https://theultimatetone.com/ Sun, 26 Jul 2026 11:58:51 +0000 MyBB https://theultimatetone.com/Thread-Zener-Diode-in-Bias-Supply Fri, 10 Apr 2026 10:40:57 +0000 Bassman]]> https://theultimatetone.com/Thread-Zener-Diode-in-Bias-Supply
On the Custom Special schematic in TUT3 there is a zener diode (100v, 1w) straddling Vb and ground.

My amp building experience is limited, I'm used to seeing resistors here.
I believe it's purpose is to provide a stable fixed bias voltage relative to ground.
So if the plate voltage varies for whatever reason, the bias remains the same.

My question is - Why is this better than the bias following the ups and downs of the plate voltage?

The amp I am building will hopefully be gigged.
It has a universal power transformer, wired as Kevin suggested at the back of TUT3.
So different countries, different mains voltages and hopefully lots of festivals with dodgy generators and clubs with terrible mains supplies.

Regards.]]>
On the Custom Special schematic in TUT3 there is a zener diode (100v, 1w) straddling Vb and ground.

My amp building experience is limited, I'm used to seeing resistors here.
I believe it's purpose is to provide a stable fixed bias voltage relative to ground.
So if the plate voltage varies for whatever reason, the bias remains the same.

My question is - Why is this better than the bias following the ups and downs of the plate voltage?

The amp I am building will hopefully be gigged.
It has a universal power transformer, wired as Kevin suggested at the back of TUT3.
So different countries, different mains voltages and hopefully lots of festivals with dodgy generators and clubs with terrible mains supplies.

Regards.]]> https://theultimatetone.com/Thread-TUT3-Custom-Special-build Thu, 02 Apr 2026 16:16:51 +0000 Bassman]]> https://theultimatetone.com/Thread-TUT3-Custom-Special-build
I'm laying out the eyelet board for my TUT3 Custom Special build (again).  Great fun.

Checking the suggested layout against the improved schematic in TUT3 I see a few discrepencies.
Some of them I can work out, some of them I can't.

Is this a good place to ask about them?

Regards.]]>
I'm laying out the eyelet board for my TUT3 Custom Special build (again).  Great fun.

Checking the suggested layout against the improved schematic in TUT3 I see a few discrepencies.
Some of them I can work out, some of them I can't.

Is this a good place to ask about them?

Regards.]]> https://theultimatetone.com/Thread-Heater-capacity-on-6-3-v-Secondary Sun, 29 Mar 2026 09:58:25 +0000 Bassman]]> https://theultimatetone.com/Thread-Heater-capacity-on-6-3-v-Secondary
I am part way through a build of Kevin's Custom Special amplifier from the TUT3 book.  Great circuit.

Checking my current needs for the 6.3VAC secondary, I calculate 4x 1.5 A for the 6CA7 valves and 3x .3 A for the 12AX7 valves.
Which comes to 6.9 Amperes.

The rating for the specified Hammond 278CX transformer is 6 Amperes on the 6.3 volt secondary.

15% over the rated capacity seems a lot to me.  Am I being overly conservative?]]>
I am part way through a build of Kevin's Custom Special amplifier from the TUT3 book.  Great circuit.

Checking my current needs for the 6.3VAC secondary, I calculate 4x 1.5 A for the 6CA7 valves and 3x .3 A for the 12AX7 valves.
Which comes to 6.9 Amperes.

The rating for the specified Hammond 278CX transformer is 6 Amperes on the 6.3 volt secondary.

15% over the rated capacity seems a lot to me.  Am I being overly conservative?]]> https://theultimatetone.com/Thread-Tube-Reverb-PT-from-Tonnes-of-Tone Mon, 06 Jan 2025 10:30:08 +0000 luxpaul]]> https://theultimatetone.com/Thread-Tube-Reverb-PT-from-Tonnes-of-Tone
I am thinking about building the Tube Reverb from the Tonnes of Tone book.
I am based in Europe so I would need a 230v Primary Power Transformer.
The one suggested in the book is the Hammond 269AX.

Does anyone know of an equivalent (or suitable) 230v PT ?

Many thanks
Paul]]>
I am thinking about building the Tube Reverb from the Tonnes of Tone book.
I am based in Europe so I would need a 230v Primary Power Transformer.
The one suggested in the book is the Hammond 269AX.

Does anyone know of an equivalent (or suitable) 230v PT ?

Many thanks
Paul]]> https://theultimatetone.com/Thread-Herzog-Output-Switching-Questions Sat, 02 Nov 2024 16:25:33 +0000 FabTone]]> https://theultimatetone.com/Thread-Herzog-Output-Switching-Questions I also wired it temporarily as a Herzog style overdrive and that worked too.

I would like to wire it to use one of the three input 1/4" phono jacks on the top panel as the TUT3 Herzog Output (the 3rd input as Output Vol) but I can't figure out how to use a new TRS jack to switch from internally wired-to-speaker to Herzog output. I do not need a bypass switch, just used by default as a combo amp and switched to a Herzog Output.

Hopefully you may have some suggestions please?]]> I also wired it temporarily as a Herzog style overdrive and that worked too.

I would like to wire it to use one of the three input 1/4" phono jacks on the top panel as the TUT3 Herzog Output (the 3rd input as Output Vol) but I can't figure out how to use a new TRS jack to switch from internally wired-to-speaker to Herzog output. I do not need a bypass switch, just used by default as a combo amp and switched to a Herzog Output.

Hopefully you may have some suggestions please?]]> https://theultimatetone.com/Thread-Grid-Circuit-Impedance Fri, 28 Jun 2024 04:03:31 +0000 physics]]> https://theultimatetone.com/Thread-Grid-Circuit-Impedance
In TUT2, figure 2-62 we're shown a "typical bias supply":


  20240627_203505.jpg (Size: 318.53 KB / Downloads: 26)

It's stated that the impedance of the supply is about 1k || 15k at balance, or about 1k. I need to work out the supply impedance for the bias supply I'm building in an amp, so I want to make sure that I understand how this calculation was done in the book.

First, is the diode assumed to be a short? Otherwise the 1k resistor is isolated. Is this because in thermal runaway, (conventional) current would flow out of the grid into the bias network, so from that perspective the diode would be forward-biased if there is enough current flowing to develop a diode-drop's worth of voltage across it?

Second, how come the resistance of the centertapped pot is ignored? At balance, the current from the grid has to flow through 5k to the centertap and wiper, then out to the 1k and 15k assuming the diode is forward biased, so the supply impedance would be (1k || 15k) + 5k ~= 6k. Admittedly the answer isn't that different, so maybe that was why it wasn't accounted for?

Also, how come the 70u capacitor doesn't factor in? Elsewhere in the TUTs, it's stated that if we have to increase the resistances to get adequate bias voltages, we can drop caps from the bias wipers to ground to get a good AC ground for the grids. Wouldn't the 70u cap act similarly, meaning that the supply impedance is just half of the center-tapped pot at most, so about 5k?

Sorry if it seems like I'm being nitpicky, I just want to make sure I understand the thought process behind the calculation so I have a better idea of how to go about the calculations for my own projects.

Thanks!]]>
In TUT2, figure 2-62 we're shown a "typical bias supply":


  20240627_203505.jpg (Size: 318.53 KB / Downloads: 26)

It's stated that the impedance of the supply is about 1k || 15k at balance, or about 1k. I need to work out the supply impedance for the bias supply I'm building in an amp, so I want to make sure that I understand how this calculation was done in the book.

First, is the diode assumed to be a short? Otherwise the 1k resistor is isolated. Is this because in thermal runaway, (conventional) current would flow out of the grid into the bias network, so from that perspective the diode would be forward-biased if there is enough current flowing to develop a diode-drop's worth of voltage across it?

Second, how come the resistance of the centertapped pot is ignored? At balance, the current from the grid has to flow through 5k to the centertap and wiper, then out to the 1k and 15k assuming the diode is forward biased, so the supply impedance would be (1k || 15k) + 5k ~= 6k. Admittedly the answer isn't that different, so maybe that was why it wasn't accounted for?

Also, how come the 70u capacitor doesn't factor in? Elsewhere in the TUTs, it's stated that if we have to increase the resistances to get adequate bias voltages, we can drop caps from the bias wipers to ground to get a good AC ground for the grids. Wouldn't the 70u cap act similarly, meaning that the supply impedance is just half of the center-tapped pot at most, so about 5k?

Sorry if it seems like I'm being nitpicky, I just want to make sure I understand the thought process behind the calculation so I have a better idea of how to go about the calculations for my own projects.

Thanks!]]> https://theultimatetone.com/Thread-TUT5-Swede-power-supply-arrangement Wed, 26 Jun 2024 07:23:30 +0000 capacitivewaves]]> https://theultimatetone.com/Thread-TUT5-Swede-power-supply-arrangement
I tried building the Swede power supply to power my next build but I haven't been very lucky


As far as I understand the schematic in fig 18-2, it's a full wave rectifier bridge, one side provides the B+ supply to the amp and the other side provides the negative voltage for the bias supply, that's why 2 diodes are reversed, and the CT is connected to ground. However, in a 4 diode bridge configuration the CT isn't normally used as far as I know (I did blow a few fuses discovering that) So i'm not sure I understand the schematic properly. Maybe someone can enlighten me? 
So far my build is only blowing fuses and would love to understand why

Thanks
Sarah]]>
I tried building the Swede power supply to power my next build but I haven't been very lucky


As far as I understand the schematic in fig 18-2, it's a full wave rectifier bridge, one side provides the B+ supply to the amp and the other side provides the negative voltage for the bias supply, that's why 2 diodes are reversed, and the CT is connected to ground. However, in a 4 diode bridge configuration the CT isn't normally used as far as I know (I did blow a few fuses discovering that) So i'm not sure I understand the schematic properly. Maybe someone can enlighten me? 
So far my build is only blowing fuses and would love to understand why

Thanks
Sarah]]> https://theultimatetone.com/Thread-Cathode-Bias-Rk-Recommended-Values Tue, 26 Mar 2024 02:21:34 +0000 makinrose]]> https://theultimatetone.com/Thread-Cathode-Bias-Rk-Recommended-Values
I've experimented with using a 470 ohm shared resistor which makes the tube set had run at about 33ma per tube. 

I'm just wonder what other people's experiences how they prefer to select the Rk value?  What values are good starting points for common power tubes?

Thanks!]]>
I've experimented with using a 470 ohm shared resistor which makes the tube set had run at about 33ma per tube. 

I'm just wonder what other people's experiences how they prefer to select the Rk value?  What values are good starting points for common power tubes?

Thanks!]]> https://theultimatetone.com/Thread-Wiring-ground-stars-and-other-busy-junctions Sun, 22 Oct 2023 02:01:17 +0000 Martin]]> https://theultimatetone.com/Thread-Wiring-ground-stars-and-other-busy-junctions  I've been reading this forum for a while, and finally decided to join in.
 When I built my first amp, a Portaflex copy as per TUT3, I found that wherever I had more than 4 or 5 wires going to the same eyelet it got quite messy. Not surprisingly I ended up with some bad solder joints to track down. What I ended up doing was replacing the eyelets in question with machine screws mounted through the same holes in the eyelet board. I then soldered ring terminals onto the ends of the leads and bolted them together. It solved the problem and I used the same approach when I built my second amp.
 My question is what do you do when you want to connect a lot of things in one spot? I've never seen wires bolted to the board in anyone else's amps, but I've never seen eight wires trying to cram into one eyelet, either.]]>  I've been reading this forum for a while, and finally decided to join in.
 When I built my first amp, a Portaflex copy as per TUT3, I found that wherever I had more than 4 or 5 wires going to the same eyelet it got quite messy. Not surprisingly I ended up with some bad solder joints to track down. What I ended up doing was replacing the eyelets in question with machine screws mounted through the same holes in the eyelet board. I then soldered ring terminals onto the ends of the leads and bolted them together. It solved the problem and I used the same approach when I built my second amp.
 My question is what do you do when you want to connect a lot of things in one spot? I've never seen wires bolted to the board in anyone else's amps, but I've never seen eight wires trying to cram into one eyelet, either.]]> https://theultimatetone.com/Thread-FX-loops-When-does-an-amp-need-one Fri, 15 Sep 2023 23:34:36 +0000 makinrose]]> https://theultimatetone.com/Thread-FX-loops-When-does-an-amp-need-one
In general, I've only thought an FX loop is needed in higher gain amps but more and more I'm seeing them lower gain amps (Bassmans, Plexis, etc) and get requests to install them in.  At what level of gain is there enough benefit to warrant the effort?  I was hoping I could get some guidance  and opinions on the matter.  Thanks everyone for the help!]]>
In general, I've only thought an FX loop is needed in higher gain amps but more and more I'm seeing them lower gain amps (Bassmans, Plexis, etc) and get requests to install them in.  At what level of gain is there enough benefit to warrant the effort?  I was hoping I could get some guidance  and opinions on the matter.  Thanks everyone for the help!]]> https://theultimatetone.com/Thread-Cathode-bypass-capacitor Sun, 11 Jun 2023 16:18:22 +0000 Champ81]]> https://theultimatetone.com/Thread-Cathode-bypass-capacitor
If I got that part correct I don't understand how a cathode is associated with the frequencies it let's through.  Because isn't it the grid where the guitar signal goes into?

I cannot visually understand it. I have heard from others a DC current flows from the ground through the cathode resistor to the cathode of the tube. Bit how van current flow from ground because the ground there is no current? I know ground is all relative but this is circuit ground to the chassis.]]>
If I got that part correct I don't understand how a cathode is associated with the frequencies it let's through.  Because isn't it the grid where the guitar signal goes into?

I cannot visually understand it. I have heard from others a DC current flows from the ground through the cathode resistor to the cathode of the tube. Bit how van current flow from ground because the ground there is no current? I know ground is all relative but this is circuit ground to the chassis.]]> https://theultimatetone.com/Thread-TUT5-Standard-Reverb Sun, 04 Jun 2023 15:27:08 +0000 sinusoids]]> https://theultimatetone.com/Thread-TUT5-Standard-Reverb https://theultimatetone.com/Thread-Speaker-blending-in-symmetric-stage-setups Sat, 28 Jan 2023 21:00:46 +0000 physics]]> https://theultimatetone.com/Thread-Speaker-blending-in-symmetric-stage-setups
I finally have a chance to try out symmetric stage setups in a band context. However, all of the cabs will have different speakers or speaker blends due to what speakers I own and can load into the cabs, impedance concerns, and what is already loaded into the other guitar players' cabs. I wanted to ask if any of you can provide advice on how speaker blending affects the outcome of symmetric setups. My guess is it would be optimal for either two cabs per player that are different but complimentary, or for two that are as similar as possible. For the former, experience with recording and mixing different complimentary speakers would seem to imply that a fuller sound would result. However, the psycho-acoustic effect mentioned in TUT where the listener/player feels like they're in the sound because of two separated sources would seem to imply that the more difference there is between the two cabs, the less they would be sources of the "same" sound and thus the effect might be weaker.

Technical details, if it matters:
The cab pairing is going to be a 1x12 in parallel with a 4x12, and a 2x12 in parallel with a half-empty 4x12. The 2x12 has a eminence swamp thang and celestion g12h 70th anniversary, wired in parallel for 8 ohms net. The 1x12 has a 16 ohm Celestion 70-80. These two cabs aren't mine, so I am not able to control the speakers loaded in them.The speakers I own and can load into the 4x12's (which are mine) are 1x16 Ohm Vintage 30, 1x16 Ohm Marshall G12 Vintage, 4x16 Ohm Peavey Sheffield 1290. The 2x12 cab will be paired with the half-loaded 4x12, and the 1x12 with the fully-loaded 4x12, because of impedance concerns.

There aren't too many permutations possible, so worst case I can probably try all the options in a band context and see how it sounds, but I do wonder if there are any general guidelines for this beyond just separating the cabs.

Thanks for any input!

P.S. Here's a video showing and comparing the three speakers I own. It inspired the selection of the speakers I now own. https://www.youtube.com/watch?v=iciye74KoFo]]>
I finally have a chance to try out symmetric stage setups in a band context. However, all of the cabs will have different speakers or speaker blends due to what speakers I own and can load into the cabs, impedance concerns, and what is already loaded into the other guitar players' cabs. I wanted to ask if any of you can provide advice on how speaker blending affects the outcome of symmetric setups. My guess is it would be optimal for either two cabs per player that are different but complimentary, or for two that are as similar as possible. For the former, experience with recording and mixing different complimentary speakers would seem to imply that a fuller sound would result. However, the psycho-acoustic effect mentioned in TUT where the listener/player feels like they're in the sound because of two separated sources would seem to imply that the more difference there is between the two cabs, the less they would be sources of the "same" sound and thus the effect might be weaker.

Technical details, if it matters:
The cab pairing is going to be a 1x12 in parallel with a 4x12, and a 2x12 in parallel with a half-empty 4x12. The 2x12 has a eminence swamp thang and celestion g12h 70th anniversary, wired in parallel for 8 ohms net. The 1x12 has a 16 ohm Celestion 70-80. These two cabs aren't mine, so I am not able to control the speakers loaded in them.The speakers I own and can load into the 4x12's (which are mine) are 1x16 Ohm Vintage 30, 1x16 Ohm Marshall G12 Vintage, 4x16 Ohm Peavey Sheffield 1290. The 2x12 cab will be paired with the half-loaded 4x12, and the 1x12 with the fully-loaded 4x12, because of impedance concerns.

There aren't too many permutations possible, so worst case I can probably try all the options in a band context and see how it sounds, but I do wonder if there are any general guidelines for this beyond just separating the cabs.

Thanks for any input!

P.S. Here's a video showing and comparing the three speakers I own. It inspired the selection of the speakers I now own. https://www.youtube.com/watch?v=iciye74KoFo]]> https://theultimatetone.com/Thread-LPSP-settings Fri, 30 Dec 2022 17:17:27 +0000 sinusoids]]> https://theultimatetone.com/Thread-LPSP-settings
My most used amp is the LPSP driving the PA in ToT (similar to a fixed bias 5E3 PA with MV) with 6V6s.  I play an SG with P-90s with vol between 9 and 6, mostly on the neck.  This amp is played with a band so is set bright to get through.  I use a pedal for vol boost on leads so the two channels are used for 2 rhythm tones.  So vol is roughly the same for both channels.

             V    H      M    L     D
Clean    5     8     1.5  5.5
Lead    3.5   8.5   4   4.5  8.5


26 years ago today I purchased TUT at Antique Elec Supply in Tempe.  Thank you Kevin, for publishing these, sharing the info and answering SO many questions. 26 years of fun.]]>
My most used amp is the LPSP driving the PA in ToT (similar to a fixed bias 5E3 PA with MV) with 6V6s.  I play an SG with P-90s with vol between 9 and 6, mostly on the neck.  This amp is played with a band so is set bright to get through.  I use a pedal for vol boost on leads so the two channels are used for 2 rhythm tones.  So vol is roughly the same for both channels.

             V    H      M    L     D
Clean    5     8     1.5  5.5
Lead    3.5   8.5   4   4.5  8.5


26 years ago today I purchased TUT at Antique Elec Supply in Tempe.  Thank you Kevin, for publishing these, sharing the info and answering SO many questions. 26 years of fun.]]> https://theultimatetone.com/Thread-Output-Transformer-Primary-Impedance-Affect-on-Tone Wed, 07 Dec 2022 04:25:11 +0000 makinrose]]> https://theultimatetone.com/Thread-Output-Transformer-Primary-Impedance-Affect-on-Tone
What has been other people's experiences? Also given the same supply voltage what effect should we expect between say a higher and lower impedance primary as far as tone? 

Thanks!]]>
What has been other people's experiences? Also given the same supply voltage what effect should we expect between say a higher and lower impedance primary as far as tone? 

Thanks!]]>