If i pull the heater fuse F4 , for the el84s and PI , it goes away . R34 / 35 test good.

I measured the resistance of the secondary of the PT with nothing hooked up to it -

HT pins = 36 ohms

Bias pins = 10 ohms

Fil. pins = short / 0.0 ohms

that filament winding shouldnt measure 0 right ??


http://www.thetubestore.com/lib/thet...-Schematic.pdf

[The Dude]

It probably won't measure much. Consider how much less wire that winding has than the HT winding. Then consider you have a bunch of filaments in parallel with it.

Edit: It doesn't track with, "only does it with the el84s in", but those amps are notorious for problems with BR1. It is for the DC filament supply of the V1-3. They are usually intermittent or open, but a shorted one wouldn't surprise me. They run very hot. The rectifier is supplied by the filament winding, so it does track with, "If i pull the heater fuse F4 , for the el84s and PI , it goes away.". It's worth checking anyway as it's a common problem. If you end up needing to replace it, stand the new one off the board a bit to keep heat away from the solder joints and board.

[Mick Bailey]

With the power tubes removed check your DC voltages on the EL84 sockets. Do you have bias voltage?

[Valvehead]

yes .

-90 mv

[g1]

You should have something more like -15VDC at pin2 of the power tubes.
Attached is the rest of the schematic.

[Valvehead]

sorry -- brainfart here... its -17vdc at 1 pair of sockets .. and 0 mv at the other pair . pin 2 . The four 10k res that feed those are all good .

It looks like i have a different board- mine is labeled DL40-60-00

[Valvehead]

i forgot i had the same model amp acting up a few years ago---found my post on it here . Ill go through all that first

[The Dude]

Here's a thread w/similar problem.

http://music-electronics-forum.com/t26055/

[Valvehead]

ok guys....after a lot of testing / looking and such... i found a broken trace to V5/6---the bias feeding R84/85. I repaired that and i have -17vdc at all the sockets now. I need to piece it together and fire it up on the current limiter...will do tomorrow...its 2:46 am now......................

[Valvehead]

Update---
amp is up and running now , bias is great , have hv to all tubes and filiment volts ac and dc .
no smoke or fire yet.

Since this amp is possessed...i now have a new problem = no signal when on the orange or red channels (dirty) . The green channel works fine . The relay is clicking / switching but i dont have the dirty side of the preamp . No signal...

[Valvehead]

Can someone tell me what kind of voltages i need to see at T9 / 12/13/14 ? Could one of those kill the ch.2 signal from getting to the relay ? Are they used to mute ?

[Randall]

If you found broken traces, does that mean you had to lift or flip the board? If so, check very closely for any and all wire connections that could have broken in the process from flexing.

[Valvehead]

ill have a look , but its all pcb mount sockets..most wires are from the PT .

[Valvehead]

Im not finding the problem--tried replacing T9 , a j174 , it looks like the OD mute ? Or am I way off ?

In OD mode i tried touching the grids even the phase inverter with an insulated screwdriver to see if i had any noise or buzz......nothing..

I would think i would hear some noise down towards the end of the preamp

checked the solder joints---even chopsticked the hell out of the board

[g1]

On page 2 of the schematic in area C-3. There are lines called ODMUTE, V2A-IN, OD1G1.
Check that they are changing in voltage depending whether clean or dirt.
Have you tried with the footswitch or are you using the panel switches?