Beiträge von bertrand_lascoup

self answer ::::: ;D

At that time R11=120 kOhm and R12=680 Ohm.....
as it is said in the manual JTM 45, R11=100 kOhm and R12=820 Ohm ......

How far can I go ???? Without destroying amp and tubes???

BL

Hi
I often play at low volume and I always have the gain at max and I want ot get more disto ..

How can I modify my amp (i don't want to add a external effect) to improve gain.

I installed the footswitch on the M15 but I have a pb with connection with the PT.

First, the lugs numbers are not correct on the manual : lug 11-12 does not exist on my PT. anyway, I found lugs to get 24V for the amp....

Then, when I solder I measure at CN2, I found about 24 V DC..... not 12 V as indicated in the manual of the footswitch ......

So I finished the assemby and I hesitate to plug a footswitch pedal now... I switch channel with front panel switch..... manually...

I controlled the wiring..... nothing, have you got an idea ?

I worked yesterday ... and now no hum at all....

I just check solder and reduced wire length (the sielded ones going to tube...) and nothing... no hummm


So go sound... using a 2x12 cab (celestion vintage 30)..

But I want to do mods :
- having more gain at channel 2 when low volume (I have to work at low volume at home and even with 1x12", it's loud to have high disto...)
- adding a reverb
- working on a headphone out


is there somebody who has idea about this mods ...

I also want to introduce a FX loop.
and I wonder if I have to use shield wire?? as the jacks will be after the chanel swith and the C14 and the actual wire is shielded ....

and as i have Hum... I deceided to finish the whole assembly (footswitch + FX loop) before working on HUM....

BL

Zitat von eBernd;327701

BTW What do you read on the DVM Display if you shorten the test leads?

I don't understand what you want me to do ????

"At the primary side you should measure about 160 Ohm, at the secondary side you should measure about 0,9 Ohm at taps 2-6 and about 0,7 Ohm at taps 2-5."

the values I measure are higher....


ok for the bias.


Is there any wire I must take care to prevent hummm ??? only the 2 we are discussing ?? the one from the input jack ???

what is the perfect position for the 2 wire (same as manual) or they can be close to other wires ??? placed closer to a part or an other ??.... or in fact, it doesn't care as they are shielded......

I did my best to use the right tool to cut and work with. The shield is connected at ONE end : OK the other is isolted but shrinking tube.
I don't think it is broken.

I removed the isolated part of the shield, twited the wire and sold it. about 1 cm of shield is twited and solder.... and about 1 cm of the center wire is not shield (1cm at both end) .... is it enought to get hummm ????

I will try to removed the shrinking tube to measure if it is connected to ground.....

another idea from the source of the Hummm....

I heard the sample done with this amp and mine is not able yet to provide such sound......




Another thing :
I receveive the "new" OT. and when I measure the primary and the secondary .. i don't have the right values as predicted in the manual ...
About 260 ohm / 1,3 ohm and 1,1 ohm .... can it be a source of problem ???

I am surprised not to have to ajust bias value for the tubes....

it's a constant sound like "bbbbrrrrr" (difficult to explain in other langage)... in french : ronronnement : purr ???
maybe it is hummm ...

when I hold the 2 wires as i explained before, this sound stop and I get the normal sound of a tube amp.....

I have ordered a M15 delux and I finished it without any big problem. I have just difference from OT and measurement of resistance (upper than those given in the manual). and difference for the Capacitor identification name....

And at first testing, I realize that I forgot 2 wires (lol) :
-From R28/R29 and C19
-From C2 and R4/C1.

But no smoke....


But when I started it, I heard a big breath ... suffle :
. constant at any volume
. both channel
. the only thing that stop the sound is holding shielded wires from V4 and V5 and putting them in a specific position. At that time, suffle is low. and I can hear my guitar... otherwize, the guitar cannot be heard at low volume....

So what I have to verify first ??

I think a ground problem (loop ??) as the potentiometer body are next to the body of the amp I though that it can be a ground loop. but after measurement, no contact at all... and no loop with green wire

Which wire must I put far from others ???

I wiil try to get an oscillo to look at the signal (maybe 50 Hz ???)

Thanks for your answer.

bertrand