Відео

In my years I can say definitely a master volume on the back is a bad place. Reaching behind the amp blindly feeling for it....not able to see or read it....trust me place it in the front!

72 year old musician here in Western Massachusetts curious about your approximate location I have a lot of parts

Is your Gibson hard case made in Canada?

The sound you hear when you put the feedback resistor is oscillation. You’ve made the feedback too strong when using a small resistor. Try leaving the resistor there and wire a 100k or more pot in series and check what’s the value at which it stops oscillating. Then place a resistor of that value there.

sounds like input polarity

The "proximity" of your parts/layout is not your problem. I've built many tighter and higher gain builds w/out your issues. Motorboating is a fairly common experience and means you've created oscillations. Your layout is not too bad but the grounding is far from optimal for sure. Without a schematic it's hard to follow what you've done regarding possible mistakes on how you made your layout. It is bad form to run your 1st preamp tube's cathodes' grounds connecting to your output transformer's ground the way you've wired it. Run the output ground directly to the star ground. Those cathodes' ground and your input jacks' ground should be ran straight to your power cap's node grounding point aka the neg lead. Proper grounding is an art in itself but critical to high gain circuits. Yours is not a high gain circuit and one of the easiest simple circuits. It's hard to tell if you're missing any grid leak resistors but could be your issue as well especially for the 6sn7 "power tube"? I assume you're running it in a self-split mode like similar Firefly amps.

Have you tried grounding the input jack, like on the original the jack is grounded when the guitar is not plugged in. Just a thought.

Hi! I have a 1961 acoustic Gibson LG-2 - and need a case. What would you recommend? The link is broken. Thanks!

Give the Marshalls a rest

The AC-10 sounds like an interesting project.. There's not really a lot around on this amp compared to Marshalls & Fenders..

This is a kit! Refurb a real one!

Can you provide the name or site where a chassis can be found?

Well done for taking those readings. I had to use a 100watt (8 ohm) celestion10" paired to a "15" watt 2 x El84 amp to get the best frim the amp, full volume...peaked at 60watts at 3/4 bias! Valve amps don't appear to obey any set laws on paper so be prepared and use a 4x12 or at-least 2x12 (70watts each minimum) so you can avoid melting that lovely New transformer or melting voice coils with too much distortion. I reckon after all this you could start thinking about the Vox AC-80 head as a possible build, now "That " would be good but don't rush. Great stuff!!BTW if you just plug an outside source in to amp (CD, phone etc) it could help get clearer readings and free-up your hands.

Earned a thumbs up for "Resourcefulness" and "persistence" , great job. Penny saved is a penny earned.

When I was a sprogg at UCL doing Electrical Engineering practical exams and theory a tutor called Dr Watts(really) told all the students present(8) to please keep any designs and any work as simply laid out as possible" Keep it simple "! he would growl in that Scottish(really) accent and I never forgot it. Bring that 50watt head back to stock(as near as poss) and it will sell. They are simple designs and a Master vol just turns them on their heads. One tip for anyone who uses a master vol Modded amp"Turn the master up full and use the gain/pre-amp knob as your volume" , a it's warmth and clarity returns and if you want fuzz just get a Rat pedal and a spare lead"! BTW you have earned a commendation from me because of your enthusiasm and that is no2 after "keep it simple".

Who made the chassis?

Would that increase the wattage of the amp?

Just letting you know there are special runs of Gibson LP's that get into Sweetwater, Guitar Center (Long & McQuade up here in Canada) where you can get some great deals. I bought a Ebony Gibson LP Classic 60's and then one of the Special runs made for L&M for -$1000 less than the Ebony (Iced Tea burst LP Classic, same pickups but Standard wiring and satin finish... The run has now been recalled to make Mod shop guitars so bonus resell value for me). My last purchase was the Gibson 2023 LP Supreme, and I can say the differences in quality and finish is very noticeable.

I have thought of putting the bias pot on the side panel near the mains transformer then just remove the back panel to adjust the pot with a large knob on.

Thanks for the info on the mod to the input jacks I am about to start building from a kit JMT 45 and will use the shielded cable mod. The jacks have a plastic nut so this will avoid having earth loop.

I have seen for sale on Ebay a IEC socket with a mains filter built in.

I have a footswitch for a Crate amp used for my half stack. The switch has a small circuit board with 2 push-buttons, but 1 side doesn't work part of the time. I figured it was from a bad connection but I can't seem to find it... any thoughts or suggestions?

Dude, that transformer mounting plate scheme @16:40 fricken genius. I've been contemplating for years trying to come up with some kind of temporary transformer mount that would allow for a more convenient way to change out and try different examples in an amp. Particularly with output transformers it's always a bit of a crapshoot of what you're going to get when you first power it on because they're so difficult to remove, you're essentially wedded to it. I like the metal plate using an electrical outlet box cover, it's been in my face the whole time and I didn't put one and one together, pretty standard for me. The only thing that would need to be figured out is a wiring scheme from the connection points to the rest of the amp. I'd be tempted to try solderless connectors but with voltages this high it would be dangerous to use screw type terminals because the metal parts of a screwdriver would have the full B+ on it if adjusted while live. I think I'll try using old PTP terminal strips and try to put it somewhere near the power tube sockets that's easy to get to with a soldering iron without burning nearby wires, unlike having to remove and install a transformer the old fashioned way 😂 Off to Home Depot to grab some electrical box covers and see how it goes. I can't thank you enough👍

You've gradualy replaced the whole thing. It came out nice though. I built my amp as well, after decades of never really finding what I wanted retail. I couldn't be happier, and I'm sure you are as well. If you don't like something, you can always change it. That's not always easy with PCB amps.

I'd be interested to know how well the silver added to the fret notches holds up over time. I have a 1996 Fender American Strat that has similar wear on the first 4 or 5 frets. So far it hasn't affected the playability of the guitar.

I wonder if you could have gotten away with using a barely damp cloth and a steam iron to get that goop off of the guitar? And who glues the knobs onto the shafts??? - that poor guitar.

Hi nice project ! So do you have size chassis

Celestjohn

Great video, thank you. Those Cliff footswitches have a nice housing but the stock cables are utter junk. They should have changed years ago to the style design you converted this one to.

👍

Just subscribed. Looking forward to the rest of the build. 😊👍

New subscriber here! I liked your detailed troubleshooting to pinpoint the source of the "microphonics" and other noise. Looking forward to the rest of your new amp build series. Your channel popped up in my recommended list after watching a "Psionic Audio" channel video.

Subbed....looking forward to what's next ; )

Was there a part two? Frankly mate, looking at the build, you're going to get noise. Your ground scheme is loopy, the resistors mounted directly next to capacitors and the generaly lack of common mode cancelation, unshelided signal runs, rf antenae's doesn't suprise me in the lesast. Pretty shitty for a grad tbh. 1.bp.blogspot.com/_16lay_eKXbA/ShhluXL9qrI/AAAAAAAAACQ/5YkMzknqc9I/s1600/plexifrontguts.jpg

Instantaneous DC measurements are not the power output from the tube to the speaker. Nothing DC gets to a speaker. You can measure the ac voltage on the speaker while playing a single note to get somewhat close to a reading, then do the math. Evan that has huge error potential since a speaker does not have flat impedance across frequencies. Use a high-power resistor and a frequency generator (e.g., phone app if needed) to get real figures.

Your amp sounds like shit...better read some books on tube amplification.

Enginerd Amps Hi, I bought a 1964 Gibson discoverer GA-8T amp and what looks like the footswitch cord for the tremolo has been cut off. Most of the cord is there as it is long. It comes out of the transformer. The tremolo footswitch has been cut off from the cord. The cord has two wires. Are these connected to AC current?

Where did you get the schematic

Wow!!! I gotta tell you your build series playlist of this amp is full of great knowledge as well as inspiring. Awesome amp in the end. Wish I had your knowledge to pull this off. Any plans to do an AC30 next ?

Nice sounding amp!

The current limiter will show shorts. If it doesn't go dim the bulb will basically run away and get brighter and brighter. If it doesn't go dim shut it down and find whats wrong!

Many techs say the mojo dijons are great replacements for the mustard caps.

Better is dedicated ground buss and dedicated pre amp ground buss. Thats what Fender developed and stuck with! With a star ground system little hum can migrate to the preamp and get amplified and it's a nightmare to track down.

About 18 months ago I finished a copy of a 1960 Vox AC15 for my son, I copied the circuit exactly, including the EF86 input and tremelo and vibrato, the hardware chassis size cab, tag board etc are very close to a Vox but not exact. I hand built the entire thing including folding the two piece chassis, making the cab, and winding the transformers. He initially asked for a master volume but eventually it was discarded as it seems a lot of the tone comes from the overdriven EL84 output stage. Good luck with your project. Link to my build if you care to have a shortt look:- ua-cam.com/video/WUQtsEAAWyM/v-deo.html

Please let us know if you finish the amp. Would love to hear it!! I built an AC15 style amp with only a single EF86 Pentode channel. Turned out great. Used Mercury Magnetics output transformer and choke as well.

Did you give up on this project? You not doing a Part 5?

Thank you , just repaired the footswitch on my Blaclstar Artist 15 by watching your video

nice