Problem with this fizzy sound

[Ross Grey]

Kleuck is correct based on my experience -- while there are many interesting mods that can be done, to address significant blocking distortion that apparently occurs in many examples of this amp, adding grid stopper resistors for the PI and the last gain stages is the solution.

Here is a photo of where I added these resistors after cutting the appropriate traces as described above.

I recommend verifying that the cut traces are really non-conducting by checking with a meter. For my mods, I simply shaped and cut the leads so that these bridge areas that they should not touch, and then soldiered these directly to the tube socket legs and the correct, existing soldier pad on the board.

Ross

[3y3less]

Kleuck is correct based on my experience -- while there are many interesting mods that can be done, to address significant blocking distortion that apparently occurs in many examples of this amp, adding grid stopper resistors for the PI and the last gain stages is the solution.

Here is a photo of where I added these resistors after cutting the appropriate traces as described above.

I recommend verifying that the cut traces are really non-conducting by checking with a meter. For my mods, I simply shaped and cut the leads so that these bridge areas that they should not touch, and then soldiered these directly to the tube socket legs and the correct, existing soldier pad on the board.

Ross


[ATTACH=CONFIG]21329[/ATTACH]

Hello everyone! I recently have night train head NT15H and wanted to make some changes to improve the clean! I have already removed C27 to eliminate some bright, remove R38. I would like to add the grid stopper but I can not see the image attached to the post of Ross Grey . Can anyone upload the image ?
which you also recommended mods to make ?
thanks

[Ross Grey]

Good morning. Here is the photo that I had originally posted.

There are actually three grid stopper resistors that I add when modifying these amplifiers, but as I recall from my original testing, the one placed on the input of the phase inverter is the most important.

These modifications require some care because you need to cut three traces on the circuit board where each of these cuts gets spanned by the resistors that are added.

In my opinion, removing the blocking distortion in this amplifier by adding grid stoppers is by far the most essential modification. When I do modify this amplifier, I always remove the bright capacitor as described in this thread, but this mod and other mods I have made to this amp for my clients all fall into the category of personal preference.


Ross

[3y3less]

Good morning. Here is the photo that I had originally posted.

There are actually three grid stopper resistors that I add when modifying these amplifiers, but as I recall from my original testing, the one placed on the input of the phase inverter is the most important.

These modifications require some care because you need to cut three traces on the circuit board where each of these cuts gets spanned by the resistors that are added.

In my opinion, removing the blocking distortion in this amplifier by adding grid stoppers is by far the most essential modification. When I do modify this amplifier, I always remove the bright capacitor as described in this thread, but this mod and other mods I have made to this amp for my clients all fall into the category of personal preference.


Ross


[ATTACH=CONFIG]37757[/ATTACH]

thanks for fast reply Ross! but i not view the picture!there is a problem in forum?
In addition to the C27 remove, the R38 remove and grid stopper mods, which mod me to make recommend ?
P.S.: Also removing the bright cap ( c27 ) , i still feel the sound bright...What can I try to do ?

thanks for your help

[Ross Grey]

I just took this photo showing two of the trace cuts on the component side of the board. These cuts were made with a small grinding bit in a Dremel tool. The other trace cut is made on the tube socket side of the board, but I do not have a photo of this.

Please do not get distracted by the many other mods made on this board. This is an amp I use for prototyping and the mods may be totally worthless.

With regard to the pictures not being posted, I think that the site moderators actually review photos to make sure that they are appropriate before they get posted. Please be patient. If you don't see them in a day or two, I can try again, but it does look like the photos were uploaded and I see code in the post text that looks like a reference to the uploaded photo.

Ross

[Ross Grey]

Hmmm... Not sure what to expect. The photo of the trace cuts got posted immediately and I tried to edit my last two posts to add the photo of the grid stopper resistors, but don't see them yet. The photo references are in the post text.

[3y3less]

yes i view image grid-stopper-trace-cuts.jpg but not view image PM Grid Stoppers Repost.jpg.

[Ross Grey]

Ha! I turned it sideways, now it will re-post.

[3y3less]

Hi! i have a question:
what is the purpose of the capacitor c25 and r34? If i remove c25, what advantages or disadvantages I would get in the Sound?
thanks

[Dave H]

what is the purpose of the capacitor c25 and r34? If i remove c25, what advantages or disadvantages I would get in the Sound?

I don't think it will have any effect on the sound. It's there to reduce noise when the input jack is unplugged.

[J M Fahey]

Agree with dave h , it grounds V4a grid when nothing is plugged in, so if you rise volume you don´t hear annoying hiss; when you plug your guitar it´s removed from the circuit (what you wanted to do )
marshall does the same, grounding the second or third gain stage: here a capacitor is needed because V4a grid is elevated from ground and would pop horribly ; R34 is there to make certain the other cap end is near ground and does not pop.

[olddawg]

It's a very inexpensive amp and a long thread, lol. If you paid yourself by the hour is it worth it. You can get a Bugera V22 for $249 free shipping and no tax if you look around. If you want to tinker, I believe you could gut it, use the iron and cab, and build an 18 watt Lite turret board into in expensively. Sometimes you have to admit you are beating a dead horse.

[3y3less]

thanks for the clarification guys!

It's a very inexpensive amp and a long thread, lol. If you paid yourself by the hour is it worth it. You can get a Bugera V22 for $249 free shipping and no tax if you look around. If you want to tinker, I believe you could gut it, use the iron and cab, and build an 18 watt Lite turret board into in expensively. Sometimes you have to admit you are beating a dead horse.

I'll tell you: after installing the grid stopper on the PI now sound all better! and then I like to experiment and improve my rig. For me it is not a waste of time indeed I have fun

[Chuck H]

For me it is not a waste of time indeed I have fun

And so you always shall

I just wanted to say that "fun" can take on many forms. I take some heat from my wife about my level of intensity and frustration when I'm working on a puzzling amp problem. She asks why I still do it and even suggests that NOT doing it might be good for me. It's probably the grimace and my crinkled brow, but she can't tell that I'm actually enjoying myself

[Carlosdrri]

Hi everyone. This is a long old thread, I don't know how many times I have reread it. thank you all for all your information. I have a doubt. I have read that for a grid stopper to work correctly the track must be cut. ok well in the case of v3 a section of track goes under the socket and is not easily seen, this is the one that goes directly to r25. On the other side of the board, another section of pin 2 track comes out to a point next to r26, this seems to me to go to the gain potentiometer. I have seen that there are several that cut this section and solder the resistance of pin 2 to this point next to r26. What is the correct placement? Should the section of track that passes under the socket be cut and from there solder the resistor from pin 2 to r25 for its correct operation? Thanks for everything.