DC Mods - Revisited...........Sort of.............

[crguti]

Blanket Removal Mod:I always seem to forget to tell people about this one, but it makes a huge difference. It gets rid of a lot of the muddy tone and over all lack of dynamics compared to some of the Holy Grail amps.
1. Right after V6 (page 7 of drawing), there is a 75pf cap that ties pins 1 & 6 of V6 together.
Replace this cap with a 47pf Silver Mica cap.

I've got a 47pf ceramic cap... is it relevant to know the voltage at which these caps works :?:

 

[Monsta-Tone]

You'll probably want to use 500v rated caps. Sorry, forgot to mention that.

 

[BlackBoxy]

I answered the Solo function question in your PM.
Didn't see the footswitchable loop question, sorry.

If multiple switching functions are needed, I use one of these: https://taweber.powweb.com/store/chansword.htm
I usually get the Optical one, and replace the LDR's with Vactec 5C1's.
You could try this for the footswitchable loop.
Their low power relay board is cool too.

You will most likely have to add a 10M resistor across the item that you are switching to avoid popping.


On a side note, if you're gassing for a DC, mine is up for sale.

Dc5's use Vactec VTL5C9, not really same photoresistor value part than 5C1


as other mods, i would put a .1 uf 715p cap to replace the terrible ceramic disk for a smoother and more usefull presence in the dc5.. follows the yellow cross wire near V6 #6 socket pin!

regards

 

[Monsta-Tone]

:lol: I was talking about the LDR's on the Weber "Optical Channel Switching Board" kit, not the LDR's in the amp....... :lol:

 

[BlackBoxy]

:lol: I was talking about the LDR's on the Weber "Optical Channel Switching Board" kit, not the LDR's in the amp....... :lol:

:lol: :lol: :wink:
i still don't know what webber Optical Channel Switching Board would bring more , mesa dc5 switching matrix is already there with a 3v supply (no need of more PS), with its own muting (ldr) network, why adding a new gear to bypass this one? its not a old simplistic fender turet's or eyeslet's board, useless !
aswell Reverb chanel in the dc5 is swithched by relays RY2 RY3 drove by optocoupler 4n33, LDR's?
not really same voltage and current at this preamp stage, different impedance than inputs(there is word "Resistor" into LDR) , with alot of maths and redesign, maybe !

Dc5 is simple,

there is 3 relays NEC MR62 5UKSRY, 2 optocoupler 4n33, and 3 LDR VTL5c9,

switch drives two matrix, 20v and 5v, eathier lights off or on leds of LDR1 or LDR2 wich mute or open inputs of Ryth/Lead chan + the 4n33 leds lights up or off that drives RY2 RY3 dpdt (reverb input/output,Master and presence) on preamp stages to ryth/lead too, its a chain ..

LDR3 is alonne and switch EQ independently as Boost pull pot drives RY1 switching on or off preamp rythm chan (filter/resistor).

would be complex stuff to break this matrix by replacing 2 relays (reverb input RY2, Reverb output RY3) with two slower LDRs , good luck!

personnally i use a cheap 2 switchs Ftsw for channel ryth/lead and eq as i rewired front chan switch jack to the place of reverb one !
would be easy to drive eq with actual switching matrix, no need to add one another bypassing the existing one!

 

[Monsta-Tone]

Maybe re-read the whole thing. I was talking about adding an LDR to the amp so that people could install the Solo function that is on most of the newer amps.

I was trying to help people.

 

[BlackBoxy]

mismatched stuffs, never mind!

solo function? i use eq to boost, and a pre amp!

a solo through the output via a LDR could be usefull , right , with a pot bleeding some power to the ground,
wouldn't it change the 6l6 attack tone?

 

[Monsta-Tone]

I didn't really like it all that much. Seemed to work great on the Heartbreaker and a few Rectos that I added it to, but on the DC I think you need as much juice going to the power tubes as you can get.

 

[BlackBoxy]

i look for less OD in the rythm channel without changing the tone, at 4 on gain it gets crunch, what would be better, increasing 150k that ground tone stack (near boost gate) or reducing 470k on V4a pin 2 divider?

i got the dc5a ..

 

[Monsta-Tone]

Take a look at the DC-5b drawing. If you look closely, there are only a few parts that are different. The B has much more headroom.
One of the things I did a lot for people was convert the A to the B clean channel.

 

[BlackBoxy]

Take a look at the DC-5b drawing. If you look closely, there are only a few parts that are different. The B has much more headroom.
One of the things I did a lot for people was convert the A to the B clean channel.

V4 pin 2 voltage divider 220k-470k for the A and /10 3.3M-33k for the B and pin 8 15uf for the B ?


thanx Monsta

 

[Monsta-Tone]

To change DC version A clean channel to Version B:

V1a - Pin 1
- Add .001mf cap across grid resistor
- Change grid resistor from 100k to 150k

V1a - Pin 2
- Remove 500pf cap to ground

V1a - Pin 3
- change 3.3mf cap to 1mf cap (I usually use electrolytic here, make sure you watch polarity)

Gain Pot
Change "Bright Cap" from 120pf to 75pf

V4b - Pin 7 (just after Gain Pot)
- Remove 82pf cap to ground

V4b - Pin 8
- Change .47mf cap to 15mf

V4a - Pin 2
- Change 220k resistor to 3.3M resistor w/39pf cap across it
- Change 470k resistor (to ground) to a 330k resistor

Resistor just before Channel Master Volume
- Change from 680k to 330k resistor

These changes make the clean channel have much more headroom than the A version. To my ears, they sound much more like a Fender.
Sometimes I experiment and only make some of the changes, or make them 1 at a time to see exactly what effect each one has.
Some of them (especially the V1a Pin 1) will add gain if you do not do some of the ones at the end, like changing the 220k after V4a Pin 2 to a 3.3M.
Experiment, have fun, it's great mad scientist stuff!

 

[BlackBoxy]

i think i'll go for a 80k on v1 to the place of 100k , and look at master pot resistor, most of the headroom is made by the weakier (inpedance) just before Master pot which with the 680k makes a voltage divider , i'll look at this because i really love my clean tone, got two sylviania black long plates D getter on V1 and V4 , its just i got crunch too early for my taste !

thx Monsta!

 

[BlackBoxy]

Well, i just finished upgrading/mods of my dc5!

all electrolytics caps been changed , all optocouplers optoisolators and relays are brand new ones, all 9pins and octo tubes sockets changed too!
most of Monsta great mods been done +first lead filter stack before gain pot with orange drop 500p/0.1/0.047, great mod, last one replaced 680k by a 330k more headroom, changed presence ceramic cap with a mustard tad 150nf, and changed 220R 5w blue voltage 50v, beware this resistor it burn on and drys the pcb, especially after 20 years , i modded chan footswitch to work in the place of reverb on stereo jack 2 switch FTsw !

got old Winged "S" 6l6gc plugged in, with v1/v4 sylvania black plates D getters NOS, V2 mullard cv4004 NOS V3 RCA long black plates NOS, V5 grey long plates sylvania, V6 mullard NOS cv4024!

i really like my tone, its a tone i was looking for, at bedroom or club's volume!

Would like to thanks all pundits bringing knowledges about this amp!

regards

 

[motormenace]

Picking up a DC-10 head in trade for my Rectoverb combo. These mods will defiantly be done to it.

Also, I was noticing the reverb mod and was wondering if it will get me close to a Twin Reverb sound?

 

[BlackBoxy]

Picking up a DC-10 head in trade for my Rectoverb combo. These mods will defiantly be done to it.

Also, I was noticing the reverb mod and was wondering if it will get me close to a Twin Reverb sound?

absolutly, very close!

 

[motormenace]

Very cool! Thanks! Now I defiantly can't wait to dig into the amp!

 

[crguti]

i really like my tone, its a tone i was looking for, at bedroom or club's volume!

clips or you don't have a good tone. :roll:

 

[BlackBoxy]

i really like my tone, its a tone i was looking for, at bedroom or club's volume!

clips or you don't have a good tone. :roll:

well shakespeare was right "Something is rotten in the state of Denmark"

 

[crguti]

Lead Channel Mods
More or Less Gain:
Between V1B & V2A there is a Voltage Divider (page 5 of the drawing).
You will see a 150K resistor going from the signal path to ground. Change this resistor.
Lower value = Lower gain
Higher value = More gain
I like 220K. 330K is really nice too, but starts to get a little bit mushy.
Any more than this and it gets really mushy but has gobs of gain.

What is the appropiate power rating of the resistor?