Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: wsscott on February 11, 2022, 02:26:54 pm
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I completed the build of a Magnatone Twilighter which was modded with the help of Sluckey, and others, which is based on the 2020 Schematic from Magnatone which I included in that prior topic. I only wanted it to have Tremolo since I had done a build a couple of years ago based on the Mag 10A circuit that Sluckey worked with me in modding, which was a head unit with just Mag's VIBRATO and also Reverb--sort of like a ReVibe.
In doing the Twilighter Mod build, I left room on the turret board to add the Reverb circuit from the Mag. Twilighter Schematic, and I also included a space on the chassis front for a Reverb pot, RCA jacks for the reverb tank, and also installed a 9 pin tube socket to take the tube for the Reverb Driver and Recovery.
So I'm thinking now of adding the Reverb to this amp. In part because I need something to do.
I'm attaching copies of the Magnatone Twilighter Schematic 2020, and the Mod Twilighter Lite Build that Sluckey was kind to create. The later is what I'm now going to be asking for help in adding the Reverb.
So as to this mod, I'd like your thoughts and tell me what I'm about to screw up.
In looking at the Mag. Schematic and comparing it to my Lite Mod, I focused on the area where Sluckey changed 3 of the components to make it work with the Mod, and which are coming off the V-1B 12AX7 tube. He uses a .047uf cap, 220K and 270K resistors instead of the .022uf, 10p, and 3.3M as shown in the attached Mag Twilighter schematic which are needed for the Reverb part of the circuit.
So, I created a "Layout" to add the Reverb circuit. Its attached, and not pretty, but hopefully accurate as to what needs to be done.
I had contemplated replacing the .047uf cap now existing in the Mod with the .022uf, and remove the 220K and 270K resistors and the.0022uf cap from the circuit.
Then the rest of the circuit layout for the Reverb is shown in my Layout attached. The remaining components connecting to the other Pins on V1 and V2 don't change, so I didn't show them in the Layout.
I've added the "New Tube" which is a 12AX7 as shown in the Mag. Schematic, and use it for the Driver and Recovery.
One other area of concern is the Grounding for this addition. I've avoided grounding anything to the Power Ground that's shown on the Mod Lite Layout. Instead, I'm grounding to the Ground Buss. Thoughts?
There's probably a more efficient way to do the Layout, but I was hoping my effort would at least get a discussion started.
Thanks for your time.
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Compare the Rev pot 100k to 1M Compare the reverb insertion point resistor 3.3M to 150k
Adding 1-tube reverb (el34world.com) (https://el34world.com/Forum/index.php?topic=7957.0)
This one tube approach is a current reverb set up in my Carolina Overdrive Special. I like it really well. I have another amp that is more Fenderish in reverb with a paralleled 12AT7 send. I like them equally. IF you use a one tube reverb approach then consider a 12DW7 which is something Sluckey suggested to me and I like quite well.
Just different ways to consider doing this. The 150k has much less of a loss in gain. The larger value reverb pot still helps with separating send and return. Not saying you should use this approach, just adding it into the mix for consideration.
with respect, Tubenit
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You need three triodes plus all this circuitry to add the Magnatone reverb to your MT Lite. You have one extra triode in V3, so only need to add one extra tube.
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Tubeinit--I looked at your referenced post, and the attached images, and had a question about the first image--the "reverb and schematic layout"-- Did you install this on a separate board and terminal strip that you mounted in the chassis, or exactly what did you do?
Also, any thoughts on grounding?
Thanks.
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I have done the one tube reverb with a terminal strip and on layout boards both. Each worked fine for me. I would suggest following Doug Hoffman's grounding on his AB763 layout.
Take a look at the ARCHIVES thread on "one tube reverbs" for examples of reverb layouts and terminals strip topology.
Tube Amp Schematics, Tube Amp Information, Tube Amp Projects (el34world.com) (https://el34world.com/schematics.htm#Hoffman_AB763_One_Channel_)
Grounds (el34world.com) (https://el34world.com/charts/grounds.htm)
Sluckey also has given you a great plan for implementing reverb on this also that is worth considering. I am thinking that his plan with the added gain stage after the reverb insertion point may give you more reverb than the plan I typically use? I don't use alot of reverb and the approach I typically take will not do surf type reverb at all. Not intense enough.
With respect, Tubenit
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Sluckey-thanks for your input. I was having trouble figuring out how to get back to the PI.
Tubenit-Thanks for the info.