Marshall Neanderthal by Ivanberg - Build Thread:

V1: TAD 7025 Highgrade
V2: Mesa STR 12AX7-A
V3: Genalex Gold Lion CV4004
V4 & V5: Electro Harmonix 6550EH

Tubes (1).JPG

With the amp's MV @ 7, and it's Preamp volume @ 7 also, the amp is ridiculously quiet. I'm not sure if it's because of the nature of these 6550's, but adjusting the Preamp volume up to 10 does provide more gain and saturation but still remains very articulate even when dialing down the guitar's volume control. More so than my 2204's with EL34's!

I also did try one of my EH 7025's in V1 of this amp, and that tube sounded really good and with exceptional low noise performance too.

With the amp running hard for an hour with the above settings, the Marstran OT remained on the cool side and the Marstran PT had a slight hint of warmness. IMO, this is very impressive and one of the good signs of the quality of these trannies.

Experienced Marshall & Tube aficionados, rightfully so, can testify that the old British Mullards and Brimars are the Holy Grail for the ultimate Marshall chemistry! "What's in your wallet?"
 
67plexi said:
Trying to smooth out the harsh sound ??
Try a 47K NFB resistor replace the 100K resistor with a Carbon Comp resistor 1 watt
Click to expand...

No,

There's zero harshness on this build. Every value is custom.

We started on the 16ohm tap, then Greg moved ot to the 4 ohm for less clean headroom...if I explained it right.
 
67plexi said:
Trying to smooth out the harsh sound ??
Try a 47K NFB resistor replace the 100K resistor with a Carbon Comp resistor 1 watt
Click to expand...
Funny thing happened after I thought I was done with the amp. Ivan H had made a comment about Marshalls with 6550 power tubes and the NFB 100k resistor tapped to the OT's 4 ohm tap, which is how I have my 2204 with 6550's set up. Anyways, as I looked back at some of the photos of Robert's amp, it looked like the NFB was tapped to the 16 ohm tap. I pulled the chassis out, and sure enough, that's exactly how I connected it... Ooops!

Knowing that the amp should get a little bit wilder and looser, and start crunching a little sooner as the master volume is turned up, I reconnected the NFB to the 4 ohm tap. I followed this up by adjusting the 60% bias up to 70%. Trannies are still running cool even with the amp running hard.

C__Data_Users_DefApps_AppData_INTERNETEXPLORER_Temp_Saved Images_presence_20style_20marshall_0...jpg
And now with goal of hitting the phase inverter harder, I'm testing & listening to alternative presence circuits but keeping to traditional Marshall implementations. Ivan drew out the illustrations of above. Type 1 with a .1uF cap is how the amp was set up originally. I'm trying type 2 right now, but with the same .1uF cap. So far, I'm noticing a bit more saturation with the presence control at noon. And maxing out the presence will drive the power section harder, without it sounding harsh... Gotta love this! Then again, I'm playing through a pair of Scumback M75LD's, which have a topology based on the sweet Celestion 12-65M's. And I also don't want to replace the 5k pot with a 25k. And I don't want to replace the .1uF cap with a .68uF.
 
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syscokid said:
Funny thing happened after I thought I was done with the amp. Ivan H had made a comment about Marshalls with 6550 power tubes and the NFB 100k resistor tapped to the OT's 4 ohm tap, which is how I have my 2204 with 6550's set up. Anyways, as I looked back at some of the photos of Robert's amp, it looked like the NFB was tapped to the 16 ohm tap. I pulled the chassis out, and sure enough, that's exactly how I connected it... Ooops!

Knowing that the amp should get a little bit wilder and looser, and start crunching a little sooner as the master volume is turned up, I reconnected the NFB to the 4 ohm tap. I followed this up by adjusting the 60% bias up to 70%. Trannies are still running cool even with the amp running hard.

View attachment 85362
And now with goal of hitting the phase inverter harder, I'm testing & listening to alternative presence circuits but keeping to traditional Marshall implementations. Ivan drew out the illustrations of above. Type 1 with a .1uF cap is how the amp was set up originally. I'm trying type 2 right now, but with the same .1uF cap. So far, I'm noticing a bit more saturation with the presence control at noon. And maxing out the presence will drive the power section harder, and it still won't sound harsh... Gotta love this! Then again, I'm playing through a pair of Scumback M75LD's, which have a topology based on the sweet Celestion 12-65M's. And I also don't want to replace the 5k pot with a 25k. And I don't want to replace the .1uF cap with a .68uF.
Click to expand...

Awesome work, Man!!!!

When you finally gonna call it done!!!! LOL
 
syscokid said:
View attachment 85362
And now with goal of hitting the phase inverter harder, I'm testing & listening to alternative presence circuits but keeping to traditional Marshall implementations. Ivan drew out the illustrations of above. Type 1 with a .1uF cap is how the amp was set up originally. I'm trying type 2 right now, but with the same .1uF cap. So far, I'm noticing a bit more saturation with the presence control at noon. And maxing out the presence will drive the power section harder, without it sounding harsh... Gotta love this! Then again, I'm playing through a pair of Scumback M75LD's, which have a topology based on the sweet Celestion 12-65M's. And I also don't want to replace the 5k pot with a 25k. And I don't want to replace the .1uF cap with a .68uF.
Click to expand...
The type 2 presence control circuit in the diagram, as seen on a few JMP's, is my favourite too. Gives the amp a little extra magic that will set it apart from "otherwise identical" amps.
I've not seen the 0.68uf value used in 50 watt amps, however it's not too uncommon in the 100 watt JMP's.
The 0.68uf value used in the type 2 presence control circuit shown in the diagram, IMO makes the presence control act kinda like a midrange grind control, which is kinda neat. Cheers
 
Originally posted by @syscokid:

In a nutshell... The RH2204 Limited Edition, one of only one, is sounding fantastic!!!

Gory details:
Few days ago, I gave the amp an extra 50 hours of electric infused juiciness. I did had a tiny fan to circulate the atmosphere behind the amp during the process. Turned it off, and let it completely cool down before I turned it back on to do some wanking at low volumes with different gain settings. It was OK, but I really wasn't feeling the love... Not sure if it was the amp or it was just me, ha ha!

Next day... I tried again, this time using my Rivera attenuator and running the amp with the master volume at 7-ish and different gain settings again. Now we're talking... more enjoyable. Solid tones... tight... articulate, yet not as sterile as before a bit of break-in and running the amp in a sweeter spot. I also checked the bias, and sure enough, it drifted a bit to the warmer side. I'm positive I set the original bias at 35-36mA's for a medium setting. Now the bias is measuring at 40mA & 39mA for V5 and V4 respectively, which is a Warm setting... A bit surprised but I'm a Happy Camper!

Yesterday... I decided to push the amp a bit further. Bumped the bias to 45mA's... We're getting into the hot side at 75% dissipation. All I can say is... WOW! I played the amp another hour straight till my fingertips shriveled up. Very Happy Camper!!

Today... I messed with that Type 2 presence circuit again by comparing the original .1uF cap with a .68uF cap. I went back and forth with various presence settings and gain settings. I chosed the .68uF cap for its "more meat on the bones" tone on single note riffage, and the fact that I could dime the presence control and almost dime the gain control for the ultimate Marshal kerrang and attitude!!!

Presence 5k .68u parallel 4.7k (1).JPG
 
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