Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Banjan73 on January 19, 2026, 06:37:12 am
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Hello again.
As promised in my recent thread, I have one more amp to present here.
This time, my goal was to make a tiny thing which I could transport on my motorcycle with as much headroom as possible.
I ended up with a kind of champ-amp.
Again, no tone controls. Only gain and volume. This amp throws out about 2,5-3W. When using the tiny, oval speaker in the cabinett, it doesn`t play much in the bass frequenzies. But with an external cabinett, its much better.
Nice amp in very small venues when playing quietly.
I found out that I have no pictures of the internal right now. Coming up, if requested.
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Looks like a fun project. I've got a somewhat similar amp - an obscure tiny amp with a sort-of 5f2a circuit, which was made in Japan. It's got solid state rectification, 12AX7 preamp, and a 6AQ5 power tube. Easy to transport and sounds good. I think the circuit was really optimized for the 6" speaker, as hooking it up to a larger speaker sounds a bit disappointing.
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Looks like a fun project. I've got a somewhat similar amp - an obscure tiny amp with a sort-of 5f2a circuit, which was made in Japan. It's got solid state rectification, 12AX7 preamp, and a 6AQ5 power tube. Easy to transport and sounds good. I think the circuit was really optimized for the 6" speaker, as hooking it up to a larger speaker sounds a bit disappointing.
Do you have a schematic for the Single Ended 6AQ5? Thanks
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Looks like a fun project. I've got a somewhat similar amp - an obscure tiny amp with a sort-of 5f2a circuit, which was made in Japan. It's got solid state rectification, 12AX7 preamp, and a 6AQ5 power tube. Easy to transport and sounds good. I think the circuit was really optimized for the 6" speaker, as hooking it up to a larger speaker sounds a bit disappointing.
Niice!
Yes, it looks as somewhat the same type of amp.
Did you build the "box" (dont remember the english word right now) yourself?
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I did one like that a while back - a vibrochamp circuit mounted on my own custom Ally folded sheetmetal plate squeezed in an old Behringer Thunderbird box. Stancor A-8092 SE OT, PT out of an old Jap signal jennie and a Mojo Choke. Makes any geetar sound awesome with a Celestion 15W 8" speaker (also has plug for external speaker cab)
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Great projects!
Tubeswell, I'm curious about the Electrical Safety sticker on the back panel. Did you have it independently evaluate?
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Great projects!
Tubeswell, I'm curious about the Electrical Safety sticker on the back panel. Did you have it independently evaluate?
Yep - here we we are, if you want to use any electrical appliance in a performance situation in someone else's venue, there's a legal requirement to have it tag-tested for the integrity of the safety ground and the adequacy of insulation between the AC power supply source and the mains earth. There are independent contractors who have the calibrated equipment who'll do that for $20 and print out the certification label. (The tag is normally supposed to go on the power cord but this has a jug cord, so I slapped it on the back of the chassis, and nobody has complained yet LoL).
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Do you have a schematic for the Single Ended 6AQ5? Thanks
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Yes, I've got the schematic that was inside the amp, and I added the values to the best of my ability - it was not easy to see all the caps and resistors because of the way it was made. I've attached that here.
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Niice!
Yes, it looks as somewhat the same type of amp.
Did you build the "box" (dont remember the english word right now) yourself?
No, I didn't build the cabinet - that's what it came in. Pretty cool looking tiny thing.
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No, I didn't build the cabinet - that's what it came in. Pretty cool looking tiny thing.
Very cool! Such a nice amp!
I did one like that a while back - a vibrochamp circuit mounted on my own custom Ally folded sheetmetal plate squeezed in an old Behringer Thunderbird box. Stancor A-8092 SE OT, PT out of an old Jap signal jennie and a Mojo Choke. Makes any geetar sound awesome with a Celestion 15W 8" speaker (also has plug for external speaker cab)
Guess I am not the only one here thinking about making such an amp, hehe. This thing also looks awesome! We should come together and have a tiny-amp.jam session, hehe :-)
Great projects!
Tubeswell, I'm curious about the Electrical Safety sticker on the back panel. Did you have it independently evaluate?
Yep - here we we are, if you want to use any electrical appliance in a performance situation in someone else's venue, there's a legal requirement to have it tag-tested for the integrity of the safety ground and the adequacy of insulation between the AC power supply source and the mains earth. There are independent contractors who have the calibrated equipment who'll do that for $20 and print out the certification label. (The tag is normally supposed to go on the power cord but this has a jug cord, so I slapped it on the back of the chassis, and nobody has complained yet LoL).
I used to work at Nemko in Norway. So I know alot about these tests.
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Using a 12V laptop brick and 0ne of the 45-390V dc boosters to supply a 12AX7 and 6V6. I did up the heat sink on the module and have it outside the chassis for cooler air. A 6K6 (with 12AX7 in series with it along with a resistor parallel with the 12AX7) or a 12AQ5 would play nicely with the module unmolested. I squeezed everything in as small a cabinet as possible, thinned the wood down, 8" speaker just fitting inside. Have a p-p switch on the treble pot and the tone stack goes in between a Marshal and Fender response. Otherwise just a SE Champ type circuit. Debating on adding a delay board or a Digilog reverb yet.
(https://i.imgur.com/eOKSYXw.jpg)
(https://i.imgur.com/d13GGMZ.jpg)
Mostly play through the Blackface position as it makes the amp sound less boxy in the small cabinet (9.5"x9"x6") but has a speaker out jack in case a larger speaker cabinet is kicking around.
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Printer2:
Thats an interresting project!
Can you tell more about the DC booster? Is that an DC-DC converter? Doesn`t those make a lot of noise for audio?
Do you have the full schematics?