Hi All,
I've been trying to scratch an itch to build something with KT88s. I've been looking for a big, loud, clean (but not necessarily sterile) amp for my tube preamps. I actually started a thread a few months back to help me get the specs right for a set of Heyboer transformers specifically for the project. Well, I was picking through my parts pile (it's a big pile) and found a box… and in the box was 2 transformers I'd pulled from a beat up old amp a friend had given me in trade 10 years ago (someone had gutted and rewired it if I remember right so I chose to salvage rather than repair at the time). I dug up the cabinet and realized that it was old Sunn head, most of which ran 2 KT88s for about 60W.
The transformers are 28-1360 and 28-2360, one is marked WTA 74. Some googling leads me to believe they are original and that the specs are right for what I'd like to do.
I put them up on the bench and the power transformer taps all yielded expected voltages in the unloaded condition… 830vAC w/CT, Heater and 5vAC for tube rectifier. The OT was trickier… first I checked the resistance between taps (20ish ohms from CT to UL taps, another 40 from UL to Anode taps) and then wired up a little 6.3vAc power transformer to the 16 ohm tap. I got 110vAC Across the anode winding… looks to be a working 4500:16/8/4 transformer.
I cleaned them up after with a wire brush and mineral spirits, almost painted them but nostalgia go the best of me.
And here they are rough placed on a 24X8" chassis. The OT is centered and the 2 KT88 will be 4"[100mm] apart (per the data sheet) aligned with the OT.
And the schematic for a Sunn amp using these transformers:
http://www.4tubes.com/SCHEMATICS/BY-BRAND/Sunn/100s.gif
I'd follow a Sunn 200S schematic but I don't like to mess with hard to find or unique tubes (like 6AN8) so I'll be doing something different for the phase splitter/driver. Given enough driver gain will a split load phase splitter w/ a 12AU7 be able to squeeze everything from these KT88s? I know these older amp companies wouldn't throw away away any useable power but not always where it might require one more triodes…. I on the other hand am willing to do more. So is there a better/more robust approach? I was thinking of using a 12AX7 for the driver/splitter and buffering it with 12AU7 cathode followers.
So, before I dive in, any feedback on the project so far?
I've been trying to scratch an itch to build something with KT88s. I've been looking for a big, loud, clean (but not necessarily sterile) amp for my tube preamps. I actually started a thread a few months back to help me get the specs right for a set of Heyboer transformers specifically for the project. Well, I was picking through my parts pile (it's a big pile) and found a box… and in the box was 2 transformers I'd pulled from a beat up old amp a friend had given me in trade 10 years ago (someone had gutted and rewired it if I remember right so I chose to salvage rather than repair at the time). I dug up the cabinet and realized that it was old Sunn head, most of which ran 2 KT88s for about 60W.
The transformers are 28-1360 and 28-2360, one is marked WTA 74. Some googling leads me to believe they are original and that the specs are right for what I'd like to do.
An externally hosted image should be here but it was not working when we last tested it.
[/URL]
I put them up on the bench and the power transformer taps all yielded expected voltages in the unloaded condition… 830vAC w/CT, Heater and 5vAC for tube rectifier. The OT was trickier… first I checked the resistance between taps (20ish ohms from CT to UL taps, another 40 from UL to Anode taps) and then wired up a little 6.3vAc power transformer to the 16 ohm tap. I got 110vAC Across the anode winding… looks to be a working 4500:16/8/4 transformer.
I cleaned them up after with a wire brush and mineral spirits, almost painted them but nostalgia go the best of me.
An externally hosted image should be here but it was not working when we last tested it.
[/URL]
And here they are rough placed on a 24X8" chassis. The OT is centered and the 2 KT88 will be 4"[100mm] apart (per the data sheet) aligned with the OT.
An externally hosted image should be here but it was not working when we last tested it.
[/URL]
An externally hosted image should be here but it was not working when we last tested it.
[/URL]
And the schematic for a Sunn amp using these transformers:
http://www.4tubes.com/SCHEMATICS/BY-BRAND/Sunn/100s.gif
I'd follow a Sunn 200S schematic but I don't like to mess with hard to find or unique tubes (like 6AN8) so I'll be doing something different for the phase splitter/driver. Given enough driver gain will a split load phase splitter w/ a 12AU7 be able to squeeze everything from these KT88s? I know these older amp companies wouldn't throw away away any useable power but not always where it might require one more triodes…. I on the other hand am willing to do more. So is there a better/more robust approach? I was thinking of using a 12AX7 for the driver/splitter and buffering it with 12AU7 cathode followers.
So, before I dive in, any feedback on the project so far?
Looks like a nice project. In the schematic, I am not familiar with the connection from the output feedback circuit to the screen-grid of the lower KT88 (marked 'E'). The usual feedback still goes to the cathode circuit of the pre-amp pentode. Is this extra connection to the KT88 screen-grid to ensure high frequency stability perhaps?
No clue! Looks like some hi-fi wizardry to me. Given the magnitudes of the signals I would think the UL tap would have more impact on the feedback loop than the other way around but I'm not sure. I've heard old Sunn amps were derived from Dynaco hifi designs so I'd hazard to guess it's purpose was linearity or bandwidth, neither of which are an overt priority for me. Looks pretty easy to add/remove anyway.
I answered my own question on drive signal... GEC datasheet says 67vACp-p for tetrode mode, 140vACpp for UL!. Looks like that cathodyne splitter w/ 425vDC should be able to just about get to that 140 theoretically... almost like someone "engineered" that stage for maximum output without going any further than necessary. 🙂
If I want to get any overdrive in the KT88 I'll probably have to consider some post phase-inverter gain stages.... but then again I probably don't need any clipping when running in UL - kind of conflicting ideas. Looks like if I can work out a tetrode mode then the 140vACp-p will be more than enough to clip the output but I'll need a 300vDC rail capable of some current. The simplest might be an amplified zener approach using a pass mosfet - not a regulator per se, just a series drop to bring the 560vDC rail down somewhere that won't annihilate my screens but still breathe with the B+.
My understanding is that a cathodyne is capable of just as much signal swing as a LTPI... and typically more gain when you account for one triode as a driver/amplifier.
Here's where my head is at for a driver stage:
I used a 12AX7 for the driver/cathodyne because I didn't want to use a weird tube like a 12DW7 or 6AN8. The AX7 can make a decent cathodyne and boot strapping back to the plate of the previous stage should max out the gain there. The driver would be biased for about 1.3mA to get the requisite 75vdc for basing the cathodyne. The 12AU7 is to buffer the cathodyne to prevent imbalanced loading and allow for smaller than normal bias feed resistors. I tried a DC coupled stage (w/ negative rail) in my last amp and didn't really think it was worth the trouble. I'm thinking on this one that the larger than normal grid stoppers on the KT88 ought to eliminate grid current at clipping and the small bias feeds should be able to keep the coupling caps at a stabile voltage without too much wandering. The AU7 followers prevent loading on the cathodyne.
Negative rails and DC coupling are cool but I think they aren't worth the trouble if you don't have a stabile dedicated winding so I'm skipping this time around.
I'll probably add a nice big grid stopper on the cathodyne too.
Brian
An externally hosted image should be here but it was not working when we last tested it.
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I used a 12AX7 for the driver/cathodyne because I didn't want to use a weird tube like a 12DW7 or 6AN8. The AX7 can make a decent cathodyne and boot strapping back to the plate of the previous stage should max out the gain there. The driver would be biased for about 1.3mA to get the requisite 75vdc for basing the cathodyne. The 12AU7 is to buffer the cathodyne to prevent imbalanced loading and allow for smaller than normal bias feed resistors. I tried a DC coupled stage (w/ negative rail) in my last amp and didn't really think it was worth the trouble. I'm thinking on this one that the larger than normal grid stoppers on the KT88 ought to eliminate grid current at clipping and the small bias feeds should be able to keep the coupling caps at a stabile voltage without too much wandering. The AU7 followers prevent loading on the cathodyne.
Negative rails and DC coupling are cool but I think they aren't worth the trouble if you don't have a stabile dedicated winding so I'm skipping this time around.
I'll probably add a nice big grid stopper on the cathodyne too.
Brian
Hi Brian,
That looks like a very nice design.
You are right about the gain of the cathodyne with driver.
I don't want to be 'picky', but just in the spirit of sharing information, I think an LTP can give a bigger voltage swing than a cathodyne, because after you have taken away the voltage across the tail (which doesn't have to be too big) all the remaining B+ is available to each triode. In the cathodyne, each output only has half the B+ to play with.
As I say, just a point for discussion, I think your approach will work very well.
Malcolm
That looks like a very nice design.
You are right about the gain of the cathodyne with driver.
I don't want to be 'picky', but just in the spirit of sharing information, I think an LTP can give a bigger voltage swing than a cathodyne, because after you have taken away the voltage across the tail (which doesn't have to be too big) all the remaining B+ is available to each triode. In the cathodyne, each output only has half the B+ to play with.
As I say, just a point for discussion, I think your approach will work very well.
Malcolm
Malcom,
Thank you for the complement. In truth, I'm as guilty as anybody of regurgitating what I hear on the internet and mistaking it for knowledge. Here is the thread that convinced me a cathodyne could keep up with the output of a LTPI:
AX84.com - The Cooperative Tube Guitar Amp Project
I think the tail resistor loss and the and gain stage's inability to saturate to the lower rail are in both play on an LTPI. These are generalizations though and need to think about my application. They were discussing a theoretical 200vDC rail whereas I will be working at 2x that.
Thanks for the help.
Thank you for the complement. In truth, I'm as guilty as anybody of regurgitating what I hear on the internet and mistaking it for knowledge. Here is the thread that convinced me a cathodyne could keep up with the output of a LTPI:
AX84.com - The Cooperative Tube Guitar Amp Project
I think the tail resistor loss and the and gain stage's inability to saturate to the lower rail are in both play on an LTPI. These are generalizations though and need to think about my application. They were discussing a theoretical 200vDC rail whereas I will be working at 2x that.
Thanks for the help.
Hi,
Thanks. A very interesting thread. There is more to it than I thought (as usual)!
I don't know if your have Merlin Blencowe's pre-amp book:
'Designing Tube Pre-amps for Guitar and Bass' (second edition) 2012.
At the beginning of chapter 9 (page 154): "It (the LTP) has the advantage over the cathodyne in that it can provide greater output swing for a given HT and load, making it the circuit of choice to drive 'big bottle' power valves."
I think it was also Merlin who was part of the AX84 discussion?
Anyway, there does not seem to be much difference in output swing, and by loading
the cathodyne with cathode followers you avoid the problem of unequal output impedances.
Thanks. A very interesting thread. There is more to it than I thought (as usual)!
I don't know if your have Merlin Blencowe's pre-amp book:
'Designing Tube Pre-amps for Guitar and Bass' (second edition) 2012.
At the beginning of chapter 9 (page 154): "It (the LTP) has the advantage over the cathodyne in that it can provide greater output swing for a given HT and load, making it the circuit of choice to drive 'big bottle' power valves."
I think it was also Merlin who was part of the AX84 discussion?
Anyway, there does not seem to be much difference in output swing, and by loading
the cathodyne with cathode followers you avoid the problem of unequal output impedances.
I actually don't have Merlin's book (Just ordered it on Amazon), I do frequent his website though. I do think it's is the same Merlin that was part of the discussion.
I'm coming to the same conclusion that it looks like a wash between the two: In UL moade the cathodyne can get me exactly what I need for full, clean output power - in tetrode mode it will be more than enough to get past full output and into power tube clipping. Now I'm starting to wonder what the signal looks like of the plate of the pentode... with an anode voltage of 75v I'm thinking the clipping is hugely asymmetrical and quite large?
Do you know if the grid signal of a cathodyne needs to be equal to the split signal magnitude or 2x the output magnitude? In other words, will 140Vp-p signal at the grid yield two 140Vp-p signals a the out... or do I need a 280Vp-p signal at the grid? I'm thinking the latter.
That makes me wonder if the cathodyne will clip when the incoming signal exceeds the cathode voltage (90ish volts) and if that means you really can't get enough p-p signal from the cathodyne for full clean output after all.
Perhaps it's time to start down the road of building...
I'm coming to the same conclusion that it looks like a wash between the two: In UL moade the cathodyne can get me exactly what I need for full, clean output power - in tetrode mode it will be more than enough to get past full output and into power tube clipping. Now I'm starting to wonder what the signal looks like of the plate of the pentode... with an anode voltage of 75v I'm thinking the clipping is hugely asymmetrical and quite large?
Do you know if the grid signal of a cathodyne needs to be equal to the split signal magnitude or 2x the output magnitude? In other words, will 140Vp-p signal at the grid yield two 140Vp-p signals a the out... or do I need a 280Vp-p signal at the grid? I'm thinking the latter.
That makes me wonder if the cathodyne will clip when the incoming signal exceeds the cathode voltage (90ish volts) and if that means you really can't get enough p-p signal from the cathodyne for full clean output after all.
Perhaps it's time to start down the road of building...
Hi,
I am not sure about the pentode, at 75V quiescent it seems that it can swing up a long way but has less room to swing down, as you say.
I believe the cathodyne would need only slightly more than 140Vp-p at the grid to yield two 140Vp-p signals at the output.
I am not sure about the pentode, at 75V quiescent it seems that it can swing up a long way but has less room to swing down, as you say.
I believe the cathodyne would need only slightly more than 140Vp-p at the grid to yield two 140Vp-p signals at the output.
Malcolm,
Thanks for sticking it out with me on this! I googled around and the consensus seems to be - all things implemented correctly - that BOTH cathodyne outputs near unity gain so it looks like you're right.
Good news, as it looks like any reasonable gain stage ought to be able to provide enough drive. No surprise really given other examples.
I'm looking at this Orange schematic as an example of a 12AX7 only option:
http://www.orangefieldguide.com/OFG_SCHEM/OR120schem_74.gif
Note the enormous 340k (390k on some schematics) plate resistor!
Brian
Thanks for sticking it out with me on this! I googled around and the consensus seems to be - all things implemented correctly - that BOTH cathodyne outputs near unity gain so it looks like you're right.
Good news, as it looks like any reasonable gain stage ought to be able to provide enough drive. No surprise really given other examples.
I'm looking at this Orange schematic as an example of a 12AX7 only option:
http://www.orangefieldguide.com/OFG_SCHEM/OR120schem_74.gif
Note the enormous 340k (390k on some schematics) plate resistor!
Brian
Hi Brian,
I am happy to stick with it - I am finding it very interesting! The Orange circuit looks good and its nice to use a 12AX7 as they are so easily available. The 340k or 390k plate resistor is certainly 'top of the scale' but I would guess it needs to be that big to bring the plate voltage down to the right level for the grid of the cathodyne (since they are direct coupled).
Malcolm
I am happy to stick with it - I am finding it very interesting! The Orange circuit looks good and its nice to use a 12AX7 as they are so easily available. The 340k or 390k plate resistor is certainly 'top of the scale' but I would guess it needs to be that big to bring the plate voltage down to the right level for the grid of the cathodyne (since they are direct coupled).
Malcolm
I found an interesting old thread on the design of a direct-driven cathodyne (especially Ken Gilbert's contribution):
I need help with a direct-coupled cathodyne PI - AMPAGE Archive
Also found that Merlin strongly recommends a big grid stopper into the cathodyne (see his website section on cathodynes).
I need help with a direct-coupled cathodyne PI - AMPAGE Archive
Also found that Merlin strongly recommends a big grid stopper into the cathodyne (see his website section on cathodynes).
Malcolm,
Thanks… Lot's of discussion on the cathodyne it seems.
I'm starting to rethink this output stage design all over again. The whole setup from the Sunn design "stock" is perfect for the UL approach - high open loop driver gain for feedback (using the pentode), Good balance from the cathodyne and no grid current at the power tube grids… so no issue with mismatched loads on the cathodyne outputs causing funny stuff.
The two issues here were the use of the 6AN8 tube and the fact that I'd really like to try clipping the output stage (in UL or Tetrode) so I need to be ready for grid current.
The plan was to use cathode followers to help "protect" the cathodyne but I've come the following conclusions:
DC coupled cathode followers would be simplest to implement, though they would impart some compression, not sure if this would end up being good or not, or if being inside the feedback loop reduce this. Also, the two outputs are at very different DC potentials so I'd either have to use very different cathode resisters to get center bias, or use very different currents.
So maybe I could use AC coupled followers. Well that made sense until I was reminded that tube followers don't saturate to near ground so I'd be throwing away some signal swing… direct conflict to the original plan. Really low cathode resistors might help but the idle currents get high.
So I thought maybe mosfet followers (I have some IRF840s) but the issues with DC coupling them still exist…. AC coupling is even worse because now I need to fiddle around with a small DC bias voltage too.
So maybe I do use an LTPI and DC couple it to either 12AU7 or IRF840 followers. That seems like the simplest thing to do because I can keep my "normal" tubes (1AX and 1 AU) and keep my low output impedance, and keep the parts count down…
The other possibility was to use a the pre-drive/cathodyne discussed before but follow both outputs up with regular gain stages and DC couple those to followers like in an SVT.
I really need a to put together a prototyping rig so I can work these things out on the fly, rather than try to decide how many holes to drill in a chassis before I'm done working out the details...
Brian
Thanks… Lot's of discussion on the cathodyne it seems.
I'm starting to rethink this output stage design all over again. The whole setup from the Sunn design "stock" is perfect for the UL approach - high open loop driver gain for feedback (using the pentode), Good balance from the cathodyne and no grid current at the power tube grids… so no issue with mismatched loads on the cathodyne outputs causing funny stuff.
The two issues here were the use of the 6AN8 tube and the fact that I'd really like to try clipping the output stage (in UL or Tetrode) so I need to be ready for grid current.
The plan was to use cathode followers to help "protect" the cathodyne but I've come the following conclusions:
DC coupled cathode followers would be simplest to implement, though they would impart some compression, not sure if this would end up being good or not, or if being inside the feedback loop reduce this. Also, the two outputs are at very different DC potentials so I'd either have to use very different cathode resisters to get center bias, or use very different currents.
So maybe I could use AC coupled followers. Well that made sense until I was reminded that tube followers don't saturate to near ground so I'd be throwing away some signal swing… direct conflict to the original plan. Really low cathode resistors might help but the idle currents get high.
So I thought maybe mosfet followers (I have some IRF840s) but the issues with DC coupling them still exist…. AC coupling is even worse because now I need to fiddle around with a small DC bias voltage too.
So maybe I do use an LTPI and DC couple it to either 12AU7 or IRF840 followers. That seems like the simplest thing to do because I can keep my "normal" tubes (1AX and 1 AU) and keep my low output impedance, and keep the parts count down…
The other possibility was to use a the pre-drive/cathodyne discussed before but follow both outputs up with regular gain stages and DC couple those to followers like in an SVT.
I really need a to put together a prototyping rig so I can work these things out on the fly, rather than try to decide how many holes to drill in a chassis before I'm done working out the details...
Brian
Hi Brian,
Plenty of interesting options!
I think DC coupling has two main advantages for guitar and bass amps: (1) avoiding blocking distortion (there is no coupling capacitor to charge up), and (2) not introducing additional phase shift (due to the RC circuit formed by the coupling capacitor and following grid leak resistor in the AC coupled case).
The avoidance of additional phase shift with DC coupling is useful for global negative feedback as it makes the loop easier to stabilise.
Drawbacks of DC coupling include: the design of the two coupled stages is more interactive and tricky, plus high cathode voltages might create a need for elevated heater reference voltages.
Good luck with the prototyping! I hope you will post about how it goes.
Malcolm
Plenty of interesting options!
I think DC coupling has two main advantages for guitar and bass amps: (1) avoiding blocking distortion (there is no coupling capacitor to charge up), and (2) not introducing additional phase shift (due to the RC circuit formed by the coupling capacitor and following grid leak resistor in the AC coupled case).
The avoidance of additional phase shift with DC coupling is useful for global negative feedback as it makes the loop easier to stabilise.
Drawbacks of DC coupling include: the design of the two coupled stages is more interactive and tricky, plus high cathode voltages might create a need for elevated heater reference voltages.
Good luck with the prototyping! I hope you will post about how it goes.
Malcolm
Well, I don't know if I want to DC couple the whole driver stage just yet. I don't think I have a good way to get to a reasonable negative rail with my current power transformer. I did this on my last amp and I'm not sure it's worth the trouble in a guitar amp to be able to draw grid current (Meaning, for softer clipping). I definitely like not having any increase in crossover when I really crank the output.
I was talking about DC coupling the mosfet gates to the outputs of the phase splitter (just to reduce component count) similarly to the tone-stack driver in a Marshall... but without all the non-linearity of using a tube. The idea being to prevent loading on the splitter, prevent mis-match loading during clipping, and to allow a lower impedance path so when clipping does happen bias recovery is fast.
I started a new thread here to get some ideas on how to do this:
http://www.diyaudio.com/forums/tube...odyne-phase-splitter-mosfets.html#post3916786
I'll give it a few days to see if this is worth worrying about and then I'll just build the easy version: By the schematic, UL output only, simple preamp.
Brian
I was talking about DC coupling the mosfet gates to the outputs of the phase splitter (just to reduce component count) similarly to the tone-stack driver in a Marshall... but without all the non-linearity of using a tube. The idea being to prevent loading on the splitter, prevent mis-match loading during clipping, and to allow a lower impedance path so when clipping does happen bias recovery is fast.
I started a new thread here to get some ideas on how to do this:
http://www.diyaudio.com/forums/tube...odyne-phase-splitter-mosfets.html#post3916786
I'll give it a few days to see if this is worth worrying about and then I'll just build the easy version: By the schematic, UL output only, simple preamp.
Brian
OK, got a little more layout work done.... I'm still on the fence about a preamp, so I'm equally on the fence about how many 9 pin sockets to install and wire.
Maybe I'll stick with the Sunn original preamp, maybe something more fendery, part of me wants do a 3 stage jcm preamp but as I imagine more gain I also creep towards putting in an FX loop as well.
Decisions!
An externally hosted image should be here but it was not working when we last tested it.
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Maybe I'll stick with the Sunn original preamp, maybe something more fendery, part of me wants do a 3 stage jcm preamp but as I imagine more gain I also creep towards putting in an FX loop as well.
Decisions!
Well, I'm still working this out I guess. Here's some more stuff.
Firstly, I'm resigned to starting out with only a UL setup at first and then hacking in a 280-300vDC rail for proper tetrode experiments later. This is the simplest setup I can envision:
I'm using the resistive divider on the 2 stacked filter caps to get a voltage reference for the mosfet… seemed like the simplest way to go since I'd be using those resistors anyway - either 2X 250k or something like what I have drawn to get closer to 300vDC. I expect the B+ to land around 560vDC but there may be some tuning. Another thought would be replace the lower resistor with a 300v Zener for a degree of real regulation on the screens. If I do that I'm thinking a diode from the gate to the B+ line would be a nice way to provide a discharge path for the lower cap.
I'm starting the filtering off with a stacked set of 500uF @ 385vDC - because I have them - and to get to the kind of filtration typically used in stiffer amps like the SLO100 - around 200uF. I don't actually see any good reason to use a filter choke in this setup.
And some more fiddling with layout:
The leads on the transforms were trimmed in their previous life so I need to be careful of placement. The 11 turret strip just below the power tubes will give 3 tie points for the 3 secondary taps (right in the middle, so I can jumper the rest of the way to the impedance selector) and 4 tie points on either end for each power tube.
The two 23 Turret strips are surely overkill for wiring up 2 12AX7s but I haven't sketched up a layout just yet. I'm sure 2 gains stages and a tone stack is plenty… but with all that space I can't resist throwing in an extra socket or 2 for later expansion. Maybe I'll build in enough gain for some overdrive.
Firstly, I'm resigned to starting out with only a UL setup at first and then hacking in a 280-300vDC rail for proper tetrode experiments later. This is the simplest setup I can envision:
An externally hosted image should be here but it was not working when we last tested it.
[/URL]
I'm using the resistive divider on the 2 stacked filter caps to get a voltage reference for the mosfet… seemed like the simplest way to go since I'd be using those resistors anyway - either 2X 250k or something like what I have drawn to get closer to 300vDC. I expect the B+ to land around 560vDC but there may be some tuning. Another thought would be replace the lower resistor with a 300v Zener for a degree of real regulation on the screens. If I do that I'm thinking a diode from the gate to the B+ line would be a nice way to provide a discharge path for the lower cap.
I'm starting the filtering off with a stacked set of 500uF @ 385vDC - because I have them - and to get to the kind of filtration typically used in stiffer amps like the SLO100 - around 200uF. I don't actually see any good reason to use a filter choke in this setup.
And some more fiddling with layout:
An externally hosted image should be here but it was not working when we last tested it.
[/URL]
The leads on the transforms were trimmed in their previous life so I need to be careful of placement. The 11 turret strip just below the power tubes will give 3 tie points for the 3 secondary taps (right in the middle, so I can jumper the rest of the way to the impedance selector) and 4 tie points on either end for each power tube.
The two 23 Turret strips are surely overkill for wiring up 2 12AX7s but I haven't sketched up a layout just yet. I'm sure 2 gains stages and a tone stack is plenty… but with all that space I can't resist throwing in an extra socket or 2 for later expansion. Maybe I'll build in enough gain for some overdrive.
A little progress update. Stayed late in the shop at work yesterday to mill out my chassis. Not sure if I mentioned but I got this folded aluminum box from WattTubeAudio.com. It's .09" thick which is much better than the real light stuff hammond uses.
I made a few mistakes and had to rush through a title rework but all is well and everything fits so far:
So I'm going for a turret strip "assisted" point to point build. I went with 3 9 pin sockets , 2 for the preamp and 1 for the splitter/driver.
I made a few mistakes and had to rush through a title rework but all is well and everything fits so far:
An externally hosted image should be here but it was not working when we last tested it.
So I'm going for a turret strip "assisted" point to point build. I went with 3 9 pin sockets , 2 for the preamp and 1 for the splitter/driver.
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