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6550 SE Stereo


 
7/20/2000 6:50 PM
Mark Buckingham
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6550 SE Stereo
I've got a Zoom gf8 multifx processor that I'm now using for the majority of my sound. It sounds decent through my ss bass amp, and incredible through my 5-watt vox ac-4 clone. It does not sound particularly good through the fx return input on my boogie or the front end of the boogie or my Princeton Reverb.  
 
I want to get something that sounds like the ac-4 clone, but louder. (The ac-4 clone is just an ef86, a volume pot, and a el84. I have no tone controls or anything else on it.)  
 
I would like to get close to 20 watts per side, so I thought the 6550 would be a good choice...  
 
So I've got a couple of questions-  
 
1) does this sound like a good idea?  
2) will a 6550 be too sterile or should I go with en el34 or 5881?  
3) would the ef86 have enough power to drive the bigger tube. It seems to do well with the el84, especially if the zoom is putting out a decent signal to begin with.  
4) The whole thing is problably going to be mounted into a 2-space rack, with nothing hanging out. Is this likely to work out?  
5) Am I barking up the wrong tree with SE idea? Maybe I should just use push-pull el84's or 6v6's? (I'm just thinking that some of the reason why the ac-4 clone sounds good is because it's SE.)  
 
 
Thanks!
 
7/21/2000 2:31 PM
Steve M.
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Mark,  
 
Sounds like you have some good ideas here.  
 
I want to get something that sounds like the ac-4 clone, but louder. (The ac-4 clone is just an ef86, a volume pot, and a el84. I have no tone controls or anything else on it.)  
 
I would like to get close to 20 watts per side, so I thought the 6550 would be a good choice...
 
 
I would think that the EL34 would be closer in tone to what you want. You might have to parallel two in SE operation to get close to 20 watts, though.  
 
So I've got a couple of questions-  
 
1) does this sound like a good idea?
 
 
Sounds like a good idea to me :)  
 
2) will a 6550 be too sterile or should I go with en el34 or 5881?  
 
I think it depends on which 6550 you use. I heard some say that the GE 6550A sounds sterile for guitar amps and the Tung-Sol 6550 sounds great for guitar amps, but they will cost you. I've heard varying reports about the Svetlana 6550s.  
 
3) would the ef86 have enough power to drive the bigger tube. It seems to do well with the el84, especially if the zoom is putting out a decent signal to begin with.  
 
Don't know on this one, I'll let someone with more knowledge tackle this one.  
 
4) The whole thing is problably going to be mounted into a 2-space rack, with nothing hanging out. Is this likely to work out?  
 
I think this will be your biggest challenge. There are very few suitable SE transformers that can be used for a 20 watt SE circuit. Take the Hammond 1627SE or 1640SE, I think either one could be used, but the dimensions are 3.75" x 5.00" x 4.56". Would this fit in your rack case? Also they weigh 11 lbs and you need two for stereo, also something to consider. Also, if you paralleled two EL34s, you'd still need to use comparable iron to the Hammonds to handle the current.  
 
5) Am I barking up the wrong tree with SE idea? Maybe I should just use push-pull el84's or 6v6's?  
 
A 20 watt circuit using 6V6s is possible, and two OTs would fit the rack case. On the plus side the 6V6 circuit would be lighter and most likely cheaper (the aforementioned Hammond 16XX series are around $100 each, repro Fender Deluxe Reverb OTs can be had for considerably less). On the downside, a push pull circuit won't sound like an SE circuit.  
 
(I'm just thinking that some of the reason why the ac-4 clone sounds good is because it's SE.)  
 
SE does have a different sound, you're right on that count.  
 
I think the 20 SE circuit is possible, but you might have to go to a 3 space rack case. Also, you're going to have to put in a *big* power transformer to handle the current draw of the tubes. A fan would not be a bad idea if you are enclosing the tubes in a rack case.  
 
Just my $.02, YMMV.  
 
Hope this helps,  
 
Steve
 
7/21/2000 8:08 PM
Mark Buckingham
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Thanks Steve-  
 
I think I'm leaning twoards the stereo push-pull 6v6 idea. I don't really want this thing to weigh a ton...  
 
I think I'll try to rig up something this weekend for one channel to get the idea of what it might sound like.
 
7/22/2000 2:07 AM
steve m.
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Mark,  
 
Just FYI, I built a stereo power amp using the output section similar to a champ, half of a 6SL7 driving a 6V6 power tube. I wasn't really happy with the sound, it was way too thin, and lacked bottom. It may have been the OT, but I've used that OT in a champ style circuit and it sounded fine. I'm still trying to figure out what went wrong with that one.  
 
FWIW, I vote for the push/pull circuit, it is lighter, less expensive to build, and will likely sound pretty good. In fact, if you wanted to save some room in the chassis, you could use 6AQ5s or 6CM6s which have similar ratings to the 6V6 but have 7-pin and 9-pin mini bases respectively.  
 
Regards,  
 
Steve
 
7/22/2000 6:05 PM
eric
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if you want to really save some space, do what lots of manufacturer's did, run 4 6bm8's, that way you cut back on preamp tubes needed. The 6bm8 is basically a triode and pentode in the same envelope, The pentode is very similar to an el84.  
good luck
 
7/24/2000 12:20 PM
Mark Buckingham
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quote:
"  
FWIW, I vote for the push/pull circuit, it is lighter, less expensive to build, and will likely sound pretty good.  
"
 
 
That's probably what I will end up doing. I was avoiding it earlier, because my processor doesn't sound all that great going into the fx-return of the my 2xEL84 boogie. I'm thinking that may just be boogie related.  
 
I've got a 15 watt el84 based amp I built for a friend sitting at home waiting to have some changes made. Maybe I ought to see what the processor sounds like through that thing.
 
7/25/2000 12:46 PM
Mark Buckingham
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Hammond 125E for EL34 SE?
Can a Hammond 125E handle a EL34 single ended? (I'm now thinking ~15 watts).  
 
I'd really like to try the single ended thing, but be able to reuse the transformers if it doesn't quite work out.
 
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