One of the guys on my job is a guitar picker. What he owns for amps is unmentionable. I know nada about guitar amps. So, I'm starting with the Fender Champ 5C1 and looking for ways to hold costs down.
Fact, "12" V. versions of tubes cost less than "6" V. versions. With that in mind, I'm thinking 12SJ7 and 12V6 as the signal tubes, with heater power provided by "Rat Shack" catalog # 273-1365.
Another fact, the most cost effective way to obtain a decent 300 V. B+ rail is via a Greinacher ("full wave") Voltage doubler. For reasons of "sag", tube rectification is desirable in this design. I think I see a way to have the cake and eat it to. The 50 VA Triad N-68X isolation trafo provides enough current to energize both the heater of a 117Z6 and a doubler formed around the twin diode. A pair of 15 μF./250 WVDC 'lytics should be about right for the doubler stack. Perhaps an increase to 10 μF. in the reservoir position is appropriate.
Please comment on the PSU concept. Also, cabinetry and a speaker driver recommendations are needed. This will be a "combo".
Fact, "12" V. versions of tubes cost less than "6" V. versions. With that in mind, I'm thinking 12SJ7 and 12V6 as the signal tubes, with heater power provided by "Rat Shack" catalog # 273-1365.
Another fact, the most cost effective way to obtain a decent 300 V. B+ rail is via a Greinacher ("full wave") Voltage doubler. For reasons of "sag", tube rectification is desirable in this design. I think I see a way to have the cake and eat it to. The 50 VA Triad N-68X isolation trafo provides enough current to energize both the heater of a 117Z6 and a doubler formed around the twin diode. A pair of 15 μF./250 WVDC 'lytics should be about right for the doubler stack. Perhaps an increase to 10 μF. in the reservoir position is appropriate.
Please comment on the PSU concept. Also, cabinetry and a speaker driver recommendations are needed. This will be a "combo".
I don't play, but built an AX84 pre and power amp combo for my son. It is more complex than a champ, but I used cheap Russian valves. 6P6S for the 6V6 and 5U4M for the rectifier. Check the usual eBay sources. I have had no problems with any of the ex-Soviet Block sellers...
I used a Celestion speaker in my project, but my son is not advanced enough o be able to tell me if it is good or bad, he is just impressed that he turn it up to 11 with 20 Watts and impress (not!) the neighbours! Maybe something like a Celestion Tube 10 might suit? They are about $45 at Antique electronics
I used a Celestion speaker in my project, but my son is not advanced enough o be able to tell me if it is good or bad, he is just impressed that he turn it up to 11 with 20 Watts and impress (not!) the neighbours! Maybe something like a Celestion Tube 10 might suit? They are about $45 at Antique electronics
I think the ripple will be a real problem.
I seem to remember you writing that you accept the tube construction itself as an acceptable form of galvanic isolation. Why not wire the Triad as 120:240 step up and run the 117Z6 off of the line side? That's what that tube was built for. That'll get you 300VDC without the ripple of a doubler.
I don't if cheap extends to the speaker, but if it does, you can use a PA driver rather than spending the cash for a real guitar speaker.
EDIT: Now that I think of it, why not wire the Triad as 120:240 and use TWO 117Z6s in a bridge heated using the secondaries. Then you'll have BOTH isolation and lower ripple.
I seem to remember you writing that you accept the tube construction itself as an acceptable form of galvanic isolation. Why not wire the Triad as 120:240 step up and run the 117Z6 off of the line side? That's what that tube was built for. That'll get you 300VDC without the ripple of a doubler.
I don't if cheap extends to the speaker, but if it does, you can use a PA driver rather than spending the cash for a real guitar speaker.
EDIT: Now that I think of it, why not wire the Triad as 120:240 and use TWO 117Z6s in a bridge heated using the secondaries. Then you'll have BOTH isolation and lower ripple.
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The 117Z6 was intended for use as a doubler. Look at the data sheet. When the anodes are exposed to voltages above that found in North American residences, protective resistors are needed. Aside from other reasons, doubled forward voltage drop pretty much rules a bridge of 4X vacuum diodes out. BTW, turning a N-68X around, for step up, is not a good idea. The single winding designated as the secondary is sized with regulation effects taken into account. Don't believe for a single moment that all the windings have exactly the same number of turns.
There will be no more ripple with the doubler than in the Fender original. 😉 Leo used an 8 μF. 1st cap. in his CRC filter. A doubler working into a 2X 15 μF. has approx. = ripple. Any slight difference will be taken care of by increasing the reservoir cap. from 8 μF. to 10 μF.
There will be no more ripple with the doubler than in the Fender original. 😉 Leo used an 8 μF. 1st cap. in his CRC filter. A doubler working into a 2X 15 μF. has approx. = ripple. Any slight difference will be taken care of by increasing the reservoir cap. from 8 μF. to 10 μF.
I have been down this road before. You can wire a bunch of unusual components together and maybe save a dollar ot two on the initial build. If this is a one off, and you can fix it forever, this is OK. If your amp will ever wind up in the hands of someone that you don't know (like if you are going to sell them) you must face the first law of building guitar amps.
If it is going to be serviced by the typical guitar amp tech, it MUST not use any trick circuits or parts that you can't buy at the typical music shop. If you have ever spent some time with an "expert amp guy" you will know what I am talking about. Fact, they will NEVER understand screen drive, and they will rewire your screeming monster amp until it doesn't work even though it did work when it came into the shop. 6AV5's don't compute, the "expert" will stick 6L6GC's in and wonder why the smoke monster appears.
So, I have learned that if you are going to sell it, it has to use tubes that are in the Sam Ash, Guitar Center, or Musicians Friend catalog. That is a rather small list. So for a small amp, you are stuck with the 5Y3 (and maybe a 5AR4 for a louder sound), a 6V6GT or a 6K6 for the output tube, and a 12AX7 for input duty. Yes, Fender used the 6SJ7 years ago, and mister wonder tech can't possibly stuff a 12AX7 into the socket, so it's probably OK. I have used other tubes in small amps (the 6W6) but you have to assume that someone WILL stuff in a 6V6GT or even a 6L6GC down the road. Funky combinations of transformers will confuse mister wonder tech too.
So for my "Champs" I use the Allied 6K56VG. You get about 300 volts with a 5Y3 and 320 volts with a 5AR4. For the big guys (50 watt P-P) I use the Allied 6K7VG, 430 volts of B+. I have been using these transformers in guitar amps for at least 15 years, and I haven't seen a failure yet. They are Hammonds so they do get hot, but they don't blow up. I built a few "Turbo Champs" that used a 12AX7, a KT88 a Hammond 125CSE OPT, and a 6K7VG power transformer. They were screamers.
Amp experts, and most users have no idea what impedance is and it is not too uncommon to find several additional speakers connected up in random fashion. I used the 125 CSE to allow for some means to achieve a match. I used a 4 way switch to select the tap on the OPT's these were used as tone / distortion controls.
Part of the "Fender sound" comes from the fact that Fender always used an under sized OPT. Saturation was part of the sound, but is was also part of the reason that Fenders ate tubes. There was a "fact" that was widley told in the 60's that stated that "a Bandmaster will blow up if you play a bass guitar through it." I can say that I saw this fact verified in flames in the 70's. It sounded cool, but after about two hours one of the 6L6GC's went nuclear and sparked out. So, the message, the OPT controls the sound. A Fender replacement" of the correct size is needed for the correct sound, but a cheap Edcor or Hammond 125 series will give a less distorted sound at full crank but be easier on the tubes.
If you build the 5C1 and the player uses a stomp box that puts out a bit more than "guitar voltage" you can get some unusual distortion by trying a 6SK7 in place of the 6SJ7. It was a common trick that I used years ago. I quit using that circuit about 15 years ago since the 12AX7 is just too common in the guitar amp world.
Well the 12SJ7 was intended for RF, so by your logic you can't use it in your amp because that's a different service 🙂
The secondary voltage will fluctuate with primary voltage. How do you avoid needing that same resistor on the secondary side if you need it on the primary side?
What does it matter if it's not exactly 1:2?
With respect to "turning around" a transformer:
I've been told that supplying a winding with higher voltage than it was designed to handle is bad mojo. I've got some oddball transformers where I thought I could "turn them around" and run my 120VAC wall voltage into a secondary, and take something useful off the primary. Apparently this kind of foolishness doesn't work. Maybe the secondary doesn't have enough turns to provide the inductive load (is that something I made up?) required to support a higher voltage. Instead of exciting the core you just end up drawing a lot of current in a low resistance winding, burning a lot of heat and (hopefully!) blowing a fuse.
I've been told that supplying a winding with higher voltage than it was designed to handle is bad mojo. I've got some oddball transformers where I thought I could "turn them around" and run my 120VAC wall voltage into a secondary, and take something useful off the primary. Apparently this kind of foolishness doesn't work. Maybe the secondary doesn't have enough turns to provide the inductive load (is that something I made up?) required to support a higher voltage. Instead of exciting the core you just end up drawing a lot of current in a low resistance winding, burning a lot of heat and (hopefully!) blowing a fuse.
It seems to work OK with the Triad N-68X, The regulation sucks though. I use a N-68X to make + and - 140 volts with a SS bridge, It works OK.
George,
Thanks for your comments. I'm a HIFI guy. IF this project happens, it will be a 1 off cheapskate special.
Thanks for the heads up about the O/P "iron". As it turns out, Triode Electronics has Champ O/P trafos with 8/4 Ω speaker taps and they cost less than $20. 😀
I still need advice about cabinetry and speaker selection.
Thanks for your comments. I'm a HIFI guy. IF this project happens, it will be a 1 off cheapskate special.
Thanks for the heads up about the O/P "iron". As it turns out, Triode Electronics has Champ O/P trafos with 8/4 Ω speaker taps and they cost less than $20. 😀
I still need advice about cabinetry and speaker selection.
You want cheap? FInd a dead little solid state practice amp. There you have a ready made little cabinet and speaker, and a chassis. Gut the chassis and build your thing in it. Typical cost - free.
Read the comments by tubelab several more times. Right on.
Push pull AB amps are one thing, but this single ended Champ runs class A, and as such, the current load on the B+ is pretty steady. SO sag is not really going to be much of an issue. SO for my money, at least in this amp, save the rectifier tube and its socket, and the extra cash for that 5v winding and use a couple 1N4007 instead.
50 years ago when Leo Fender was coming up with amp designs, caps were more expensive than they are now, and Leo was a master of "good enough" engineering. WHy use a 10uf cap when an 8uf cap was good enough. There is no magic to 8uf, they were just cheap. You can find an 8uf today maybe, but a 22uf cap is a lot more common. And cheaper.
You can use that pentode 6SJ7, but the 5C1 was the first Champ. Here is the 5E1, and they have replaced that tube with a VERY common 12AX7. And note the larger filter caps. He also replaced the CRC with a CLC, but cost quickly won out and CHamps went back to CRC filters in later versions. Nothing stops you from building the 5E1 withe a 500 ohm resistor instead of the choke.
http://www.schematicheaven.com/fenderamps/champ_5e1_schem.pdf
WHile there, explore the whole rest of the Fender and other brand schematics at Schematic Heaven.
I am curious about power. If $$$ is important, is it really cheaper to use a Radio Shack transformer for heaters and an isolation transformer side by side feeding some sort of esoteric doubler tube? COnsider something like an Allied 227-0001. It has an amp of 6v ( enough for a 6V6 and a 12AX7) and 250v for B+, which would rectifiy up to about 350 for you. Under $16.
And looking up tubes, I find the 6SJ7 is a dollar more than the 12SJ7, but at $5.30 neither one is expensive.
The speaker. In a guitar amp the one single thing that affects the sound the most is the speaker. My main advice is to keep in mind that a guitar amp is nor designed to REproduce sound. it is a primary producer of sound and is really part of the instrument. The point of hifi stuff is it is not supposed to have a sound of its own. Other than subtle performance nuance, they all should sound more or less the same. Guitar amps are intended to add character of their own. That is why a musician says "I play a Marshall," or "I play a Fender.." SO you can stick some throw-awat little radio speaker in there, and it will sound like it. I wouldn;t tell you you gotta spend a lot on a speaker, but be aware of its part in the performance. And the one that came with the dead practice amp carcass might be fine.
Read the comments by tubelab several more times. Right on.
Push pull AB amps are one thing, but this single ended Champ runs class A, and as such, the current load on the B+ is pretty steady. SO sag is not really going to be much of an issue. SO for my money, at least in this amp, save the rectifier tube and its socket, and the extra cash for that 5v winding and use a couple 1N4007 instead.
50 years ago when Leo Fender was coming up with amp designs, caps were more expensive than they are now, and Leo was a master of "good enough" engineering. WHy use a 10uf cap when an 8uf cap was good enough. There is no magic to 8uf, they were just cheap. You can find an 8uf today maybe, but a 22uf cap is a lot more common. And cheaper.
You can use that pentode 6SJ7, but the 5C1 was the first Champ. Here is the 5E1, and they have replaced that tube with a VERY common 12AX7. And note the larger filter caps. He also replaced the CRC with a CLC, but cost quickly won out and CHamps went back to CRC filters in later versions. Nothing stops you from building the 5E1 withe a 500 ohm resistor instead of the choke.
http://www.schematicheaven.com/fenderamps/champ_5e1_schem.pdf
WHile there, explore the whole rest of the Fender and other brand schematics at Schematic Heaven.
I am curious about power. If $$$ is important, is it really cheaper to use a Radio Shack transformer for heaters and an isolation transformer side by side feeding some sort of esoteric doubler tube? COnsider something like an Allied 227-0001. It has an amp of 6v ( enough for a 6V6 and a 12AX7) and 250v for B+, which would rectifiy up to about 350 for you. Under $16.
And looking up tubes, I find the 6SJ7 is a dollar more than the 12SJ7, but at $5.30 neither one is expensive.
The speaker. In a guitar amp the one single thing that affects the sound the most is the speaker. My main advice is to keep in mind that a guitar amp is nor designed to REproduce sound. it is a primary producer of sound and is really part of the instrument. The point of hifi stuff is it is not supposed to have a sound of its own. Other than subtle performance nuance, they all should sound more or less the same. Guitar amps are intended to add character of their own. That is why a musician says "I play a Marshall," or "I play a Fender.." SO you can stick some throw-awat little radio speaker in there, and it will sound like it. I wouldn;t tell you you gotta spend a lot on a speaker, but be aware of its part in the performance. And the one that came with the dead practice amp carcass might be fine.
Use 6JC5 tube, "end of evolution" of 6V6 tubes. The same tone, little stronger, no change of any other component (only socket), cheep and will work 10-15 years in "Champ".
"Celestion Tube10" is very good speaker, but sounded different from characteristic "Fender" amps, more "British" with strong middle. Any old "Jensen", "Oxford", "Utah", "CTS" will be better. I bay from USA 2x"Cletron 12" "(65$ WITH shipping to Croatia!) from 1958.year with "AlNiCo" magnet and use it in one "Champ"(modify). Sound is better than any other speaker I try.
"Celestion Tube10" is very good speaker, but sounded different from characteristic "Fender" amps, more "British" with strong middle. Any old "Jensen", "Oxford", "Utah", "CTS" will be better. I bay from USA 2x"Cletron 12" "(65$ WITH shipping to Croatia!) from 1958.year with "AlNiCo" magnet and use it in one "Champ"(modify). Sound is better than any other speaker I try.
My 1st build was a 5F1. $2 flea market chassis from a computer power supply or something. Used leftover 3/4 birch ply from an entertainment center project.
As mentioned, no PS "sag" in this design so no need for tube rectification unless you like looking at more tubes. I do. 😎 Don't use Sovtek 5y3 since they yield a higher voltage than expected.
Mine is still my best amp when comparing them all at around 5watts of output, which is about the most the Champ will do.
Finally picked up a Tremolo pedal to use with it recently. Used Danelectro for $15. All my other amps have built in trem.
old clip: http://home.comcast.net/~jjsant3250/champo_sm58.mp3
As mentioned, no PS "sag" in this design so no need for tube rectification unless you like looking at more tubes. I do. 😎 Don't use Sovtek 5y3 since they yield a higher voltage than expected.
Mine is still my best amp when comparing them all at around 5watts of output, which is about the most the Champ will do.
Finally picked up a Tremolo pedal to use with it recently. Used Danelectro for $15. All my other amps have built in trem.
old clip: http://home.comcast.net/~jjsant3250/champo_sm58.mp3
Eli, 300 volts is ok for an el84 but it's too polite for the 6v6. It just sounds better with 350 volts at the plate. You'll also get a louder clean tone and since there's not much clean tone to start with, it really makes a difference.The EH 6V6 is a cheap tube and can stand the abuse.
I agree with Tubelab about the output transformers. Open back cabinet sounds best with this amp.
I agree with Tubelab about the output transformers. Open back cabinet sounds best with this amp.
Eli,
Go with SS Diodes in a doubler. No need for the tube.
12SJ7 and 12V6 are OK assuming you already have them, if buying go with the 6 volt heater versions.
For inexpensive guitar amp, I like the princeton circuits, they add a "tone" control and the 5D2 uses 12AX7 (easy enough to find and the sections do not need to match)
Cheapest speakers would be Celestion or Jensen. The Jensens can be found on Ebay for very little $$$ BUT a 10" or 12" Paper cone speaker from an old console or cheap tower speaker is good to start with.
I built one for my brother-in-law and used an 8" Jensen (green??). A small 6BQ5 OPT from a reel to reel recorder. I used a small "baking pan" from Walmart ($8) as the chassis and the box I built from 1/2" Plywood for the top, sides, and divider. I used 3/4" MDF for Speaker baffle and rear support and 1/4" Luan for the front face.
Go to a fabric store and "tweed" is cheap. I just spray glued an "upholstery" type thin batting to the outside and glued and staple on a tan tweed.
My brother-in-law has 4 or 5 solid state amps of varying power BUT spends more time on my $70 "junkbox" amp!!!
Go with SS Diodes in a doubler. No need for the tube.
12SJ7 and 12V6 are OK assuming you already have them, if buying go with the 6 volt heater versions.
For inexpensive guitar amp, I like the princeton circuits, they add a "tone" control and the 5D2 uses 12AX7 (easy enough to find and the sections do not need to match)
Cheapest speakers would be Celestion or Jensen. The Jensens can be found on Ebay for very little $$$ BUT a 10" or 12" Paper cone speaker from an old console or cheap tower speaker is good to start with.
I built one for my brother-in-law and used an 8" Jensen (green??). A small 6BQ5 OPT from a reel to reel recorder. I used a small "baking pan" from Walmart ($8) as the chassis and the box I built from 1/2" Plywood for the top, sides, and divider. I used 3/4" MDF for Speaker baffle and rear support and 1/4" Luan for the front face.
Go to a fabric store and "tweed" is cheap. I just spray glued an "upholstery" type thin batting to the outside and glued and staple on a tan tweed.
My brother-in-law has 4 or 5 solid state amps of varying power BUT spends more time on my $70 "junkbox" amp!!!
Reading back over the posts it seems we are mostly in agreement as to choice of tubes.
The AX7 and 6V6 or 12V6 are the MOST common so go with those.
I used the little tranny because I KNOW it won't be used with anything other than the 8 ohm load that is in it and I had also heard of Tubelabs comment on "under sized" trannys being part of the "fender sound".
One place I diverted from the original schematic was I increased the cap size feeding the screens and input section to 20uF.
I also "Hard wired" the speaker NO jack so he can't blow it up. (I hav him DEATHLY afraid of the voltages inside the cabinet)
The AX7 and 6V6 or 12V6 are the MOST common so go with those.
I used the little tranny because I KNOW it won't be used with anything other than the 8 ohm load that is in it and I had also heard of Tubelabs comment on "under sized" trannys being part of the "fender sound".
One place I diverted from the original schematic was I increased the cap size feeding the screens and input section to 20uF.
I also "Hard wired" the speaker NO jack so he can't blow it up. (I hav him DEATHLY afraid of the voltages inside the cabinet)
The R/S filament trafo carries a $6.29 price tag. $11.41 buys a Triad N-68X. Yes, the cost of an Allied 6K1VF (227-0001) is $15.72, but it's rated for only 25 mA. of B+. 🙁 That's not nearly enough for a SE 6V6 family "final". FWIW, I advise using the 6K1VF in making PSUs for tweaked RCA phono preamps. 😉
AES' prices for the tubes I propose to use follow: $3.95 for the 12SJ7, $8.50 for the 12V6 (NOS), and $6.00 for the 117Z6. AES' prices are $5.30/$21.95, respectively, for a 6SJ7 and a NOS 6V6. $10.50 is Jim McShane's price for a properly culled current production EH 6V6.
The 12SJ7 does work in the pre-stages of guitar amp. I have built several using it for my son. The amp sounds great, and he uses it daily in school band.
You just have to follow the rules in the tube data and then turn it up a notch till it smokes, then back it off a little. 🙂 I am not saying that it is a common settup, nor was it ever intended for this service, but it will work.
"Imagination with tubes work with dedication to the art"
Michael Thompson (mltube)
You just have to follow the rules in the tube data and then turn it up a notch till it smokes, then back it off a little. 🙂 I am not saying that it is a common settup, nor was it ever intended for this service, but it will work.
"Imagination with tubes work with dedication to the art"
Michael Thompson (mltube)
And this is what you get for your $20, shown next to a 12AX7. I couldn't get it to sound good, so I used a transformer that I ripped from an old radio. It was bigger too. Find a used SE radio transformer and spend the money elsewhere.
As stated the speaker is important, very important, in a guitar amp. I have used Weber speakers (6 inch or 8 inch Alnico) in my champ type amps with excellent results. I have not built a guitar amp in several years and there was some speculation about who is running the show now that Ted Weber has died.
If you are building a one off, and cost is the major factor skip the high priced tubes at AES and go directly to the $1 rack at ESRC. I have several favorites here, and unfortunately when I mention them, they disappear, but here goes. The 6EZ5 is a sleeper. It plugs into a 6V6 socket and in most cathode biased amps it will work without changes (300 volt max VS 315 for 6V6). A bias adjustment is needed in a fixed bias amp. I am sure that you can find a $1 TV tube (dual triode, or triode pentode pair) that would work as a driver. I would investigate the pentode as the driver using the champ circuit you have and add the triode for an extra high gain input. You already know about the 6AQ5. It works in the champ circuit within its ratings.
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