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Old 30th May 2004, 09:56 AM   #1
diyAudio Member
Join Date: May 2001
Location: Denmark
Question what tube replacement 6550??

Hi I have buyed a all tube bass amp 300W at ebay when i got it the output tube had broken durieng transportation.


So i have to replace with 6 match new tubes 6550.
the tube that was inside was from ruby tube's

now im not sure what tube is best ´reliebel i know that groove tubes are used in ampeg svt.

does any body know what is the best tube if the price is not to high i'll be happy

thanks jc dk.
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Old 31st May 2004, 09:49 AM   #2
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Location: Newcastle, Australia
I'd stay away from the Ruby tubes - they are mostly Chinese origin. GrooveTubes can use a variety of sources, and this is reflected in the price of the sets, and they have the advantage of being sold in matched sets. In practice, I don't find matching tubes makes a big deal of difference, but stay away from Chinese tubes. Quite a lot of suppliers have Sovtek or Svetlana brand tubes in single units at quite reasonable prices, and these will work well.
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Old 20th July 2004, 05:06 PM   #3
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as i said before i have this eden amp that i need to re tube the output stage. 6 match tubes.

can i choose any type of 6550 tubes?

i thing i'll buy tube amp doctor or svetlana any coments on that?

i don't know much about tubes and the diferent sound they might produce compared to each other. any help is welcome

thanks JC> DK
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Old 23rd July 2004, 09:54 AM   #4
tuneman is offline tuneman  Australia
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from the site it says its availible with either 6550's or EL34's, so you can use it with either if it has a small selector switch on the back to change between preset bias's.
if it dosent' the bias has to be changed inside the amp for it to use EL34's.

as for which brand! its hard to say' usually theres not much difference in sound between them, although the chinease and cheaper ones can sometimes sound thin' and usually dont last as long due to poor construction.
I use 'Electro harmonix' EL34's i think there excellent but i don't know where there made though, one thing i have found is you need to by good preamp tubes cheap ones can cause really bad feedback! so any of the good russian or american brands will be ok, although i have some groovetubes that are chinese! so they get them from anywhere, carnt say i was that impressesd with them.
you are best to get the 6550's and see what they sound like if you havent heard them before, then mabe switch to el34's later to see how they compare in sound, there usually very 'marshall' sounding crisp, with a very tight bottom end!
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Old 23rd July 2004, 10:23 AM   #5
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Location: Rosmalen, The Netherlands
Hello Partyjups,

That's a great amp! I'm using a Trace all tube bass power amp that uses the same complement of tubes (6x6550). I think this is THE way to amplify bassguitar.
As to the difference in sound between different types of output tube, in "the tube amp book" by Aspen Pittman (of Groove Tubes) he says EL34 are a bit "warmer" while 6550's are "edgier" of course he refers to guitar sounds. For bass I'd guess I'd go for "edgier" because I associate "warmer" with vintage gear like Ampeg Portaflex and Fender Precision, which is not my thing (and I guess not yours either, if you buy Eden).
Of course, by switching to EL34's you also turn your amp into a 150Watt amp (the weight, however remains backbreaking, at least with my amp it is (35kg)).
As for much matching of the tubes, I think you only need matched pairs, but I'm not sure of this (and if somebody knows more about this I'd like to know because one of these days I myself also need new output tubes). I opened my amp, a while ago, and what struck me was that there are actually differently shaped output tubes in mine, hence my conclusion that you only need three pairs (instead of one set of six).
If somebody has got a schematic of these amps, I'm interested. Posted a thread last week, zero response

Good luck with your amp, it's a shame it was damaged during shipping (it's amazing because 6550 are actually quite sturdy)


Oemptempa petoempetapap
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Old 23rd July 2004, 10:30 AM   #6
dhaen is offline dhaen  Europe
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Although it is available for 6550 or EL34, there will be differences in the bias arrangements. You can't just plug a different type in.
If you require more advice, ask a moderator to move this thread to the 'tubes' forum. There are many experienced people there
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Old 23rd July 2004, 11:03 AM   #7
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Location: Newcastle, Australia
Originally posted by tuneman
I use 'Electro harmonix' EL34's i think there excellent but i don't know where there made though

The Electro Harmonix are usually rebranded Sovteks, but selected for particular qualities (sound wise).

Different brand / type tubes in the output stage should be avoided, but if absolutely neccessary, then should be installed to keep the output "balanced". If your amp has 6 tubes in a row, then the first 3 will be parallelled on one side of the output transformer and the other 3 on the other side of the transformer. Therefore, make sure the two "inner" tubes are the same (ie numbers 3 & 4), the next outer pair the same (numbers 2 & 5) and the outermost the same (1 & 6). IF you ever have to run the amp with less tubes (say one gets broken), then run it with one PAIR less, selected as above.

Quite often, different tube brands will require different bias settings, and the mixing of brands can result in some tubes hogging the power and possibly being overtaxed. NEVER mix Russian and Chinese tubes - asking very short life from one of them.

As for brands, Sovtek or Svetlana for unmatched sets, ElectroHarmonix or the more expensive Groove Tubes for matched sets (if you can't get a matched set of 6, then get 3 matched pairs and install them as indicated above).

BTW, the EL34 will overdrive at a lower volume level than the 6550, which is why it is usually preferred for guitar amps - the 6550 would be more suitable for bass where you want the cleanest sound up to maximum volume.

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Old 23rd July 2004, 11:55 AM   #8
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Location: Rosmalen, The Netherlands
Most of the bigger tube poweramps have some scheme where you can switch to lower power levels, my Trace Elliott switches between 2, 4 or 6 tubes (although there are other ways of obtaining different power levels, Seymour Duncan Convertibles use another scheme).
Oemptempa petoempetapap
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