Sluckey's Dual Lite variant project

[Loomer]

First off, hi everyone! Been lurking on the forum and website for a while but only just registered and starting off with this first post.

I've been toying with the idea of building an amp for a while and finally been boiling it down to a design that would make a good start. I've bounced a couple of ideas on the 18watt forum, where I received a few good pointers, and tweaked my ideas to the point of coming up with a VERY bastardised version of an 18 watter, based on the forum's own Sluckey's Dual Lite amp, hence me taking the conversation over here.

What I wanted was an amp I'd genuinely enjoy using for low gain/clean/edge of breakup tones mostly in a home studio setting (usually play through a dummy load and into IRs for recording at any time of the day) but would also be practical enough to take out for practice or live use. 18w seems like a good balance for this.

I've always loved Vox chimey, jangly tones (I own a lovely AC30/6TB - amazing amp, but painfully loud/heavy/impractical) and, having owned a JTM45, know I love edge of break up Marshall cleans, too. I'm not interested in high gain or hard rock tones, mostly those "dirty cleans" to build upon and that can be cleaned up through dynamics.

The Dual Lite looks great for a couple of reasons: simple enough circuitry to make for a good first project (easier to assemble but should also make for a good tweaking and modding platform, more so than a complex circuit where changes might not be as straight forward to identify tone-wise once made if that makes sense), has a couple of flavours of tone for versatility and covers some nice Vox+Marshall ground (no doubt in its own way rather of course). I like the look of the High Pass 6 way tone control too, I'm hoping cutting some low frequency content might clean up the sound a bit for those chimey, jangly near-cleans (think September Gurls!).

I've researched into mods to pre, PI and Power sections and settled on the Jason PI mod values for components around the PI and Power tubes - not being interested in high gain that should give me a little more control over the clean,break up and low gain settings.

I've mocked up a first schematic, attached. Thought I'd share to see if anyone sees anything fundamentally wrong with it or has any suggestions on any tweaks I might want to consider?

I appreciate it's quite approximative (to say the least), for example at the input jacks and, above all, in the power section. That is the one area I'm yet to fully dive into. Ultimately I'll probably stick to the Dual Lite spec as with everything else, thus benefitting from the tried and tested layout, though I'm keen to check values agains other similar builds (such as the Trinity TC15) since I will be using a more traditional 18w PT and OT rather than the Hammond parts used in the original project.

Hope the above all makes sense and thank you in advance for any bit of help or insight you may be able to provide :)

[sluckey]

That's still my goto amp. Lotta fun to build and a lotta fun to play. Enjoy. Keep us posted.

[Loomer]

That's still my goto amp. Lotta fun to build and a lotta fun to play. Enjoy. Keep us posted.

Thank you Steve, looking forward to getting stuck in!
Out of curiosity, which of the two channels tends to be gainier? I'm thinking on making the 12AX7 channel a dual input with single and parallel options to have a cleaner flavour and a fatter, crunchier side...

[Jennings]

You'll really like the amp...I built a version into a 1x12" combo using a Weber alnico speaker.  It's my go to amp for recording and gigging for the last few years now.  I find the 18W channel to be the gainer of the two, but I tend to default to using the Vox channel almost all of the time.  That channel's really my kind of flavour.

[Loomer]

You'll really like the amp...I built a version into a 1x12" combo using a Weber alnico speaker.  It's my go to amp for recording and gigging for the last few years now.  I find the 18W channel to be the gainer of the two, but I tend to default to using the Vox channel almost all of the time.  That channel's really my kind of flavour.

Cheers, I need to slowly amass the parts now and then I'll be off. Will take a while I think but looking forward to the day I'll plug in and play :)

About that EF86 channel, do you guys know what the differences are between the original Vox and the Matchless variants?

[sluckey]

About that EF86 channel, do you guys know what the differences are between the original Vox and the Matchless variants?

Just compare the Vox AC-15 schematic with the Matchless DC-30 schematic.

The most obvious difference is the simple on/off bright switch and the 6-position tone switch. Less obvious is different resistor values for plate and screen. My dual lite uses the AC15 EF86 circuit combined with the DC30 tone switch, but I have different cap values on my tone switch.

One forum member used a 12 position tone switch with 12 different caps on his AC15.

[Loomer]

Just compare the Vox AC-15 schematic with the Matchless DC-30 schematic.

The most obvious difference is the simple on/off bright switch and the 6-position tone switch. Less obvious is different resistor values for plate and screen. My dual lite uses the AC15 EF86 circuit combined with the DC30 tone switch, but I have different cap values on my tone switch.

One forum member used a 12 position tone switch with 12 different caps on his AC15.

Thanks Steve!

I like the look of the 6 position rotary switch, and will no doubt experiment with caps to find a range I like.

In terms of the screen and plate resistors, are these bound to make much of a difference and if so, of what kind? I’m guessing it should slightly alter the headroom/saturation in the pre?

[sluckey]

In terms of the screen and plate resistors

No idea. I used the AC15 values, liked it, and never looked back.

[WiderGates]

Hello Loomer,
R10, R13, C10 seem to be the wrong values.

[sluckey]

I'm thinking on making the 12AX7 channel a dual input with single and parallel options to have a cleaner flavour and a fatter, crunchier side...

This is the correct way to wire the input jacks for single/parallel operation...

[Loomer]

Hello Loomer,
R10, R13, C10 seem to be the wrong values.

You're spot on, got too trigger happy with the copy and paste there...
R10 should be 820R, R13 should be 100k and C10 should be 50 or 68u. Will correct once I'm home, thank you for your help there!

[Loomer]

I'm thinking on making the 12AX7 channel a dual input with single and parallel options to have a cleaner flavour and a fatter, crunchier side...

This is the correct way to wire the input jacks for single/parallel operation...

Thanks again Steve - I didn't have the switched stereo jack symbol in my DIYLC so kept it to the mono, thus showing incorrectly. But the input wiring is definitely something I want to go over again to make sure I'm getting it right once I'll be wiring and soldering, so that's very helpful indeed 👍

[sluckey]

The jacks are not stereo. They're just a mono jack with switch lug, Switchcraft 12A or Cliff 4 lug.

[Loomer]

Slow progress but been looking at output transformers - I can get a well-reviewed and low price one in the form of the Amp Maker 18w OT, which is a drop in for the classic Marshall 18w OT and has a primary rating of 8kOhm.

As my design is veering more and more towards the Voxy end of the spectrum and leaving high gain Marshallness behind, would it be worth it to consider an AC15 style OT (it would probably be the Hammond 1750Y) with a lower primary of about 6.6kOhm?

Reports online seem to state lower primary impedance should make for a cleaner amp with higher headroom, but realistically would this be a very marked difference? The Hammond is twice the price of the Amp Maker, and while the difference in itself isn't too huge, I'm weighing whether it would be worth the change on what would be my first build? 🤔

[sluckey]

I can get a well-reviewed and low price one in the for of the Amp Maker 18w OT, which is a drop in for the classic Marshall 18w OT and has a primary rating of 8kOhm.

I would use this one. My OT is 8K:4Ω

[Loomer]

Resuscitating this thread as the idea of this build is gathering momentum. I've been reading, copying and going through a few layouts and schematics and it has been a hugely helpful process in forming a better understanding of what is involved and certainly has given me better tools to judge what should (at least empirically) be better versed to get to my end goal. All the schematics I've been drawing from and which I will refer to in this post are linked at the bottom.

Essentially this will still be a Dual Lite variant, but will feature Matchless values throughout, which would make it a Spitfire with a bolted on Nighthawk/DC30 EF86 pre for CH2.

So, couple of nagging questions at this point...!

Firstly, I'm looking into the power section at the minute. In the Spitfire preamp and PI receive voltages from two separate but identical filtered points (C and D), both being taken from B via a 22k in series followed by a 22u to ground. Steve's Dual Lite goes from C to D via another series R followed by a large value cap to ground. The Marshall 18w on the other hand does away with the double filtering and supplies C to both preamps and the PI.

Long story short, is there any particular advantage to filtering twice over having one common C supply for all the 12ax7 stages? And if doubling up, what are the differences and pros and cons of having C and D in parallel as per the Matchless or in series as done by Steve?

Second question is about the layout. Both the 18w Modern Classic (of which a version with an EF86 pre exist and is very easily adapted to my plan) and Steve's layout look very good (and naturally have a lot of overlap), but I've been drawing mine up after the 18w one because the likelihood is that I'll be working off a pre-drilled board rather than drilling my own off a blank - or is the Dual Lite layout easily adapted to that format? Being a first for me means it's probably harder for me to visualise the actual components on the board than I suspect would be for most of you... I'll need a little extra width as I'm probably going to forego the cap can and mount the filter cap for B+ to the left of the turret board. On the fence whether to use a choke or a 1k sag resistor, but might bite bullet and go choke because why not...!

Lastly, the tone control for the 12ax7 channel will probably be consistent with the Spitfire control. I heard the bright cap on those is very bright (which I like the idea of) but considering making it switchable between 180p/off/470p to avoid fettling and have a couple of options readily available. In terms of layout this wouldn't make a difference since it's all pots-mounted. Nevertheless, to understand a little better what goes on there and be able to compare with the stock Marshall control, is the frequency response of these two tone controls available anywhere? Unfortunately neither seem to feature in the Duncan TSC, but I'd have loved to be able to get a simple snapshot to understand if any difference there would be perceivable and if so in what way.

Hope this all makes sense!



Steve's Dual Lite: https://sluckeyamps.com/dual_lite/dual_lite.pdf
Matchless Spitfire: https://www.thetubestore.com/lib/thetubestore/schematics/Matchless/Matchless-Spitfire-Schematic.pdf
Matchless DC30 (EF86 preamp section): https://www.thetubestore.com/lib/thetubestore/schematics/Matchless/Matchless-DC30-Old-Schematic.pdf
18w Marshall (modern classic version): https://www.18watt.com/files/JMPGuitars_18_Watt_Modern_Classic_Schematic.pdf
18w Marshall modern classic w/ EF86: https://www.18watt.com/files/JMPGuitars_18W_EF86_Modern_Classic_v2_Schematic.pdf

[PRR]

> is there any particular advantage to filtering twice over having one common C supply for all the 12ax7 stages?

Signals sneak-back through the power system. The >40V at the PI plates sneaks-back to the <1V at the first preamp. It will howl. The conservative plan is to have only TWO sequential plate-loaded stages per power filter node. If you build thousands you may wish to do the hard work to validate stability with less filtering; clearly Marshall did. And at his production level, that second cap hurts! Do you know more than he did?

With exceptions, commercial amp plans are already minimalized as much as is good for them.

[Loomer]

> is there any particular advantage to filtering twice over having one common C supply for all the 12ax7 stages?

Signals sneak-back through the power system. The >40V at the PI plates sneaks-back to the <1V at the first preamp. It will howl. The conservative plan is to have only TWO sequential plate-loaded stages per power filter node. If you build thousands you may wish to do the hard work to validate stability with less filtering; clearly Marshall did. And at his production level, that second cap hurts! Do you know more than he did?

With exceptions, commercial amp plans are already minimalized as much as is good for them.

Thank you very much, this confirms what I suspected. It completely stands to reason and while I can expect the circuit to remain stable with that Marshall style common C I guess my name isn't Jim and throwing in an extra cap and resistor won't be an issue for space nor cost for extra insurance and cleanliness!

General follow up Q here regarding my point on adapting turret layouts - how important/practical do people value having passthrough holes for wires vs having wires soldered at the bottom of the turret?

[tdvt]

General follow up Q here regarding my point on adapting turret layouts - how important/practical do people value having passthrough holes for wires vs having wires soldered at the bottom of the turret?

I will be interested to hear the opinions on this.

While it sure is easy to connect a wire to a turret from the bottom (as I have done that myself),  I have stuck with the practice of using a pass-through hole for under-board wires, next to the the turret, with a wrap around connection above the board.


Having everything visible & accessible makes tracing/servicing stuff later on, WAY easier.

[sluckey]

General follow up Q here regarding my point on adapting turret layouts - how important/practical do people value having passthrough holes for wires vs having wires soldered at the bottom of the turret?

I would never solder a wire to the bottom of a turret. Too easy for that wire to become detached should you do any soldering on the turret.

[Loomer]

Thanks both, and completely agree on the simplicity of being able to see/probe all connections from one side.

So if I were to use a pre punched board, would I just look at using the next spare hole to run the wires through, or simply have the wires soldered at the lower end of the turret on the same side as the components?

[sluckey]

So if I were to use a pre punched board, would I just look at using the next spare hole to run the wires through

Depends on the hole spacing. May have to skip a hole if spacing is close.

or simply have the wires soldered at the lower end of the turret on the same side as the components?

That's how I did all my earlier builds. Hoffman has never used any "wire thru-holes". I switched to wire thru-holes simply because I prefer the look. Certainly more work. And no electrical or mechanical advantages.

[tdvt]

So if I were to use a pre punched board, would I just look at using the next spare hole to run the wires through

Depends on the hole spacing. May have to skip a hole if spacing is close.

or simply have the wires soldered at the lower end of the turret on the same side as the components?

That's how I did all my earlier builds. Hoffman has never used any "wire thru-holes". I switched to wire thru-holes simply because I prefer the look. Certainly more work. And no electrical or mechanical advantages.

I agree, it is much neater looking, but I also find it easier to follow the circuit when tracing paths.

You may want to enlarge the pass-through holes depending on how big or small they are to begin with. A larger hole is easier to work with if you have the space.

I also adopted the practice of adding edge holes for single wires running off the board heading to tube sockets &/or pots after seeing the very tidy builds by Sluckey & P2P.


The attached pic is one of Doug's AB763 boards but with added pass-through & edge holes.

[Loomer]

Thank you all once again for the precious advice - it's so very helpful to have people who have done there before chime in with suggestion and every bit of wisdom shared has always been truly appreciated!

Next two things I'm considering at this point (and they are very much consequential) are regarding power filtering/supply and layout.

Attached below is the schematic I'll be working off of. It's a Matchless Spitfire with the Matchless EF86 pre from the Nighthawk/DC30 using the other side of the PI; only differences are a bump in value to the screen (which are double to have one per tube) and cathode resistors. The schem shows two different options I've been looking at in regards to the power section:

-one is effectively taken straight from Matchless, with choke and three parallel RC networks using a 22k and 22u
-the other is taken off Steve's Dual Lite and works in series with a 22k/22u off B+ followed by 1k/22u and another additional 1k/22u. Steve's project files seem to show that the 1k resistor doesn't do too much in terms of dropping voltage so I think this could work well in providing similar voltages to D and E without too big a drop from C.

Would either approach have significantly different outcomes in terms of supply or filtering or are they fairly mutually exchangeable so long as voltages end up in the ballpark? I made a point of keeping each preamp on its own RC as it seems many have reported how tweaking the voltage at the EF86 can very markedly alter tone, so that would leave more room for easy experimentation should I not be satisfied with the first attempt.

Which leads me to the second question(s), which is about the layout - should the caps off C, D and E be grounded on the preamp bus or the PT bus? Most layouts seem to suggest the former but have seen the odd exception, or other mentions suggesting C (the PI network) should be grounded with the PT, D and E with the preamp bus. Am I splitting hairs here?

And lastly, any advantage having those off to the side with wires taking C, D and E to the main turret board individually? Or is having long wires carrying voltages near and around the board not best practice? Again, I've seen layouts placing the RC right next to the components they pertain (like Steve's), others keeping all the big caps together off to the side and long wire runs for C, D etc (think that's how Matchless do it).

Once again, most gratefully thanking in advance. I feel like I'm getting close to cracking my recipe and am really looking forward to start gathering parts and components and build it up!

[sluckey]

Not saying my ground scheme is the only or best way to do it, but if you follow my scheme you will not have to chase any ground gremlins.

[Loomer]

Thanks Steve, I figured sticking to a tried and tested layout would be the best way forward and so was keen to adapt yours to suit the schematic.

Based on that I've started drawing up a layout that does just that. Still drawing up the off board connections etc but attached is the WIP. Main difference is that this makes CH1 the EF86 channel, as some reports have it as ideally dropped in voltage in case of muddiness.

Alternatively, would drawing wires from B+ (ie middle row, 4th hold from the left) to make the supplies parallel (and therefore individually tweakable if needed) work cleanly or could it throw any curveballs into the equation?

[Loomer]

Slowly making progress on this. More reading, more tracing, more drawing. Long post incoming, with a few updates and a couple of Qs…

Started ordering some valves, got a Mullard EF86 on its way as well as 4 matched 6P14P for the power section - I’ll be interested to swap these around with the JJ EL84 I have in my AC30 and see how, if at all, different they are.

Already have a JJ 12AX7 that a tech somehow had installed in the aforementioned AC30 instead of the ECC82, so that’s the EF86 side, PI and Power Amp taken care of, just one 12AX7 to go!

Will grab an 18 watter chassis from Modulus amps along with a custom faceplate to match (though I might wait to order that as I might want to play with PPIMV, cut control etc and see what I’ll eventually keep).

Cabinet will be built and will probably forego tolex as it seems like a pretty involved process, going for a stained look instead. Tempted however to have a go at covering the front panel as I love the idea of using a Morris and co fabric for pattern and decoration.

Looking to order transformers now and pretty settled on the below, which seem bang on in terms of both spec and price - they are essentially an 18w set, but any wisdom in terms of suitability would be much appreciated!

Power transformer: https://primarywindings.com/product/amp-maker-pwam01-275v-190v-160ma-6-3v3a/

Output transformer: https://primarywindings.com/product/amp-maker-18w-push-pull-output-transformer/

The aim is for a B+ of around 350/360 and that power transformer is 10v below Spitfire spec, which I don’t see as a huge problem. I will install a tube rectifier socket to have the option but might well start off by making a diode+resistor plug in rectifier which should give me the right voltage. A GZ34 should make for a good tube alternative. When people talk about sag resistors, is a series resistor all there is to it or would that be a resistor to ground alongside the second filter cap?

On the fence about the choke. Again, might start off simple by just having a ~1k/5w resistor across the cap can and see from there.

I will consolidate the layout in the coming evenings. It’s very much Sluckey-inspired but with a little extra filtering wiring to allow for parallel filtering for each stage.

[sluckey]

You can't use a GZ34 with that PT.

[Loomer]

You can't use a GZ34 with that PT.

Ah, yes! It becomes blatant when you call it a 5AR4 - no 5v winding 🙈.

Would an EZ81 be the only realistic tube option with that PT?

Or should I either commit to SS or look elsewhere for a PT?

[Loomer]

Been scrambling my brains/learning more about rectifiers - consensus seems that in a PP 2xEL84 configuration a GZ34 wouldn't offer much in terms of sag as it can cope more than well enough with the current an amp like this needs.

Which leads to the temptation to just simplify and go for SS rectification and perhaps trying a 100/150R resistor after the diodes to quench any drop+sag curiosity.

My only doubt at this point is, looking at the PT I have been eyeing up, would I be looking at a half wave rectifier or would I be able to use a bridge rectifier?

I winged a quick enquiry to Primary Windings and I was impressed at how John was quick in replying offering help, which makes me want to be sticking to their products even more, but I thought I'd post a couple questions here before going too deep in my email thread with him and risk clogging it up with nonsense on my part...!

Really enjoying the process of learning and piecing the puzzle and constantly grateful for the suggestions, hints and guidance I've been solidly receiving; I'm now hoping I might be able to kick off the orders and build in September after a little bit of holidays. Will keep updating the thread as I hope it might eventually be of help to other novice builders chancing upon it through web searches as other build threads have been for me!

[sluckey]

Use a full wave bridge (FWB) with that PT. You could also use a hybrid FWB as seen in this schematic...

     http://sluckeyamps.com/misc/VAC-4.pdf

[Loomer]

Use a full wave bridge (FWB) with that PT. You could also use a hybrid FWB as seen in this schematic...

     http://sluckeyamps.com/misc/VAC-4.pdf

Thank you for confirming! I make a FWB rectifier as per the attached, right?

That hybrid version does look interesting! However, from the voltage readings on that schematic it looks to ma as though the EZ80 would drop way too much voltage for my application.

My B+ aim is for ~350V, meaning a full SS FWB from that PT would keep me on the high side (using 1n4007 which have a 1.1V drop I make it ~386V rectified. So perhaps the same arrangement but with an EZ81 (which I gather should keep the drop at around 20V, whereas the EZ80 should be twice that or more?) might be the ticket...

Thankfully it's an easy switch, so long as I factor in an extra socket, that is, and perhaps a noval plug option with diodes could be an elegant solution to try both methods. In that case, would it be a case of diodes between 1-3 and 7-3 (cathodes to pin 3)* plus 4 and 5 bridged?

* or cathodes to ~100-150R/10W resistor for a little extra sag and drop

[sluckey]

Your FWB is correct. That AC-4 with hybrid FWB was the only example of a hybrid that I had. The low B+ is due to the small PT and that 1K dropper. The EZ80 was only a small part of the low B+. Yes, an EZ81 would be a better choice for your circuit and PT. Just wanted to show you an alternate option for the FWB.

[Loomer]

Thank you once again Sluckey for chiming him and guiding me through this.

I looked at a few affordable but suitable power transformers and I've done some calculating of what I should expect for B+ once rectified (secondary Vdc*1.4142)...

This 250/160mA + 6.3V/2A + 5V/2A and this 250/160mA + 6.3V/2A should give me around 350V with a SS rectifier. That's the voltage I'm aiming for but doesn't leave much wiggle room should the V drop more than I expected when filtered etc and hardly affords the option of a valve rectifier (I like a little squishy sag under my fingers) - the 5V version would allow for the use of a GZ34 which would keep voltages in the ballpark, but likely not bring much difference compared to SS rectification (the GZ wouldn't break a sweat in what is effectively a paired down 18w), while using a EZ81 off the 6.3 would drop the voltages by too much (15-25V)

The previously mentioned 275 non CT would rectify to around 385 with SS and should get me at my target voltage with hybrid rectification using an EZ81 and replacing the choke with a resistor (might need to try a few values - recommendations seem to vary from 100R to 2k2).

This is another option with a 300V secondary and more current than I'll ever need should rectify to 420 or so, which would be usable but require a lot of voltage dropping. As it doesn't have a 5V winding I wouldn't have a lot of choice in terms of valve rectifiers as a means to achieve that and would rely in bigger and bigger filter resistors. Not ideal but gives me a lot of ideas for my next builds...

So yeah, the middle choice, which was always my first choice, takes the cookie, which means I've now fixed up the schematic, now attached.

Will soon be away for a bit so will wait to place the order but here we are!

Should anyone spot any clear flaws in my plan, please do flag - I'm definitely learning a lot and gaining some confidence but I'm a long way from fully being confident in my own tweaks, designs and speccing.

[Loomer]

Holidays drawing to a close (sigh) and looking to order parts and components soon.

Will go through the schematic again (the one posted above should just about be there bar a couple things, like the wrong grid leak R values) as well as finishing up and publishing the intended layout, at which point I will no doubt invite and willing pairs of eyes to have a look for things I will have missed.

This being my first build I'm not sure where I might end up wanting to try little value changes or mods so I'm curious to know, which extra components/values do you thing might be worth ordering to give myself options? I'm thinking I might order a few different values for the 5w filter resistors in case my voltages end up being somewhat off the expected targets but perhaps you all would have suggestions on the topic? For the price of those I figured I might as well order a few spares off the bat rather than go back and forth with new orders later on.

And lastly - how much hook up wire should I expect to end up using? I'm planning to order a few colours to keep things easier to spot (red for all things HT, black for ground connections, then 2/3 more colours?) but would only be making guesses as per the length. Also, to connect buses on the turret board, would that simply be stripped wire?

[Loomer]

Gone through the schematic and fixed a couple of errors I had in the previous version and this I can now consider a final version. Which leads to a fresh couple of simple questions....

 - Finishing up the layout, in regards to which: as it stands I've opted for full FWB SS rectification, should I make space for this on the turret board or leave separate? I have considered using a row or two of stripboard which has one lug grounded to accommodate both the rectifier and act as power section star ground. Would this be a fairly clean way of doing it or are there any drawbacks? While the layout of it per se isn't an issue for me to draw up, I'd love some feedback around the "best practice" way of doing or not doing things to avoid adding risk of ground loops or other gremlins...

 - As per the schematic, I expect to have a play with the value of the resistor on the cap can in order to get voltage and "feel" where it needs to be. Having said that, will that one resistor be enough as a "sag" resistor, or should I be implementing another single resistor before the first side of the cap can, right after the rectifier? I've seen people using heat-sinked 25w resistors for sag, but the fact that Steve's original design has a simple Metal Oxide 3-5W across the can suggests that might be slightly overkill, or is that just the case after the first round of filtering?

Should be ordering it all up soon but having problems with the transformers as Primary Windings aren't giving an option for anything bar drop through for their PT and, after stating a frame or standing option wouldn't be an issue in a quick first email reply, have since fallen silent so I have no way of ordering it at the moment. Had a look at alternatives and Modulus as options (though would end up around twice the price) and I've seen some OEP branded sets which would fit the bill for not a lot more then the PW options, though I've never heard of any build report using those... 

Thanks in advance and looking forward to update as the project moves on! :)

[sluckey]

The layout of the bridge rectifier is not critical other than to keep it close to the PT. I would put it on the board but a separate terminal strip is fine too. Your choice.

The resistor on the cap can will not give you any sag. For sag, you need a resistor ***BETWEEN*** the rectifier and first filter cap. Another option for sag would be to use an EZ81 hybrid bridge.

Why are you struggling with a PT? I would just get a Hammond 370DX and simplify life.

     https://www.hammfg.com/files/parts/pdf/370DX.pdf

[Loomer]

The layout of the bridge rectifier is not critical other than to keep it close to the PT. I would put it on the board but a separate terminal strip is fine too. Your choice.

The resistor on the cap can will not give you any sag. For sag, you need a resistor ***BETWEEN*** the rectifier and first filter cap. Another option for sag would be to use an EZ81 hybrid bridge.

Why are you struggling with a PT? I would just get a Hammond 370DX and simplify life.

     https://www.hammfg.com/files/parts/pdf/370DX.pdf

Thank you once more Steve, it's really reassuring getting feedback from you! Will incorporate a 100ohm 10/25w post-rectifier. Not too keen to go down the EZ81 hybrid route, mostly because of a few too many complaints of unreliable 81s, I just figured a resistor should get me most of the way there for cheap and likely cause less trouble further down the line, while keeping the voltages a touch higher, given a 275 secondary wouldn't leave me with too much wiggle room in aiming for approx 350 B+.

Not struggling as such in sourcing the PT, there's a few options, but I was hoping to be able to order from Primary Windings as I could nap PT and OT for under £100, which is nigh on half price compared to most other sources, but might just have to bite the bullet and invest a few extra £££s.

Also, staying true to myself, am currently tinkering with the choice of OT. Could either going for an 18w OT which I could then use either as an 8k primary or try the 4k primary Matchless try by "mismatching" the speaker (eg 16 output to an 8ohm speaker), or grab an Hammond 1750Y with a 6.6k primary, which is the drop in replacement for the AC15 and is considerably heftier than the average 18w OT and seems to be well liked for similar builds.

[mresistor]

The Hammond OT for a Marshall 18 watt is the 1750PA and is what is in my Dual Lite which I really like. Multiple secondaries. https://www.hammfg.com/files/parts/pdf/1750PA.pdf


I don't think the Y is more substantial in size than the PA it just has end bells that make it appear so.  The PA looks like it might be the better of the two to me.  Looking at Henries and impedance.

[Greenwichpaul]

Why are you struggling with a PT? I would just get a Hammond 370DX and simplify life.

In an ideal world it would be easy and perfect, but thanks to fantastic recent trade deals in the UK, they're £110 and up and impossible to source cheaper from Europe. Fortunately there are alternatives like the Primary Windings PT and other small producers for half that amount.

Update: Hammond was always cheaper if you bought from tube-town; you can still get them direct from Mouser etc, but they add 20% VAT to the price, not listed until you check out. Some Hammond are still reasonably priced, like iirc the 290CAX, which is less than £90 (used to be around £75). Some sellers (Piemme) refuse to sell to the UK full stop because of the paperwork. It's a pain, but for brits choice has suddenly narrowed.

[sluckey]

I get that. However, Primary Windings has fallen silent. I thought Hammond was easily available in the UK.   

[Loomer]

I get that. However, Primary Windings has fallen silent. I thought Hammond was easily available in the UK.   

They are but I just wanted to weigh my options between doubling my PT budget!

Gave PW a nudge and I trust I’ll hear back, so hopefully that’ll be that 🤞

[RoadShow]

Why are you struggling with a PT? I would just get a Hammond 370DX and simplify life.

In an ideal world it would be easy and perfect, but thanks to fantastic recent trade deals in the UK, they're £110 and up and impossible to source cheaper from Europe. Fortunately there are alternatives like the Primary Windings PT and other small producers for half that amount.

Update: Hammond was always cheaper if you bought from tube-town; you can still get them direct from Mouser etc, but they add 20% VAT to the price, not listed until you check out. Some Hammond are still reasonably priced, like iirc the 290CAX, which is less than £90 (used to be around £75). Some sellers (Piemme) refuse to sell to the UK full stop because of the paperwork. It's a pain, but for brits choice has suddenly narrowed.

For those here in the USA, I've found hawkusa.com to be the lowest cost for Hammond transformers, and fast and cheap for shipping. Several sets for different builds over the last few years and I've never been disappointed.

The 290CAX mentioned above is listed at $75, $10 less than Mouser.

[Loomer]

Well, it's been a hot minute! Got sidetracked by things like settling into a new job/slight career change and bringing a small human into this world and just like that this project's been more or less shelved for a year...!

I say more or less since a couple of things have moved on, namely I got a hold of the transformers, turret board and turret staking tools and more or less only needing a chassis and some valve sockets now!

Ended up getting the transformers from Piemme back in Italy, and getting them back when I travelled with hold luggage. OT is a Fender Deluxe/Vox AC15 friendly 6.6k with switchable 4/8/16 secondary while the PT is 0-280, which should be just right for the higher-than-18w voltages I'm after. Will most likely stick to the tried and tested Dual Lite layout, the tone control differences between the 18w and the Spitfire are easily dealt with on the pots.Same for the power supply, will simply add a sag resistor to prevent any stiffness in feel.

Will double check layouts in the coming days and share. Not promising this is going to move quickly, but looking forward to finally making some inroads!