John Mayer Signature New Build with Reverb Issue

Overdrive Special, Steel String Singer, Dumbleland, Odyssey, Winterland, etc. -
Members Only

Moderators: pompeiisneaks, Colossal

User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: John Mayer Signature New Build with Reverb Issue

Post by martin manning »

Indeed it does, and your Va-k is ~50V higher than that. That is why I looked for an alternate power supply. There are a couple of options, though. What is the extra winding you mentioned on the PT secondary?
User avatar
dorrisant
Posts: 2613
Joined: Tue Sep 21, 2010 1:27 pm
Location: Somewhere between a river and a cornfield
Contact:

Re: John Mayer Signature New Build with Reverb Issue

Post by dorrisant »

There is a bias tap that looks to be about 60V. The PT also has a low voltage tap for DC filaments throughout the preamp and a 5v secondary I used for the pilot. Maybe I should be using and older (made much better) tube for the CF... What do you think. I'm wondering how many have tried this setup and what voltages they are getting.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: John Mayer Signature New Build with Reverb Issue

Post by martin manning »

The driver stage cathodes will be at power tube DC bias voltage any way you do it, so it just comes down to what voltage you put on the plates. What if you connect the plates of the CF driver to a lower voltage node?

Or, how about two 100k 1W in series off the screen node and a 22u 250V cap to ground from the junction of the resistors. That will give you about 200V for the plates of the driver stages and a 250V Va-k. The 120k resistor and 250k pot bias set-up you have should be fine as-is.
User avatar
dorrisant
Posts: 2613
Joined: Tue Sep 21, 2010 1:27 pm
Location: Somewhere between a river and a cornfield
Contact:

Re: John Mayer Signature New Build with Reverb Issue

Post by dorrisant »

Ok... So I took the CF plate supply from a lower voltage node. B=3 was sitting at 337v and looked to be good for it. Guessed at 10k for a dropping resistor and put another 22µF 500v filter on the end. This made the new node settle into 290v. (Pretty good guess?) It will be noted as "B+3b". Still biasing to 21 watts per tube. Here we go:

John Mayer Signature Prototype
***Schematic Date = 16-07-12***
Used PT, Choke, Rev TX and OT from Epiphone SoCal 50
Built 5/14
Voltages take @ 120vac line

B+1 = 439 OT CT
B+2 = 437 Screens
B+3 = 319 Reverb Driver
B+3a = 314 Reverb Input & Return
B+3b = 290 Cathode Follower Driver
B+4 = 246 Mixer
B+5 = 242 Stages 1 & 2

V1 - 12AX7 Stages 1 & 2
P1 = 156
P3 = 1.28
P6 = 157
P8 = 1.27

V2 - 12AX7 Reverb In & Return
P1 = 208
P3 =1.56
P6 = 185
P8 =1.28

V3 - 5751 Reverb Driver
P1 = 314
P3 = 3.60
P6 = 314
P8 = 3.60

V4 - 12AX7 Mixer
P1 = 167
P3 = 1.18
P6 = 167
P8 = 1.20

V5 - 12AX7 Phase Inverter
P1 = 227
P3 = 46.5
P6 = 215
P8 = 46.5

V6 - 12AX7 Cathode Follower Driver
P1 = 290
P3 = -44.6
P6 = 290
P8 = -44.6

V5 - 6L6GC Power
P3 = 438
P4 = 436
P5 = -45.3

V6 - 6L6GC Power
P3 = 438
P4 = 436
P5 = -45.3
You do not have the required permissions to view the files attached to this post.
Last edited by dorrisant on Thu Apr 26, 2018 12:55 am, edited 1 time in total.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: John Mayer Signature New Build with Reverb Issue

Post by martin manning »

Looks like you have it pretty well in hand now. I didn't like the 400V negative bias supply because when you switch the main power on (in standby) you get the full bias voltage on the cathodes of the driver tube, however since you have the 220k on the power tubes, grid-to-ground, that divides the voltage by two so you get half of that, or -200V. Some tubes, even some old ones, are only rated to -100V. I suggest reducing the 220k grid-to-ground resistors on the power tubes to 100k to limit the Vh-k to around -125V in standby as well as with signal applied.

I liked your -100V bias supply since none of this is an issue, but I suspect that the time required for that to stabilize was quite long, and might have caused momentary over-dissipation on the power tubes if you took it off standby too quickly.

Really good looking build, BTW!
mabruk
Posts: 16
Joined: Wed May 09, 2012 8:57 pm

Re: John Mayer Signature New Build with Reverb Issue

Post by mabruk »

There is something calling my attention in this schematic. I mean all those resistors, one after the other, between V1B plate and V4B grid. I doesn't look correct. The 68k resistor should be connected after the 1M one, I think, to implement an attenuator of around 24db plus some more by the local nfb. The way it is now will be overloading the plate and reducing a big amount of lows through the 20n capacitor.

I wonder why so much attenuation to later amplify the main signal instead of entering it through V4A grid and mix there, ignoring V4B.
Also, why not taking the signal for the reverb from V1B plate, instead of grid, and saving another triode?
Are there any reasons for not going that way?
User avatar
dorrisant
Posts: 2613
Joined: Tue Sep 21, 2010 1:27 pm
Location: Somewhere between a river and a cornfield
Contact:

Re: John Mayer Signature New Build with Reverb Issue

Post by dorrisant »

mabruk wrote: Sat Sep 30, 2017 3:18 pm There is something calling my attention in this schematic. I mean all those resistors, one after the other, between V1B plate and V4B grid. I doesn't look correct. The 68k resistor should be connected after the 1M one, I think, to implement an attenuator of around 24db plus some more by the local nfb. The way it is now will be overloading the plate and reducing a big amount of lows through the 20n capacitor.

I built that section with the 68k to ground at the junction of the 1M and the 208K (actually I used a 100k and a 105k in series), like the picture and schematic below. There is a ground wire from the right side of the 68k that is obscured by the Orange Drop just below it. I obviously had to deviate from the other schematic a bit.

Martin... I'm getting a bit of the ringing back with the reverb again... Wondering if it might be a tank/tx proximity issue when inside the head. I'm thinking I liked the tone with the 120k resistor and associated bias supply in place of the 820k and all of that... The iron is hot. :shock: It's a sickness, right?

Thanks for the like on the build... I'm glad I built it like this. It is not too bad to mod.
You do not have the required permissions to view the files attached to this post.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
User avatar
Guy77
Posts: 906
Joined: Sat May 31, 2014 2:46 am
Location: Toronto, Canada

Re: John Mayer Signature New Build with Reverb Issue

Post by Guy77 »

Great looking build! I always keep the tank out jack ( red rca jack) furthest from the power transformer when I place the tank in head units. I find its quieter that way. I also found that increasing the 68k resistor to 120k-150k sounded much better with the 50 watt version of these amp.

Cheers
Guy
User avatar
M Fowler
Posts: 14017
Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

Re: John Mayer Signature New Build with Reverb Issue

Post by M Fowler »

I don't go around designing reverbs because there are already so many to choose from.

The amp I built from the above schematic is the best sounding amp I've had the pleasure of using for the right type of music. We compared this circuit to the Ceriatone JM100 build and we liked the above schematic the best. Has such a sweet deep tone and the reverb was luscious.

I'm thinking about going with three knob reverb in a Fender Twin Reverb chassis I have sitting around something like this Old Flame Reverb Section
2007 Old flame Reverb Section Schematic.jpg
You do not have the required permissions to view the files attached to this post.
dbeasley
Posts: 144
Joined: Fri Jul 28, 2017 3:07 am

Re: John Mayer Signature New Build with Reverb Issue

Post by dbeasley »

Did you omit the cut control when implementing the cathode follower driver?

Sent from my SAMSUNG-SM-G920A using Tapatalk

User avatar
dorrisant
Posts: 2613
Joined: Tue Sep 21, 2010 1:27 pm
Location: Somewhere between a river and a cornfield
Contact:

Re: John Mayer Signature New Build with Reverb Issue

Post by dorrisant »

dbeasley wrote: Sun Oct 01, 2017 5:17 pm Did you omit the cut control when implementing the cathode follower driver?
No, I already have an etched faceplate with "Cut" specified. So I wouldn't want to remove it from the scheme. Why do you ask?
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Post Reply