Le sigh. The previous attempt on this amp's life: • Bogner Shiva | A Tale ... For more info, Subscribe to this channel, join us at PsionicAudio, or email us at info@psionicaudio.com.
I like that you're up front about charging a fee to even look and you're confident in being good. One of the things we used to say in the shop was "a poor man buys twice." You're not only paying me for the work, you're paying me for my experience in diagnosing problems quickly and repairing them accurately. Good stuff. I haven't had a Bogner on my bench and I hope not to.
Great video, I watch your videos regularly as I am a guitarist/amp tech(out of necessity) since all the old great techs I used in my youth in the 80’s are now passed on or retired. Finally after some bad experiences with so called “good techs” I finally started reading books early on in the 90’s. I was always interested in electronics as a kid and played around but made my career in the machining world as a CNC programmer, certified toolmaker and mechanical engineer. Now in retirement from the machining world I do mostly tube amp repairs and mods and occasionally some solid state analog stuff such as older power amps and bass amps. I recently got a ‘72 Twin from a friend who is a good player and builds some killer guitars but is not an amp guy. He bought this from a well known guitar store in upstate New York that has been around for nearly 60 years. He’d been in the market for a Twin and tried 4 or 5 they had and picked the one he thought sounded the best. The store said they had been all gone through by a guy they refer to as “The Doctor”! When I got into this amp and looked at the work I thought this guy needs a doctor for training in just basic soldering skills. He replaced the filter and bias caps, instead of just unsoldering the caps he clipped and poorly j hooked them in which made no sense on a Twin of that era all the leads were on top instead of between the fiber boards with hidden jumpers like 60’s era Fenders where some times properly j hooking is an easier and less invasive if properly soldered. This guy never changed the cathode bypass caps, didn’t realize it had a bias balance control and not an adjustable bias. He must have put a bias probe on one socket and turned the balance completely to one way to bring in the one tube. My customer said it had very low output. I bet since one pair of tubes were about 5mA and the other pair around 20mA. After cleaning up the soldering mess which looks like it was done with a 25 watt Weller $15 special, adding a trim pot to give a bias adjustment and balance control, changed all the ceramic caps in the vibrato to film caps that eliminated 95% of the tick, changed it over to AB763 specs, changed out some leaking coupling caps from the PI to output that were making the bias voltage unstable and adding a 3 way negative feedback circuit using the old ground/polarity switch after wiring correct to today’s standards ( courtesy of Rob Robinette ) the amp now has that nice rich chimney tone that we love about a vintage Twin. Customer took to a open jam the day he picked it up and texted me that night on how it sounded and couldn’t believe it was the same amp. Like you said, it is just amazing what people will push as a complete fix or whatever. I didn’t charge that much even though I had a good amount of time in it. I made money and most importantly he was very happy. Now I have his early Bogner Shiva with the hot F/X send, any advice on a good way to make this usable with pedals or rack mount f/x? they make special cables they sell that just have some kind of dropping resistors built in for pedal use. I have read this was a big issue in many Bogners and finding schematics for them are like hens teeth. Thanks for all your knowledge sharing!
Thanks man. The Shiva loop sucks hard. You can add a 25K pot before the send jack (wiper feeds send) or repurpose the existing Return level pot to be the Send pot. Or hardware a voltage divider (keep total series resistance around 25K) before the Send. Note that it is low impedance so not all pedals will sound good there, but most modern time-based effects will be OK. I did this for a client about a year ago with good results but I can't find my notes on what I did. They're in one of those journal books around here somewhere. I used spice to model it but you can just temp in a 25K pot, turn it until you are happy with the levels, then measure and replace with two resistors.
@@PsionicAudio Thanks for the tip on the Shiva F/X loop send. I had that idea in mind. Just rewatching your Fender AA763 amp series. I agree on not changing out ceramic caps because of tone but two of three were very microphonic and one was creating an oscillation on the Twin I just fixed/modded. I popped in some really good old stock film caps I got in a big grab box of components that look to be from the mid 60’s. I’ve used them when needed and they don’t seem to color the tone much from the ceramics. I know I like PIO caps in the tone circuits of my guitars over ceramic. Just the ear of the player I guess. Ceramics do drift much more with temperature changes which wouldn’t be much of an issue in a guitar but an amp it could change the value some when heated up. Cool Twin, never heard of a AA763 Twin either. I just rebuilt a 1963 Blonde Brown panel Bassman head. Saw a stamp on the back, Dawk Sound. The legendary Dawk Stillwell who hot rodded all Richie Blackmore’s Marshall’s and Jon Lord’s B3 rig, did work for Springsteen and many others. He signed it inside too from 1/9/1973. Dawk lived only about 40 miles from me. I’m friends with his younger brother Dan. I snapped off some photos for Dan since his brother passed about 10 years ago. Dawk used to have a website and forum. One night I got chatting with him and told him I played one of his hot rodded JMP 100 watt Marshall heads from ‘76-‘77 or so that belonged to a local guy I admired as an 18 year old player back in 1981. He remembered every detail and mod he did to that amp and that it had some brand of caps that were only used rarely in that model……….I was amazed he reeled that off 35 years later. A bit eccentric but quite a mad genius at amp work. He was a bit out there like Dumble was. He definitely could squeeze some cool tone out of those old non master Marshall heads.
Looks like someone had a go at melting the insulation on that Orange/White and the Black wires , so might have been attempting to lift the board and gave up . Another useful , entertaining and informative video . Keep 'em coming .
I often wonder how people manage to burn wire insulation so badly in so many amps. If you are capable of feeding yourself with a spoon, getting the food in your mouth, or writing your own name with a pencil, you should be okay guiding an iron around wires. And if they're in the way, just move the bloody things
All of these videos are really eye-opening. I'm really pretty jaded that these supposedly 'boutique' (and very high priced) amp companies like Mesa and Bogner are using crappy Chinese PCBs and cheap, cost-saving components. They're never getting a penny from me.
No no no! I don't want you to get that impression! They are using crappy American PCBs and crappy German PCBs. Seriously, the Bogner PCBs are good quality. It's the lead free solder they have to use that sucks.
Well done as always Lyle. I know this is a tough time for gigging musicians- you’re the man, man. I bet if you had the time, that board would have had a bath too. Can’t all that grime be a problem later ?
I honestly don't know why some people think it's perfectly okay to replace a blown fuse with one grossly over-rated for the job, fuses tend to blow at about 1.5 times the rated current.
You sure are hard on anyone but you lol if you think this is a mess you ain't seen nothing yet, my. Father was a real tv repairman ( not a tube jerker as we called them ) and there was one guy in town if he found a loose solder joint he would whittle out a stick and put in in the TV with tension on it , then there was another one who would cram the high voltage can around the flyback transformer full of butter cartons trying to keep the voltage from getting to ground lol. Years later when silicon sealant came out on the market and it would hold the high voltage sometimes daddy would say I wish old Roy would have lived to see this day lol so remember it's not been all that long ago that getting parts wasent what it is today lol and in the sticks there still are few techs of your caliber so give the old country boys a break lol 😆
Oh man, my first thought was this is a no win situation. Once the inept have left their mark on the amp, lord only knows what the hell will blow up next. But, once again, you were thorough, checked the entire amp out and with a little more patience than many other "rushed" techs would have put in, you have likely exorcised the demons. Still, you do need to charge a fair price for your work. (I am not suggesting you stick it to your customer.) At the same time, he needs to know that allowing his tech to work on the amp (if he actually did) is something that should never happen. At the risk of stating the obvious, the guy is not qualified to do this kind of work and, based on what you said about him telling you he removed the board, I'd question his honesty.
I charged him a fair rate, just no rush fee. I try to keep the local "in the trenches" players going. Particularly after the hellish Covid time without gigs.
Hi Lyle, thanks for sharing you vast knowledge on tube amplification. I have one of those Shivas on the bench today. The amp came with an HT fuse blown and a bad EL34 tube. Everything looks quite new inside. Initially I thought it was just a tube gone dead. So I removed the power tubes, connected the device to a current limiting bulb and everything went fine. But when I install new power tubes and turn the amplifier on, the bulb lights intermittently. Never have had to deal with this sort of behaviour, could that be the switched power supply issue? Take care.
@@PsionicAudio Thanks for your answer. The limiter is flashing just in Stand By mode with power tubes on, I forgot to mention the owner reported too that the amp was shutting down randomly. With power tubes out I'm measuring 12VDC from ground to Pin 5 of all preamp tubes in stand by. For the power tubes I get 12.12 VDC from the black to the red cables that go to the filaments. One to V8P2 and the other to V9P7.
I don’t remember if there are more than one 12V supplies in the amp but I know the preamp 12V supply is coming from the switched power supply. Might want to lift that and see if the current surges go away. That CUI board is a likely culprit but don’t rule out a new bad power tube.
@@PsionicAudio Hi Lyle, someone shared the following info on a group I belong on facebook. Seems pretty relevant. I'll leave it here in case is interesting for you too, I'm a complete rookie to this power supply type. "This is normal and not a problem. The shiva has a smps (not digital) heater supply. The smps has an UVLO (under voltage lock out) circuit. As your dim bulb limiter starves the circuit of voltage, the SMPS shuts itself down. This turns off the heaters, reducing current draw, meaning your dim bulb stops dropping voltage, so the SMPS turns itself back on and the cycle repeats. Don't use a dim bulb to test this amp. The SMPS circuits only fail if the EL34 fails with a short to the heater, which is made more likely by the stupidly high screen grid voltage on this amp. You can add a bulky zener to protect the smps for a bit." Maybe you already know that. What I will proceed to do is to bring the voltage up with a Sencore Powerite and check wattage consumtion in the process (in stand by mode), if the thing goes well I'll repeat the process full power. Does it make any sense? I don't want to burn the new EL34s. I read on another place that BIAS should be set to 29-30mA because it goes way up when the amp is fully warmed up. Regrads.
I think we all have at least one story of taking an amp to a tech, paying about $200 and it coming back worse. I know I do. The Mesa in my profile picture, the poor bastard. I thought about bringing it to you but then I saw like three videos saying how much you hated working on them 😂 Turns out, everyone does, apparently.
Whoever designed the PCB made several mistakes. C1 labeled wrong and component silkscreen over pad. The PCB manufacturer should have also caught that error and never ran the silkscreen layer over the pad.
I know. I try to do topside work on those when possible. It isn't always possible, especially after a hack has been in it Look for a Trem-O-Verb video soon where I hope to change out some coupling caps without pulling the board.
I freaking LOVE my Shiva.. but it has the same blacked-out 2 on the fuse holder.... amazingly stupid design. WAIT.. what's this lifted resister thing??? ???? ?????
Interesting fix..! You would wonder how someone can call themselves a tech and charge for such a crap job.. Embarrassing, to be honest..Cool repair..Ed..UK..😁
What are the advantages of using Orange drop Capacitor in guitar amplifiers? I never understood why techs keep pushing people to recap all their amplifiers using Orange drop capacitors. If you swept the frequency from 20hz to 20Khz are Orange Drop Caps better at passing the frequencies or what is the hype about?
First, there are about six different series of caps called "orange drops." None of them offer any real advantage over other kinds of comparable quality caps. In this Shiva the use of a giant 1uF "orange drop" is why the cap fell out to begin with. High mass cap + small solder pads = gravity won out. A smaller film 1uf would never have had that issue.
@@PsionicAudio The 1uf is an electrolytic and an Orange drop is not an electrolytic so the designer choose that big fat cap because he must have heard a difference in tone. I do think its overkill to use such a big cap with small solder pads because of the stress points will cause solder fractures from heat and vibrations. So the designer gets an F-minus on that for sure.
A PCB is not a deal killer if it designed properly. I have seen in older transistor radios and stereos where a higher surface area of copper traces has been used as a makeshift heat sink, and those old radios only require an occasional dried up cap or a scratchy pot serviced.
