The Eagle Supre - Big SE Amp

[Zippy]

Zippy, did you ever build your Tweed Eagle, if so how did that turn out? I reread this whole Eagle thread a while back and have been wondering about the tweed Eagle and curious about what you did with that.

RJ's working on a custom board - I'll need to restuff it and then I'll reveal all. I don't recall how much I shared - my design is to wire up a 5F2 Princeton tone knob and switch it out to get 5F1.

Cheers.

g

[RJ Guitars]

<applause>

Great news, Aaron. I look forward to hearing about your tweaks. I drilled my front panel for a Mid pot - 25k with a 10k tail to ground. I know RJ is talking about MORE MIDS but I think he's got a lil' hearing loss. I'm not worried about him reading this 'cause I think his vision is going too.

Got any Strats around?

I am sorta used to this... it's like the "anti" form of "tone envy"... you can't hear it therefore it doesn't exist

besides, who said I could read anyway?


...consider that using a 100K ohm mid resistor (or pot) starts to look schematically closer to the infinite resistance of the tone stack removal switch and this will start to add up.

Congrats Aaron - looking forward to more reports on how she sounds!

rj

[RJ Guitars]

Eventually you want to tweak that amp for the specific tube you are using. Since this is a self biasing amp you have a lot of leeway in tube choices without having to rebias... sooner or later you want to optimize but for testing you can try it. For something like a 6K6gt it might red plate but for the big stuff probably not.

looking forward to the first report of sonic output. I am just about ready to start dialing mine for optimum tone. Maybe get that started this weekend.

rj

RJ It's taken way longer than it should have but I'm almost finished with my Eagle Supre build and the end is finally in sight.

What's the best way to tweak the grid resistor to find the optimum resistor value to use for a given tube, trial and error? Is there a more scientific method than that? I don't have an EL-34 on hand so I'll be trying out both 6V6 and 6L6 tubes. Since it's good to use a nice hefty grid resistor where's a good source to buy different values of the ohmite 10 W resistor you sent me and which values would be good to have on hand for tweaking?

In our offline email correspondence you mentioned something about tweaking the dropping string resistors so I was wondering what the general consensus is on this. What dropping string resistor values is everybody using in their Eagles? Is this also an area to tweak based on which tube is used?


To Zippy, did you ever build your Tweed Eagle, if so how did that turn out? I reread this whole Eagle thread a while back and have been wondering about the tweed Eagle and curious about what you did with that.

Thanks

Ed

Ed,

The primary source I use for buying modern components is Mouser. If you want to get really fancy you could use a big rheostat or maybe a rotary switch with several options.

I think most SE Fenders use a 470 ohm resistor but I know from experience you can get by with less resistance in the Eagle builds. Your power tube might not last as long and only your ears can tell you if it sounds better. I typically start with a conservative value then start swapping parts, measuring, and listening until my ears are happy. Sometimes I might have to play it a few days to know if I like it.

Also consider varying your cathode and plate resistor values on the preamp tubes as you tweak. A scope can really help but you ears are ultimately the best tweaking tools you've got.

Looking forward to your first flight.

rj

[yowza]

Ed,

The primary source I use for buying modern components is Mouser. If you want to get really fancy you could use a big rheostat or maybe a rotary switch with several options.

I think most SE Fenders use a 470 ohm resistor but I know from experience you can get by with less resistance in the Eagle builds. Your power tube might not last as long and only your ears can tell you if it sounds better. I typically start with a conservative value then start swapping parts, measuring, and listening until my ears are happy. Sometimes I might have to play it a few days to know if I like it.

Also consider varying your cathode and plate resistor values on the preamp tubes as you tweak. A scope can really help but you ears are ultimately the best tweaking tools you've got.

RJ,
Right after I wrote my last entry I went and looked at schematics for several Fender SE amps and saw the use of the 470 ohm resistor so I'll stick with that for now especially since a lot of those amps use 6V6 tubes.
I was afraid you were going to say you ordered from Mouser. I have not ordered from there yet because their website is so overwhelming and every time I go there I get really frustrated trying to find anything. There are so many options it's overwhelming. Any tips for navigating their website?

Thanks!

[RJ Guitars]

RJ,
Right after I wrote my last entry I went and looked at schematics for several Fender SE amps and saw the use of the 470 ohm resistor so I'll stick with that for now especially since a lot of those amps use 6V6 tubes.
I was afraid you were going to say you ordered from Mouser. I have not ordered from there yet because their website is so overwhelming and every time I go there I get really frustrated trying to find anything. There are so many options it's overwhelming. Any tips for navigating their website?

Thanks!

In Mouser use the "Project Manager" and once you find what you need store the parts numbers as a project. For your big cathode resistors you can use their search function and search for a 10 watt wirewound resistor... this should narrow it down and get you a manageable list to sort through.

next time I am in there I'll grab the part number and send it to you.

rj

[Berger]

RJ,

Got to play with the amp more over lunch. Finally got to crank it and play with the tone knobs. The treble control seems to work really well. But I agree with you on the bass control. It works ok. but I would think it would be better.

Looking over some fender schematics I see the Princeton aa964 has a bass and treble controls. As does the Champ aa764 must be from the same era...

Any one played one with that setup?

Aaron

[Berger]

Got to do a little work on the amp last night.

First I played it with my strat. Sounds pretty good. A little noisier, but its a noisy guitar.
I hooked up the Negative Feedback Loop and it tamed it a bit.

Next I finally got to hook up my triple triode tube. I pulled the 12ax7 and wired up the 12 pin socket to the 9pin socket. I paralleled 2 of the triodes for the input triode and then used the third for the recovery after the tone stack.

I used as 6u10 and a 6ac10. triodes 1 & 3 were paralleled with triode 2 being the recovery.

the 6u10 dropped the output considerable. Probably because the input plate only got ~70vdc on the plate. while the post tone stack plate had ~165vdc.

The 6ac10 sounded like the 12ax7 and had ~165vdc on both plates.

I re-read the parallel triode section of Merlin's book last night and realized that I need to change the plate resistance on the parallel triode section. Hopefully I'll get to do that the next time I get to play with it.

[surfsup]

Crazy pic. That looks like a science fiction alien craft coming down to steal your mojo! Never heard of that tube, I will check it out.

the 6u10 dropped the output considerable. Probably because the input plate only got ~70vdc on the plate. while the post tone stack plate had ~165vdc.

Could you elaborate more? I thought the plate voltage defined headroom and distortion. Lower voltage will put the BP/LL in the more curved section distorting more and lower voltage produces clipping/cutoff earlier, so wouldn't the output simply be more a function of the difference in gain with the new tube vs the 12ax7's 1st stage gain into the TS?

I have a cascode driving my TS on my Eagle now, in this thread here:

http://ampgarage.com/forum/viewtopic.php?t=15968

I am about to kick up the plate resistor value on the first tube. For the parallel stage I think you want to reduce it, as well as the Rk, and also double the bypass cap value if you still have the bypass cap.

[Berger]

I'm not sure I can elaborate since I'm not sure exactly whats going on either. I agree with you that lower voltage should decrease headroom.

I'm guessing that that there must be some problem with the impendence or something of that nature. This was more of an experiment of hooking it up and seeing what happened, more than me really understanding what was happening

Looking over the spec sheet I don't think the 2 triodes I'm tying together in the 6u10 tube really match, which is probably the bulk of the problem.

I printed both spec sheets off (6u10 and 6ac10) today and will be bringing them and the Designing Tube Preamps for Guitar and Bass to my relatives this weekend. So I should be able to draw out the load lines and hopefully figure some things out better.

I may just add a second 12ax7 and parallel it instead. But these triple triode tubes looks so cool! I guess I could always just have 3 separate game stages instead of trying to parallel them.

I've been watching your thread as well, its been really cool to follow!

Aaron

[RJ Guitars]

Congrats - you're only the 2ng guy I ever knew that used a 12 pin tube in a guitar amp... the fact that you got it all wired up is noteworthy. I would have to give the absolute prize in alien spacecraft vacuum tube technology to the 829 tube though... not a 12 pin tube but it throws all kinds of Rocket science mojo potential at a guitar amp. R2D2 meets Leo Fender and rumored to sound a little like a 6L6.

[Berger]

Thats a cool little tube. I'm going to have to look that one up!

Sadly mine doesn't sounds how I'd like it for now. but I have all my spec sheets printed out and I'll see what I can figure out this weekend. I'd love to be able to just switch between a 12ax7 and the triple triode tubes with out a switch or mods, but I'm not sure thats going to happen.

My quest for this amp is to build a nice high gain little combo. But like I said that may require more mods than I originally thought.

Oh well this is a really cool learning experiment

[surfsup]

Yea if you want high gain I think you're gonna want another tube. Check out the ax84 UberSEL I think it is three 12ax7 stages into a CF into a kt88. The eagle supre kit trannies should handle that no problem All you need is one other hole and there's room for that though the board starts getting crowded so you gotta get creative.

[Berger]

I knew of the ax84 SEL but not the UberSEL

That looks great! I'll print that out as well.

Man, lots of good ideas here

Also here is a good link of Compactron tubes.
http://www.junkbox.com/electronics/Comp ... ndex.shtml
The 6C10 is a three-section 12AX7, and the 6D10 is a three-section 12AT7. unfortunetly they are both pricey on ebay.

[RJ Guitars]

For a little bit of high gain and not so much work see if you can find a 12BZ7 tube. It wires up the same as a 12AX7 and also has a gain of 100. However, it has half the plate resistance so you don't loose as much gain. I especially like them in the V1 hole.

[Berger]

Looked through my 12b*7 collection of tubes..12bv7,12by7,12dq7,12bh7 I believe I was going to use the 12bh7 as the 'powertube' in my ax84 firefly...anyways

Got to play with the amp again tonight. I changed the treble cap to 250pf while it sounded nice the drop of volume was too much for me. I currently have a 3900pf cap in there, not enough different from the .01uf I had in the first place. Will probably just settle on the 500pf.

Played with the resistors and got some better values on the triple triode, it sounded better, but I think there is more there. I'm thinking I should de-parallel the input and instead have 2 gains at the begining...

I also got my 6l6 tubes in. They sound pretty good. Hopefully I'll pick up some 6550 tubes this weekend.

I did start to have a little problem with the turrets. Initially it went well but now they seemed to have plugged in the middle and its been annoying to change parts..but thats probably my fault

Oh well lots of fun so far!

Aaron