Looking for a project - need some advice

[Amped]

Hi.

I came across the attached diagram - probably from here (can't seem to find the post again), Tubenit may have marked it up with a single valve reverb addition(?).  It looks intriguing, looks like a 15W mod of the Matchless DC30.  Does anyone have any knowledge of this design - has it been built before?

Thanks 

[Papa Jim]

You came to the right place. Sluckey on this Hoffman forum has tons of knowledge and possibly designed this amp.
Here's a link to another forum with info.
https://www.ax84.com/index.php/oldprojects.html?project_id=november

[sluckey]

That looks like Tubenit's work. Here's the discussion. Attachments are long gone. Tubenit may still have the original sch file.

[Papa Jim]

But schematic has your name on it as the designer Sluckey?

[sluckey]

But this is the internet. You can write anything you want! 

I didn't design that and I didn't put my name on it either. The date is about the same time that I built a November amp that was designed by the gang at ax84.com. But that schematic is a far cry from the November amp from ax84.com.

[tubenit]

Looks like something I might have "cut and pasted" based on some Hoffman thread?  I don't remember doing this & I don't have an original SCH file for it.  Since I have NO interest in EL84 tubes, it's not something I'd build for myself.

with respect, Tubenit

[Amped]

Thought I was on to something there.
Ah well, my search continues....
As always, thanks for your help

[sluckey]

See if there's anything interesting on my website.

[bmccowan]

I second the notion of looking at Sluckey's projects on his website. His documentation is second to none: schematics; layouts; commentary - can't beat it.
For what its worth, I'm with Tubenit in saying no to EL84 amps, after building several and always preferring other power tubes. But if you like the Matchless avenue, the Spitfire is a good EL84 amp, just too bright and "harsh" for me. And I like the Matchless preamp used in the Clubman. A pentode in V2. I've used it a few times with a 6SJ7 or a 5879 - nice.
In the power range you are looking at, I can also recommend the Brownface Princeton (recently finished one) the Physician Z Z-28, although mine uses a 5879 preamp, and the Gisbon GA-40. They all have readily available schematics although all Z schematics are unofficial.

[shooter]

I'm with Tubenit in saying no to EL84 amps

I'll also agree, with an exception, I've done a couple PSE, and a QSE, when you "add" that "next" tube, you add a fuller sound, but going from sweet to harsh is only 1 volume number apart.

I find "substituting" self biased 34's in (your favorite EL84 amp) makes for nicer amps

[bmccowan]

Hmm Shooter - I may have to try that EL84>EL34 thing. I built a Spitfire a few years ago - it is a clean, powerful amp, takes pedals great, just does not have the sweetness. Its sitting around unplayed, so I might as well give it a shot.

[vampwizzard]

Looks like something along the lines of Sluckey's dual lite with reverb? Id bet someone asked how to add a low impact reverb from the master and tubenit just drew something up.

I converted an AO-39 to a spitfire but added a tone cut control in place of the master volume. Fixed what I didnt like about the amp. It's my rudimentary understanding that the DC30 is very similar to the EF86 AC-30s but with a lot more power filtering.

The spitfire with tone cut worked out fantastically and my lead playing friends love it. Its not a bad choice if you dont want to mess with an EF86. The nighthawk and nighthawk reverb would be the matchless 15w, one channel version of the EF86 amp.

If youre starting from scratch there are a lot of the old gibson tweed era amps that utilize EL84s that havent been built in a long time. They seem worthy.

[tubenit]

I second the notion of looking at Sluckey's projects on his website. His documentation is second to none: schematics; layouts; commentary - can't beat it.

This is good advice!  Tubenit

[Amped]

See if there's anything interesting on my website.

...There is plenty of interesting projects on your site, I have to wonder; how do you find the time??  I'm glad you did though. 
There's two of your projects that really stand out, the Matchless Lightning, and the Dual Lite.  I first saw the Lightning and thought "That's a keeper", but didn't look at the Dual Lite close enough obviously, it's really sparked my interest.  It's pretty much exactly what I was excited about with the first drawing, I know it's been built before and was successful so I've got no excuses   There may be some judgement on build quality though (how do you make it look so tidy?  Challenge accepted :-D).

Looks like something along the lines of Sluckey's dual lite with reverb?

Good spotting - thanks @vampwizzard, could have missed it if you hadn't brought it up.

I'm with Tubenit in saying no to EL84 amps

I don't know why but I'd like to try build one of the Matchless 15W circuits, and as they use EL84's I guess I'm going down that road.  Surely it can't be too bad (I'll let you know :-))

I've done a couple PSE, and a QSE...

QSE; is that Quad Single Ended?  Never seen that before - sounds pretty cool, I'll have to look it up.

Thanks to everyone for their advice, I really appreciate it.

[sluckey]

how do you find the time??

That website has been going for 13 years thanks to a good hearted forum member. So, it's really only two projects per year. And I've been comfortably retired for the last 7 years so I have plenty of time.

I was really intrigued by the Lightning when I built it. But I never bonded with that amp. I could never get it to sound agreeable to me. I'm sure it's just a personal preference. May have even been due to a lack of speaker variety. The Lightning was the shortest lived amp I have built. It soon became a donor for the Vox AC-15. Now that's a keeper in my book! So is that Dual Lite. And I'm hoping my latest project, the Phoenix, which is an all American dual lite sister to the British Dual Lite is gonna be a keeper too.

how do you make it look so tidy?

I just take my time. I had a 40+ year career working with very high quality electronics that provided inspiration and set the bar pretty high for my simple projects. Big focus on reliability. All my stuff has a certain home-made look to it and that's how I like it. But you should see some of the stuff over on the Amp Garage. Man, some of those guys take this hobby to a real boutique level. Very nice looking gear!

[shooter]

I'll have to look it up.

I invented it 

I did 2 quads, the 1st was just driver and 4 EL84's for my Audio PA
the 2nd was gonna be a Clubman with the quad PA, design changed when I "found" Gibson's GA-5T that used a tranny for it's PI!  so I used a inter-stage PI tranny n 2 EL34's, self biased for the PA.  never looked back

[bmccowan]

I don't know why but I'd like to try build one of the Matchless 15W circuits, and as they use EL84's I guess I'm going down that road.  Surely it can't be too bad (I'll let you know :-))

Please don't take our comments on EL84s as anything other than personal preference. More people like them than don't. They are on the bright side - all else being equal - and I tend to like darker amps. For Hi-Fi audio I have rebuilt two Fisher mono-blocks, and a stereo power amp with 84s. And I like those better than my Hi-Fi amps with 34s, or 6L6s. So - just preferences (and prejudices too!)

[shooter]

stereo power amp with 84s

totally agree, if you keep it clean, they have a chimey clarity that does sound nice.  my QSE EL84 was a sweet audio PA.  I ran it into a pair of Audio Nirvana 8" in custom built cabs n I had perma-grin whether I was smoking or not 

[ALBATROS1234]

go for something with a pentode preamp tube. my favorite amp i have built so far is a hybrid with one channel an ef-86 and the other channel has half of a 12ax7 they combine like a 5e3 fender each having a volume with one tone knob and then go through the other half of the 12ax7 it is single ended 6v6. the volumes are interactive so you can blend the ef-86 with the 12ax7.  second favorite is a one channel amp using a 6SJ7 v1 a 6SL7 follows with a stage the the other half of the 6SL7 is a pi set up just like a 5e3 deluxe feeding 2 6AQ5s . will be experimenting more with pentodes, have used 6U8a , and have other types like 7199 and 5879 that will get put in something. pentode preamps seem to have a harmonic texture that triodes dont have and get a really nice smooth breakup. good luck

[Amped]

Please don't take our comments on EL84s as anything other than personal preference.

Thanks, yea I certainly appreciate your point of view, it just looks like a really interesting project.  I'll make a parts list and work out what I have here already (= cost to build) and hopefully I'll be in a position to build it, fingers crossed.

[Amped]

I'll have to look it up.

I invented it 

Nice work  

[Amped]

go for something with a pentode preamp tube.
...
good luck

Thanks.  Yea a pentode preamp didn't even really feature as an option until I saw a Matchless DC30 schematic.  I had to learn more...  Hopefully I can build this Dual Lite of sluckey's, I'll post back once I get approval from the war and finance committee (or I just go rogue - could get messy  ).

[Amped]

how do you find the time??

That website has been going for 13 years thanks to a good hearted forum member. So, it's really only two projects per year. And I've been comfortably retired for the last 7 years so I have plenty of time.

I was really intrigued by the Lightning when I built it. But I never bonded with that amp. I could never get it to sound agreeable to me. I'm sure it's just a personal preference. May have even been due to a lack of speaker variety. The Lightning was the shortest lived amp I have built. It soon became a donor for the Vox AC-15. Now that's a keeper in my book! So is that Dual Lite. And I'm hoping my latest project, the Phoenix, which is an all American dual lite sister to the British Dual Lite is gonna be a keeper too.

how do you make it look so tidy?

I just take my time. I had a 40+ year career working with very high quality electronics that provided inspiration and set the bar pretty high for my simple projects. Big focus on reliability. All my stuff has a certain home-made look to it and that's how I like it. But you should see some of the stuff over on the Amp Garage. Man, some of those guys take this hobby to a real boutique level. Very nice looking gear!

2 a year?  That's good going, nice work...    Your projects all look fantastic and your documentation is awesome.  I'm pretty excited about the possibility of using your schematics and notes to build something that I hope will be close to as good as you've created, and I'm truly appreciative of being provided the opportunity.  I'll run some numbers and see if I can make a case for building your Dual Lite.
Thanks Sluckey, I'll post back when I know my next steps.

[shooter]

I'm pretty excited about the possibility of using your schematics and notes to build something

They are the standard!  I take a pdf to my office supply and have them print out in color 14" height and whatever width based on aspect ratio.
aside;
I've had them do prints of some of my artwork, (I do abstract),  the 1st time I took one of Sluckey's drawings in the girl commented that that was a really cool piece of art 

[Amped]

I'm having some difficulty finding exactly the same transformer.  Do you think it would be better going for a 275-0-275 and changing the rectifier to a lower voltage drop 5AR4, or a bigger transformer 325-0-325 and use a voltage divider (or is the voltage difference not big enough to worry about)?

I did some maths - Did I butcher it or am I close?

315-0-315 Original transformer:
315 x 1.35 = 425V - (5Y3 = 60Vd) = 365V

275-0-275 Transformer Hammond 290MX:
275 x 1.35 = 371.25V - (5AR4 = 10Vd) = 361V

325-0-325 Transformer Hammond 290CEX:
325 x 1.35 = 438.75V - (5Y3 = 60Vd) = 378.75Vs
(voltage divider: R1=27R R2=680R)
378.75V x 680R / (27R+680R) = 364.3V

Got the "x 1.35" from Merlin's post #11 from here: https://el34world.com/Forum/index.php?topic=22550.0

Just to clear things up, for a typical cap input rectifier:

VOLTAGE:
For a non centre-tapped transformer you get an ideal DC voltage of 1.4 times the AC voltage. However, in practice at full load it is usually closer to 1.35 times.
300Vac --> 420Vdc in theory, or about 400Vdc in practice (diode drop further subtracts from this figure).

For a centre-tapped transformer it is exactly the same if you're talking about one half of the winding.
300 - 0 - 300Vac --> 420Vdc in theory, or about 400Vdc in practice (diode drop further subtracts from this figure).

[SILVERGUN]

I'm having some difficulty finding exactly the same transformer.  Do you think it would be better going for a 275-0-275 and changing the rectifier to a lower voltage drop 5AR4, or a bigger transformer 325-0-325 and use a voltage divider (or is the voltage difference not big enough to worry about)?

Try not to worry about getting your B+ to some exact spec. until you know exactly what you're building and what your desire is for output/breakup. It takes big differences in voltages to actually hear a difference so don't spend too much time splitting hairs over 10, 20 or even 30 volts.

The first schematic you posted is for a made up amp that no one can say how it sounds.
There are some "industry standards" for EL84 plate voltages but there are multiple reasons for that....mostly it is because most people just copy something they find on the internet. 

Higher plate voltages usually mean more input signal before clipping.

The use of different rectifiers results in different amounts of sag. Sag (voltage drop) occurs with current flow, so you'll want to learn more about that before you just pick a rectifier to get to some seemingly written in stone voltage number. If you don't care about or want/need sag then go with a solid state rectifier. Sag IS cool, so there's that.

[sluckey]

If you build my Dual Lite and use the same PT (315-0-315) that I used, then your B+ will be 325VDC at the first filter cap. That's a real world measured voltage. What does that tell you about your math and those fictitious multiplication factors?

The only multiplication factor that is real and meaningful is 1.414, the square root of 2. This is the proven mathematical relationship between RMS voltage and PEAK voltage. Those other numbers are just guesses and cannot be proven simply by knowing the value of the PT voltage. The value of the AC voltage is only one factor. The current capacity of the PT is another. The rectifier (more on that in a bit) is another factor. And the load is a big factor.

Look at your example for the 315-0-315 PT. You calculated the B+ to be 365V using a 5Y3. The math is correct but the 1.35 and 60V drop for a 5Y3 are meaningless. I used a 315-0-315 PT with a 5Y3 and actually measured 325V. Why such a difference?

You may have seen a chart that tells you that for a 5Y3 just multiply 1.2 times the PT AC to get the B+, or for a 5AR4 just multiply 1.3 times the PT AC to get the B+. etc, etc, for other rectifier tubes. Hog wash! That may work for a particular amp using a particular PT and having a certain load, but the multiplication factors quickly fall down as soon as you try to apply them to a different amp using a different PT and having a different load. The only way to know the voltage drop for a certain rectifier tube is to use the tube charts for that particular tube. For example, a 300-0-300PT and 5Y3 will give a B+ of about 350V when the load is 40mA. Increase the load to 100mA and the B+ drops to about 300V. That's a 50V change in voltage dropped across the 5Y3 simply by increasing the load current from 40mA to 100mA.

Enough of this stuff. What you really want to know is which PT to use. If I had to buy a new PT I would get Hoffman's Marshall 18W PT. It's rated at 290-0-290 and the current rating is right for a 2xEL84 amp. I would get the matching Marshall 18W OT also.

Or, if going with Hammond, get the 290PAZ. That 290MX you mentioned is meant for a 4xEL84 amp. Too big.

But I like using old Hammond iron, so I would just buy an AO-39 amp on eBay. There's one listed right now for $100 or make offer. You get PT, OT, and EL84s. That's how I built my Dual Lite.

[bmccowan]

I'll second that notion on the AO-39. I have converted more than a few of them and the iron is always solid. And in addition to what Sluckey mentioned you get a nice rectifier tube and some cool power brown devil type resistors.

[Amped]

Try not to worry about getting your B+ to some exact spec. until you know exactly what you're building and what your desire is for output/breakup. It takes big differences in voltages to actually hear a difference so don't spend too much time splitting hairs over 10, 20 or even 30 volts.
...
The use of different rectifiers results in different amounts of sag. Sag (voltage drop) occurs with current flow, so you'll want to learn more about that before you just pick a rectifier to get to some seemingly written in stone voltage number. If you don't care about or want/need sag then go with a solid state rectifier. Sag IS cool, so there's that.

Thanks Silvergun, I was guessing that a few volts wouldn't make much difference - I've seen a wide variety of voltages for valves and circuits, I guess what I need to learn is just knowing how much difference is too much in context with the specific amp.  So much to learn...
Sag - yes, as I read it a 5AR4 apparently hasn't got much where a 5Y3 has it in spades.  I'd like to keep as close to sluckey's design as possible and I guess this is going to be a big part of it too.

If you build my Dual Lite and use the same PT (315-0-315) that I used, then your B+ will be 325VDC at the first filter cap. That's a real world measured voltage. What does that tell you about your math and those fictitious multiplication factors?

Yea power supply maths and even simulations using PSU Designer II are doing my head in a bit.  I can enter all the right loads and R/C circuits and the numbers that come back don't match any of the real world measurements.  I'm either doing it wrong or missing something (maybe something to do with loads I'm adding being peak from charts - not idle loads?  ).  The maths matches PSU Designer II output too...  So with this obvious lack of knowledge what I've been doing is matching using %, ratios and experimentation - like in this example I did the maths on the 315-0-315, and tried to get as close to the same voltage as I could with other transformer/rectifier/resistor circuits.  I knew it wasn't accurate, but hoped that it was replicating the other circuit close enough that it would work, then posted here so smarter people than me will hopefully let me know if I'm right or wrong.  Probably should have explained myself better but trying to keep posts short so they get read  .  I appreciate your explanation of this in more detail, I won't make this mistake again - but please bear with me while I make many more.  I'm worth it - promise  .

But I like using old Hammond iron, so I would just buy an AO-39 amp on eBay. There's one listed right now for $100 or make offer. You get PT, OT, and EL84s. That's how I built my Dual Lite.

That would be a perfect start for sure.  I am in Australia, not too many of those over here unfortunately, I'm not sure how to get one.  I know there's services you can pay for to ship between the US and Australia, never tried that I'd expect it would be pretty pricey due to weight.  If anyone knows of a way I'd be interested to hear how they've done it before(?)...

Enough of this stuff. What you really want to know is which PT to use. If I had to buy a new PT I would get Hoffman's Marshall 18W PT. It's rated at 290-0-290 and the current rating is right for a 2xEL84 amp. I would get the matching Marshall 18W OT also.

Or, if going with Hammond, get the 290PAZ. That 290MX you mentioned is meant for a 4xEL84 amp. Too big.

I looked at Hoffman's transformers, they say they are no longer in stock.  Shame, might have been a good option, would have to see about overseas shipping costs and import tax etc. but the prices potentially looked good. 
So a 290PAZ - and the matching 1750PA 18W output transformer seem like a good option, the only concern I have (and the reason I initially discounted the 290PAX) is that the 6.3V supply is only good for 2A.  Heater supply for the valves calculated out at 2.32A, I wasn't sure if it was too much.  Can I go over the current rating a bit on the 6.3 supply and get away with it?

[Amped]

Back to the silly questions;

#sluckey you mentioned the 290MX was too big; I (probably mis)understand this concept, I thought that if the voltage was OK, and current was enough or greater, it would be OK to use.  Is their other factors I'm not taking onto account?  Relates to question below...

If I have trouble getting the 290PAZ transformer (out of stock at my local supplier), would the 290CEX and 1750PA combination be OK to use - or too big still?

Also - I have a few F&T caps I acquired, can I use these instead of the can cap in the diagram or am I best to use the 32-32uf can?  I have; 2x47uF, 1x30uF, 2x22uF, 2x10uF (all 500V), and 1x100uF (450V).  The 5Y3 (can only find 5Y3S and a Sovtek 5Y3GT at my local supplier) rectifier looks like it's rated for 20uF and I'm guessing ~30 is still OK, but can I get away with 47uF at the filter?
47-47-22-22
or
30-47-22-22
or
buy another 30 (30-30-22-22)
or
bite the bullet and buy a 32-32nF (only $25) can?

Lastly; coupling capacitors/tone capacitors in the nF range; I'm looking at Polypropylene axials for the Dual Lite schematic - I know as long as the voltage is greater it is usually OK, but what if they are for high voltage, like 1.6kV?  Still OK?  (e.g. Panasonic ECW-H16102JV 1000pF)

[sluckey]

The 290PAZ has a 6.3VCT @3A. It will work just fine.

https://www.hammfg.com/files/parts/pdf/290PAZ.pdf

[sluckey]

If I have trouble getting the 290PAZ transformer (out of stock at my local supplier), would the 290CEX and 1750PA combination be OK to use - or too big still?

That's fine. In fact any of those PTs that are advertised for a 2 x EL84 amp are fine.

I only said that 290MX is too big because you will be buying a new PT and you may as well buy a proper one. If you use that 290MX in a 2x84EL amp your B+ will be higher than you expect and you will probably start a thread some day that starts with "Help. My B+ is too high". Or how do I lower the B+ on my amp.     Having said that,,,  ***IF*** I had to choose between a 290MX that's already sitting in my parts bins and a 290PAZ that I must buy, I would use the 290MX to build the dual lite.

Here's the deal... That 290MX is rated at 275-0-275 @ 230mA. The 290PAZ is rated 290-0-290 @ 140mA. Voltages from each amp are fine for a 2xEL84 amp. So look at the current rating. That 290MX has a much higher current rating (because it was designed for 4xEL84s. The higher current rating is obtained by using larger wire. Larger wire has less resistance/foot than small wire. Therefore the 290MX will have less internal voltage drop when a load is applied. This means that the 290MX will likely put out more voltage than the 290PAZ if used with the same load.

I would not connect a cap bigger than about 33µF to a 5Y3. Out of those you listed I would use the 22s.

I'm not picky about coupling caps. Others are and that's OK. I'm fond of those brown chicklet Xicons because they are small and cheap and work just fine in my layouts. High voltage caps are OK but usually cost more and are bigger. They may not neatly fit on my board. I like the 1/2w metal film resistors because of their low noise and skinny leads. I can easily get four leads in one turret and my layouts are designed with that in mind. Look at that "crow's foot" in the center of my dual lite board. Use any other kind of resistor and you will likely have to wrap some of them around the turret. Still works the same but may not look as neat.

These are just some of my ideas. There a plenty of other ways to successfully build this little amp. The main things are work with the tools and components you have available. And most of all, have FUN. 
 

[Amped]

Wire diameter - current rating - internal resistance affecting voltage drop...  There you go, some missing piece(s).  Cheers sluckey! 

3A...  So it is.  My mistake, the website I was looking at has an error and I didn't double check the spec sheet.

That all makes sense, and I definitely appreciate your help.  I'm really looking forward to building this, hopefully not too many more silly questions 

[sluckey]

Not silly at all. I would never type that much for a silly question. 

[vampwizzard]

your B+ will be higher than you expect and you will probably start a thread some day that starts with "Help. My B+ is too high".

Been there. Done that LMAO.

Make sure you get a PT to match the voltage coming out of the wall. And like Slucky says.. have fun! get your hands dirty and stay un-electrocuted.

[PRR]

> internal resistance affecting voltage drop...  There you go, some missing piece(s).

All power sources sag. When I run my well-pump my lights dim. When all of LA runs their A/C, Hoover Dam sags. Our size PTs sag about 20% from no-load to full-load. The voltages are cited for full-load.

If you run a PT at half-load you may only have 10% sag. Voltage higher than you expect. More to the point, you are paying-for, shipping, and lugging twice as much iron as you really need.

If iron-in-the-hand is oversize but never has to be lugged, and half-load voltage is acceptable, oversize may be fine. If you play 4 different venues every weekend, you may want more right-size for luggability.

[Amped]

Hi again all.

It's been a while, I thought I'd post an update.  I've pulled the trigger today and ordered all the parts for a Dual Lite 18W (had a tip-off, was waiting for a sale to come up).  Some parts are on back order so it may take a few weeks for the order to arrive but this is what I've gone with:
https://www.evatco.com.au/18w-tmb-kickstarter-pack
This starter pack comes with PT/OT, chassis, a turret board and faceplates.  Was an easy starting point and the chassis is thicker than the one I was going to get (those Hammond chassis are pretty thin), not exactly the same layout as Sluckey's Dual Lite plans however, pretty close so I'm hoping I can shoe-horn it in. 

When my parts arrive I'll start another post and document my progress.  Slightly nervous, but thanks to you guys I recon I can build this.  I'd like to thank you all for your support so far, I really appreciate it.

I'll try not to electrocute myself - one hand in pocket...