This one has tone control and a speaker. One euro left for mods. Maybe it's time to change the thread title to the hundred-buck tube preamp challenge. 
PEAVEY ROYAL 8 VALVE KING - Thomann UK Cyberstore
Not for winning but I'm going to build an awesome sounding EL84 PP triode/pentode amp for less than 100$. Not everybody can do that. I deserve some respect. Maybe we could start a separate thread: Cheapskate's challenge - How to build a great amp (no cheesy 70$ amp) with only 100$/€. Tips: Iron and tubes from ebay Germany; chassis from public property (some traffic headlights in Madrid have a nice metal box with a sound generator that goes tweet tweet at the right time so the blind know when it's safe to cross the street); the rest from old tube junk collected in dumpsters.
PEAVEY ROYAL 8 VALVE KING - Thomann UK Cyberstore
Not for winning but I'm going to build an awesome sounding EL84 PP triode/pentode amp for less than 100$. Not everybody can do that. I deserve some respect. Maybe we could start a separate thread: Cheapskate's challenge - How to build a great amp (no cheesy 70$ amp) with only 100$/€. Tips: Iron and tubes from ebay Germany; chassis from public property (some traffic headlights in Madrid have a nice metal box with a sound generator that goes tweet tweet at the right time so the blind know when it's safe to cross the street); the rest from old tube junk collected in dumpsters.
Speaking of iron from ebay Germany, 100 monetary units will go a long way
http://www.diyaudio.com/forums/tubes-valves/191691-1-stage-killer-literally-amp-made-junk.html
I found a couple threads on The Kustom 5H over on a forum called SEWATT.com. They have gut shots, a mod thread and schematic(unofficially drawn)
You have to join to view the forum and conversation though.
Yep. And it is nice modern Champ version. What is bad, how electrolytics are placed near EL84.
Or, they may sell wast excess of production in order to save on space in warehouses.
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That and the row of electrolytic caps are so close to the front panel exactly where someone might want to neatly add a tone control.
Thing is, If they are offering them right now for 99.99us SHIPPED, I find it hard to believe they are costing much over $20.00 per unit.
Chinese military surplus EL84s (6p14-J from 1970's) are $1-2 a piece when bought by the box (and are not that bad either). There may be a similar deal for 12AX7s or perhaps they go for more but still you get both tubes for $5.
I find it interesting that they are claiming compliance with FCC Part 15 class B 'digital device", and many if not all of the specs they claim comformaty with are from 1994/5(out of date?).
The latest EN60065 (IEC60065-E) I've seen is 2005, and I think there may be a later one.
No mention of UL1449 Although that may be a cap on the ckt board not a varistor.
The latest EN60065 (IEC60065-E) I've seen is 2005, and I think there may be a later one.
No mention of UL1449 Although that may be a cap on the ckt board not a varistor.
Tonight I tried a alternate equivalent output tube from the former Soviet Union.
So I now have two options for the output tubes, and both take the abuse.
I've cranked them up to 330V B+ and got over 3W into 4 ohms at 1KHz.
When I pushed it to 13Vp-p square wave out into 4 ohms, it failed to elicit red plates after 20 minutes so I gave up. I did increase the cathode resistors to 220Ohms to limit the cathode current to 25mA and plate current to 2X rating. (I guess it is a tad less plate dissipation since that includes the screen current in with the plate current, bad math.)
I like these tubes.
So I now have two options for the output tubes, and both take the abuse.
I've cranked them up to 330V B+ and got over 3W into 4 ohms at 1KHz.
When I pushed it to 13Vp-p square wave out into 4 ohms, it failed to elicit red plates after 20 minutes so I gave up. I did increase the cathode resistors to 220Ohms to limit the cathode current to 25mA and plate current to 2X rating. (I guess it is a tad less plate dissipation since that includes the screen current in with the plate current, bad math.)
I like these tubes.
Not to throw a monkey into the wrench, but for the output tube could we use a buck 6n6p in pp with a 4k load? That should be good for 2watt at least.
http://www.pastisch.se/faktiskt/amp86.gif
http://www.pastisch.se/faktiskt/amp87.gif
http://www.pastisch.se/faktiskt/6n6p_6h30.jpg
http://www.pastisch.se/faktiskt/a_qrps.gif
http://www.pastisch.se/faktiskt/amp86.gif
http://www.pastisch.se/faktiskt/amp87.gif
http://www.pastisch.se/faktiskt/6n6p_6h30.jpg
http://www.pastisch.se/faktiskt/a_qrps.gif
Since the only restriction is availability, I would think you could. You might want to test with the JJ ECC99 or a set of 12BH7s if you can find them. Wiring for optional 6V /12V would make the 12BH7 an option.
6FQ7 might work as well, althought he 12BYH7 and 6FQ7 have lower plate ratings.
6FQ7 might work as well, althought he 12BYH7 and 6FQ7 have lower plate ratings.
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OK, well, I've been thinking about building a guitar amp for probably 20 years, much more seriously for the last 5 years since my son plays. This thread got me going to sort through some of my very old parts. I have a real lot of "junk" for a person who is not that into tubes. A friend gave me an old Realistic integrated stereo tube amp for "parts" many years ago. I told him several times I did not want it, LOL, but he insisted. It had 6BM8 outputs, and was a rather odd design so I gutted it to use for some tube preamp experiments and it has been sitting ever since. Today, it would probably go for $200-$300 at that site but who would have known back then!
I'm going to use this to do some prototyping and I had planned, years ago, to do something with a small 20-40W power amp for testing. I have a good number of octals, 5881, 6L6GTs so I cut the chassis to take octal sockets for the outputs. Rebuilt the power supply and am getting +380V no load, 340 at 100mA with 5881s in the outputs.
I'll probably use some 6V6 type tubes for 10-15W if I decide to enter this contest. I've got a pair of old 6V6s where the glass is black all the way around, why was this done? One is a Raytheon/Germany 6V6 GTA and the other is a Kenrad 6V6GT, don't remember where I got these. I also have a nice old pair of Amperex 7408s that match up pretty well.
I'm going to use this to do some prototyping and I had planned, years ago, to do something with a small 20-40W power amp for testing. I have a good number of octals, 5881, 6L6GTs so I cut the chassis to take octal sockets for the outputs. Rebuilt the power supply and am getting +380V no load, 340 at 100mA with 5881s in the outputs.
I'll probably use some 6V6 type tubes for 10-15W if I decide to enter this contest. I've got a pair of old 6V6s where the glass is black all the way around, why was this done? One is a Raytheon/Germany 6V6 GTA and the other is a Kenrad 6V6GT, don't remember where I got these. I also have a nice old pair of Amperex 7408s that match up pretty well.
Doubt if you would get a design with 6V6's that would come in for under a hundred bucks. The whole idea was to come up with a design that more or less anyone can build under that amount. Mind you with the price of cheap amps on the market it is only us real diehards that would bother.
It's fun to build things from parts you already have. But the contest requires you use parts that are available from current suppliers that add up to no more than $100. I think surplus vendors are specifically excluded. You have to use NEW parts.
a 6V6 powered push pull amp will be hard to build for $100 because your budget would be mostly consumed by the two transformers. Nothing left for the other parts.
But do go ahead and try it. Build with what you have and tweak it until the sound is "right". Or better yet buy your own guitar and in 8 weeks you'll be playing simple tunes.
I have a PP design using similar but low cost tubes in a spreadsheet that is coming in at $90 with just about everything covered as outlined for the contest. I used parts that do not have issues with aging from Apex Jr such as pots, line cord, etc. The rest are from normal suppliers.
I'm aware that it has to be built from new parts, this is the prototype, and it will probably morph into something much more complex to test out our Soldano variant.
I asked if Apex Jr. was acceptable and got no response, also asked if 10-15W was - also no response. So if it turns out not to be, then I will not enter.
Anyone know what's up with these black glass 6V6s?
I'm aware that it has to be built from new parts, this is the prototype, and it will probably morph into something much more complex to test out our Soldano variant.
I asked if Apex Jr. was acceptable and got no response, also asked if 10-15W was - also no response. So if it turns out not to be, then I will not enter.
Anyone know what's up with these black glass 6V6s?
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I kind of lost interest in building a $100 amp head when I found that the Kostom 5H sells for $99, shipping included. You can buy a 5H fromGuitar Center, Music123, Amazon.com any of several others. I'm headed out to the local music store right now to buy some odds and ends, I'll look at a H5 close up when I get there.
For $149 the Fender Champ 600 is a combo in a vinyl covered wood cabinet that sounds as you'd expect with a name like "Fender Champ".
Building it yourself for $100 would not catch many people's attention with retail prices so low. $50 would be truly impressive as would be a combo in a wood cabinet for $100
I don't think using Apex is cheating but the winner is determined by votes so you need to look good to the voters and Apex may not help.