Видео

It’s a beard cone. Though it’s already a few years ago, I think I ordered it from Stewmac.

Hi Rob. That sounds really frustrating . To answer your questions: Changing the value of the cathode resistor to 82 or even a 100 ohm won’t change the sound. I had a AC 30 CC in for a service lately, and these models have a switch on the backpanel to choose between two different resistors. The standard 50 ohm and a higher value to protect the tubes. I couldn’t hear a difference. But: are you shure, that the popping noise is caused by the tubes? That sounds to me like a cracked solderjoint. When the amp is cold, it has continuity, when it gets hot the crack opens and weerd noise appears. Try to chopstick the circuit board. Press the board carefully to flex it and see if the noise increases or decreases. Especially the tubesockets get hot like hell and tend to open the joints on the board. But be aware of the high voltages, don’t get zapped!!! Good luck! Greetings from Germany

@@martinstubeampworkbench2299 I appreciate you taking the time to offer your advise. No, I'm not 100% sure that it is the tube(s), and will check the board per your suggestion. This model, unlike the CC, doesn't have switch to change the resistor selection. It would have to be physically changed.

⁠​⁠I replaced my stock tubes cuz they were slightly microphonic and roughly 6 years old, got quad matched jj el84’s and within a month one total failed, glowing violently purple and making the amp snap crackle and pop. New tubes can fail, luck of the draw. Next time I get new tubes I’m gonna order 6 matched el84’s and 6 12ax7’s, it’ll make trouble shooting easier. Edit: I bought the new tubes in 2018, the 3 jj 12ax7’s are still just fine, 3 of the 4 jj el84’s are still holding strong, as well as a one 2012 china el84.

Well, yeah! Splendid is the right word. And yes, there are so many fabulous amps out there, that are in bad shape and need some care. That’s my crusade 😆

Thanks for your oppinion. Actually the farty sound might be caused by the low volume I recorded it (I have neighbors). It will sure come to live on higher settings. These beasts are soooo loud! In the near future I’m going to release another video, this time repairing a Kitty Hawk Standard. Another nightmare for an amptech 😬. Take care

Hello @@martinstubeampworkbench2299 , Yes they are beastly loud even on the 50 Watt setting. I am considering to put in class A converter sockets to bring it to 30 Watts. At practice room levels, even with a loud drummer, it feels like I need tweezers to adjust the volume in the Overdrive channel. A half mm makes the difference between too quiet and overwhelmingly loud. And this amp needs a certain Master level in order to sound really good, as you apparently also experienced! A good overdrive pedal in front of the OD channel makes this amp sing! A Voodoo lab Sparkle Drive works really well for me - much better than and Ibanez TS 7 for example!

Hi Nick, I couldn’t find a schematic of the 15 c1, but looked at the AC15 reissue. The biasing of the preamp tubes are pretty much standard, so there is no reason for burning preamp tubes . Maybe one of the prevalent rumors that you find in the internet. Don’t be concerned, wait until it happens. The cathode resistor in the reissue has a value of 100 ohms, all the vintage ac 15 go for 130 ohm. So the old amps run definitely cooler. But again, I don’t have a schematic of the c1 model. So I don’t know what value of cathode resistor is in there. Greetings from Germany

@@martinstubeampworkbench2299 I believe it’s a 120 ohm.

I designed the faceplate on my computer. Put it on an usb stick and brought it to a printshop. They printed it on a selfsticking foil, that I put on the raw aluminum faceplate. A lot of work and a little bit complicated, especially the design job, to get the right dimensions. Took a lot of experimentations. Printed it on paper first, to check the right fit over and over again, but looks good after all.

No a Vox amp is class A and doesn’t need to be biased like a Marshall Amp

Before!

@@martinstubeampworkbench2299 OK so the difference could just as easy be because of you improving the spider or a combi of that and the new cone. Thanks I just wondered.

Ah , no . Even properly set up , a generic import cone will not sound like a Premium Cone . ( But it would be noticeable improvement over the baseline .)

I'm not really concerned whether it sounds like another cone I'm just concerned which I like the sound of most and the sound obviously could be the result of the set up and the cone because one was played before the set up and one was played after the set up. Clearly both cones should be trialled under exactly the same circs to give a fair test, otherwise, like your comment it is just opinion without basis. It may be popular opinion but still opinion.

Cooling down the bias won’t solve the noise problem. It extends the tubelife. I ordered the 82 ohm resistor on eBay, if this value is not available, go for a 100 ohms, won’t change the sound either! Crackling and popping points to a bad connection. Check the tubesockets, the pcb board for cold solderjoints. Tap on components like capacitors resistors, jacks etc. with a wooden chopstick. If the noise appears or gets worse you found the spot to take a closer look at. Could be a bad preamp tube, too (improbable). Wiggle the tubes in the sockets. These sockets are crap and can cause the problem. Good luck. Be careful because of high voltage, don’t get shocked! And let me know if you find the cause of the problem. Greetings from Germany

@@martinstubeampworkbench2299 thanks brother

I agree. Everything you mentioned is a good idea. But in this case, my customer told me : make that thing work, I want to sell it. And that’s what I did. He also owns a Kitty Hawk Standard which he stated is a much better amp than the custom. Maybe I ´ll get it on the bench for an overhaul some day. Would be interesting though, to compare one of the first Kitty Hawks, equipped with the Dumble bords, with the later versions. They might have a lot of Dumble DNA either. Greetings

@@martinstubeamprepairshop7155 I prefer the extra control’s of a Custom, but I agree, the sound of a Standard is much better! I currently have a modified Custom which takes it closer to that of the Standard, but I’m also thinking about modding it further… I really don’t like the tube sockets being mounted to the PCB. It was a bad design choice, and they pretty much all end up burning the PCB. I also don’t like how close the tubes sit to the speaker magnet, and how heavy the thing is. In my opinion, it’d be a much better amp with just those issues addressed. I originally was going for a ‘Dumble’ sound when I found the KH… But the KittyHawk’s do have their own uniqueness to them! It’s not a Mesa, it’s not a Dumble… But it does seem like a mash of the two. So I’m torn on if I should modify it, change the circuit board’s, but keep the original transformer? That would make it like the original 20, but would it take away that uniqueness? Would it sound better? These are questions I can’t answer without hearing at least one of the original 20, or just going for it & hoping for the best! If you ever want to give it a go, the best gut shot I’ve found up to yet of one of the original’s, is on Reverb. Item: 10792143-dumble-kitty-hawk-overdrive-special-50-w-head-1980-mahagony-nature There’s probably better, but I haven’t looked into it too much. It’ll need a bit of reverse engineering, and cross referencing with Dumble schematics… But it’s gave me some food for thought! And if I ever plan on going ahead with it, maybe you might just be the person to contact to help me with the project! Loved the video!

For my early Standard Series Kitty Hawk I actually had a matching (oak) ooden head enclosure handcrafted at some time and used the combo cabinet as a speaker only cabinet with the original EV speaker. This eases the pains you've got to take when you have to move the amp by some degree. Both parts are heavy enough separately, though! However, I recently put it all together again for old times’ sake and yeah: the weight of this thing is absolutely brutal - makes you regret having a rehearsal room several stairs up... Your sound examples seem to be quite spot on - I have not used the overdrive channel lately but the clean channel sounds exactly like your example (my computer’s connected to a decent home stereo so it's halfway realistic I guess). My Kitty Hawk Standard is a 50W only model but the that tough bottom end and the amount of clean headroom is amazing with this version, too. As to the channel switching: I've had problems here right from the start - really loud switching "pop“ initially and I had the switching circuit changed to get rid of it (I don't know how precisely, any more, though) And I had the footswitch connection modified as well (even with an additional ground wire that goes (ground only, of course) into one of the unused speaker outputs... Furthermore: with my amp those original big (filter?) caps went up in smoke(!) during a private gig after about 10 years of moderate use - these amps are quite impressive when they work, but apart from the weight issue they can be sort of „difficult“.

Thank you, and congratulations! This amp is absolutely fantastic. And the tremolo…….oooooh!

Just type in: Champ Amp AA 764 Clone Sound Demo. Then it´s the first video in the list. Greetings

@@martinstubeampworkbench2299 thanks, appreciate w

Ím sorry, there is no easy solution for your problem. These amps have a lot of digital components. This is almost unfixible. Try a new preamp tube. Might be a bad solderjoint that opens up, as soon it gets hot. So check the solderjoints on the pcb board, especially the ones on the tubesocket. Good luck!

Also that ´China cone´ may sound better with a heavy steel bar, may ´sound just right´ and give it that Dobro twangy, a little banjo-y sound, were as that ´Beard cone´ with that same heavy steel-bar will give it a too ´liquid-y tone´ which is great sounding for the Hawaiian steel guitar, but will lose that bite and bark in the Bluegrass sound. *"Let´s bring out Josh here to do us a number on the ´ole hound-dog´" -Lester Flatt*

What y'all mean to say is : The generic import cone , has less sustain , harsher sound , and more limited tone , to make it sound more like a Biscuit Bridge Resonator . If you actually * want * to sound like that , great ! That's certainly a valid choice , that's why there are three styles of Reso designs , to give choices . But compared to what a Spider Cone is * supposed * to sound like , it's embarassing .