Want Pre500 tone? Here's how to get it!

[JCDenton6]

What can be done on a 3 channel dual just to increase the upper mids a little. I'm happy with the gain where it is. I'd just like to open it up a little i guess. Thanks in advance!

What you can do is remove and jump the (3) 100 ohm resistors on the cathodes of V1, V2, and V3 and remove the 82pf cap/2m circuit from V1.
That will give you want you described above without the gain boosts of changing the pots.

 

[Anonymous]

What you can do is remove and jump the (3) 100k resistors on the cathodes of V1, V2, and V3 and remove the 82pf cap/2m circuit from V1.
That will give you want you described above without the gain boosts of changing the pots.

(100 ohm)

What can be done on a 3 channel dual just to increase the upper mids a little. I'm happy with the gain where it is. I'd just like to open it up a little i guess. Thanks in advance!

Not sure how technical you are, but for Red modern, a 100k feedback loop to the 4 ohm tap works really nicely for opening up the mids.

Another thing you could do that's a little easier would be to increase the value of the cap on the gain pot. I believe it's 1nF stock. Maybe try 2 or 3nF? That would give you a little bit of a gain boost too, but it should be a pretty good mod. I'd only do it with a 250k or 500k pot. Would probably just get muddy with the 1k.

 

[JCDenton6]

I don't know why I keep labeling them as 100k instead of 100 ohm resistors, DOH! :evil:
All awesome ideas posted above if you don't want to switch out the gain pots. What power tubes do you have in the recto?

 

[rpurdue]

Thanks for the awesome info guys. Truthfully, i'm pretty much an idiot when it comes to amps. I'm a decent solderer so if it's detailed directions to the location of which caps they are on the board i'm good to change them etc but other than that i'm pretty lost. I've tried with 6L6's and Tung Sol EL34L's. I think i prefer the Boogie 6L6's still but until i get a bias mod i won't be certain.

 

[JCDenton6]

I will go through my documents and pull up a schematic of the 3 ch dual rec and circle out the locations of the said resistors.

If anyone can upload (or PM) some high rez shots of both a old 3 ch and a multiwatt when they can that would be awesome, thought I had some but they're of bad quality :roll:

 

[rpurdue]

I will go through my documents and pull up a schematic of the 3 ch dual rec and circle out the locations of the said resistors.

If anyone can upload (or PM) some high rez shots of both a old 3 ch and a multiwatt when they can that would be awesome, thought I had some but they're of bad quality :roll:

I can take some of mine if that would work.

 

[rpurdue]

Here you go. These are all taken with the knobs away from me...starting Right side to left. And then again for the small boards on the back

 

[JCDenton6]

Awesome, thanks a lot! I'll get this sorted out in a bit!

 

[JCDenton6]

Reborn:



Old 3 channel:



Mesa used 10 ohm resistors here in both amps for some reason when they are listed at 100 ohms on the schematics, and 100k gain pots :?
No wonder why the old 3 ch heads differed so from the 2 ch heads, my old head was setup just like this, found an old pic and compared with those above :twisted:

 

[rpurdue]

Reborn:



Old 3 channel:



Mesa used 10 ohm resistors here in both amps for some reason when they are listed at 100 ohms on the schematics, and 100k gain pots :?
No wonder why the old 3 ch heads differed so from the 2 ch heads, my old head was setup just like this, found an old pic and compared with those above :twisted:

So these should be replaced with 100 ohm then? What would that due in turn to the tone?

 

[JCDenton6]

The 100 ohm resistors should be removed and jumped, the 82pf/2m circuit should be removed and the 20pf cap should be removed.
Forgot to include that in the pictures.

It will allow more mids and highs to pass through the preamp gain stages tightening the tone and adding mids.

 

[Shemham]

Reborn:
Mesa used 10 ohm resistors here in both amps for some reason when they are listed at 100 ohms on the schematics, and 100k gain pots :?
No wonder why the old 3 ch heads differed so from the 2 ch heads, my old head was setup just like this, found an old pic and compared with those above :twisted:

I've measured the stock gain pots from my Reborn head and they were definately 250k ohm.

What 10 ohm resistors do you mean? At least the resistors after the cathode bypass caps are 100 ohm as written in old 3ch schematics (br-bl-bl-bl, 1% tolerance). Just trying to prevent confusion

 

[Anonymous]

Mesa used 10 ohm resistors here in both amps for some reason when they are listed at 100 ohms on the schematics

Not sure on the gain pots, but those resistors pictured are 100 ohm (brown black black black = 100*10^0).

 

[rpurdue]

Reborn:
Mesa used 10 ohm resistors here in both amps for some reason when they are listed at 100 ohms on the schematics, and 100k gain pots :?
No wonder why the old 3 ch heads differed so from the 2 ch heads, my old head was setup just like this, found an old pic and compared with those above :twisted:

I've measured the stock gain pots from my Reborn head and they were definately 250k ohm.

What 10 ohm resistors do you mean? At least the resistors after the cathode bypass caps are 100 ohm as written in old 3ch schematics (br-bl-bl-bl, 1% tolerance). Just trying to prevent confusion

I'm curious where the differences the circuit are between the 3 channel and the reborn actually. Was it just a few values changed or was it completely changed.

 

[rpurdue]

The 100 ohm resistors should be removed and jumped, the 82pf/2m circuit should be removed and the 20pf cap should be removed.
Forgot to include that in the pictures.

It will allow more mids and highs to pass through the preamp gain stages tightening the tone and adding mids.

Will it decrease the bottom end as well?

 

[Shemham]

I'm curious where the differences the circuit are between the 3 channel and the reborn actually. Was it just a few values changed or was it completely changed.

Well, from what I've gathered so far, channel 2/3 pre-amp circuit in Reborn head is practically identical to old 3 ch circuit. Differences can be found in the tone shape circuit after V3. Reborn heads have 500pf caps there with 180pf caps behind relays to make the both orange and red channels identical for vintage and modern modes. Then there are the stacked presence pots for vintage and modern mode. There could be other minor differences there, but I haven't spotted them yet.

So far I haven't tried to trace the differences in the raw mode, but I believe it has been altered somewhat.

The clean channel circuit is drastically different.

The power supply for the Reborn heads seems to be somewhat different from old 3ch model. There's one new 6800uf cap and 1000uf cap where the 10000uf cap used to be (low voltage supply?).

 

[rpurdue]

I'm curious where the differences the circuit are between the 3 channel and the reborn actually. Was it just a few values changed or was it completely changed.

Well, from what I've gathered so far, channel 2/3 pre-amp circuit in Reborn head is practically identical to old 3 ch circuit. Differences can be found in the tone shape circuit after V3. Reborn heads have 500pf caps there with 180pf caps behind relays to make the both orange and red channels identical for vintage and modern modes. Then there are the stacked presence pots for vintage and modern mode. There could be other minor differences there, but I haven't spotted them yet.

So far I haven't tried to trace the differences in the raw mode, but I believe it has been altered somewhat.

The clean channel circuit is drastically different.

The power supply for the Reborn heads seems to be somewhat different from old 3ch model. There's one new 6800uf cap and 1000uf cap where the 10000uf cap used to be (low voltage supply?).

Interesting! I hope at some point there's a mod that can take the pre recto reborn 3 channels to convert them to the current schematic.

 

[JCDenton6]

I was kinda drunk so I ranted a little in that post with the pics, no confusion meant on purpose.

Weird, a far as the 100k gain pots I'm pretty sure they were because I had to max out the gain on both channels on my old 3 ch head, while with my 2 ch triple was stock, my gain stayed around 2:00

 

[Shemham]

I was kinda drunk so I ranted a little in that post with the pics, no confusion meant on purpose.

Weird, a far as the 100k gain pots I'm pretty sure they were because I had to max out the gain on both channels on my old 3 ch head, while with my 2 ch triple was stock, my gain stayed around 2:00

Yeah, you might be right about the old 3 ch head. Perhaps this could be one of the differences between the old and new 3 ch heads?

 

[kramerxxx]

Cap goes on the same way for both pots.

This is the cap for a 2ch, correct? On the 3ch amps it looks like the gain cap is on the main PCB where the flying leads connect from the Pot. It is not green, but tan. Correct?