Here is the Eagle schematic that I used to design the PC board for AMP1.2. I will post the complete BOM once I have time to finish tweaking it out. The only mod so far is a 47 uF cap from pin 4 of U4 to ground to kill a background buzz from the series heater string.
Anyone can build this using a more conventional power supply and PTP wiring. Use a 6AU6 for the first tube, a 6AV6 for the second tube and 6AQ5's for the output. That's where I started before optimizing for cost.
Anyone can build this using a more conventional power supply and PTP wiring. Use a 6AU6 for the first tube, a 6AV6 for the second tube and 6AQ5's for the output. That's where I started before optimizing for cost.
Mellow? I'm sure there must be some "mellow" designs out there somewhere.
What I don't quite understand is using the word "mellow" in the same post with the words "Tubekit's design."
I'm quite sure that's the wrong word in this case.
Put a 6LY8 into the socket and it screams. Did someone mention acoustic "feedback"? As in some number of inches between guitar strings and speaker? Change inches to feet for what we're talking about here. Can you say "sizzling"?
There are more than five different options listed in the 73 RCA .
I tried four of them.
I only heard "mellow" once.
The 6LF8 is "mellow." Good for Jazz rhythm and Funk.
The 6KV8 is pretty crunchy, but it can't touch the 6EB8.
Haven't tried the 6KR8 yet.
Or the 6LQ8.
Or the 6JV8.
I'm fairly sure there are others.
I have reason to believe that the 6EB8 is the right one for general use.
Not being as stupid as I've been made out to be, and all.
It looks like there's just no way around it. It's going to take a MOTU and a Shure SM57 to evaporate all these ephemeral pipe dreams and replace them with some substance.
Some people just can't hear the sheet music.
What I don't quite understand is using the word "mellow" in the same post with the words "Tubekit's design."
I'm quite sure that's the wrong word in this case.
Put a 6LY8 into the socket and it screams. Did someone mention acoustic "feedback"? As in some number of inches between guitar strings and speaker? Change inches to feet for what we're talking about here. Can you say "sizzling"?
There are more than five different options listed in the 73 RCA .
I tried four of them.
I only heard "mellow" once.
The 6LF8 is "mellow." Good for Jazz rhythm and Funk.
The 6KV8 is pretty crunchy, but it can't touch the 6EB8.
Haven't tried the 6KR8 yet.
Or the 6LQ8.
Or the 6JV8.
I'm fairly sure there are others.
I have reason to believe that the 6EB8 is the right one for general use.
Not being as stupid as I've been made out to be, and all.
It looks like there's just no way around it. It's going to take a MOTU and a Shure SM57 to evaporate all these ephemeral pipe dreams and replace them with some substance.
Some people just can't hear the sheet music.
OK, I will admit that I might have used the wrong word late last night. I was trying to state that both designs have practical uses and audiences. So far most of the time I have spent playing with my own amp has been with everything maxed out and wishing it would go to 11.
As I stated before I have no experience with the actual Tubekit design. I threw together a quick lashup of an SE amp using the 9DX base and ran several tubes through it. The schematic was similar to what you posted. I can state that it did sound quite nice and could go well into the distortion zone with some tubes. Choice of OPT and speaker makes a big difference too.
There are more than 20 pin compatible tubes that can fit the 9DX socket. I have several samples of most of them and have tried most in several designs. No guarantee that they can all work in your design. They are:
6AU8 6AW8 6BA8 6BH8 6CX8 6EB8 6GN8 6HF8 6HZ8 6JA8 6JE8 6JL8 6JT8 6JV8 6KR8 6KT8 6KS8 6KV8 6LB8 6LF8 6LQ8 6LY8 6MV8 and a few more with odd heater voltages.
The design that I tried was not what I was looking for and I chose not to go further down that road. I have already ditched several other designs too, including the original version of AMP1.2 . As I stated I tend to prefer something that can do clean and transition all the way to full metal racket. With my little speaker 2 watts isn't loud enough either. Other builders might and probably do have different preferences. Eventually we will both get sound clips posted and then we can really hear them. Until then it is all speculation that gets zapped by the moderators.
The 4 tube design that I posted last night does go well into the distortion zone in a good kind of way, but it is still not the ultimate design that I am looking for. The 5 tube design that cranks out about 20 watts and requires all of the $100 budget does get there, but it is more complicated than both of these budget amps combined. I am still working on exactly the right sound but it won't be a $100 amp either.
Speaking of tube specs . . .
I expected there would be more tubes that would fit the 9DX socket, but that's quite an impressive list!
I haven't verified all of them but I do have the 6KT8 and it seems I remember a reason for leaving it off of my list and never putting it in the socket. Ah yes, according to the handy old 73 RCA it's not a 9DX tube. Pin 5 is heater, yes, but also g3 and internal shield. Not compatible with the AC filament in this design, but I do have some designs using a DC filament that should work with that side of the filament grounded. Hmmm. Maybe the rest of that list could stand a little review and verification, too.
I'm working on a four-tube 3.5 watt design that goes from sweet and clean to full metal fuzz with a broader frequency response than this one, and includes bass, mid, treble, and spring reverb for the $99 target. It would already be prototyped except that I'm also trying to squeeze a tube compressor into the design without adding any more tube sockets.
Just finished building a test jig with a front face full of milliammeters, multi-position switches and pots, plus two or three separate pairs of binding posts for voltmeters and ohmmeters. I've got this interesting tube for which the published specs don't even begin to tell the story about what happens to plate current when its various electrodes are subjected to the permutations of possibility. I plan to find out. So I'm making spreadsheets, recording the voltage and current in various places.
Making spreadsheets is boring. Very, very boring. But the secret hidden within this tube has begun to reveal itself to me. And that, my friends, is exciting. Very, very exciting! (You've all heard of negative resistance, right?)
From spreadsheets to graphs. From graphs to designs. From designs to the above stated goal. It's all top secret right now, but I'll keep you posted.
Incidentaly, the amp built from the circuits I submitted above puts out over 1.5 watts RMS into an 8-Ohm speaker as measured using a guitar single coil pickup as input.
I expected there would be more tubes that would fit the 9DX socket, but that's quite an impressive list!
I haven't verified all of them but I do have the 6KT8 and it seems I remember a reason for leaving it off of my list and never putting it in the socket. Ah yes, according to the handy old 73 RCA it's not a 9DX tube. Pin 5 is heater, yes, but also g3 and internal shield. Not compatible with the AC filament in this design, but I do have some designs using a DC filament that should work with that side of the filament grounded. Hmmm. Maybe the rest of that list could stand a little review and verification, too.
I'm working on a four-tube 3.5 watt design that goes from sweet and clean to full metal fuzz with a broader frequency response than this one, and includes bass, mid, treble, and spring reverb for the $99 target. It would already be prototyped except that I'm also trying to squeeze a tube compressor into the design without adding any more tube sockets.
Just finished building a test jig with a front face full of milliammeters, multi-position switches and pots, plus two or three separate pairs of binding posts for voltmeters and ohmmeters. I've got this interesting tube for which the published specs don't even begin to tell the story about what happens to plate current when its various electrodes are subjected to the permutations of possibility. I plan to find out. So I'm making spreadsheets, recording the voltage and current in various places.
Making spreadsheets is boring. Very, very boring. But the secret hidden within this tube has begun to reveal itself to me. And that, my friends, is exciting. Very, very exciting! (You've all heard of negative resistance, right?)
From spreadsheets to graphs. From graphs to designs. From designs to the above stated goal. It's all top secret right now, but I'll keep you posted.
Incidentaly, the amp built from the circuits I submitted above puts out over 1.5 watts RMS into an 8-Ohm speaker as measured using a guitar single coil pickup as input.
The 6LF8 and 6LY8 looked like some of the best cantidates in the 9DX pin out and I have both but have not tried them since I only had time to finish working with the 6DX8 design (9HX pin out).
9AE is another pinout that looks promising, at least for preamp/driver tubes but I havn't found any tubes in that pinout that will reach a 2W output level.
6GV8 looks good for power but in a somewhat rare pinout, 9LY.
The only spreadsheet I've done was broken down by pinout and different sheets by power level. I probably have a quarter of the tubes in it that George listed.
More confusing is why are 9DC and 9AE the same pin out? Are there others like them where two designations are used for the same pin out?
9AE is another pinout that looks promising, at least for preamp/driver tubes but I havn't found any tubes in that pinout that will reach a 2W output level.
6GV8 looks good for power but in a somewhat rare pinout, 9LY.
The only spreadsheet I've done was broken down by pinout and different sheets by power level. I probably have a quarter of the tubes in it that George listed.
More confusing is why are 9DC and 9AE the same pin out? Are there others like them where two designations are used for the same pin out?
I stuffed it into the amp any way since I have pin 5 at AC ground but elevated to about 30 volts DC. I don't remember the details on which tube worked the best in that design.
I still have the 1973 RCA tube manual that I bought new at a Lafayette Radio Electronics store in 1973. It still has the $1.25 price sticker on it. It has seen better days. You can download a PDF of the 1975 edition here:
Tube Data
Pete is a forum member here and has scanned more vacuum tube related books to PDF than anyone can possibly read. They are all on his web site to download.
The list was compiled by a few of us tinkering with cheap tubes. I did not verify every number on the list, so yes check carefully before plugging in.
There are a few but I don't remember them all. I'm guessing that different manufacturers registered their new tubes with RMA or RETMA (both now part of EIA) at the same time and the duplicity wasn't caught. There were no computers then.
Octal: 7AC = 7S 8EP = 8ET
9 pin: 9AJ = 9DE
7 pin: 7BK = 7CC
Tell me about it. 38 years as an RF engineer, spreadsheets and Powerpoint slides have become a way of life in big corporation engineering. It's not about the circuit design...it's "He who has the best presentation wins." The tennis player selling Canon cameras said it best years ago "Image is everything."
Unfortunately to hit the $99 target with a long list of features, you are going to need a spreadsheet to determine how best to utilize the budget
Remember, the published data was drawn up with the tubes intended operation in mind. Just about every tube mentioned in this entire thread was not intended for use in a guitar amp. Most were not even intended for audio. There are lots of secrets yet to be discovered in the tube world even though tubes have been around for a long time. This becomes more true when you allow judicious use of silicon. Screen driven audio power amps come to mind.
Sort of, maybe yes it will almost work but you will not like the result.
I'm slowly building what I call a modernized clone of a Fender 6G15. The reverb pan came in the mail long before I had electronics built to drive it. So I was messing around with an audio signal generator and a scope. And I was pretty much able to verify that everything on the Acutronics web site about how to use a reverb pan is correct.
Now to your question: Yes the pan is microphonic. If you shake the pan you get signal out of the pan even with input disconnected, however the fidelity is horrible. In other words the frequency response and noise of the mechanical coupling is such that the method is useless for audio. You really do need a reverb driver amplifier. And just as stated in the Acutronics web site the driver needs to be powerful enough to totally swap any input from the mechanical coupling. It also turns out it is very easy to mechanically "over drive" the pan and then the only sound you hear is "spring crash" which sounds even worse than microphone handing and wind noise.
Leo Fender was smart. He must have figured that he could improve the sound not only by going over the top with a big driver but also at the same type removing the pan from the combo amp and flying the pan on a spring suspension inside it's own cabinet. The signal to noise as very much improved when you do what he did with the Fender 6G15. This means (1) isolate the pan from the speaker as best you can and (2) drive the pan as hard as you can, to just below saturation. Using a speaker to drive the pan violates both of the above in a big way.
Hah ha. Then you have to go one giant step further and make one so simple a lead singer can build it.
..Todd
Sorry if this topic is OT wrt the amp challenge, I am just curious to learn from you experienced builders on how one would start to guess at what may or may not work before buying the transformer
The math on how to calculate the impedance is pretty straight forward, since we can derive the turns ratio from the transformer's spec, but how do you figure out the inductances, thus frequency response if the manufacturers do not provide the data in their spec sheets?
Anyway, did you check out the Piltron 4002-1? It goes for $12 and its spec looks pretty good, but may be under-powered for your needs...
Jaz
I thought I saw a link to the $12 price for this a while back, did that turn out to be fake? Seems too good to be true ... and I can't find the link now.
A couple more low cost transformers at Triode Electronics
1) Single ended 7.5K load matched to 8 ones. up to 28ma $16.40
Output Transformer for 6G15 Add-On Reverb Unit OT47605 MADE IN USA
2) Single ended, 25K to 8 ohms The claim "3.5 watts". $15.96
Fender Vintage Style Reverb Driver ClassicTone 40-18034
Both are made in the US by Magnetic Components Inc. under they "Classic Tone" brand name. They are intended to drive an 8 ohm spring reverb pan and so are only good for a 1 or 2 watts. Yes they are spec'd for more but you never but bass through a reverb so these would only be flat to about a few hundred Hz at full power, but for a flea powered bedroom amp these two transformed are ideal. They were designed for guitar amps. Classic Tone claims to use "vintage" production techniques, correct interleaving and paper between the layers and so on. You can read their sales pitch here:
ClassicTone Transformers By Magnetic Components, Inc.
I have the first one listed above. Build quality is good. I's going to be powered by a 6K6 tube. The 6K6 is a lower powered version of the 6V6 and 6L6 tubes and sounds like it. THese are easy to buy for about $3.50 each
If you can live with about 1W power a Classic tone 7.5K:8 transforer and a 6K6 and one 12AX7 tube lets you build and authentic but with limited power Fender Champ. The smaller tube lets you get into power tube distortion more quickly although it's still to loud for bedroom volume.
The second transformers is good if you want use something like an 12AU7 section as a single ended power tube.
No, it was a scam, the moderator deleted most of the posts relating to the topic, I also informed Plitron about it, perhaps the phony site will get shut down soon...
Jaz
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