I am an engineer that takes complex math and systems and breaks them down into simple math building blocks. I "show and tell" on my RU-vid channel. If you need a schematic or have questions, please email me.
Hello, I have a Fender Vibrolux Reverb Custom in which I removed the circuit board and replaced it with a eyelet board just like they did back in the day. I didnt have any problem for some time and I started to get a squel at times and buzzing and then disappear. I did notice that it followed from the normal channel to the vibrato channel and then I removed the Phase inverter tube and replaced it with another tube. It was gone. I had a old RCA nos tube in the PI socket. thanks for your video......
Youll not find any " UL". or other certificates on these Communist Chinese manufactured devices. China does not care. It mimicks, copies snd plagiarizes everything the West or the industrialized East produces. I have the identical variac, and from almost day one outlets fractured, fuses were blowing, and there was substandard quality for such an important device. These items are a clear and present danger to ones health. Thanks for the expose' this will save lives.
Sir this was confusing me a lot, so there is no simlpe formula, to find wire temprature, unless we get them expermentally, but now we can aproximate all by saying for example,the energy in,I*V, Which is dependent on the resistance of the wire, determines the temprature of the wire, assuming all other things are keept the same for identical wires( nichrome 80 or 60) of different length and diameter( eg 0.9mm and 0.7mm) Thanks you for the best explanation and insights
Metal is a sponge that soaks up heat. Therefore the calcs must be done over time to get how much heat is soaked up between each time interval. Wire temp is not a single calculation like converting degrees F to C. The graph I show is required because air "boils" on the surface of very hot wire. As the wire heats, more air boils faster.
I stay away from all newly made Russian tubes. The only Russian tubes I’d use are the old Soviet Union made Reflector tubes from back in the day. Otherwise I only use USA made NOS tubes. I also try to get the JAN tubes when available and priced well.
I have a question. My output tube cathode has the parallel resistor/capacitor, but not the other resistor to the cathode. Can I attach R hum directly to the cathode? Thank you.
If you're boosting 15kHz by 17dB and 10kHz by 15dB then maybe they should have put a tweeter where the Bose logo is. An Eminence APT80 would do nicely. What's particularly worrying is the 14dB boost at 60Hz. It's a good way to get speakers making farting noises as you turn up the volume.
Would the same steps apply to trying to diagnose 180Hz hum? Not entirely sure where it is coming from, but it is present with all knobs at minimum and nothing plugged in. The hum then increases with the REVERB knob, even with volume at minimum. Interesting. And, it is present even if the reverb tank and footswitch are disconnected entirely. Thoughts? '65 Princeton Reverb clone. Thank you, your channel is very informative!
Hi James. Thank you for this great lesson on speakers. This is fascinating as I never heard this from any techs. I have all my speakers in parallel. Can I just reverse polarity on 1 of the twin cabinet speakers or 2 of the 4 on my bassman speakers?
As an electrician/guitarist that has gotten into electronics and amp building, this is an amazing video with lots of interesting information, really well presented. Thank you sir.
Hello, it was a nice surprise to see a new video from you. I really like the depth to the detail you go into, others perhaps may not bother to do so. I have followed all your videos and found them very informative, in particular the feature you did on the Fender Deluxe and your own Premier Twin 8. Regards, Jeff.
I used to buy repair parts from MCM Electronics. However, they are out of business and are now owned by Newark Electronics. Newark does not sell parts. Which means you need to find parts on sites like Mouser. MCM was great for getting OEM parts. sigh...
Had this happen on a Collins KWM2A, on 6AZ8 that acted as 3rd transmit audio amp and second stage receiver IF. When I turned down the MIC gain, it was a high pitched squeal in receive mode. Yes, it had a cathode follower. In my case, I had just replaced the tubes. re-capped and cleaned the tube pins. I got rid of my squeal by swapping out another 6AZ8, however, I'm sure the initial cause has to do with re-capping, or perhaps just a bad tube. If it returns I'll put a stopper resistor on the grid. Also, I found a great way to locate a squealing tube is to simply place your hand near it, fingers around it (your fingers make a great inductive tuning capacitor) and it should change frequency as you move your fingers around the outside glass. Thanks for the advice.
Hi mate, I`ve got the same Mackie sub & I`ve hardly used it tbh & at one of my gigs we had set the sound up before starting, then it started making like thunder noises even when it was turned down etc, sounded just like thunder, do you have any idea what the issue is, and could that be a solder issue aswell?! Thanks again for youre video, thanks Paul
Anytime you adjust a pot and it sound like "thunder" it is a bad pot. Replace the pot, forget spray cleaners because the pot has a worn spot and a cleaner does not repair worn wipers in the pot. Thank you for watching.
Thanks for youre response, we had pot turned to 12oclock and hadnt adjusted it, and the sound just started out of the blue with no music on @@deepblueharp
I have a similar issue on my VHT Special 6, it helped a bit to move the output wires away from the preamp but it still sounds terrible. I have changed all the caps (amp is 13 years old) but no luck, any further ideas? ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-13HJgjXa1HU.html
GREAT video!!! I am using 18 gauge nichrome wire as a dummy power resistive load. Do you know how a maximum current or wattage load can be calculated for a given nichrome wire, as not to damage it? For example a 1 meter length of 18 gauge wire in air at room temperature? Similar to the way nichrome wound power resistors have power ratings. THANKS MUCH!!!
The maximum operating wattage/current depends on the application as governed by the NEC code. You can download my spreadsheet from my website and do the calculations.
I remember the first time hearing a Bose 802. I was 12 and it was Easter Sunday 1978. I was at King's Island in SW Ohio (you remember the Brady Bunch ep where cardboard tube with Mike's drawing gets swapped with the poster...). Anyway, I was sitting there eating an elephant ear concession snack with my parents and little brother, when up comes this little impromptu, 3-4 people music singing group with pre-recorded backing music. Their sound system was portable, and I just remember sitting there hearing the small Bose box with two holes pouring forth the cleanest most perfect fidelity I'd ever heard. I was a technically minded kid and yet I was absolutely baffled by what could be in that box, not knowing it was just speaker cones. When I did finally learn this it was 10 years later. It made me realize the significance of giving the consumer a mystery to keep them guessing.
Thank you VERY much for this video and remedy! My Mackie SRM1801 wasn’t working and your instruction totally fixed the problem. I had to install and solder in a new post/clasp cause one was fried. Cleaned up the contact points, soldered the heck out of it for a strong connection, put it all back together, and BOOM, back in bass business! Now we’ll see how long it lasts because I do push my subs pretty hard! Luckily these are just my old, back-up subs. 🤘🏼
"I recapped the amp, I changed out the carbon comp resistors, the tubes are new, hopelessness starts to set in..." 100% accurate. The fifth step for me (prior to watching this video) was deducing that by performing these updates on a 50 year old amp, it was now more powerful and thus out of spec compared to the original design. Thanks for the help!
I would advise the use of two fuses: one on the input in case anything goes wrong with the auto-transformer/Variac, AND a second one on the output to prevent the load from drawing too much current. Neither is ideal as you would ideally also want to monitor the input & load-shared part of the windings for RMS overcurrent as well, but you can't safely do that with a conventional fuse as you wouldn't want a fuse on the neutral side of the transformer to blow with the live side still connected; so ideally you would need an active current overprotection circuit to monitor the RMS current through the common windings, or be conservative with the conventional fuses ratings in the live in and live out. Also, you said the brush on yours failed; depending on how it fails the brass brush carrier could simply short a few adjacent turns of the windings, which no fuse external to the transformer would be able to detect...
By the early 1950's most power companies had push their line voltage to 115. So sure if you have a 1930's amp, it was probably ment to use 110 volts, but I think you can safely assume that even if they printed 110 volts on the lable in the 50's, they knew it was more likely 115 - 117 volts in most parts of the US during the 50's and early 60's. Power companies have continued to push the voltage up to improve efficiency. Mine now measures 122 volts. This device does provide an option where needed.
That particular tube is known to behave differently than expected....... there's a few tubes in the JJ line that are a "bit different"...... and I suggest pulling the sheets on these. The Sovtek sheet LACKS the mention of voltage drop.
