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Main :: DT50/DT25

replacement tubes in DT25
by packet on 2012-12-10 07:32:29


after a week one of the EL-84 tubes (Electro-Harm) begins to make unwanted crackling noises. Warranty is 90 days I think. As the EH EL-84 are Russian, I like to change them with Sovtek EL-84 M (military spec) without trouble . I already had very bad experiences with tube rolling (eg JJ EL-84). I am in need for some reliable good EL 84's .

Re: replacement tubes in DT25
by packet on 2012-12-10 07:38:00

Is there someone who knows how to bias an amp. I just found that the EL 84 in a DT25 needs +/-25 mV

Re: replacement tubes in DT25
by Hummelong on 2012-12-10 07:52:06

The DT-25 is very simple to bias.

I copied the following from another thread:

1. Remove the upper panel on the back. It is six screws and then you might have to gently use a screw driver or some other object to pull the panel out. The tolex is sticky.

2. Remove the 4 screws on the bottom.

3. You have to use some force here but be careful and gently wiggle the amp out of the chasis. You might want to remove the tubes but it isn't required. Push from the front and pull from the back. Again the sticky tolex makes it difficult but it will finally come out. 

4. You will see round holes identified as Bias V2, Bias V3, Ground and Adjust Bias V2 and V3

5. Set your multimeter to DCV 200m or volts 200m

6. This is where I had to be creative. My multimeter tips were not long enough to protrude through the hole and touch the measurement point so 1 cut the tips off and stripped the wire back so about an inch was exposed. I then was able to stick the wire into the measurement hole. You will see there is a small goldish color hole down inside the hole cutout that you can stick the wire in. I stuck a black in the groud and red in the V2 and powered on the head. I let it warm up and then after making sure I had a speaker load and the other end hooked to my guitar I took it out of standby.

7. Make sure you are in AB mode and you should get a reading close to 25.0. If it's off, turn the adjustment screw with a small screwdriver until it is at 25 +- 3. I then put it in standby and moved the red lead to the V3 side and did the same.

Re: replacement tubes in DT25
by lef38 on 2012-12-10 12:59:40

Yes the stock tubes really suck. You should go for the warranty.

I had to change mine 3 and 1/2 month, that's a shame

Check this:


Ifyou have the combo, 2 screws are in the handle; it took me 15 mn to figure it out !!

Re: replacement tubes in DT25
by kguitars on 2012-12-11 02:08:52

I changed mine to a set of JJ EL84s.  It didn't really do much other than the tubes got new.

It may be just me not hearing any changes???  When I retubed my boogies, they really changed quite a bit.

The information above may not be current, and you should direct questions to the current forum or review the manual.