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Unread 03-04-2013, 11:03 AM   #91 (permalink)
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Re: DSL 15H - Modded.

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Originally Posted by Derek S View Post
Sorry, I did search, but can someone tell me or post a link to the tube layout. I'd like to try some swapping before I do anymore snipping (maybe, lol). Thanks
Follows actual DSL, but also from schematics

V1 is farthest from Power tubes has cover. V4 is closest

V1
V1A First stage gain both channels
V1B Additional gain stage Red Ch only

V2
V2A and V2B are cascaded gain stages for both Chs

V3
Cathode Follower (Might have a triode that is another gain stage, can't remember, but half of it is DEFINATELY the Cathode Follower).

V4
Phase Inverter.
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Unread 03-04-2013, 11:32 AM   #92 (permalink)
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Re: DSL 15H - Modded.

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Originally Posted by cybermgk View Post
Follows actual DSL, but also from schematics

V1 is farthest from Power tubes has cover. V4 is closest

V1
V1A First stage gain both channels
V1B Additional gain stage Red Ch only

V2
V2A and V2B are cascaded gain stages for both Chs

V3
Cathode Follower (Might have a triode that is another gain stage, can't remember, but half of it is DEFINATELY the Cathode Follower).

V4
Phase Inverter.
Awesome. Thanks!! I do think I'm gonna try the 76 snip anyway...amp was still pretty bright/zingy. I won't mind turning the dials a bit to tweak the tone.
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Unread 03-04-2013, 02:51 PM   #93 (permalink)
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Re: DSL 15H - Modded.

Tried it (snipping C76). Soldered it back. Definitely did not like it.
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Last edited by Derek S; 03-04-2013 at 03:51 PM.
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Unread 03-04-2013, 04:10 PM   #94 (permalink)
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Re: DSL 15H - Modded.

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Heh..I must be losing my mind, when I snip C76 I get nothing! Almost no volume and no gain (red channel). Weird.

EDIT: Nevermind, working now, lol!
Yes, it is weird. I had exactly the same experience after I snipped C76 and changed V2. Came alive after I turned it on and off a couple of times. Works perfect now. Snipping C76, as a final touch, took the the amp exactly where I wanted it. I guess I am done modding. Thank you, Cybermgk, thank you Johnnyeggs!
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Unread 03-04-2013, 04:27 PM   #95 (permalink)
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Re: DSL 15H - Modded.

Welcome!
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Unread 03-04-2013, 05:26 PM   #96 (permalink)
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Re: DSL 15H - Modded.

Yeah, that's exactly what happened on my end (@ vivan) as well, nothing, then a few clicks on/off and it simply "woke up". It was kinda like when you first plug two new pieces of HiDef components together via an HDMI cable for the very first time, they have a "handshake" moment, then they work together. Still, after trying C76 snipped I simply didn't care for it, became a bit mushy, had to nearly dime the treble to get back some open clarity.

I think I'm sticking where I'm at. The green channel is great for cleans, it takes pedals really well, and now, thanks to Johnnyeggz and Co. I've got a killer, more traditional "Marshall" crunch on the red channel. All is well! Peace.
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Unread 03-04-2013, 08:19 PM   #97 (permalink)
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Re: DSL 15H - Modded.

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Still, after trying C76 snipped I simply didn't care for it, became a bit mushy, had to nearly dime the treble to get back some open clarity.
Did you already have C75 snipped? Leaving C75 in, and C76 out, well that might get mushy. All removing C76 would do, is give the same EQ at low Gain settings, as with the Gain cranked.

That said, as soon as some Caps come, I'm wiring in some leads, and I'll clip in some other values for C76, from 100pF to 390pF. JUST because I'm curious.
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Unread 03-05-2013, 01:51 PM   #98 (permalink)
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Re: DSL 15H - Modded.

I put in a 100pf.
I like it better than snipped,but I think I'll go a bit higher like 120 or 150.
Also I put the 10k back in series with the 1uf.
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Unread 03-05-2013, 09:13 PM   #99 (permalink)
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Re: DSL 15H - Modded.

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I put in a 100pf.
I like it better than snipped,but I think I'll go a bit higher like 120 or 150.
Also I put the 10k back in series with the 1uf.
100pf would match the green ch. I have a series coming from 100pf-300pf to try. They are also a tad better quality than the crap disc that was there.
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Unread 03-07-2013, 11:25 AM   #100 (permalink)
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Re: DSL 15H - Modded.

K, While I wait for the better tolerance, silver mica caps to get here, I did some playing with crap I had on hand (mostly ceramic disk, generic crap). I soldered to micro aligator clip leads to the C76 spot, then tested at 90 and 11ish gain, for each cap. Did it with presence and all eq at noon, then my preferred EQ.


To my ears, taking into account that the caps I used were not the greatest tolerances or quality, the sweet spot appears to be in the 150pf to 180pf, maybe as high as 200pf. At 220pf and above, that harshness and over brightness kicks in to my ears, unless you really turn back the presence trebles and mids somewhat.


THat sweet spot range removes the slight muddiness at lower gain settings that no cap brings, but doesn't get to harsh or bright, reigns it in at higher gain settings.


WHEN I get the better caps, I'll redo and post clips for you all of different cap values before I solder it in. Then you can decide which you prefer, as everyone's tastes and ears are different.
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Unread 03-07-2013, 04:09 PM   #101 (permalink)
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Re: DSL 15H - Modded.

I'm still playing on 100pf.
I was thinking along the same lines,150-220pf.
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Unread 03-09-2013, 01:26 AM   #102 (permalink)
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Re: DSL 15H - Modded.

Yes, after I played a little more I had to bring C76 back. No C76 at all, in my case, a sort of killed lower mid-range. Used 150 pf and 10000 resistor with C34 - looks like everything sounds great now.
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Unread 03-15-2013, 08:48 PM   #103 (permalink)
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Re: DSL 15H - Modded.

Lost you guys. Are we talking about 150pf as a better value for C76 instead of just lifting the stock cap? what's the value on the stock c76? and this is with C75 left in or modded?

BTW, I rolled a JJ 5751 into V1, with 12AT7/ECC81 in V4, and I'm loving it.
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Unread 03-23-2013, 04:46 PM   #104 (permalink)
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Re: DSL 15H - Modded.

OK now I swapped out the 5751 from V1 and used a reclaimed from an old Heathkit (would that be "used old stock?") Mullard ECC83 12AX7 with “BUA” logo, made in Gt. Britain in V1.

This 12AX7 is brighter than the 5751, no longer have any concerns about overdoing it by snipping the bright cap. The clean channel has a real crunch, it's almost not necessary to peg the gain on the green channel (but I do). The red channel just about picks up where that leaves off, and of course goes on up from there distortion-wise.

So much happier with this head than I was with the rattles and boxy sound of the Class 5. That might still have its place for grab-n-go practices, but it's not a tone machine IMHO. Well, that's another thread really.
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Unread 03-26-2013, 02:17 AM   #105 (permalink)
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Re: DSL 15H - Modded.

The stock value of C76 is 470 pf. Lower values will ensure more low end.

Intreresting what you say about about 5751. Will try it out.

Agree about C5. It can be very loud and small in the same time.

Last edited by vivanchenko; 03-26-2013 at 08:26 AM.
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Unread 04-09-2013, 01:06 PM   #106 (permalink)
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Re: DSL 15H - Modded.

What I have now is 10K resistor in series with C34 at its stock value of 1uF (is that a cathode resistor bypass capacitor?);
and I changed R40 from stock 1K8 to 2K2 (is that the cathode resistor?). {EDIT: forgot to mention that I added a 100K resistor in the blank R82 place, which is probably the most important thing of making 1-10 on the gain knob more like the original 1-6.}

So that part's done; I just have a question on the caps near the gain pot of the red channel.

I left C75 (stock 470pF);

and I clipped (lifted) C76 (stock 470pF).

Ok so this is a little dull/dark on the red channel compared to the green, but not by much.

What you're suggesting (in addition to the resistor added to C34), is to clip the 470Pf C75 out, and change the value of C76 from stock 470pF to somewhere in the range of 150 to 180pF? before deciding that I think I need to understand better what these components are doing.

Now's the part where I have to disclose that I'm not good at reading schematics (not new as much as never got past switches, resistors, and capacitors). From what I understand from the schematic, the two caps in question basically bypass the wiper of the VR3 gain pot to the input lug (C76) and the wiper to the ground lug (C75). C76 would be like a "bright cap" or "treble bleed" cap on the volume control of a Telecaster where some of the highs get past no matter what the voltage divider is doing - I get that. But in stock configuration with the same values in C75 and C76, what is C75, the cap on the other side of the pot, doing dumping the same range of frequencies back to ground??? (the green channel doesn't have that).

Last edited by BobV; 04-10-2013 at 10:13 AM.
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Unread 04-09-2013, 03:51 PM   #107 (permalink)
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Re: DSL 15H - Modded.

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Originally Posted by vivanchenko View Post
Yes, after I played a little more I had to bring C76 back. No C76 at all, in my case, a sort of killed lower mid-range. Used 150 pf and 10000 resistor with C34 - looks like everything sounds great now.
exactly where I ended.
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Unread 04-09-2013, 03:56 PM   #108 (permalink)
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Re: DSL 15H - Modded.

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The stock value of C76 is 470 pf. Lower values will ensure more low end.

Intreresting what you say about about 5751. Will try it out.

Agree about C5. It can be very loud and small in the same time.
Yes, its basically a high pass filter that bypasses the red ch's gain knob.
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Unread 04-09-2013, 04:47 PM   #109 (permalink)
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Re: DSL 15H - Modded.

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What I have now is 10K resistor in series with C34 at its stock value of 1uF (is that a cathode resistor bypass capacitor?);
and I changed R40 from stock 1K8 to 2K2 (is that the cathode resistor?). So that part's done; I just have a question on the caps near the gain pot of the red channel.

I left C75 (stock 470pF);

and I clipped (lifted) C76 (stock 470pF).

Ok so this is a little dull/dark on the red channel compared to the green, but not by much.

What you're suggesting (in addition to the resistor added to C34), is to clip the 470Pf C75 out, and change the value of C76 from stock 470pF to somewhere in the range of 150 to 180pF? before deciding that I think I need to understand better what these components are doing.

Now's the part where I have to disclose that I'm not good at reading schematics (not new as much as never got past switches, resistors, and capacitors). From what I understand from the schematic, the two caps in question basically bypass the wiper of the VR3 gain pot to the input lug (C76) and the wiper to the ground lug (C75). C76 would be like a "bright cap" or "treble bleed" cap on the volume control of a Telecaster where some of the highs get past no matter what the voltage divider is doing - I get that. But in stock configuration with the same values in C75 and C76, what is C75, the cap on the other side of the pot, doing dumping the same range of frequencies back to ground??? (the green channel doesn't have that).
R40 IS the V1B cathode resistor.
C34 IS the cathode bypass cap. Stock it fully bypasses the cathode resistor. Just clipping/lifting it, will lower gain, but increases cathode current feedback and will give a more compressed, less aggressive tone on the V1B stage. However, putting the 10K in series with the cap, makes it a partial bypass of the cathode resistor, setting a knee frequency. I.e. higher freqencies are bypassing etc above the knee. BUT, that means the cathode resistor has less affect on the gain, so you need to increase it as well. To me with the partial bypass in, red ch was much more dynamoc and organic, bettter growl and thicker/fuller tone. Had to adjust R40 to gain tase though.

This is how I understand it. Could be wrong. Yes, C76 acts as a high pass filter bypassing the red ch gain pot straight to V1B (red Ch only) preamp stage. So everything above a certain frequency goes straigt to the input of V1B. C75 is from the output of the pot to ground, and acts as a low pass filter (only certain higher frequencies have enough oompf to get past cap) to ground, or a high pass filter on to to V1B, depending on how you look at it Together they make for a very bright red ch. Other DSL Lead1, doesn't even have a C75 equivelent. C76, in and of itself has less effect at higher gain settings. C75 affected ALL gain settings.

In a practical sense, removing C75, to my ears made for a more marshall tone on the red ch and reduced a LOT of the buzziness at all gain levels, as well as rducing the huge difference in brightness between the ch's. Also could run it with the presence above 9 o'clock without being shrill.

Removing C76, to my ears, made the two ch's able to use the same EQ settings, and could run presence, eq knobs at noon or higher and sound good. But, it made the rd ch a little muddy at gain settings from 10 o'clockish ish down (even on bright G12H30s). Needed something in there. So, I soldered leads, and then tried various different caps, for my rig and ears. IMHO somewhere between 150pf and 220pf is where most people will find best. I liked 150-180 best, but that was me. Green Ch uses a 100pf on it's equivelent of C76 btw.

How I understand it anyhow, and I am NOT an expert.
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Unread 04-10-2013, 10:11 AM   #110 (permalink)
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Re: DSL 15H - Modded.

So working together, depending on where the gain knob is set, C76 is a high-pass ("bright cap") at low gain settings (when C75 isn't doing anything because there's not much resistance going around/past it), and C75 is a low-pass at high gain settings (and now C76 isn't doing as much)?

I'm still getting used to the idea that with the gain pot at noon, it's really not in the middle because I added 100K at R82. So basically I've been playing in a lower-gain range, and with C75 in place but C76 clipped, the red channel seems a little dull - maybe a difference of 1 or 2 on the guitar's tone knob - compared to the green channel (whereas stock it was too bright on the red channel).

So I think I'll try a different value on C76 first, with C75 still there, and then try it with and without C75. Just when I thought I was done tinkering...
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Unread 04-10-2013, 11:09 AM   #111 (permalink)
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Re: DSL 15H - Modded.

How about some other sources? Antique Electronic Supply (tubesandmore.com) has silver mica 500V in 150pf and 220pf values, and will sell them individually so next time I order tubes or an amp cover (BTW it looks like I could cut down a Blues Jr cover and it would fit nicely on the DSL15-H) that might work.

Otherwise TEDSS only sells $10 worth of any one item, and Mauser seems to have space-aged unobtanium items that are fifty times more expensive (their web site makes my head spin anyway).
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Unread 04-10-2013, 01:45 PM   #112 (permalink)
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Re: DSL 15H - Modded.

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How about some other sources? Antique Electronic Supply (tubesandmore.com) has silver mica 500V in 150pf and 220pf values, and will sell them individually so next time I order tubes or an amp cover (BTW it looks like I could cut down a Blues Jr cover and it would fit nicely on the DSL15-H) that might work.

Otherwise TEDSS only sells $10 worth of any one item, and Mauser seems to have space-aged unobtanium items that are fifty times more expensive (their web site makes my head spin anyway).
Try Amplified parts
Silver Mica Capacitor, Amp & Guitar Tone Cap, 150pF - 500V: Amazon.com: Industrial & Scientific Silver Mica Capacitor, Amp & Guitar Tone Cap, 150pF - 500V: Amazon.com: Industrial & Scientific

They had 100, 150, 200, 220, 250, 300, 390 and 500 pF silver mica. May have others now. But wiring some in serial you can get other values (2 390s in series = 195pf, 1/c = 1/c1+1/c2...)
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Unread 04-11-2013, 01:56 PM   #113 (permalink)
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Re: DSL 15H - Modded.

Hi All,
So I have been able to complete all "red" channel mods except the C58 to a 2n2. Everything else was easy to accomplish without removing the board. Being that mine is a "DSL15C" with reverb (and all of it's associated static sensitive DSP's, etc) I would prefer not to open that can of worms. From what I can tell the cap in C58 is a 1n (102J400) and I am assuming that I can up that to a 2.2n by adding a 1.2n in parallel to the 1n? When looking at a schematic, it appears this could be physically accomplished by adding that 1.2n across the non-common legs of R80 and R81. This would help avoid the removal of the board and seems that it would be the same from an electrical standpoint? All the other mods provided the expected improvements, but that C58 cap seems it will be the icing on the cake. Please correct me if I am on drugs,or at least bitch at me for not sharing!
Thanks,
Gene
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Unread 04-11-2013, 02:02 PM   #114 (permalink)
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Re: DSL 15H - Modded.

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Hi All,
So I have been able to complete all "red" channel mods except the C58 to a 2n2. Everything else was easy to accomplish without removing the board. Being that mine is a "DSL15C" with reverb (and all of it's associated static sensitive DSP's, etc) I would prefer not to open that can of worms. From what I can tell the cap in C58 is a 1n (102J400) and I am assuming that I can up that to a 2.2n by adding a 1.2n in parallel to the 1n? When looking at a schematic, it appears this could be physically accomplished by adding that 1.2n across the non-common legs of R80 and R81. This would help avoid the removal of the board and seems that it would be the same from an electrical standpoint? All the other mods provided the expected improvements, but that C58 cap seems it will be the icing on the cake. Please correct me if I am on drugs,or at least bitch at me for not sharing!
Thanks,
Gene
Don't have the schematics with me right now, but will check when I can.
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Unread 04-12-2013, 08:53 AM   #115 (permalink)
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Re: DSL 15H - Modded.

C58 is a 1n on the schematic. I didn't change mine.

And thanks for the sourcing tip; wasn't sure if Amazon was the way to go.
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Unread 04-12-2013, 08:03 PM   #116 (permalink)
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Re: DSL 15H - Modded.

Hi guys! I just buy a Marshall DSL 15C and is too much gain for me. I want to apply just the mods listed in the first post. I don't anything about electronics but my brother in engineer. Can someone please post schematics? Also if someone can explain what this mean would be great for me. I need to explain a person who ever touch an amplifier what we need to do

R82-add 150k resistor(spot is already there ,but unused)
C58-2n2
C34-snip
C75-snip


Cheers!
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Unread 04-12-2013, 11:04 PM   #117 (permalink)
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Re: DSL 15H - Modded.

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Hi guys! I just buy a Marshall DSL 15C and is too much gain for me. I want to apply just the mods listed in the first post. I don't anything about electronics but my brother in engineer. Can someone please post schematics? Also if someone can explain what this mean would be great for me. I need to explain a person who ever touch an amplifier what we need to do

R82-add 150k resistor(spot is already there ,but unused)
C58-2n2
C34-snip
C75-snip


Cheers!
FIRST, be CAREFULL. Amps can have lethal votags stored in the capacitors. WHOMEVER does this work needs to know how to drain the amp's capacitors and safe amp work.

If not, then try lowering gain via tubes. Just using a 12AU7 or 12AY7 in V1 (small tube with the metal cover) will really reduce your gain. Effects Gr ch too,, is the problem

R82 means on the circuit board there is already a spot for a resistor. It;s is labelled R82 and will be near the gain knob for the red channel. Whomever needs to solder in a 150K resistor there.

C34 and C75, means to snip one leg of the capacitors C34 and C75. This takes them out of the circuit. C75 will be near the gain pot as well. It's a small tan ceramic disc capacitor. C34 is on the edge of the circuit board (big cylinder electrolytic capacitor). Or they can be desoldered and removed.

The above can all be done, just removing the chassis out of the cabinet.

This one, the circuit board has to be removed from the chassis.
C58 MAY already be a 2n2 or 2.2 nano Fared capacitor. Find C58 (rectangle shape). It should have 222J400 on it. If so, it is already a 2m2. If it has 102J400 then it's a 1n0 or 1nF and you want to remove it and replace with a 2n2.
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Unread 04-13-2013, 07:04 AM   #118 (permalink)
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Re: DSL 15H - Modded.

Great help cybermgk. Now i need to find schematic to get that circuit positions i think.

About tubes, do i need to re bias the amp when changing a pre amp tube?
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Unread 04-13-2013, 07:20 PM   #119 (permalink)
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Re: DSL 15H - Modded.

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Originally Posted by TSP View Post
Great help cybermgk. Now i need to find schematic to get that circuit positions i think.

About tubes, do i need to re bias the amp when changing a pre amp tube?
Nope. Only output tubes, as long as you use tubes that can work in a 12ax7 slot.
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Unread 04-13-2013, 10:49 PM   #120 (permalink)
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Re: DSL 15H - Modded.

I decided to keep mine stock... I keep the gain on the red channel just slightly above 2 on the dial to keep that high-end shrillness in check....

For a 15-watter, it's loud so I have the 7.5w setting all the time.
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