Robben Ford Discussion

Leftbender · Posted: Mon May 17, 2004 12:04 pm Post subject: Marshall??

O.K. help me out here, guys! Last weekend I bumped into a Marshall combo that looked like a bluesbreaker (JTM45) but at a closer look turned out to be a 50 Watts master volume combo from end 70's. Usually I never pay attention to anything from Marshall because I don't like the 'fizzy' sound but the guy in the shop, who knows what I like, insisted to try it. So I did and I was knocked over by it's sound!! Definitely NOT Marshall!! After a brief examination I found out this combo carries two 6550 tubes, and two Celestion 12H- 65W speakers. The speakers I know (you guys talk about them all the time) but what about the tubes? I have experience with both 6L6 ans EL34 but these ones I don't know. The combination of tubes and speakers seems to give this amp a very vintage sound with an overdrive to die for! The guy in the shop adviced me to change the tubes for EL34, though. IS this a good idea?
_________________
"Don't play what's there, play what's not there" Miles Davis

Aeolian · Posted: Mon May 17, 2004 2:08 pm Post subject:

Very interesting, haven't seen a two 6550 amp since the Sunn's in the early 70's. Whatever overdrive you're hearing is not coming from the output. 6550's were used in the SVT, big Sunn's and the 200W Marshall's. They are still popular with high end audiophile tube amp makers like Audio Research Corp. A pair of 6550's will give a solid 60 watts as compared to 6L6's which the old RCA tube handbook lists as 42 watts in class AB. Remember, us guitar players don't care about a few percent distortion so guitar amps often ran tubes way past their normal limits. If anything, an overdriven 6550 sounds kind of sharp. Definitely not sweet.

Most master volume Marshall's use a diode clipping circuit, which is essentially a simple fuzz box built into the amp. This accounts for the "fizzy" sound and launched all the noises you hear in the music stores today. There are some that were made with cascading tube circuits, the Boogie-to-Dumble concept we know and love. I'd suspect that the amp you found is one of these. A well done cascaded tube preamp followed by a clean and stiff output is basically the concept behind a Dumble. Saggy, distorted output sections are great for vintage amps at one volume setting, but they won't have the dynamic response of a Dumble style amp. Or be able to play at different volume settings.

This may be a real find. Imagine the look on folks faces when you get fat, sweet, dynamic sounds out of a Marshall.
_________________
There are no such things as wrong notes, there's only the look on your face.
My Stuff: www.stevekirbymusic.com

Leftbender · Posted: Tue May 18, 2004 12:24 am Post subject:

Thanks for your reply and info Aeolian! It seems I found something special. I need to take my Tele to the shop and try that out. If that sounds just as fine as I expect it does I will buy this amp.
_________________
"Don't play what's there, play what's not there" Miles Davis

Aeolian · Posted: Tue May 18, 2004 1:15 am Post subject:

Talked to a buddy tonight who is more gear aware and knoweldgeable on Marshall's. Apparently, 6550's were not uncommon in various Marshall's over the years.

But I'd still, say, if this amp lets you get the sound you hear in your head, then that's the one.
_________________
There are no such things as wrong notes, there's only the look on your face.
My Stuff: www.stevekirbymusic.com

diatonicdude · Posted: Tue May 18, 2004 4:11 am Post subject: 6550

Hi Leftbender,

the only info I know (unless I look this subject up) is that Marshall used 6550's in place of EL34's when their EL34 stocks were depleted. I believe that the USA versions of some of their amps also used 6550's as standard. This type of alternative substitute was apparently common, dictated by the manufacture of valves at the time in China & Russia. Essentially speaking, the two valves (EL34 & 6550) are intercahngable with only the slightest mod (a grid resistor change if I remember correctly!)

Infact I modified a JCM 800 to take these valves (schematic supplied direct from Marshall). perhaps the amp in question had succumbed to the same mod, reccomended by Marshall??

I got to admit I did not like the mod I tried but I have heard some warm / sweet sounding Marshal's using this arrangement. All in all, I personally do not like the Marshall sound as much now a days. i prefer boogie / Fender tonemaster / and the boutique amp sounds like Bruno.

Cheer's,

DD
_________________
Music is the universal language; speak it with emotion, listen with a passion.

Leftbender · Posted: Tue May 18, 2004 5:55 am Post subject:

Thanks for this reply DD!!
If I understand you correct it's best to leave the 6550 where they are, although here in Holland they are much more expensive as the EL34.
_________________
"Don't play what's there, play what's not there" Miles Davis

diatonicdude · Posted: Tue May 18, 2004 7:46 am Post subject: 6550's

It is all personal preference of course; you may like to keep the amp in its current format for the reason that it may be the actual manufactured version, therefore, perhaps it is a a rare find and more desirable in cost and tone.

Cheers,

DD
_________________
Music is the universal language; speak it with emotion, listen with a passion.

edpesco · Posted: Fri May 21, 2004 11:58 am Post subject:

As far as I know those 6550 tubes were installed for USA Marshalls a long time instead of EL 34s because they distort much later.
ed

Aeolian · Posted: Fri May 21, 2004 1:03 pm Post subject:

The 6550's will be more neutral sounding too. The EL34s have more of that typical Marshall rock sound that I'm guessing isn't your cup of tea.
_________________
There are no such things as wrong notes, there's only the look on your face.
My Stuff: www.stevekirbymusic.com

Sonarguitar · Member Joined: 23 Nov 2003 Posts: 15

Leftbender · Posted: Sun May 23, 2004 12:03 pm Post subject:

Thanks for the info Sonar! It is indeed the 2204 Combo with JMP on the front plate. It carries two Celestion G12-65's in it and it is dated '81. It sound fine for me, that's why I bought it. The Printed Circuit Board look perfect, no damage at all. It only picks up some radio frequencies at higher levels. Should be a grounding problem I guess. I think I can fix that. I bought it for $275,-. Not a bad deal I think. I have heared that this amp could have some minor mod's that sound even better. Has anyone heared of this?
_________________
"Don't play what's there, play what's not there" Miles Davis

Sonarguitar · Member Joined: 23 Nov 2003 Posts: 15

Leftbender · Posted: Sun May 23, 2004 10:48 pm Post subject:

Well, what can I say Sonar. You seem to be a tweaker yourself! The info you gave me is very valueable. Thanks a lot! I studied electronics back in my schooldays but Tube technology is before my time. I'm quite capable to tweak any tube amp because I have the skills, but it's much different then I'm used to. Still I like the simplicity and solid designs a lot. I't still amazes me that you can achieve a great sound with hardly any components! This Marshall is indeed very basic. That's the way I like them! I find the printed circuitboard a disadvantage, but I'll live with it. So perhaps I will tweak this amp, after I kill those radio stations!
_________________
"Don't play what's there, play what's not there" Miles Davis