Advice on < 30 watt EL84 new build

Planobilly

Member
2015-12-11 4:35 pm
Hi guys,

I am about ready to build a EL84 based amp. I would like to build something that sounds like a Zinky Blue Velvet. I have never seen a schematic. Perhaps Bruce Zinky would give me one. Here is a link to a demo video. It may not give you much of an idea what a Zinky really sounds like.

https://www.youtube.com/watch?v=JSQKGUb_mKc

I want to build just a head as I have several speaker cabs I can use.

I am looking for ideas and recommendations and schematics for these types of amps. I don't need or want a lot of volume. 25 watts or less would be fine.

Requirements:

Good warm clean sounds
Overdrive channel but not super hot
Tube reverb
Master volume
Normal tone stack, it could have two tone stacks
Perhaps switching between low watt output and full power
Built on a turret board
diode rectification...could have both tube rectification and diode
Perhaps usable with both EL84 or EL844
The amp will only be used in my home studio...so weight is not an issue
Budget= $1200 to $1500

First class components...which I would buy from my normal suppliers

All ideas welcome.

Thanks,

Billy
 

Planobilly

Member
2015-12-11 4:35 pm
Hi Mozz,

For sure you can pick up one used for around $800. I have had two of them in the past. I want some other features that do not come on a Zinky. The Zinky is built on a PCB which could be modified I guess but not what I want to do. The Zinky example was just to give some idea about the generaal type of sound I am looking for.

This project is not about cost, well to a certain extent at least.

I want to use certain components, Merren transformers, Clarostat pots, F&T filter caps, and other things I have found I like.

Thanks,

Billy
 
Hi Guys

I would seriously think about the EL-84 choice versus octal-based tubes. With EL-84s, you have one basic tone even if you switch to E84L, EL844 or N709. They all sound about the same.

On the other hand, there are a tonne of pin-compatible octals that you can use in pairs or mix to explore a wide range of textures. You can get tones very much like EL-84s using octals. Keep in mind that using a physically larger tube or one with high ratings doe NOT mean the amp will be more powerful. Rather, it may just play cleaner louder but maximum power won't change.

Turrets look nice and are good for a finished design that isn't going to change.

Terminal strips are the quickest to wire but difficult to change parts or do mods with.

Eyeylets are the easiest to service and to change values. The eyelets can be placed on the board wherever is handy to match the component sizes, as Fender did in their early amps.

I would NOT use F&T caps - especially multi-section ones. The latter contradict proper grounding principles and in most cases these types of cap are not as good quality as a long-life Nichicon, Panasonic, or similar. TUT3 discusses all of this in detail. Also avoid axial-lead electrolytics as they have twice the imperfection of radials.

Of course, as you say, you like some of these things and you are perfectly correct to do so and to use them. There are ways to use them that do not compromise grounding, though, which is also shown in the book.

Whether you use the EL-84s or octals - or a mix of 9-pin and 8-pin -get the power supply and power amp running first, then add a clean preamp and build the distortion tone from the clean sound. Do not skimp on the number of preamp tubes, but as a guide: the best clean sounds use two stages or more; the best distortion sounds use three stages or more; you do not need more than four stages to have the wildest saturation you can imagine. So, two dual-triodes dedicated to preamp functions unless you want separate tubes for the different sounds; the best reverb sounds use two-tube circuits.

Anything you put together you can rip apart and redo, so expect to have to do that to some extent particularly if you are exploring a lot of tonal options.

Remember too that the 12A_7 family has four commonly available members and you can change the raw gain simply with a tube swap.

Have fun
 

Planobilly

Member
2015-12-11 4:35 pm
Hi Struth,

Thank you every so much for the ideas. Nothing is set in stone with me. I only mentioned EL84 based amps because of one I have played a lot and like. Bruce Zinky has always been a great guy to deal with.

As I get a better idea of what exist and what options are out there I can make better decisions of what to build. Not having a lot of experience with amp building I have been a little hesitant to just build everything myself from scratch.
I though it perhaps better to buy a kit or two. I don't need another amp to play through but at the same time I don't want something that does not sound good or work well. I am way past the point that I need a "starter kit" to learn how to solder or put things together.

As I have been thinking about all this more, what I think I really want is a test bed of sorts that will let me experiment with a lot of ideas. Perhaps the octal idea is really the best solution.

I was a bit surprised about your comments about F&T caps. I am not in love with any brand but I have used a lot of F&T axial caps to repair amps for clients with out any issue. If there is something better I am more than willing to give it a try. I buy Nichicon, Panasonic, all the time but just never used them for typical filter cap replacement in Fender amps for example.

I have kicked around the idea of building a chassis with a bolt on plate. I have the tooling to machine holes but no sheet metal break. That would make it easy to just cut a new plate to change position of tube sockets and transformers. Just thinking out loud.

Thanks,

Billy
 

Gnobuddy

Member
2016-03-01 4:10 pm
Could be a matter of how progressively (or not) audible distortion sets in. For instance, if you add some negative feedback, the amp will stay relatively clean until it gets close to maximum output, and then break into distortion fairly abruptly.

By contrast, design for gradual and progressive distortion, and you can make an amp that starts to distort gently even at low output, and gradually gets more and more distorted. Most guitarists would say that amp had little clean headroom.

This is all based on the assumption that "maximum power" for a guitar amp means "heavily overdriven till the output is virtually a square wave".

If you use the standard Hi-Fi way of specifying maximum power (no clipping allowed, i.e., amp is still completely clean), then, of course, your point makes perfect sense.

-Gnobuddy
 
Hi Guys

If you have an amp rated at 10W, you can use 6V6s and get 10W or 6L6s and get 10W. The V's will sound "creamy" or "muddy" compared to the "clean" or "flat" sound of the L's, depending on which sound you prefer and/or of your impression of each tube's sound.

The PSU and OT set the limit for power. It is usually the case that the low-power rated tube distorts much more as it gets to its power limit than does a lager tube. This difference is made more obvious in a low-watt amp where you can try out either.

Do not be fooled by those who say these differences are caused by some "less than optimal" loading for one tube versus the other in the given amplifier as such statements belie a huge lack of understanding about tubes and impedance.

"Clean" as I use it does not mean anything more than the word implies. Each tube has its own character and you can hear the difference between tube types at low levels very easily. An amp like a Fender Deluxe is rated for 25W but actually provides 17W of clean sine wave power. If you sub in 6L6s and run them at the same 17W, you see a clean sinewave on the scope. The scope tells you both are the same but that trace hides 5% THD easily and does not show you what the tubes do with complex signals. Plug in a guitar and you hear the 6L6s staying cleaner up to the 17W point. The V's get progressively muddier/creamier up to the 17W the scope says is "clean". Your ears hear something else.

Lots of players have put 6L6s in their Champs and Deluxe reverbs to the peril of the PT. They don't get more output but they can play the amp louder cleaner so it feels like they've got more power. This is an especially prominent effect in cathode-biased amps.

So, we have stayed away from the amp's clipping point as that is obviously not a clean sound. You do not even have to get to the cusp of compression or anywhere near those levels to hear the differences of how much cleaner the larger tube stays compared to the smaller one when both are played to the same loudness.

EL-84s and EL-34s have a similar tone. If you take an AC-30 and modify it to support EL-34s, you hear the same effect. Where the 84-tone turns to mud about a third of the way to full power, the 34's stay clean up to full output then clip.

Officially, power ratings for guitar amps are no different than for hifi amps. It is maximum clean sinewave power. Some companies will list the THD at the rated output - PV uses 10%, for example. Many builders just "ball park" it. Others rate output with slight flattening of the output, others well below even the maximum clean sinewave point. So, there is a wide and vague field of numbers for players to be dazed and confused by.

It is often said that MI builders aim more often for maximum output from a tube than do hifi builders, but this is not true. That aim occurs just as frequently in both worlds. What you see more frequently in MI is the use of under-sized OTs - something I do not do and do not promote. Such a choice has a huge impact on the clarity of tone as full output is approached and also makes the loudest sound from the amp inherently different from quieter ones, all else being equal.

Have fun
 
Hi Guys

How to make this as plain as possible:

The load impedance does not matter for such an evaluation.

The range of acceptable loads for each tube greatly overlaps the range for every other tube. There is no "single" or "magic" load impedance for each tube type - such a notion is hogwash.

If the amp you have or build can use 6V6s safely AND has enough heater current to support an EL34, then the amp will work with ANY of the common pin-compatible tubes. Adjust the idle current to a value that turns the tube 'on' and does not sound obviously distorted BUT make sure this does not exceed the plate power rating.

Similarly, if you only have a large amp but it has adjustable bias for each socket, then you can plug in ANY tube including 6V6 PROVIDED you are not trying to play the amp flat out. Amps like the older Fender Twin Reverb rated at 100W have the same voltage environment as a Deluxe Reverb. You can plug in 6V6s pretty cavalierly and it is safe. The V's will produce 48W, as TUT shows, and idle at a current appropriate to themselves - the beauty of chance: two RCA-designed tubes that have identical control-voltage requirements. If you like the sound you can run the amp this way forever with no stress on the tubes or the amp.

Each tube has its own character and you hear it at ALL signal levels. As long as you can bias the tube within its limits in the test amp, then you can compare any tube you want to at modest loudness. You have to respect the tube's power and voltage limits to test at significant power levels in higher-voltage amps, say >540V. All the common tubes are fine at these voltages.

And again, the load impedance does not matter.

Have fun
 

Printer2

Member
2010-04-02 6:34 pm
The reason I asked about the impedance is different tubes have different distortion profiles at different impedances (that is diff to the 3rd, :spin: ). Didn't want to bias the experiment in favour of one tube or the other. Have a 25W (minimum) OT from a Wurlitzer organ, think it is suppose to be 6.6k, will have to measure it.

Still, I am wondering about how much audibly cleaner it can be with the bigger tube. It is not like we play clean anyway, what ratio of cleans do we get, 3dB, 6dB? Won't be building this one till fall most likely. Wallowing in the acoustic guitar world for now as I can build in the garage.