Best 6550s for Marshall Super Bass

R

Rickenhofner

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Jun 11, 2012
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#1
Looking for everyone's take on what 6550s are "best" and what sonic differences they offer in a Marshall Super Bass.

My story: I just acquired a '73 PCB Marshall SB 100 that had fresh EH 6550s in it. Using this primarily for guitar (no surprise there). Amp had incredibly broad range of response on bass control, fair amount of dirt even at volume around 1-2 on either channel or bridged channels.

Ran the SB through a Power Soak, dimed amp, choked attenuator to lowest setting ... fizzle, pop, nothing. Replaced 4 amp fuse and took to tech. Tech said one of EH tubes blew and made remark about them being Russian crap. Without really consulting with me as to the sound I was going for, he decided to go with Ruby Tubes because he likes them and has good luck with them.

Now, the amp sounds quite a bit cleaner, I feel, and the bass control does not feel nearly as responsive as "rangy" or "big" as it had.

I've since found a couple of comparisons of 6550s:

6550 Tube Selection Guide - Tubes for Amps
www.thetubestore.com - 6550 Tube Types

Your thoughts? Thx!
 
#2
What kind of ruby tube? Ruby is a rebrander, they don’t make tubes they just test and package them. They might be the same “Russian crap” that was in there before, or could be some vavle art/Chinese production. Or could be rebranded JJs. Might also want to look into KT88s.

Edit - the only Ruby 6550 currently listed on their website looks like the valve art 6550 so it could be those. I have an older set of ruby branded winged C's and they do sell ruby branded JJ and new sensor in other tube variants but I'm not seeing much for 6550s.

Properly biased (before and after) I wouldn’t expect huge changes in sound from just a power tube swap though. More of degrees of subtlety. Did the tech do any other work on the amp? Change any preamp tubes?
 
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#4
A very good question...was it the EH's or the fact that one of them was on the way out causing you to enjoy the sound? Rubys are just rebranded other types of tubes, so it's very possible that they're Russian, too. Sounds like your tech needs to get with the now...all new tubes are made in Russia, China, or Czech Republic.
 
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#5
coreyfyfe said:
What kind of ruby tube? Ruby is a rebrander, they don’t make tubes they just test and package them. They might be the same “Russian crap” that was in there before, or could be some vavle art/Chinese production. Or could be rebranded JJs. Might also want to look into KT88s.

Edit - the only Ruby 6550 currently listed on their website looks like the valve art 6550 so it could be those. I have an older set of ruby branded winged C's and they do sell ruby branded JJ and new sensor in other tube variants but I'm not seeing much for 6550s.

Properly biased (before and after) I wouldn’t expect huge changes in sound from just a power tube swap though. More of degrees of subtlety. Did the tech do any other work on the amp? Change any preamp tubes?
Click to expand...

Sorry, should have noted they are 6550ASTRs. Tech did not do any other work that I am aware of ... but he also never asked me at any point what sound I was going for, what style(s) of music I play, etc. Just told me that was going with Ruby Tubes unless I could exchange the EH tubes if they were under warranty. EHs had just been put in by the person who sold me the amp, only about a month ago.
 
#7
Rickenhofner said:
Sorry, should have noted they are 6550ASTRs. Tech did not do any other work that I am aware of ... but he also never asked me at any point what sound I was going for, what style(s) of music I play, etc. Just told me that was going with Ruby Tubes unless I could exchange the EH tubes if they were under warranty. EHs had just been put in by the person who sold me the amp, only about a month ago.
Click to expand...
Tube quality is a lot better than it used to be, but you can still get a dud right out of the gate.
 
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#10
Rickenhofner said:
That's a take I had not heard; usually it's all NOS or nothing. It's certainly heartening if tubes are of better quality now.
Click to expand...
There are always going to be people who say that, and there are certain tubes I will still say that about, like the 6SL7 and the 12DW7. But for the more common tubes, NOS supplies are ridonkulous expensive, getting depleted, and I really don't know if there's much advantage to getting them anymore, as I've had some failures with them as well. For the 12a_7 series, 6550's, and 6L6GC's, I doubt if I'll ever go NOS again. I think some of the new ones are about as good as anything made in the old days. But you'll still get a dud occasionally.
 
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#13
I like the Svetlana and Tung-Sol 6550. The current Tung-Sol offerings in general are very good. What’s important is buying from a reseller the burns in the tubes and then matches them well. This helps avoid early issues. Matching to a high standard is something that you want.

www.thetubestore.com - 6550 Tube Types

The Tube Store is good. Also check out 6550 | Antique Electronic Supply with their Apex matching system.
 
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#14
My take. If I'm in the studio and some NOS have some specialness then why not? If I'm gigging then I need a replacement that I can actually get to
resupply my backups.

I tried NOS JAN RCAs in a Monique. They sounded sweet and had a different and superior quality when playing one note. The OEM Shuguangs actually sounded better when playing actual music. You know, one note after another. Novel concept I know!

Whether using the NOS or new tubes a brand new EH rectifier was the ticket. Where the RCA NOS had the sag guitarists love, the EH was tight like bassists tend to love. This allows for clear dynamic changes and punch.

I want my pre to be consistent between stage & studio and from Wichita to South Beach.
 
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#15
JJ KT88's from Eurotube are my favorite for bass amps. On my Bass 400 I noticed they added some character- bigger low end, silky top end, but also when pushed they get a nice threshold range where things compressed/saturated before overdriving. Currently have Tung Sol 6550s in my 400 and wish I could play loud all of the time so I could burn through them faster. They are fine but lack the mojo.

I love 6550s (which tend to have more of a flat response, more mids than 6L6) in guitar amps though. I use them in my Tremoverb and it is br00tal.
 
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#16
I've had enough trouble with JJ tubes that I prefer not to buy them, but everyone has different luck and preferences. I think it's the major and not the super bass that runs the tubes really hot, but JJ's 6550 specs are low on the data sheet compared to most 6550 sheets (as are many of their tubes). Whether the spec max matters is a different question as plenty of people seem to be running JJ's in their SVTs which would definitely be over the plate rating.

In my KT88 amp I've got a quad of Ruby branded valve art tubes. I bought a set of the genelex gold lion reissues but they were noisy and didn't seem to like the high voltages in that amp so I went back to the ruby branded tubes and got a replacement quad for the future. Put the gold lions in something with lower plate voltage and they were fine. I know they're all coming out new sensor, but I've really like what I've tried of the tung-sol and mullard reissues. Lots of noise problems with their gold lion branded tubes though.
 
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#17
You can not beat the GE 6550A's in an old Marshall. Unless you get into the old Tung-sol 6550 or GEC KT-88, but those are both ridiculously expensive. Old Sylvania or GE 6CA7's work very well also, have you tried those?
 
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