Part 6 starts with a little tech tip on building a capacitor discharge "stinger" tool, along with a short demo of its use. Afterwards, it's all down hill :( ......... I guess it's good news for those of you who want a part 7!
Awesome video. You have inspired me to try to build an amp, soon. I am sorry about the tube sockets. If an item has the words MADE IN CHINA on it, I move to another item, if possible. Here in Salt Lake City, we have an old-fashioned honest-to-goodness electronics surplus store, called RA Elco. It has been here since the mid-seventies and I spend many of my Saturday mornings there. I can get just about anything I want there, and usually just about every item has those magic words MADE IN THE USA printed right on it. The store has lots of tube stuff, of course, but it also has a bunch of cool solid state goodies. I just bought some germanium transistors and a pair of NOS Darlington power units this morning. The owner is a great guy, and if he doesn't have something that I need, he'll look for it for me. He even sends vintage radio repair customers my way. If that isn't enough, I also have the good fortune to have a local tube broker who gets me all the good stuff. I almost never use Chinese or Russian tubes. He gets me American, British, Japanese, and European tubes, mostly NOS. This hobby would be a lot less fun for me if I didn't have these local sources!
Hi, That 330Ω resistor together with the grid-cathode capacity creates a LPF. Just like in a MOSFET. Without it, you might have ringing. At 36:00 the low frequency signal is 180° out of phase on the lower channel. At high frequency seems to be correct though. This might mean something, I think.
Mark from Blueglow Electronics,had the exact same problem as you have had,with exact same Single ended output transformers you are using the Edcors.I have just bought two single ended output transformers,and power transformer,just waiting for delivery for my amplifier project.
Hi Tony, Nice set of videos and very nice work. I have had many of the same issues with "fuz" on my outputs from oscillations in the 50-70 KHz range and it almost always seems to be an issue with NFB. Recently I built a stereo version using a group of six vintage Actosound transformers and found out pretty quick that these old transformers do not all perform the same. Not sure if it is just the way they were built or age - or both. I haven't seem all your videos but wanted to mention how I have started using a USB sound card and SpectraPlus or ARTA on a laptop for my spectral analysis. Much better noise floor than the HP 3580A and so much quicker at low frequencies. Thanks for posting a series of very nice videos.
Thanks for the great comments! I would be thrilled to see a video review/demo on the SpectraPlus using the laptop. I currently only have a Keithley 2015 THD Multimeter to measure distortion. It only tests at one frequency and doesn't allow me to do spectral analysis. My spectrum analyzer is only for RF measurements, as it only goes down to 9kHz. The soundcard setup may be just the ticket! Anyways, thanks. I've been a subscriber to your channel for a good while. Your videos and work are very informative. Thanks for sharing!
Looking forward to the next one! I found some information on global negative feedback, if you google "Empirical implementation of global negative feedback" it should be the first result and has some good information.
Did you have a test load, you should never test a valve amp without a load at any point. It alters the feedback fraction so the amp can oscillate. If a signal is accidently injected it can damage the output transformers due to flyback induced EMF as the output valves are driven to full cutoff. I can see you have wires connected so I'm guessing you have a load. I built that amp with parallel output valves (4 per amp). I had to reduce NFB by a good chunk to stop it oscillating. My general approach is a 1khz square wave test and adjust NFB so there's as flat a wave as practically possible. Square wave testing is a powerful tool and can tell you a lot about where any problems may lie.
"Did you have a test load, you should never test a valve amp without a load at any point." Exactly - As explained here www.valvewizard.co.uk/Book1.html
Great series! I know it’s off topic but since it has been mentioned twice now, in part 5 as well, a medical defibrillator does not start a heart. For reader info, it actually stops a heart that isn’t conducting properly and also some of the associated reentry loops that cause dysrhythmias. Shocking a non-conducting(“stopped”) heart won’t do anything but it can stop a good heart(which is why you are so correct in the warning). The algorithm for starting a stopped heart doesn’t use a defibrillator at all. I’ve actually seen inappropriate defibrillation convert an undesirable but non-lethal rhythm into a much worse lethal rhythm. I know that wasn’t the point you were making and that such power is indeed dangerous but just had to respond to one of many common healthcare myths. Exciting nodes with a pacemaker is another topic as is an internal defibrillator but same principle. Sorry if this post is trollish as I watch it for the tube amp info. Awesome stuff! You are a good teacher!
Great series of videos, Tony. I have enjoyed it thoroughly. Why, at low frequencies, are the two channels not perfectly in phase? Or am I missing something?
Hello, excellent video sets, I'm learning, I'm not electronic, I'm studying, please tell me where I can see the schematic and list of components and power supply, best regards from Argentina
Yellow/White wiring problem appears because you have two inverting stages before a final power one. And perhaps a transformer manufacturer meant a standard one stage preamp.
i just noticed something.... no fuse on the ac line? also, the meter showed some bounce back on the cap when you removed the stinger..... no mention of that "gotcha" in the video :)
Expect to spend anywhere from $300-$500 for an amp like this, provided that you have to buy the transformers and you have some of the components on hand. If you can find used/salvaged transformers and are good at fabricating the chassis yourself, it can cost a lot less. If you want top-shelf transformers, capacitors and chassis, it can easily approach or exceed $1000. I spent around $40 on each output transformers and around $90 on the power transformer. I used decent film capacitors that only cost around $1 or less each. Hope this helps.
TB, I am working on the PHILCO 40-124 and a couple tube sockets are resisting the tube when I go to install them. They are LokTal tubes 7C7 and 7A8. Do you have a source for these that you can pass along?
On the last Philco that neede a socket, I found one at TubeDepot.com. Part number SK-8PINL for $4.95 ea. A bit pricey, but they were very good quality ceramic.
Yeah right,,, in the guitar world amps they all say don,t skimp get beltons, they are cheap and super quality. 20 years someone will go into it and say wow this is a nice build.
Hmm .. 3rd time .. “socket to me?” .. hmm enjoy? .. I had both a science & art teacher tell me “this is a science and an art” .. but .. the art teacher also said “art is 10% inspiration, 90% perspiration” ... LOL (oops .. not funny here tho) ...
Ok, all the videos were good up until this one. I feel a BUNCH of stuff has been left out. Such as, 3 times on the sockets? What are you referring to as I don't remember seeing the other two times? And now I am at 31:45 and your talking about adding a resistor and distortion, Where did I miss this?? Then you mention something about "looking alot better now than we were before" WHAT BEFORE? I would like to follow every step of the way and try to learn something about this amp and design but for now I call a bad video...
