I had some nice emails with a guy named Patrick, starting from a video on youtube...He just made a GREAT tube amp, based on the Firefly...I asked his permission to post it here to share with all of you, as he's been so kind and ready an'willing (sorry, whitesnake fan here...) to share his work with others...So here it is...
this is the video he made...
http://www.youtube.com/watch?v=_l1kowPgmH0
and the schem...
http://www.bilder-hochladen.net/files/b3cc-4-jpg.html
Thank you again Pat! You're really kind!!!
PS Great Vid you made - it sounds SO GOOD!!!
Explore in here a little: http://www.aronnelson.com/gallery/main.php/v/DougH/amp/ (http://www.aronnelson.com/gallery/main.php/v/DougH/amp/)
Out of all the projects I've built over the years, the Firefly is a real keeper !
Doug Hammond really did an exceptional job on his FIREFLY design.
A guy named John Calhoun made a wonderful contribution to Doug's project
by designing an elegant PCB to make Doug's project really simple. It's a very
clever layout too. PCB website here (http://web.me.com/calhoun/Site/Firefly_PCB.html)
I built two of them for myself and like them both VERY much. The Firefly is a
LOT louder than you might think with the ECC99, and it has terrific tone.
I always plug straight-in (http://home.swbell.net/deewm/images/Guitar4.jpg) and it sounds awsome with a 12" Vintage 30 from
Warehouse Guitar Speakers (http://warehousespeakers.com/).
I used AX84's 1x12 cabinet design.
The Firefly has a real nice touch sensitivity to it. No stompboxes required !!!
John's new PCB (v8.0) eliminates ALL of the hum that the older versions were
burdened with.
This new board is damned_near silent, noise wise, even at full gain volume.
(I'm the guy that came up with the mods to fix the groundloop hum in the older
version 7 boards. The newly designed board (v8.0) incorporates those mods, so
it's good-to-go!)
Some say that the Firefly is a "one trick" pony... but with the ECC99, I find that
I can get a little more headroom out of it.
Without the hum... it's a much better amp... I'm sure it sounds closer to what
DougH designed in the first place.
Keep in mind that most of the sound clips and commentaries you're likely to find
are older projects that use the noisy PCBs and the 12AU7 for the output stage.
Similar... but different. I think the ECC99 and the new PCB sounds much better!
The PCB makes this project a snap to build. I built the board in one evening.
The chassis took a little longer because I'm a perfectionist.
I would suggest upgrading to MusicalPowerSupplies' (http://www.musicalpowersupplies.com/3.html) OP5PP output
transformer over the Hammond though. I've used both, and MPS's sounds a whole
lot better - a tighter bottom end and less high frequency hash/hiss.
I haven't tried the Doberman OT........ yet.
If you decide to build one, don't forget to re-bias the ECC99 using a 220 instead of
the 440 ohm resistor (R13).
I'd wish you luck... but you probably won't need it.
More references:
AX84's Firefly Archive (http://ax84.com/index.php/oldprojects.html?project_id=firefly)
AX84's Forum... look in the Firefly discussion group. (http://ax84.com/bbs/index.php)
Look out you'se kids... don't put yer lips on it!
OMG that sounds incredible
QuoteI would suggest upgrading to MusicalPowerSupplies' OP5PP output
transformer over the Hammond though. I've used both, and MPS's sounds a whole
lot better - a tighter bottom end and less high frequency hash/hiss.
I haven't tried the Doberman OT........ yet.
A big part of that will be influenced by the speaker too. I found that my Peavey 4x12 is
much kinder to the Hammond transformers. I have been trying to come up with a 1x12 solution for my Dragonfly. I don't like the sound with the Red Fang or the G12H30. I just ordered an Eminence Swamp Thang to try in that cabinet. It's supposed to have more bass, subtler highs, and it is 150W so it won't add its own breakup like the Red Fang does. The RF breakup sounds good with the "Voxy" Chime & Grind, but sounds fizzy with the Dragonfly, which is more midrangey and higher gain. I'll find out in week or so if I can get happy with this amp through the 1x12. Through the 4x12 it's killer.
That sounds really nice. I'm planning on building a Firefly this winter and that's given even more of an incentive :)
Doug,
I would never argue with you, especially about your own design, but have you actually tried using MPS's OT5PP ?
I lost my hard drive recently, and all my email archives went with it. But I seem to recall Matt telling me that his OT5PP measures approx 30H. Whereas Hammond's 125E has about 15H.
The OT5PP is slightly smaller in physical size, but not by much.
I noticed a marked improvement right away. And since I'd built two Fireflys, identical except for the OT, I was able to compare them directly. The OT5PP sounds way better - tighter bass, and much less hash.
So now, both of my Fireflys are running the OT5PP and the Hammond 125E had to find a new foster parent, via ebay.
The Hammond 125E sounded fizzy on everything I've got.
2 - 2x10 JBL E110's
4x10 JBL E110's
1x12 JBL D120
1x12 Eminence - Red White and Blues
1x12 Eminence Wizard
1x12 Eminence Cannibus Rex
Vintage 30 WGS
G12H30
OT5PP... less fizzing... tastes great!
DougH,
U-DA-MAN, so I won't argue the point, but I would like to rationalize my suggestion if I may.
As you've pointed out, the Hammond may require an exclusive speaker configuration just to "get-by."
So unless someone has already bought the Hammond, why not instead just get the better transformer that's about equal in price from the "get-go"?
YMMV, but hindsight indicates to me that the Hammond is a false economy, because its purchase doesn't save enough money to pay for the speaker needed to mask its deficiency.
What I wasted on the Hammond would have covered half of the cost of a speaker - that being an EXTRA speaker, rather than a NECESSARY speaker.
No offense intended, just my observation.
Oh, I would agree with getting a better output transformer to start with. I have also heard that the reason the Hammonds sound the way they do is due to inductance. If I were starting from scratch, I would try the Heyboer transformer that was made for the ax84 4-4-0 studio amp. I'm sure the one you mentioned sounds better too. I'm just saying to pay attention to speaker choice too.
DougH,
Yes. You are absolutely correct. I should have been more accurate and specific in my initial post.
The "Doberman transformer" that I thought was available from Doberman is in fact a different transformer altogether.
I meant to say that it is offered from Chappellamps and is manufactured by Heyboer for the 4-4-0 studio amp project, which is not actually an AX84 design. It is credited as an "associates design", just like your Firefly.
Chappellamps (http://chappellamps.com/) currently offers the Heyboer 4-4-0 transformer for $65 outright. (DougH approved!)
I would definitely like to try a Heyboer someday, especially to compare it with MPS's OT10SE in an AX84 High Octane I just finished.
But at less than half price, a $29 OT5PP is pretty hard to resist, especially when it out-performs the more expensive Hammond 125E, which is supposed to be Hammond's "upgrade" to their 125A/C.
BTW... I looked it up... the OT5PP measures 35H inductance, not 30H as I inaccurately reported earlier.
However, price should never be the only consideration... because some of the most expensive things in life are FREE.
(Of course congress disagrees, which proves my point!)
Interesting, I haven't played with my firefly for quite a while now, getting tempted to change it, might try this one out :D
Has anyone tried the trainwreck inspired one that's on amp garage?
So... are there any 6SN7GTB vs ecc99 comparison threads anywhere.?
i know one is octal and one noval.
Hi @all,
I'm Patrick the guy who built the amp and recorded the clip. First thanks to all the kind words, especially to Renegadrian for his interest in my video! ;)
My main goal was to build a small tube amp for practice and recording purposes at lower volumes that fits in a Hammond type BB enclosure, uses some common tubes and nails this slightly overdriven crunchy tube tone I prefer with my tele.
The amp started from the AX84 Firefly rev. 3 schematic without the boost stage (Thanks to Doug Hammond for his awesome design!). Then I started to modify the amp. I changed the poweramp tube to an ECC99 for slightly more headroom and a better bass response, especially at low volumes. I think it was DougH himself who wrote somewhere that this changes the amp from a toy to a "real" amp or something like that and I have to say you're absolutely right! And the second thing I did were some modifications to the preamp to shape the overall sound and overdrive behavior to my taste. I'm quite satisfied with the result. :)
So I used the Hammond 125A mainly because of its miniature size and price. ;)
Here is another video with the final modified version and a modified colorsound wah I built:
http://www.youtube.com/watch?v=Lz03ZnOJnDc
And I also made a video directly after building the amp, with the unmodified Firefly preamp and a 12AU7 in the output-stage:
http://www.youtube.com/watch?v=bPi-RG7-y48
greets
Patrick
Hey Patrick. I really enjoyed your videos on youtube. Especially that you sort of step through the process of building an amp from scratch and even though you don't go through all the details it's valuable to see that process from vision to completed project.
I've got several tube radios sitting around and am literally surrounded by boxes of parts and tubes and just keep running out of time to work on projects with school started again. Your videos though have renewed my vigor to make time and finally build something.
Also could you elaborate a little bit about the swap to the ECC99? I've read that it is classified as a "super" triode and that it has a high gm and a low Rp. This certainly sounds interesting to me as some of the 70-volt line transformers I bought as OT are fairly low impedance... <8K.
Also do you have any tips for scavenging or acquiring low cost alternatives to the traditional power transformers? Those are my current stumbling block as I've acquired a few OTs... lots of tubes... a few chassis but I have no power transformers as of yet.
Quote from: doitle on September 09, 2009, 02:45:33 AM
... Also could you elaborate a little bit about the swap to the ECC99? I've read that it is classified as a "super" triode and that it has a high gm and a low Rp. This certainly sounds interesting to me as some of the 70-volt line transformers I bought as OT are fairly low impedance... <8K.
...
I basically chose the ECC99 because it was recommended in the AX84 forum for some better bass response in this circuit. I am using it with the highest impedance I can get from the 125A wich is around 22K I think and I adjusted the cathode resistor to its needs. But from what I've read it seems to be quite flexible when it comes to OT impedance. But perhaps someone else with more experience can tell you more about the OT impedance problem with those triodes. One other thing you should consider is that the ECC99 needs 800mA instead of the 12AU7s 300mA with 6,3V heater voltage.
Quote from: doitle on September 09, 2009, 02:45:33 AM
... Also do you have any tips for scavenging or acquiring low cost alternatives to the traditional power transformers? Those are my current stumbling block as I've acquired a few OTs... lots of tubes... a few chassis but I have no power transformers as of yet.
Yes, I know what you're talking about. Unfortunatly I don't know much about the US transformer market, but as you can see I used a toroidal transformer from an online shop here in europe called "Das Musikding" with the secondary specs: 185V/0,04A and 6,3V/1,4A, perhaps you can find some US equivalent somewhere, it was about 22€ (~32$) were a suited Hammond would cost about 60€ (~87$) over here. here is the link (http://www.musikding.de/product_info.php/language/en/info/p943_Ringkerntrafo-230V----185V--6-3V.html)
greets
Patrick
You can usually pick up a decent surplus 110/208VAC isolation transformer for around $10 or so. Those work perfect for these amps with relatively low current drain. Add a surplus 6.3VAC filament xformer for $4 and you are all set. That's what I used for my Firefly (and now Chime & Grind).
One more comment on the "is it the output transformer or is it the speaker?" discussion.
Last night I plugged my Octal Fatness into my Red Fang in my 1x12 and didn't particularly like the sound. It was fizzy and harsh, somewhat. So I subbed the little $15 AES output xformer with a Heyboer S/E output xformer on my bench and did some experimenting. Through the same speaker and cabinet- the sound improved marginally. There was better low frequency response and a slightly "fuller" sound. But the fizz was still there and it wasn't really that big of an improvement. Fortunately the Heyboer has a 16 ohm tap, so I tried it through the 4x12. The sound of this amp came alive at that point. The fizz was all gone, better lows and mids, etc, etc. It sounded really great and solved all the problems I had with the other speaker. Also, I had been using beam tubes (6L6, 6AR6) because with an EL34 it was unlistenable with the 1x12. But through the 4x12 it didn't matter. It loved all the tubes and I could dial up the gain, master volume, tone controls anywhere I wanted to and it sounded great.
I think one of the keys is that the speakers in the 4x12 are 50W speakers and don't add any distortion of their own. In contrast, the Red Fang breaks up real early, and you can definitely hear it. Don't get me wrong- I love the Red Fang, and I think for Voxlike amps it sounds great. But for midrangey high gain amps it doesn't seem to work very well for me.
Unfortunately I cannot physically fit the Heyboer on this amp chassis, so I'll have to go back to the AES which only has an 8 ohm tap. (I'll probably build another s/e amp on a bigger chassis with the Heyboer at some point.) I'll see when my Swamp Thang comes in if that solves this issue with the 1x12, and then it doesn't really matter. It's coming in tomorrow and I'll have to give it a few weeks to break in.
So yeah, if you're building an amp from scratch, get a decent output xformer. But don't neglect the speaker. It has a big influence on the overall sound. And so far I'd say, a 4x12, at least this one, makes up for a whole host of ills.
Hi!
As Renegadrian, I saw the video that Patrick uploaded and I decided to build one of these! I used the same chassis and layout that he used, because I really liked the size, It's tiny! I ordered all the components from "Das Musikding" (I'm Spanish), except the ECC99 and a few vintage carbon resistors that I ordered from "Tube Amp Doctor". I built the amp in only two days and took a few photos of the process. As Patrick told me in an email, I set up the cathode resistor in 220 ohm (I had trouble drawing the load line, because I'm not too good with tubes theory, at the moment :icon_redface: :icon_lol:).
I've been testing the amp with 12AY7 (Groove Tubes Gold Series) and ECC83S (JJ)... and I cannot decide between them, because they both sound great :D. The cab is a Framus 2x12 (Celestion Vintage 30), but I have to try with the 1x12 cab that I'm building now, with a Jensen P12Q Alnico speaker.
These are the photos of the amp, I hope you like it (sound samples coming soon!).
http://www.megaupload.com/?d=TNDNM2KL (http://www.megaupload.com/?d=TNDNM2KL)
THX for the report and welcome!!! :icon_wink:
Hey, sounds interesting - but can't you find some other way to host the photos? Photobucket maybe? I don't really want pop-up ads and to have to wait 3 minutes to download files just to see them...........
Wow that is an amazing difference from the first version to the ecc99 version (I listened to both vids)
I really liked the mellow song with the subtle lead/melody and the tele and old albums at the end was nice.
What are the specs on that toriodal you are using? and where did you get it?
After hearing this I am glad I didnt start one of these low wattage PP amps yet,I almost ordered the tubes last month but now I will get the ECC99 tubes instead.
I think I will make mine with a 125E and use 4 ECC99 tubes for 10 watts and just pull 2 of em for 5 watts.
I really am impressed by how well the amp sounds after you modded it and switched the output tubes.
UGGGHHH Now I really want to build one... but I have to buy a new big amp before the next talent show.... It's okay, I'll do a sharp tug on my hair everytime I get distracted because of wanting to build this.
I hosted the photos in photobucket, this is the album:
http://img21.imageshack.us/slideshow/webplayer.php?id=dsc02932c.jpg
Nice build, very tight.
You may want to put some shrink-tube (or what's it called) on the OT taps though.
I've been zapped by not doing it on one of my builds.
Quote from: alternative84 on September 27, 2009, 08:33:01 AM
I hosted the photos in photobucket, this is the album:
http://img21.imageshack.us/slideshow/webplayer.php?id=dsc02932c.jpg
Aah, very nice build! Thanks for taking the time to rehost the photos. :icon_biggrin:
Quote from: alternative84 on September 27, 2009, 08:33:01 AM
I hosted the photos in photobucket, this is the album:
http://img21.imageshack.us/slideshow/webplayer.php?id=dsc02932c.jpg
SUPERB I like the way that looks! So compact and yet clean looking,I like the way you made the bridge rectifier.
Quote from: Brymus on September 27, 2009, 07:36:03 PM
SUPERB I like the way that looks! So compact and yet clean looking,I like the way you made the bridge rectifier.
Thanks :). I took as a reference the FcKw's build, and tried to fit the power jack, so I had to "compress" the bridge rectifier. It's a very small box (Hammond BB type), but is worth the effort, it's tiny!
Hi,
sorry for my late response but I moved to another home in the last weeks and the internet is just right back up. :)
@alternative84
nice to hear that you made it and some nice documentation you got there! I like the power jack, I thought I would get some space problems with it, but you actually did it. :) How would you discribe the differences between the 12AX7 and 12AY7 in this circuit?
@Brymus
The toriodal is this one HERE (http://www.musikding.de/product_info.php/language/en/info/p943_Ringkerntrafo-230V----185V--6-3V.html) and thats where I got it.
The specs are: Primary 230V, secondary 185V 0,04A and 6.3V 1,4A
Nice you liked the video, actually it's my girlfriends album and it just happend to be there on the pictures/videos. :D
Patrick
Not do dig up an old thread... but has anyone had any luck finding a similar toroidal transformer with a 117V primary? That transformer seems to be made by a company called Multi PCB in Germany: http://www.multipcb.de/eng/sites/pool/index.html . However they do not have an English translation of the pages related to the transformers. My German is a bit lacking (think nonexistent) and machine translators don't seem to handle the navigation of the site... Perhaps they offer a comparable transformer (in terms of size, weight and electrical specs) with 117V primary ? Anyone speak enough German to figure it out from the site? :)
Hi, alternative84, eautiful b buil (and nice sound, Patrick.) Are those 1/4 watt metal films? Do they get hot? They look like they are going to get eaten by those massive old carbon comps.
Quote from: armstrom on October 13, 2009, 09:12:41 PM
Not do dig up an old thread... but has anyone had any luck finding a similar toroidal transformer with a 117V primary? That transformer seems to be made by a company called Multi PCB in Germany: http://www.multipcb.de/eng/sites/pool/index.html . However they do not have an English translation of the pages related to the transformers. My German is a bit lacking (think nonexistent) and machine translators don't seem to handle the navigation of the site... Perhaps they offer a comparable transformer (in terms of size, weight and electrical specs) with 117V primary ? Anyone speak enough German to figure it out from the site? :)
They only sell to companies...
up to ten primaries with taps...
up to 14 secondaries with taps...
at any voltages, any power,
generally without higher pricing for individual configuration...
I keep coming back to this thread. I'm in love with this build. Finding the perfect USA supplier for the power transformer is my hand up.
You can build your own with two back-to-back transformers or use a 6 or 12V AC wall wart and a "backward" transformer.
I'm looking into the LO_PO transformer from weber that might do the trick. The spec sheet indicates a max heater current of 1A but a 12AX7 + ecc99 needs 1.1A (close, but over the spec). I have sent an email to the guys at weber to see if I can exceed the heater current rating by 10% and still be safe. Other than that, the HT current should be adequate.
Hi there...I'm back.
I contacted Antek and asked them for a substitute for the 269EX. They came back with this http://www.antekinc.com/details.php?p=46 . It's not an "exact" match but it's pretty darn close. Anyone see any potential problems with using this transformer? It's WAY cheaper and I like the idea of using a torroidal. The first and only thing I see is dropping voltage down a little bit to match the schematic voltages.
Anyone?
Hi,
the 200V should be just fine, but it's got a 6,3V output like in the datasheet not a 3V output like it is described on the website, right?
Patrick
Thanks for taking a look at that for me Patrick,
It was a bit confusing for me too. The first page in the product spec shows 3Volts but then when you look at the PDF detail, it shows two secondaries with 6.3 at 3amperes each. The part that's got me a little cuatious is the cost...it's $30 USD which is significantly cheaper then the hammond and by the looks of things...a little smaller perhaps (lower profile certainly) and again, the appeal of a torroidal from the noise standpoint is really attractive.
Steph
Yes, it's significantly cheaper, but it should be right, because over here in europe you can get similar torroridals for about 20€ wich is around 29$, too. ;)
Patrick
Hello uncle Visa ;D
Thanks Patrick
Everything I've read online seems to indicate these Antec transformers are very high quality. One nice thing about that 100VA rating is that it will support a MUCH larger amp than what we're talking about in this thread. The secondaries, when used together (either in parallel with a full-wave bridge rectifier or as a center-tapped setup) should supply 440mA at 200V. In comparison the 269EX is only rated at 65mA. Of course, Hammond rates its transformers in maximum DC current while the Antec is rated in AC current, but the gap between the two is still huge. You also have more than enough filament current to drive as many tubes as you could want :) I wouldn't let the price put you off though. Keep in mind that hammond pretty much owns the market when it comes to traditional EI power transformers for tube amps. They charge what they do because they can. Antec makes all sorts of toroidal transformers and being a smaller manufacturer they can easily tool-up to make all sorts of variations. Not to over-simplify the design process for toroidal transformers, but my guess is that it was pretty easy for antec to simply adapt some of the existing designs they have to be suitable for tube amps.
I contacted Antek a month or so ago and asked if they did custom work and if so could the reproduce a transformer similar to the one found on that german site. They didn't really give a clear answer but did say they would be coming out with a 50VA version some time soon. That should help cut down on the size and weight while still suppling more than enough current to run most small to moderate tube amp projects.
I wonder if it's worth contacting that German reseller to see if they can order a batch of 120V primary transformers from the supplier. If we can get enough people together it may be worth the effort. If we could get a small toroidal tranny like the one Patrick used in his build (but with North American friendly 117-120V primaries) how many people would be interested?
I think I'd be in for one or two but wonder if shipping would make it cost prohbitive again.
It depends.. The cheapest option is usually to package all of them up in one box and ship it overseas. Then someone here can re-ship to individuals. These are pretty small/lightweight transformers. And if there's no rush it shouldn't be TOO expensive to ship surface mail. Depends really. I see that Antek has posted some higher voltage (325V) 50VA power transformers on ebay. I'll contact them later to see if they have the 100V x 2 50VA available yet. It should be about 3.5" diameter x 1.5" tall. Bigger than the one from the german company, but also MUCH higher current rating. You could build an AX84 P1 or a a low-voltage champ using a transformer like this without a problem.
-Matt
Since the topic pretty much is about OTs now, i would inlude a small question.
I have a higly modded Champion 600 with switchable cathode bypass for lower bass response, new tubes, appropiate cathode resistor on the output tube, bypassed tonestack, upgraded coupling caps, variable NFB and i bought a new speaker (Jensen C8R) which i play sometimes without a cab, just for breaking it in.
The thing sounds really nice clean, but when i turn the volume up, the highs are getting harsh and fizzy. I one played the amp with in-ear phones which lock the treble better than the bass and i liked the tone much better.
Cna the shitty stock output transformer cause the bad treble response?
Or the speaker? Sometimes it's the cab, and if the spkr is on the floor, it'll do weird things...
Quote from: GibsonGM on November 28, 2009, 08:12:34 AM
Or the speaker? Sometimes it's the cab, and if the spkr is on the floor, it'll do weird things...
The stock speaker is dark actually and bad sounding but both of the speakers doing it when i crank the amp. The stock speakers fart badly too, the small cab and the weak speaker can't take it. The Jensen doesn't fart, it is just harsh. And when i will put the Jensen into a cabinet (which i should have done 2 weeks ago but the local carpenters don't glue wood and they use only sh*tty particle boards and i don't have any wood working tools) that won't solve the high end harsness imo. (i know that the lower frequencies can block each other out so it sounds thinner of course but the high end should be much milder)
It sounds nice when i "overdrive" the clean amp with a pedal. But when i just crank up the amp it starts to sound harsh, so thats why i think that the crappy stock OT can't take the increased volume.
Since i bypassed the tonestack with a 0.022uF Orange the EQ should be flat. Plus the midrange and bass is definitely there because it sounded quite good when i had an inear phone in my ears which blocks high frequencies easier than bass or mids so it is a bit like an equalizer with the treble turned down.
Wow, those are some odd symptoms, man. What are the output tubes? EL-84's can sound really fizzy if they're pushed hard. My 18W currently does that when I crank it too much (need to increase power tube grid stoppers & decrease PI tail resistors). Maybe you've got something like that going on?
Quote from: GibsonGM on November 28, 2009, 03:41:30 PM
Wow, those are some odd symptoms, man. What are the output tubes? EL-84's can sound really fizzy if they're pushed hard. My 18W currently does that when I crank it too much (need to increase power tube grid stoppers & decrease PI tail resistors). Maybe you've got something like that going on?
The amp is a modded Champion 600 reissue.
Stock OT and PT.
Tung-Sol 12AX7 preamptube and a JJ 6V6 output tube.
Tonestack bypassed with an Orangedrop 0,022uF cap so it is like a 5E1 circuit now. Cap between the preamptube and the powertube is changed to a Orangedrop.
Feedback resistor is switchable between stock and no feedback but it is not the source of the problem, its fizzy at both settings.
There is a switchable cathode bypass cap (stock 22uF and 2,2uF) at the first half of the preamptube for less bass.
I saw a post somewhere that the amp is like factory misbiased. Fender raised the B+ without changing the bias of the tubes or something like that.
Quote- One thing that this amplifier invariably needs is power tube bias adjustment. The Champion 600 Reissues that we have seen have had the 6V6 power tube biased for too much power dissipation. The correct power dissipation for a 6V6 is considered to be between 12W and 14W (12W for vintage 6V6s and up to 14W for some of the newer 6V6s). The Champion 600s that we have seen were biased for between 15.5W and 16.5W. This is simply too high and does not sound optimal. We have found that the installation of a 200 Ohm to 240 Ohm 2W resistor in series with the factory installed 470 Ohm resister in R10 will achieve approximately 12W to 13W power dissipation.
Your measurements are absolutely correct... it's Fender's design which isn't :).
So i changed the 6v6 cathode resistor to a 680ohm one.
My voltages:
All my measurements are DC:
TP2: 218VDC (First input triode plate voltage)
TP6: 1,63VDC (First input triode cathode voltage)
TP5: 218VDC (Second input triode plate voltage)
TP7: 1,7VDC (Second input triode cathode voltage)
TP9: 347VDC (Output tube plate voltage)
TP8: 21,4VDC (Output tube cathode voltage)
TP10: 336VDC (B+ after two resistors)
TP11: 355VDC (B+ after one resistor)
A schem of the stock amp: http://www.schematicheaven.com/fenderamps/champion600_reissue_fullmanual.pdf
As xou can see i did a lot to get rid of the problem, i did the steps one by one, during a 1 month period on the weekends, the amp got better step-by-step, i even get rid of the low end rattling when the amp is cranked (after i changed the cathode bypass resistor of the 6V6) with the Jensen, but the too dominant high end harsness is still there.
Thats way i think the only stock stuff left is the transformers which could be bad, or something is wrong in my circuit, like something gone wrong or i don't know.
I have contacted the vendor in Germany who sells the small toroids. He says if we can get together an order of 5-10 transformers he could have them built with 120V primaries and keep the price the same. (22 euros). I'm not sure at this point what shipping would run. Keep in mind that the 22 Euro price includes German VAT (a sales-tax built into the price). I would have to check but there's a good chance that we wouldn't have to pay that 19% since the part is being exported outside the EU, however I'm not 100% sure as I've just begun discussions.
So, the real question is, how many people are interested? And for how many transformers? I would probably pick up more than one myself just to have an extra on hand should I want to build another low power tube project. I would be willing to organize this and handle the single order and shipment from Germany then do the redistribution here in the US. I have no idea about shipping or lead-times right now but I wouldn't expect this to be a very quick process since the trannies would have to be manufactured then shipped from Europe.
I'm also looking into manufacturers here in the US but so far no one has been able to get close to the small size / low price of the German transformers. If the super small size isn't an issue I may have a good solution for a similar price, but I'm waiting to hear back on that.
-Matt
Quote from: WhenBoredomPeaks on November 28, 2009, 06:35:12 PM
Quote from: GibsonGM on November 28, 2009, 03:41:30 PM
Wow, those are some odd symptoms, man. What are the output tubes? EL-84's can sound really fizzy if they're pushed hard. My 18W currently does that when I crank it too much (need to increase power tube grid stoppers & decrease PI tail resistors). Maybe you've got something like that going on?
The amp is a modded Champion 600 reissue.
Stock OT and PT.
Tung-Sol 12AX7 preamptube and a JJ 6V6 output tube.
Tonestack bypassed with an Orangedrop 0,022uF cap so it is like a 5E1 circuit now. Cap between the preamptube and the powertube is changed to a Orangedrop.
Feedback resistor is switchable between stock and no feedback but it is not the source of the problem, its fizzy at both settings.
There is a switchable cathode bypass cap (stock 22uF and 2,2uF) at the first half of the preamptube for less bass.
I saw a post somewhere that the amp is like factory misbiased. Fender raised the B+ without changing the bias of the tubes or something like that.
Quote- One thing that this amplifier invariably needs is power tube bias adjustment. The Champion 600 Reissues that we have seen have had the 6V6 power tube biased for too much power dissipation. The correct power dissipation for a 6V6 is considered to be between 12W and 14W (12W for vintage 6V6s and up to 14W for some of the newer 6V6s). The Champion 600s that we have seen were biased for between 15.5W and 16.5W. This is simply too high and does not sound optimal. We have found that the installation of a 200 Ohm to 240 Ohm 2W resistor in series with the factory installed 470 Ohm resister in R10 will achieve approximately 12W to 13W power dissipation.
Your measurements are absolutely correct... it's Fender's design which isn't :).
So i changed the 6v6 cathode resistor to a 680ohm one.
My voltages:
All my measurements are DC:
TP2: 218VDC (First input triode plate voltage)
TP6: 1,63VDC (First input triode cathode voltage)
TP5: 218VDC (Second input triode plate voltage)
TP7: 1,7VDC (Second input triode cathode voltage)
TP9: 347VDC (Output tube plate voltage)
TP8: 21,4VDC (Output tube cathode voltage)
TP10: 336VDC (B+ after two resistors)
TP11: 355VDC (B+ after one resistor)
A schem of the stock amp: http://www.schematicheaven.com/fenderamps/champion600_reissue_fullmanual.pdf
As xou can see i did a lot to get rid of the problem, i did the steps one by one, during a 1 month period on the weekends, the amp got better step-by-step, i even get rid of the low end rattling when the amp is cranked (after i changed the cathode bypass resistor of the 6V6) with the Jensen, but the too dominant high end harsness is still there.
Thats way i think the only stock stuff left is the transformers which could be bad, or something is wrong in my circuit, like something gone wrong or i don't know.
Off the stock schematic I would try raising R17 to 10K or higher that should tame the "high end" some.
Quote from: armstrom on January 18, 2010, 04:18:17 PM
I have contacted the vendor in Germany who sells the small toroids. He says if we can get together an order of 5-10 transformers he could have them built with 120V primaries and keep the price the same. (22 euros). I'm not sure at this point what shipping would run. Keep in mind that the 22 Euro price includes German VAT (a sales-tax built into the price). I would have to check but there's a good chance that we wouldn't have to pay that 19% since the part is being exported outside the EU, however I'm not 100% sure as I've just begun discussions.
So, the real question is, how many people are interested? And for how many transformers? I would probably pick up more than one myself just to have an extra on hand should I want to build another low power tube project. I would be willing to organize this and handle the single order and shipment from Germany then do the redistribution here in the US. I have no idea about shipping or lead-times right now but I wouldn't expect this to be a very quick process since the trannies would have to be manufactured then shipped from Europe.
I'm also looking into manufacturers here in the US but so far no one has been able to get close to the small size / low price of the German transformers. If the super small size isn't an issue I may have a good solution for a similar price, but I'm waiting to hear back on that.
-Matt
I am interested but I wont have any funds to commit to that for at least two months or more.
I bet some others here would want one as well.
Do you hae more details?...number of secondary outputs, voltages, current handling etc.?
Sure. As of right now I would just be asking for a change to the primary winding so the secondaries would stay the same as the standard transformer which are:
185V @ 40 mA HT
6.3V @ 1.4A Filament
Neither secondary has a center-tap so a bridge rectifier is needed on the HT and 100ohm resistors will need to be used on the 6.3V heater secondary to create a "virtual" center tap. Nothing unusual. This is the exact transformer used int he initial schematic first posted in this thread so you can use it to build the amp as shown with no changes. Since this amp is nearly identical to Dough Hammond's firefly you could use the transformer for that amp as well. Finally, you could use it for all sorts of high voltage tube preamps / stompboxes. You wouldn't be able to use a super small enclosure but at 63mm (~2.5") in diameter and 31mm (~1.2") tall it should fit in lots of tight places.
-Matt
Hmm.. so not as much interest as I would have hoped :( oh well. I'll keep trying to dig up cheap alternative power transformers.
referring back to rotylee's comment, thinking about 6sn7 as an alternate for the ecc99...i have been thinking similarly,
along the lines of a 6cg7, which is the 9-pin equivalent of the 6sn7.
datasheet
http://www.drtube.com/datasheets/6cg7-ge1956.pdf
found updated schematic
http://diyguitarfreak.files.wordpress.com/2010/09/miniamp2-schematic.jpg
from blog post
http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168
Quote from: rotylee on September 22, 2010, 10:02:49 AM
found updated schematic
http://diyguitarfreak.files.wordpress.com/2010/09/miniamp2-schematic.jpg
from blog post
http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168
It's actually not an update but a new mini guitar amplifier I built with two 12AX7s in the preamp and an ECC99 in the poweramp, providing a full tone stack and a "real" push-pull design with a phase-inverter. Only thing similar are two of the three tubes. ;D
here are some soundsamples:
http://www.youtube.com/watch?v=lOb-RVET8So
greets
Patrick
Quote from: FcKw on September 22, 2010, 10:19:37 AM
Quote from: rotylee on September 22, 2010, 10:02:49 AM
found updated schematic
http://diyguitarfreak.files.wordpress.com/2010/09/miniamp2-schematic.jpg
from blog post
http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168
It's actually not an update but a new mini guitar amplifier I built with two 12AX7s in the preamp and an ECC99 in the poweramp, providing a full tone stack and a "real" push-pull design with a phase-inverter. Only thing similar are two of the three tubes. ;D
here are some soundsamples:
http://www.youtube.com/watch?v=lOb-RVET8So
greets
Patrick
Thats sounds absolutely fantastic !! :icon_mrgreen:
I listened to your demo and found the link to your blog. http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168 (http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168)
I was going to ask for a schematic but you alreadt posted it there .
THANK YOU ! :icon_cool:
IMO this amp is worthy of its own thread.
And nice job again, on the demo and the blog.
+1
Quote from: Brymus on September 22, 2010, 05:20:20 PM
Thats sounds absolutely fantastic !! :icon_mrgreen:
I listened to your demo and found the link to your blog. http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168 (http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168)
I was going to ask for a schematic but you alreadt posted it there .
THANK YOU ! :icon_cool:
IMO this amp is worthy of its own thread.
And nice job again, on the demo and the blog.
+1
Thanks! OK, I started a new thread including the schematic HERE (http://www.diystompboxes.com/smfforum/index.php?topic=87184.0).