El 84 Single Ended Guitar Amp

A Decware EL84 Zen Amp clone

Making a low power single ended amplifier has always been in my designing plans. Obviously such a construction requires the appropriate speakers, particularly horn type designs, so that the output of the amp can reach an efficiency satisfying level. Once at a certain point, I came across the designs of the Decware SE EL84 Zen amp, which had quite good reviews among the tube amps DIY and Single Ended tube amp builders. This simple and clever design was exactly what i had in mind. The most convenient way to develop my idea was to use an already existing design.

May 13, 2005 I built a single ended EL84 little amp last week. Its a hybrid of many things, but probably closest to an 5F1 champ with solidstate rectifier and an EL84 instead of a 6V6. I expected to have some hum since it is single ended - I even left out a pilot light to keep things isolated as much as possible in a 6 x 10 x 2 aluminum chasis. Mar 15, 2021 11+ El84 Amplifier Schematic. 6w tube amplifier project single ended el84 6p43p ecc83. The golden ear amplifier is not a particular amplifier as most seem to believe, but a series of schematics by joseph marshall. 6W Tube Amplifier Project Single Ended EL84 6P43P ECC83 from 320volt.com. Schemat kt ry za czam stworzy em na podstawie.

Tube amp diy

Chassis are made of wood, and i build the whole construction in an aluminum plate (3mm thick). All parts are mounted on the aluminum plate. Finally i coated the aluminum plate with plexiglass (acrylic sheet colored dark gold) I ordered the output transformers in a local workshop, (Greece / Thessaloniki). All tube sockets are porcelain, and all the critical paths wired using silver-teflon cables. I also used metal film resistors, and WIMA capacitors. The whole circuit is very simple. It is a common cathode design with the 6922 tube driving the power stage with EL84. I changed only the two cathode resistors (150Ω /8 watt) with heavy duty type for heating resistance. In the Power supply I used the 5U tube for rectifier according to Decware manual.

How it sounds this tube amp ?

This simple EL84 tube amp meet his first 'crash test' when we put it in the same rack with the GRAAF GM20. We connected it with George's Valmas Coherence II Jeff Rowland pre amp, and we used George's Amati Homage loudspeakers. Clear voices incredible solo's unbelievable mid and high - frequencies ! absolute separation and purity not expected! But .... we needed POWER ! If you have horn loudspeakers in your living room then its time to build this EL84 tube amp... 'monster' because ... sound does matters ! costas sarris acknowledgements :

El 84 single ended guitar amp set
  • Decware Zen EL84 Amp
  • George Valmas for his effort

Overview

I got five new EL84/6BQ5 (the EL84 was the European designation;the 6BQ5 was the USA designation) type tubes fromLord Valve,Ned at Triode Electronics andJim McShane .for comparison purposes. I also had an old Raytheon thatwe still use in my son's Model 1 Kalamazoo, because it soundsso nice.

Tech Notes

According to the RCA tube manual, a single 6BQ5 can produceup to 5.7 watts, with 10% THD. The design center maximumratings were 300 volts on the plate, 65mA cathode current,and 12 watts static plate dissipation. The Kalamazoo Model2 runs about 270 volts on the plate, with around 45mA platecurrent, or roughly 50mA cathode current. The amp iscathode-biased, and all the tubes pulled between 47mA and 52mAat the cathode, so I didn't worry with rebiasing.

Tubes

Equipment

I compared these power tubes in aKalamazoo Model 2,a point-to-point, single-ended(true Class A 8^) practice amp from the 60s. This amp has allnew caps, a new 6X4WA rectifier (through a typical, multi-stagecapacitance filter), and a Sovtek 12AX7LPS in thepreamp section. It has a single volume and tone control, anda simple tremolo which was not used for this test.It has a beefier output transformer than stock,and was tested through an open cabinet with a single, 12' vintagespeaker of uncertain origin.

El84 Single Ended Guitar Amp For Sale

The primary guitar was a Hagstrom 1with two DiMarzio SDS-1s and completely flexible pickupselection. I also used a BC Rich ST Platinum (Strat clone)with a humbucker in the bridge slot.

Caveats

The Kalamazoo Model 2 is fairly representative of the sortof single-ended practice amps these tubes are commonly usedin, and in fact has recently become a mild collector's itembecause it can be made to sound so good. The results heremay or may not apply to your specific amp, especially if ituses a push-pull output stage with two or four EL84s. Iwould love to compare these in a VOX, but don't have one available.

I played for 15 - 30 minutes, minimum, per tube. Most tubesgot much more play time, in particular the Raytheon, Tesla,Sovtek 6BQ5 and EI.

Results

There were some obvious leaders and an obvious trailer.There were no complete duds, but one of the tubes didn'timpress me very much.

The Tests

  • Ei EL84 - This tube seemed slightly down on power compared to the others at first, despite drawing similar idle current. I later realized this was partly because it needed to warm up and partly just the fact that it followed the loudest tube. You also have to push it slightly harder before it starts pumping out any power. It had a sweet tone, but not quite as bright as the Tesla. Tons of creamy midrange. It broke up early and quickly, so I suspect it may prefer a higher plate voltage. It had good definition with chords. Single note lead tone was good, but playing chords when overdriven didn't have a lot of crunch. It definitely needs to warm up to yield its best sound.

    Appearance: This tube almost looks like a clone of the Raytheon, except that it has an even smaller bottle. The logo (circled 'Ei', Yugoslavia, EL84) is rather crude, as if it were put on with a rubber stamp in off white.

  • JJ/Tesla EL84 - good all around sound, brighter than the others but not at all shrill. Very warm clean sound. Excellent dynamics and sustain. Good definition on chords. Breaks up gradually. Perhaps the loudest of the lot. Good crunch, but not quite as good as the Sovtek.

    Appearance: Slightly fatter than the Ei, with only the JJ logo and 'EL84' in red ink. The best looking of the new tubes tested here.

  • old Raytheon 6BQ5 - Good clean sound. Loud. Excellent dynamics. Breaks up gradually and thoroughly into a wonderful, snarly crunch. Warm, not quite as bright as the Tesla. (Remember that this tube is 30 - 40 years old, with a lot of hours on it.)

    Appearance: A little taller and wider than the Ei, this tube is the cleanest looking of those tested. Some of the paint is faded, but it is clearly and cleanly marked with the Raytheon International logo, '6BQ5', and 'Japan' (!), along with various faded runes.

  • NOS Raytheon 6BQ5 - Just like the old Raytheon except slightly brighter. Very quiet.

    Appearance: Similar to the above tube, but all there. 8^) A faint, boxed '6BQ5/EL84' at the top. Below that, a faint, yellowish Raytheon in a clear oval cut from a faint, yellowish rectangle, with 'Registered' beneath that in the same color. On the back, across the top mica spacer, it says 'N-20' in gray, with a smallish 'JAPAN' 1/2 inch below that.

  • Sovtek EL84/6BQ5 - Very full sounding, plenty of range. At clean levels, this was the most transparent tube, capable of delivering a very Fender-like sound. Good definition, great tone, very good dynamics (only slightly compressed when clean). Breaks up gradually and turns into a raging crunch tone monster. Stays clear no matter how hard it's pushed, and as it moves into overdrive, it gets brighter with great harmonics. It even sounds good cold. I've been told these can get noisy pretty fast, but so far the only time I've heard this one sound funky is just as it comes on line, and at shutdown.

    Appearance: Large bottle, with lettering in faint gray. 'EL84/6BQ5', 'Sovtek', 'Made in Russia'. Has a number (e.g., '18') molded into the base.

  • Sovtek EL84M - Very warm, tons of bottom end, not very bright. Good definition at clean levels, with a great single note, jazz lead sound. The dirty sound is just OK, and it muddies up fairly quickly. Fairly compressed, good sustain but some loss of attack. Pulls a little more current than the other tubes in the Model 2. This is most definitely not a 7189, but is made to run at the higher voltage of that tube. For higher voltages, this may be your safest bet.

    Appearance: Same large bottle as the Sovtek 6BQ5, but more legible lettering: 'EL84M', 'Sovtek', 'Made in Russia'. Has a number (e.g., '15') molded into the base.

Rankings

El 84 Single Ended Guitar Amp Set

The Raytheons are my favorites, with the Sovtek 6BQ5 and Teslamore or less tied in a reasonably close second.The Ei EL84 comes in a solid third and the Sovtek EL84Mcomes in last. The EL84M isn't horrid, but it'snot real exciting, either (although I would consider itfor a jazz sound). The Tesla wins out slightly in termsof dynamics and is the brightest, but the Sovtek 6BQ5 wins in mostother areas I can think of. I'd suggest getting both if you can,and seeing which works for you. I was torn between leaving the Sovtek6BQ5 in the Model 2, with the Tesla as a backup, and vice versa.Then Jim told me about his Raytheon stock, and the NOS Raytheonclaimed the working spot in the amp. The old Raytheon went backinto my son's Model 1.

These results were also posted in thealt.guitar.ampsnewsgroup.

El84 Single Ended Guitar Amp Layout

Last updated: 09 January 2002
Taste Test copyrighted Y2K by Miles O'Neal, Austin, TX.Incidentals copyright Y2K Miles O'Neal, Austin, TX.All rights reserved.Miles O'Neal<meo@XYZZY.rru.com>[remove the 'XYZZY.' to make things work!]c/o RNN / 1705 Oak Forest Dr / Round Rock, TX / 78681-1514