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#1
The 1st amp we are going to be building is the blackface Princeton Reverb. I'm putting together kits for Rasker, Bellerophan, and myself. I still have 1 extra princeton kit if anybody else is interested in doing this with us.

After the Princeton Reverb build I’m going to push on and build some modified super reverbs, tweed pro’s, tweed twins, and an 18 watt 1974 with vibrato.

I’m hoping for as much group participation as possible so anybody that has any ideas about how to modify schematics and layouts that may improve tone and/or versatility then please, speak up.

You can expect to at least 7 different amps built in this thread and if we come up with enough ideas so that it's not just the same amps over and over again you may see as many as 16 amps built here. Expect soundclips too.
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#2
Is this the result of the co-op amp build thread then?

Have little experience with amp building myself, but I shall watch this with interest and bid you good luck.
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#3
^Yup. I didn't get as many people from UG as I had hoped, but music shops in the area were very excited to have me supply some amps for them so luckely I was still able to get the good prices for us.

So here are my mods and ideas for the Princeton reverb I’m building that I plan to keep for myself.

1, The capacitor for the midrange is going to be .033 instead of .047. This is something that was done on the earliest Princeton reverbs. It gave more presence to the high end and made the bass tighter which really improves the overdriven tone. No more buzzsaw tone when you crank everything to 10.

2, I’m using a pushpull pot on the bass control. When pushed in the amp will perform as normal but when pulled out it’ll switch the resistor for the midrange from 6.8K to approximately 15K (I’m going to play with the value to see what I like best). Doing this will give me a midrange boost, more gain, and much better overdriven tone.

3, I’m changing the reverb driver tube from 12AY7 to 12AX7. This will drive the reverb tank harder and give me and clearer signal coming out of it.

4, I’m adding a switch that will make it so that when I’m not using the reverb, I can use the tube driving the reverb as a volume boost. This means might cause a phase problem so I’m not sure it’s going to work, but I’m going to try it and see what happens.

5, I’m adding a 250K resistor from hot to ground on the jack that comes after the reverb tank. This has 2 purposes. One is that it will protect my V3B and stop it from blowing if my reverb tank is accidentally unplugged. The other reason is that it lowers the impedance which will give the reverb a warmer voice.

6, I’m changing the value of the 3.3M resistor and 10PF bypass cap between V1B and V3A to 1.5M and 22pF. I’m hoping this will improve fidelity and high end when the reverb is turned off.

7, I’m adding a master volume after the phase inverter. The type of master volume I’ve chosen to use will have a stacked 250K pot. This type of master has the smoothest roll off of any of the master volumes I’ve tried and it changes the tone the least. When it’s all the way up it sound exactly as it would if there was no master volume at all.

8, I’m adding a push pull pot to the intensity control which will switch from fixed bias to cathode bias switch. A cathode bias will cut volume and give me more compression and smooth, full, “singing” overdrive. I won’t ever be using the vibrato when I’m driving the amp so I’m setting it up to cut the vibrato when the cathode bias is on. That way the vibrato won’t be sucking away tone when I’m not using it.

The last mod is something I’m going to try but not sure if I’m going to use it. I then want to add a switch that will let me toggle between 220 volts and 240 volts. Here in midwales our power is 230 volts. Telling the transformer that it’s getting 220 volts will give me higher voltages inside the amp which means clearer tone with more headroom and better high end. Telling it I’m using 240 volts will mean I’ll get a browner tone with less high end. This toggle switch will also have to change the bias of my power tubes and I haven’t worked out how I’m going to do that so I haven’t added this last one to the schematic yet.

Here is a link to my schematic so that you can get a closer look
http://www.rockmonkeyguitars.com/images/princrv.gif

Here is pic that should fit better on the board
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Last edited by CorduroyEW at Sep 18, 2008,
#4
sounds awesome. I have a question: where are you getting these kits? and how much are you selling the amps for?

I have a few ideas.
1.) Footswitchable. You probably are doing this anyways but it couldnt hurt to mention it anyways.
2.) Built- in attenuator. Again, Im not sure if your already doing this.
3.) On a more modern-ish amp, I'd wanna see something with 2 gain knobs. One would be sort of an Overdrive knob, and the other would be a Distortion knob. You could mix and blend them and such.
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Last edited by BD 425 at Sep 18, 2008,
#5
I'm getting them from www.mojotone.com

When I come up with the idea I has no connection with Mojo. After ordering enough parts to make 86 kits I've now become one of the UK dealers for them. For most of the world, shipping and tax cost more than the amp. If you are in the USA or Canada then it's going to cost about half as much as it is if you are in the EU. So if you are seriouse about building an amp send me an email or PM telling me where you live and which one of the Mojo amps you want and I can then get you a price.
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#6
The princeton currently uses a cathodyne phase inverter. I actually wonder if there would be a tonal difference between cathodyne and a long tail pair or voltage splitter phase inverter.
Some of my suggestions would possibly require modifications to any sort of chassis that you have so they may not something you would want to look into.

Maybe remove the negative feedback in one of the amps to see how it sounds?
#7
^so far all the mods except the master volume can be done with the existing chassis. I will have to drill a hole to add the master volume but because this isn't a real vintage amps it's not going to hurt the value.

A long tail voltage splitter is something I've given a lot of thought too. Using it will give me more gain but it'll also take an extra tube. I thought about dropping the vibrato all together and using the extra tube for the phase inverter but that isn't exactly ideal. That is why I thought of using the 1st tube in the reverb as a volume boost. I'm hoping it will have a similar effect without sacraficing the amps functions. If it doesn't work (I don't think it will but figure it's worth a shot) then I might still drop the vibrato and use the long tail phase splitter. That would give me 2 extra holes for switches too
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#8
I'm actually interested in hearing how a Philco Phase Inversion would affect the tone. It is supposed to be the most correct mirroring of the sound waves. It also uses the power tubes, and not an extra phase section.

I can draw up some schematics for the different phase inversion's if you want. I've got a few books that i'll look into sometime in the future for different things you may want to try. Maybe manipulate the different components in the vibrato circuit to get different sounding or more dynamic vibrato.
#9
^You cought my attention with the philco phase inverter, I'm not sure if I just know it with a different name or if it's one I've never seen before. Schematics would be very nice.
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#10
i'll definitely wish you guys good luck with this!
i still wish i could participate, but a) i'd mess it up and b) which is my main reason - i dont have the dough, since im planning on getting an ac30 soon (couple of weeks)

!

Whodicted



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#11
Quote by CorduroyEW
^You cought my attention with the philco phase inverter, I'm not sure if I just know it with a different name or if it's one I've never seen before. Schematics would be very nice.


i think it has more to do with the fact that you've never seen one before, I am very curious to hear how it sounds in a guitar amp. It also frees up a tube that you could use for a volume boost etc. I'll work out an overall mod of the schematic, I think other component values will have to be changed in order to do a philico phase inversion. I may throw a few mods in the schematic.
#12
^cool, I can't wait.

Is the philco phase inverter going to effect my bias switch and/or my master volume? I could live without the master volume but I don't think I could live without a cathode bias/fixed bias switch.
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#13
Quote by CorduroyEW
^cool, I can't wait.

Is the philco phase inverter going to effect my bias switch and/or my master volume? I could live without the master volume but I don't think I could live without a cathode bias/fixed bias switch.


It does eliminate the ability to have the master volume control, but the cathode biased/fixed bias should remain the same. I'll have the schematic sometime for you in the next day or too (college football game here tomorrow so it may be sunday)
#14
Quote by CorduroyEW
^Yup. I didn't get as many people from UG as I had hoped, but music shops in the area were very excited to have me supply some amps for them so luckely I was still able to get the good prices for us.

So here are my mods and ideas for the Princeton reverb I’m building that I plan to keep for myself.

1, The capacitor for the midrange is going to be .033 instead of .047. This is something that was done on the earliest Princeton reverbs. It gave more presence to the high end and made the bass tighter which really improves the overdriven tone. No more buzzsaw tone when you crank everything to 10.

2, I’m using a pushpull pot on the bass control. When pushed in the amp will perform as normal but when pulled out it’ll switch the resistor for the midrange from 6.8K to approximately 15K (I’m going to play with the value to see what I like best). Doing this will give me a midrange boost, more gain, and much better overdriven tone.
3, I’m changing the reverb driver tube from 12AY7 to 12AX7. This will drive the reverb tank harder and give me and clearer signal coming out of it.

4, I’m adding a switch that will make it so that when I’m not using the reverb, I can use the tube driving the reverb as a volume boost. This means might cause a phase problem so I’m not sure it’s going to work, but I’m going to try it and see what happens.
5, I’m adding a 250K resistor from hot to ground on the jack that comes after the reverb tank. This has 2 purposes. One is that it will protect my V3B and stop it from blowing if my reverb tank is accidentally unplugged. The other reason is that it lowers the impedance which will give the reverb a warmer voice.

6, I’m changing the value of the 3.3M resistor and 10PF bypass cap between V1B and V3A to 1.5M and 22pF. I’m hoping this will improve fidelity and high end when the reverb is turned off.

7, I’m adding a master volume after the phase inverter. The type of master volume I’ve chosen to use will have a stacked 250K pot. This type of master has the smoothest roll off of any of the master volumes I’ve tried and it changes the tone the least. When it’s all the way up it sound exactly as it would if there was no master volume at all.

8, I’m adding a push pull pot to the intensity control which will switch from fixed bias to cathode bias switch. A cathode bias will cut volume and give me more compression and smooth, full, “singing” overdrive. I won’t ever be using the vibrato when I’m driving the amp so I’m setting it up to cut the vibrato when the cathode bias is on. That way the vibrato won’t be sucking away tone when I’m not using it.

The last mod is something I’m going to try but not sure if I’m going to use it. I then want to add a switch that will let me toggle between 220 volts and 240 volts. Here in midwales our power is 230 volts. Telling the transformer that it’s getting 220 volts will give me higher voltages inside the amp which means clearer tone with more headroom and better high end. Telling it I’m using 240 volts will mean I’ll get a browner tone with less high end. This toggle switch will also have to change the bias of my power tubes and I haven’t worked out how I’m going to do that so I haven’t added this last one to the schematic yet.


I like to do this as well. Though nothing is boosted, just frequencies are not cut as much.

If your using both triodes of the tube I would think it would be fine. It would be in the same foramtion as when it entered the dual stage. I would think there would be bigger issues with that mod than phase.
#15
This thread will consume UG. And I'm on the first page!!

Good luck man. Also, you should do amps with built in effects. Its coolio.
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#16
Quote by kurtlives91
I like to do this as well. Though nothing is boosted, just frequencies are not cut as much.


Technically yeah. A tonestack can only remove signal it can't add it, but it's still easier to say mid boost than to say a stop filtering so much of switch


If your using both triodes of the tube I would think it would be fine. It would be in the same foramtion as when it entered the dual stage. I would think there would be bigger issues with that mod than phase.


I'm using both triodes but they are in parallel so that they can drive the reverb tank better so it will be out of phase with the original signal but that might not be a bad thing. What i'm hoping will happen is that when the signal travels through the extra gain stage it will be too loud and the phase cancellation that happens when it mixes with the original signal will bring it down to the right volume. This is going to take a lot of trial and error to get the values right but I do think it can work.
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#17
right! I'm off to buy a soldering iron

I just want to say that I'm intending to use my amp as a clean amp mainly, if not only. and it's purpose will be for recoring. I will get as many photos as I can and when (or if) I get it running soundclips aswell.

and my initial intent is to keep it unmodded. and if curiosity gets the worst of me later on, I'll go back and add the mods I'd like.
#18
^I am going to suggest a couple mods (when I get the chance to draw them up) to the layout which you may want to do. It won't change the curcuit or the tone at all. It just moves the phisical location of some caps which will get rid of some hum.
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#20
Ok rasker, here is what I would suggest using for a layout if you want to keep the amp stock. It's exactly the same components just moved around a bit.



I put the tone caps on the tone pot. Once the signal travels through the cap it changes from hi Z to low Z. Low Z signals pickup a lot more noise than hi Z signals so you want the signal to stay high Z for as long as possible. Moving them over to the pots gets rid of about a 12" of wire which is good, and it gets rid of about 15" of signal traveling at low Z.

I also moved one of the caps in the vibrato circuit up to the pot. This isn't going to be as significant as rearranging the tone stack, but it's still going to quiet hum and make the amp more stable.

The final change in the layout is that I flipped the power stage up side down. This makes it so the High Z signal running from the phase inverter has to travel an extra 3" before it gets to the coupling cap, but it takes out about 6" that the low Z signal has to travel before reaching the power tubes. When the wires from the coupling caps to the power tubes are just 1" too long it can make your amp virtually unusable at high volume. By getting rid of 6" of wire you guarantee that you won't have a problem.

I won’t hurt my feelings if you don’t use my layout suggestions but I thought I’d through the idea out there for you.
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Last edited by CorduroyEW at Sep 21, 2008,
#21
I'm all for using a hum reducing mod! thanks for that! the thing's I don't want to add are those who change the tone, and especially those who will make the overdrive better since it will be used for cleans.

a higher res pic of that schematic would be really nice also. it's abit hard for me to read as it is now.
#22
I don't have a higher res pic on hand but I'll make something up and include it with the instructions for you so you will have it to work off of when you are building the amp.

There is 1 more mod that you might like to consider. If you double the filtering on the main power supply it'll give you more headroom. I'll only change tone at high volume and then it'll be more defined with less compression. I could add that to the layout if you are interested. It's just one capacitor so you could try it with and without and go with what you like best.


And for the next update for what I'm doing, I make a rough layout of my amp. I had to shift parts a bit so that I could lable them and there are a couple wire that I'm not 100% sure what the best rout for them will be so It is going to look a little different when I'm done, but it gives you a good idea.

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#23
A crapload of crap, lol. I'm interested in these builds as well.

I think you have your understanding of impedance and noise backwards.
#24
^Perhaps I just oversimplified things. Everything after the 1st gain stage of the amp is Hi Z but the impedance does get lowered slightly after passing through the coupling cap. Lower impedance signals are easier to manipulate which is why Marshall style amps use a cathode follower to change the signal to low Z right before their tonestack. Master volumes tend to work better after a cathode follower as well. If the signal is Hi Z and you try a master volume it won’t be smooth. You will have high volume and then all of a sudden the volume will drop to almost nothing. Lower the impedance with a cathode follower and all of a sudden you can get a smooth drop off. My theory is that because it’s easier to manipulate low z signals within the amp, this makes them more susceptible to the noises introduced during the wiring between the tubes. That explains half of my reasoning for the mods

The other half has to do with the way the circuit behaves. The worst noises in an amp are the ones that are at such high frequencies that we can hear them. They cause parasitic oscillation problems that make your amp noisy at best and completely stop it from working at worst. The cap acts as the end of the prior gain stage and the beginning of the next gain stage. By having the extra wire before the cap it increases inductance on the plate which helps reduce unwanted noise and parasitic oscillation. The cap also blocks other unwanted noises so it actually stopping the signal from getting to the next stage in 2 different ways. After the signal passes through the cap you are then at the beginning of the next stage. At this point extra inductance is bad because it deadens your tone. Also, all that extra wire will act as an antenna picking up unwanted signals and sending them to the tube to be amplified which means it's best to keep it as short as possible.

My blackface bassman had horrible parasitic oscillation problems and after I did these mods it completely went away. I was even able to add an extra gain stage and still have the thing work like a dream.

So to sum it all up, it is possible that my reasoning for trying these mods was flawed, but the mods still work.
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#25
So I've changed a few things on my schematic, the layout is still going to be almost exactly the same so I'm not going to bother drawing a new one but I did make a new schematic.

I've added a standby switch
Doubled the power filtering
Changed the non-adjustable fixed bias to adjustable fixed bias

I also found the schematic for the silverface deluxe reverb boost switch which is where I got the idea for my boost switch from. I drew in blue the fender boost switch and I left mine in orange. There are a few reasons I thought the way I did it would be better but I can also see an advantage to the fender method. Before I explain myself I want to get your oppinions as to which method you think will be better and way.

Here is a link to a big pic of the schematic
http://www.rockmonkeyguitars.com/princrv.jpg

Here is message board friendly sized pic

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Last edited by CorduroyEW at Sep 29, 2008,
#27
^I do still have 1 princeton. I If you check my website you will see that normal price for a princeton kit is £787.15 but I'm offering the 1 that I still have left at £622.00 to UG'ers. If you want it fully assembled and either compleatly stock or with my basic laylout change (the one I posted for rasker) then I can do that for £722.00. I can customize things too but to get into that it'll be best if we talk in email or on the phone.
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Last edited by CorduroyEW at Sep 29, 2008,
#28
This is going to be stunning!
ESP Eclipse-II VTB (With 18v Mod)
Randall RG75
Tapco Mix60
New Zealand
#29
I would like to say that I'm very impressed with anyone who can build their own amp. I have absolutely zero electronics knowledge and I'm blown away when someone shows a thread like this. Awesome work Corduroy.

P.S. Cords are the comfiest pants ever.
#31
Don't worry, when I get the kit the threads will be flying in...

Where does this go, whats that for, should that be on fire...
#33
Quote by Mecler
I would like to say that I'm very impressed with anyone who can build their own amp. I have absolutely zero electronics knowledge and I'm blown away when someone shows a thread like this. Awesome work Corduroy.

P.S. Cords are the comfiest pants ever.


Thanks. I only got into this kind of thing because I got a broken bassman off ebay. It was supposed to be in perfect working order but you know what ebay is like. When I sent the amp to a tech to be fixed all he did was rob the valuble original parts and then send it back with a bill. It was at that time that I decided I needed to learn about this stuff and I started buying all the electronics text books I could find that were published in the 50's and 60's. Thats how it all started and now I can build an amp from scratch but I can't figure out how to call somebody with a cell phone.

Quote by Invader Jim
Damn, I can't believe it's only 1 page still.

Good luck, Cord. Looks like you'll need it.


Nah man, we are on page 2 now

Quote by Invader Jim


I kinda want a kit, but I'm State-side and prolly can't afford it anyway.


I can have mojo drop ship any of their kits too you so you could avoid paying shipping and taxes to and from the UK. If you choose to do one of the kits that I've listed in this thread I can get you one for the +10 price.

Quote by bellerophon
Don't worry, when I get the kit the threads will be flying in...

Where does this go, whats that for, should that be on fire...


Yeah, when all you have are a few schematics it's not real interesting for most people. The kits landed in Felixstowe yesterday and should be in Manchester today. Then they clear customes and get shipped to me. I could be seeing them by the end of this week if I'm lucky which means you could possibly have yours by the middle of next week. Fingers crossed
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Last edited by CorduroyEW at Sep 30, 2008,
#35
So somebody has to have on opinion about my boost vs the fender boost!

I'll go ahead and explain myself anyway so perhaps those that may not have wanted to speak up will jump in and point out why I'm right or wrong.

The big drawback with the fender boost was that all the signal passed through a 500pF cap which turned it into a bright boost and it made the signal too thin. That was 1 of the things I tried to improve upon.

In my design I still run through a 500pF cap (I may increase the value before I’m done) but I increased the resistance of the circuit which should help reduce the highest frequencies. I'm also allowing more of the high end from the original signal through which should act as a negative feedback circuit and help balance out the high end even more. By lowering the resistance of the original signal it's going to let more of the original low end through but because low end can't pass through my 500pf cap running into the reverb it means that all and all I'm going to have a more balanced tone. This is still going to be a high end boost but I’m hoping that it doesn’t sound as thin as the fender boost did.

The other modification I made was using a .01 cap coming off the plate of the tube rather than taking it from the secondary of the reverb driver. One reason I did this was because I didn't want to change the impedance after the reverb driver. I know it's not that big of a deal but why do it if you don't have to. The second, and much more important, reason was that coming off the reverb driver puts that extra foot of wire I have to use running to on the grid of the next gain stage will create a lot of noise. Using a .01 cap and placing it on the switch means that extra foot of wire will increase inductance on the plate of the previous stage which will help midrange and it will introduce far less noise into my circuit.

So that was my thought process when redesigning the boost circuit of the silverface deluxe reverb. I don't know how well it's going to work, but I'm keeping my fingers crossed. In the meantime, any input you can offer would be great.
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#36
Hmmmm... Interesting.......


(lol)
ESP Eclipse-II VTB (With 18v Mod)
Randall RG75
Tapco Mix60
New Zealand
#38
Quote by Invader Jim
^ That's almost as bad as saying tl;dr or LOL WUT.

Sorry, Cord. I have no idea how either of those sound.


Nether did I so I thought i might be awesome and say sumthing.
ESP Eclipse-II VTB (With 18v Mod)
Randall RG75
Tapco Mix60
New Zealand
#39
LOL Thanks anyway guys

There are a few people here that have a better understanding of this stuff than I do and I'm just hoping one of them sees the thread and chimes in. If I weren't so damn proud I might actually PM them and tell them to come look at my thread... On the other hand I'll probably be trying it both anyway so I guess it doesn't really matter that much.
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#40
Quote by CorduroyEW
^Yup. I didn't get as many people from UG as I had hoped, but music shops in the area were very excited to have me supply some amps for them so luckely I was still able to get the good prices for us.

So here are my mods and ideas for the Princeton reverb I’m building that I plan to keep for myself.

1, The capacitor for the midrange is going to be .033 instead of .047. This is something that was done on the earliest Princeton reverbs. It gave more presence to the high end and made the bass tighter which really improves the overdriven tone. No more buzzsaw tone when you crank everything to 10.

2, I’m using a pushpull pot on the bass control. When pushed in the amp will perform as normal but when pulled out it’ll switch the resistor for the midrange from 6.8K to approximately 15K (I’m going to play with the value to see what I like best). Doing this will give me a midrange boost, more gain, and much better overdriven tone.

3, I’m changing the reverb driver tube from 12AY7 to 12AX7. This will drive the reverb tank harder and give me and clearer signal coming out of it.

4, I’m adding a switch that will make it so that when I’m not using the reverb, I can use the tube driving the reverb as a volume boost. This means might cause a phase problem so I’m not sure it’s going to work, but I’m going to try it and see what happens.

5, I’m adding a 250K resistor from hot to ground on the jack that comes after the reverb tank. This has 2 purposes. One is that it will protect my V3B and stop it from blowing if my reverb tank is accidentally unplugged. The other reason is that it lowers the impedance which will give the reverb a warmer voice.

6, I’m changing the value of the 3.3M resistor and 10PF bypass cap between V1B and V3A to 1.5M and 22pF. I’m hoping this will improve fidelity and high end when the reverb is turned off.

7, I’m adding a master volume after the phase inverter. The type of master volume I’ve chosen to use will have a stacked 250K pot. This type of master has the smoothest roll off of any of the master volumes I’ve tried and it changes the tone the least. When it’s all the way up it sound exactly as it would if there was no master volume at all.

8, I’m adding a push pull pot to the intensity control which will switch from fixed bias to cathode bias switch. A cathode bias will cut volume and give me more compression and smooth, full, “singing” overdrive. I won’t ever be using the vibrato when I’m driving the amp so I’m setting it up to cut the vibrato when the cathode bias is on. That way the vibrato won’t be sucking away tone when I’m not using it.

The last mod is something I’m going to try but not sure if I’m going to use it. I then want to add a switch that will let me toggle between 220 volts and 240 volts. Here in midwales our power is 230 volts. Telling the transformer that it’s getting 220 volts will give me higher voltages inside the amp which means clearer tone with more headroom and better high end. Telling it I’m using 240 volts will mean I’ll get a browner tone with less high end. This toggle switch will also have to change the bias of my power tubes and I haven’t worked out how I’m going to do that so I haven’t added this last one to the schematic yet.

Here is a link to my schematic so that you can get a closer look

Here is pic that should fit better on the board

Can you explain this a bit more.
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