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Topic: 6550 tubes in a 135 watt Fender Amp--your input |
James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 8 Nov 2008 8:16 am |
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Anyone use 6550 power tubes in the ultralinear twins? Some have stated that the tone is well "above and beyond". I know there are mods required, such as upgrade the filter supply. What other mods are required? How much more heat do 6550's generate, is it damaging to the amp, eventually?
AND----do you have to reverse all the mods to go back to 6L6's? |
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ajm
From:
Los Angeles
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Posted 8 Nov 2008 10:08 am
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For one thing, 6550 tubes draw way more heater current. This is not something that is easily accounted for. My advice is to stick with the 6L6 tubes.
THD makes several amps that allow you to play with different output tubes. Just a thought. |
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John Fabian
From:
Mesquite, Texas USA * R.I.P.
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Jim Sliff
From:
Lawndale California, USA
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Posted 8 Nov 2008 2:52 pm
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James - PLEASE do some research on Torres before ordering anything. Check the alt.guitar.amps newsgroup - he's...errr..."legendary". Or check the WeberVST and other amps forums. Let's just say he's VERY well known in the tech community.
Anyway, I would not do it without a separate small power transformer for the heaters (meaning drilling holes in the chassis and major surgery), beefed up screen grid resistors and you might have to mod the bias circuit to be able to get them to 40ma or so - and with that amp it's just not worth the trouble, You have plenty of power to work with and the 6550's would be far more of a complication than they would be worth.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 8 Nov 2008 3:00 pm
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IMHO, it's not worth the effort (I've tried it). By rebiasing and adding a filament transformer for the 6550's, you can acccomodate the extra demands of the larger tubes, but it only gives you a little more power with the stock power tranny, and it doesn't do squat for the clean tone. Overdriven, a metalhead might like it, though!
And yes, you'd have to undo everything but the filament tranny to go back.
Want unreal power and and clean tone?
Get a Super Twin Reverb, install NOS American 6L6's...and you're done!!! |
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Cartwright Thompson
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Posted 8 Nov 2008 3:32 pm
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I assume you're talking about using four 6550's, which opens up a can of worms as explained in the previous posts.
My suggestion is to use 2, beef up your screen resistors, switch to a 15" speaker (8 ohms), rebias and enjoy a beautiful beefy tone. |
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Casey Lowmiller
From:
Kansas
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Posted 8 Nov 2008 3:42 pm
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James...don't change anything and give your amp to me for safety sakes. 
If Jim Sliff & Donny Hinson don't recommend it, I wouldn't do it!!!
Besides, you've already got tone to the bone!!!
Casey
_________________
Known Coast to Coast as
"The Man with The Plan" |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 8 Nov 2008 5:12 pm
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Easy now fellas, There's a method to my madness. This is just a recon pass, right now. LOL!!
A few years ago, there was some pretty good coversation going on about this subject, more directly about turning Twin Reverbs into steel amps, and 6550's came up. So it stimulated the "what if" in me. Please read this thread----
http://steelguitarforum.com/Forum11/HTML/000431.html
Pay special attention to forum bros, Bob Metzger's comments, and Steve Hinson's comments about some of Red Rhoades work.
This has inspired my curiosity. I had an opportunity to play a fender tube amp('77 bassman 10, of all things) that was beefed up with a pair of 6550's and the tone was, well let's just say it's haunted me ever since.
Donny, I appreciate that the Super Twins are spectacular, I've had a couple. But I'll assure you, for me, I have boucoup power out of my ultralinear. This is not about power, but rather tone.
Casey, come on now, do you think the tone quest ever ends??  
So fellas, that thread, is where I'm coming from, and I'm one to think there has been more discovered since that thread was written 8 years ago. So at this point, I'm diggin' for info.
I apologise about that being a loooong thread I refered ya'll to, but it's loaded with plenty of good ideas and experience. |
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KENNY KRUPNICK
From:
Columbus, Ohio
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Posted 8 Nov 2008 6:02 pm
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| I like my Ampeg SVT with 6 "6550" tubes. Sweet!!! |
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William Matthews
From:
New York, USA
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Posted 8 Nov 2008 6:23 pm
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| If you're looking for a cleaner version of the 6L6GC's, you can try the Sylvania 7581's. They work very nicely. |
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Jim Sliff
From:
Lawndale California, USA
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Posted 8 Nov 2008 7:17 pm
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James, one thing to remember is that when Red was modding amps at his old shop (Red's Royal Amplified Service) and then later while he was at Groove Tubes the vintage craze was still in its infancy; even that thread you linked to is 8 years old and really dated.
But Red's mods almost always included things like drilling a hole in the faceplate for a MV, larger power transformer ( as I recall all his Fender 6550 conversion had PT replacements - I don't remember whether or not he replaced the OT's) - in other words, he was doing what we now call "hack butcher" mods. Knowing Red, he would not be doing them that way now, but things you are reading about almost always require holes and major parts expenditures. Most stock Fender PT's will not handle the filament demands of 4 6550's - honestly, if I wanted 4 6550's I'd buy a US-version JCM-800 100-watt version. That's one Marshall you can set up for headroom galore - get a 4x12 slant cabinet and load it with 75 watt Celestions...you'll be playing steel but look like a rock star!
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 8 Nov 2008 8:22 pm
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| William Matthews wrote: |
| If you're looking for a cleaner version of the 6L6GC's, you can try the Sylvania 7581's. They work very nicely. |
Yeah those are real nice tubes. I have Jan Philips 7581A's, and I love them.
Jim, Thanx for that insight on Red. I was pretty curious about Bob M.'s comments. Wonder what he had to do to his twin? But your right, if it were that easy, everyone would be doing it, right? |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 8 Nov 2008 9:10 pm
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John Fabian, thanx for the links--very informative.
Thanx everyone for your input.
Keep it coming.  |
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Rich Gibson
From:
Pittsburgh Pa.
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Posted 9 Nov 2008 7:22 am
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| I have a blackface showman head that was modded to use 2 6550's.I like it allot.Gives a warmer sound at a lower volume and at least as much if not more clean headroom.I bought it that way,and only had a stock reissue twin as a comparison so whether it's worth doing on your paticular model I can't really say... |
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Cartwright Thompson
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Posted 9 Nov 2008 8:26 am
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Hey Rich,
I think I know that amp! Wanna sell it!?!
Two 6550's is a pretty sweet set-up eh? I can't seem to get anyone to listen to me. If you use an 8 ohm load, you hardly loose any headroom at all, get a nice impedance match and get the wonderful sound of the greatest power tube of them all. |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 9 Nov 2008 4:20 pm
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| Cartwright Thompson wrote: |
Two 6550's is a pretty sweet set-up eh? I can't seem to get anyone to listen to me. If you use an 8 ohm load, you hardly loose any headroom at all, get a nice impedance match and get the wonderful sound of the greatest power tube of them all. |
Hey Cartwright, I'm listening.  With two 6550's, is that ALL you had to do, is up the screen resistors, rebias and go to an 8 ohm speaker? 16 ohm if you have a vibrosonic? Did you notice volume loss, or did you stay about the same? |
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Rich Gibson
From:
Pittsburgh Pa.
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Posted 9 Nov 2008 4:41 pm
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Hey Cartwright whats up?
Cartwright speaks gospel on this.He is the original
owner of my amp and I use it with a 8ohm D130. |
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Cartwright Thompson
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Posted 10 Nov 2008 1:56 am
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Rich's amp is a '68 Dual Showman (with Blackface Showman cosmetics)so the output transformer wants to see 4 ohms with 4 power tubes. When you remove 2 tubes (Inside pair or outside pair)it effectively doubles what the tranny wants to "see", so in this case (or with a Twin Reverb)by going with an 8 ohm load you get a good impedance match.
I think I went with 1K ohm 5 watt screen resistors (feeding pin 4), it's been so long I can't remember exactly-I know they were the white, block-shaped ones.
Don't be afraid to bias them as high as 60 mA plate current- I think mine are at around 45 mA per tube.
In Rich's amp and my '66 Twin, I didn't notice much power loss and the tone of 6550's is really great. In one of the few far-sighted things I've ever managed to do intelligently, I bought a bunch of matched quads of GE 6550A's when they were about $25 each. They last a very long time so I can't tell you what the Russian or Chinese stuff sounds like.
You can always just put four 6L6's back in, the sceen resistors will work fine either way.
I'd also reccomend the use of 5751's for your first pre amp tube. |
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