Beiträge von krusty

Hi there,
recently I noticed that my A15Mk1 takes up to 5 or 6 seconds to light up the power supply switch...
I mean I turn the switch on and after 5 or 6 seconds the light inside the switch turns on and the amp becomes fully funcional. I did not noticed it in the first days of use. Is it normal? what can cause my problem?
Is seems like a capacitor has to charge before the light on the switch turns on...
Any help is really apreciated.
Krusty

Hi,
I have just bought a a15Mk1 amplifier but it's very noisy even when no signal is applied to the amplifier (I mean the guitar (EMG pickup) is connected with volume pot off), all the pot of the amp are turned to the maximum no matter which channel is used (on clean channel the noise is less than in ch 2 that is less than in ch2 boost ++).
The amp seems like a radio with has no station broadcasting...this is the kind of noise i hear from the amp...
I have already changed and swapped the preamp Tubes, the power amp part seems not noisy (using return loop jack). Can someone please help me with practical tips?? no matter if I have to desolder some parts...but I want to get rid of this noise (that according to me is a problem)! I tried to follow the layout and the wiring specified in the mounting instruction.. I can add a picture if you need so you can see how my amplifier looks like in the inside...

Re: A15Mk1 Volume pot

Any news about this strange "feature" ????

Re: HUM problem again (A15Mk1)

Yes It is...0.02 Ohm when switch is in channel 1 position and 255K Ohm when in channel 2 position (no boost) and 280K Ohm when boost++!
so the wiring seems ok...

One solution is to post some MP3 with the "normal noise" a well build A15MK1 does when all the pot are to the maximum...Just to know if I have some mistake or that is the "normal noise level"

Hi I was just wonder if in a15mk1 alpha pot MUST be insulated from the chassis with some plastic "ring" or something similar...just as you know to prevent hum and some current flowing from the ground star re-entering the pot through the chassis...
In my kit I did not find any plastic part to insulate them..I was just wondering..
Any help is really apreciated!
Krusty

Re: HUM problem again (A15Mk1)

I tried the power amp stage only using return input...
The power amp is very silent so the noise in my amp comes out from the pre amp stage...

Regarding the point 4 (removing paint) I found that there was a bad soldering on resistor R33 on V3. Now better situation ma always noise comes out...
I was just asking about paint and insulation on the chassis...
My tube has shield on it...and the situation doesn't change if i put the shield or if I remove it...

The strange thing is that noise comes out even from the clean channel (al pot at maximum of course)...of course the noise is less on the clean channel and on channel 2 (no boost)

Another strange thing that happens (I started another topic to explain it because I'm not the only one that has this prob) is that if i have all pot in chan 2 turned to off and the gain to the max some sound comes out from the speaker...so there must be a signal path from gain pot bypassing the other chan 2 pot and this is wrong I think...I used alpha pot and the volume pot on chan 2 seems to work correcly (checked resistance on it when all closed)...

Thanks again
Krusty

Hi,
I have a bad hum problem with my a15mk1. The layout of my amplifier looks like the one on the schematic, the wiring seems ok (double checked) but lot of noise comes out from the speaker (zzzzzzzz hhsssss ) even from the clean channel of course with the pot all at noon position.
Now what I want to do is desoldering the second channel and insulate it and try to debug the first channel in order to understand where the hum comes from and then debug just the second channel with the first completely insulated (not just turning off the channel select switch)
I want to pinpoint out the problem and try to figure out if there is some wiring problem I haven't found yet! so I just want one part of the circuit board to work at time!
So now comes the questions:
1) Which wires I have to desolder from a complete circuit in order to have just the first channel working? and nothing more?
2) Which wires I have to desolder from a complete circuit in order to have just the second channel working? (no boost mode) and nothing more?
3) which wires I have to desolder from a complete circuit in order to have just the second channel boosted working?
4) I bought a deluxe version of the amp, so another question is about the paint (that insulate the chassis)..
Have I to remove this paint under the socket tube to better ground them that could be a problem I have noticed that if I press with my thumb the chassis between socket 2 and 3 with a lot of strength as i would like to bend the chassis (not just putting finger on it) the noise disappear!

any other help is really apreciated!

Re: what is the number on the tube box?

but then how I have to set the bias voltage? always 35 mV on resistors R51 and R52 regardless the value on the tube I mean when I will have to buy new tube?

Re: a15Mk1 ground problem

Thanks, but you did not answer to my questions about paint on deluxe version chassis...
I have already tried in other wall plug and the noise is always present!

Hi there,
there is a number written on the box of my power tubes (6v6) box.
The number is 20!
Is this the value of the grid voltage or what other value it can be? I mean when I will have to change the tube Do I have to buy a matched pair with the grid voltage of 20?
Thanks a lot!
Krusty

Re: A15MK1 Voltage problem

Can I have an updated version of the schematic then?
Thanks a lot!

Re: a15Mk1 ground problem

Hi Mad,
thanks for the answer...
the chassis is connected to eath.
The signal ground is connected to earth throug the chassis (removing some paint on it) (as specified in revision 1.4 no 100 Ohm resistor between ground and earth) and if I measure resistance between star ground and earth I have 0 Ohm.
Probably the problem is the painting (deluxe version)...that Insulate the shield of the tube on the upper part of the chassis....
Do You think I have to remove paint on the exterior side of the chassis just under the socket tube??
what do you mean with "Are the tube sockets grounded?"
The tube sockets are grounded as you mean that the center pin of the socket of the tube 1, 2 and 3 is connected to ground via green wire and then to the star ground point!
Thanks again
Krusty.

P.S. any news about gain pot and volume issue (there is a topic on the forum regarding this)?

Re: a15mk1 bias voltage

well I have a wiring problem...
found it all the voltages were ok and on the resistor tension is 35mV and 33.7 mV
check again your power supply board...I'm sorry I don't have any other help!
Krusty

Hi,
I think my brand new A15Mk1 has some ground problem (probably due to a bad assembly )
It's a bit noisy, but if I touch the shield on the pre amp tubes (expecially 3rd and 2nd tube (as in the schematic)) it becomes silent as it should be...
What can I do to avoid that hum and hiss? (which soldering I have to carefully check and double check again? any other hint)...of course as I release the shield the amp is again noisy :(...
Thanks again!
Krusty

Hi there,
I've just built an A15Mk1 amp and I was trying to debug it because the one I've built it is too noisy (according to me).
I started trying to verify the voltages...all voltages seems ok (+- 5 or 7% ) but the voltages in the schematic in SW3a Boost are completely wrong ( I have 0.1 mV instead of 3.5V and 2.1V)
something simialar happens for Voltages on pin 6 on V3a tube...I have 113V that is ok, but in the schematic there are also 45V and 25.4V don't know how they come out because no resistor or capacitor between 113V and 45V and 25.4V) and I don't have that voltages...
I'm referring to schematic Rev 1.4 sheet 1 of 2!
Now...probably I'm doing something wrong with measures...could someone explain how to do that?
how the voltages in SW3a boost are measured? against ground? How are the switches positions? what does mean a green voltage on the schematic? sorry for this silly question but I'm a novice...
Thanks a lot for your help that is really apreciated.
Kind regards.
Krusty

Re: A15Mk1 Volume pot

Hi, I have the same problem,
Alpha pot and some sound comes out of the speaker (channel 2) even if the volume pot is off! The more I increase the gain the more the sound becomes louder..
I made the check you said measuring resistance from the middle lug of the pot and the ground when the pot is completely off and I measured 0 ohms!!!!!
Is there any wiring mistake or some other issues?
I used revision 1.4 (27.05.2006) instruction to build the amplifier!
Thanks a lot.
Krusty

Re: A15MK1 questions

1) I have double checked 100 Ohm resistor doing the soldering again on power supply board but the ffffsss and the zzzzzz still comes out from my speaker...:((( any other suggestion? I think this is the main problem with my amp...is it possible to have some audio sample of a A15MK1 amp (all channels) with all the pot open (all to right) to hear how much noise should come from a well assembled amplifier? (this is my first one)

2) is it normal that in channel 2 if I raise the gain a lot I hear the sound coming out from the speaker even if the volume pot is completely closed? it seems strange to me...but as I told you i'm a novice and still trying to learn...

3) my amp seems always to lack on bass freq on channel 2 and channel 2 boost...have to use smooth mode to mitigate the high frequences (at low volume)...any suggestion?

Thanks a lot again!
Krusty

I've just finished building this kit...and I have some questions...here they are:

1 )The amp is a bit noisy in clean channel too with no volume...if I turn up the volume some more noise comes out from the speaker (like frusshhh frussshhh it doesn't seems 50Hz) even if the guitar has the volume turn down...what I have to check to get rid of it? And I think is related to this if I touch with my hand the clean channel treb pot this noise increase...is it a ground problem?
Of course the noise increase in channel 2

2) It seems that at low volume the channel 2 ( ++ switched) has few bass...and seems a mosquito...any issue or just because the volume is so low?

3) what is the function of the smooth switch (no explanation found so far)?

4) Have I to put the shield on the tube or can I leave the tube without the metal shield on them? (if yes on all tubes or just on the Pre amp?)

5) any additional check I can do to find and assembly mistakes? (the voltages seems ok so far)

Thanks a lot MAD for this kit!
Krusty

Hi there,
I have this problem with a15mk1...
When I measure tension at the secondary of the power transformer I have 23,7 V (pins 11 - 12)
Then when I measure the bias tension on pin 2 and 3 on the power supply board I have -17,1 V (range is -19V , -24V) (the bias pot is completely open) and If I rotate the bias potentiometer I have -0.4 V. Do you think that there is some mistake or is my tension acceptable?
Other tension (i.e. At the rectifier (+), output of the power supply board, Heater voltage are ok).
Thanks a lot.
Krusty

Hi there,
first of all sorry for this silly question...
I have an A15MK1 deluxe kit with alpha pot..they does not fit in the chassis...I mean there is a metal thorn (preventing the pot from rotate) on the front on every pot that prevents it to fit to the chassis so when I put one in the hole of the chassis it does not stick to the chassis because of this thorn that hits the chassis itself...what I have to do? (can I remove that thorn (how?))
Thanks a lot.
Kind regards.
Krusty