Miles's Taste Tests for 6BQ5 / EL84
OverviewI got five new EL84/6BQ5 (the EL84 was the European designation; the 6BQ5 was the USA designation) type tubes from Lord Valve, Ned at Triode Electronics and Jim McShane . for comparison purposes. I also had an old Raytheon that we still use in my son's Model 1 Kalamazoo, because it sounds so nice.
Tech NotesAccording to the RCA tube manual, a single 6BQ5 can produce up to 5.7 watts, with 10% THD. The design center maximum ratings were 300 volts on the plate, 65mA cathode current, and 12 watts static plate dissipation. The Kalamazoo Model 2 runs about 270 volts on the plate, with around 45mA plate current, or roughly 50mA cathode current. The amp is cathode-biased, and all the tubes pulled between 47mA and 52mA at the cathode, so I didn't worry with rebiasing.
EquipmentI compared these power tubes in a Kalamazoo Model 2, a point-to-point, single-ended (true Class A 8^) practice amp from the 60s. This amp has all new caps, a new 6X4WA rectifier (through a typical, multi-stage capacitance filter), and a Sovtek 12AX7LPS in the preamp section. It has a single volume and tone control, and a 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" vintage speaker of uncertain origin.
The primary guitar was a Hagstrom 1 with two DiMarzio SDS-1s and completely flexible pickup selection. I also used a BC Rich ST Platinum (Strat clone) with a humbucker in the bridge slot.
CaveatsThe Kalamazoo Model 2 is fairly representative of the sort of single-ended practice amps these tubes are commonly used in, and in fact has recently become a mild collector's item because it can be made to sound so good. The results here may or may not apply to your specific amp, especially if it uses a push-pull output stage with two or four EL84s. I would love to compare these in a VOX, but don't have one available.
I played for 15 - 30 minutes, minimum, per tube. Most tubes got much more play time, in particular the Raytheon, Tesla, Sovtek 6BQ5 and EI.
ResultsThere were some obvious leaders and an obvious trailer. There were no complete duds, but one of the tubes didn't impress me very much.
- 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.
RankingsThe Raytheons are my favorites, with the Sovtek 6BQ5 and Tesla more or less tied in a reasonably close second. The Ei EL84 comes in a solid third and the Sovtek EL84M comes in last. The EL84M isn't horrid, but it's not real exciting, either (although I would consider it for a jazz sound). The Tesla wins out slightly in terms of dynamics and is the brightest, but the Sovtek 6BQ5 wins in most other 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 Sovtek 6BQ5 in the Model 2, with the Tesla as a backup, and vice versa. Then Jim told me about his Raytheon stock, and the NOS Raytheon claimed the working spot in the amp. The old Raytheon went back into my son's Model 1.
These results were also posted in the alt.guitar.amps newsgroup.
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