xxJPMxx

Maynard is a classy dude! This forum is more than lucky to have a great guy like him around.

I think Rout or Ro is fine and most likely the most accurate description. I usually label them Rout and Rload like this;

People need to realize as the average age before death increases there will need to be a form of population control. Which means people need to stop popping kids out that don't need to be. I see so many people that reproduce that shouldn't whether they can't financially support the kids or they just are too retarded to have kids. My messed up opinion is that the stupid people breeding far out weight the smart ones. We are all doomed.

Yes you got it now Depending on the amps power supply yes the the increased current demand could drop the rail voltage; e.g. The amp's power supply has a high impedance out. My main concerns are usualy the speaker coil and the the amps output active device. FIrst the speaker coil. Let's say you have an "8 ohm" speaker rated at 100 watts. You look at your amp and see it is indeed a 100 watt amp @ 8 ohms. Let's just say the amp is a perfect voltage source and the speaker impedance plot shows it dips to 4 ohms at 100Hz. The speaker's voice coil could be blown due to the amp delivering 200 watts at that frequency. Now let's think about the amp. The increased current could cause the output device to exceed it's rated power dissipation and or current rating and it goes poof.

Your assumptions are incorrect. Consider the amp a voltage source with say an output impedance of .5 ohms. If reactance of the speakers dips to 4 ohms at a particular frequency the current increases not the voltage. If anything the voltage will drop due to the increase in current creating a larger voltage drop across the amps output resistance. A perfect voltage source will have an output impedance of 0, meaning no matter the load the voltage will always be the same but the current will just increase, voltage stays the same. This is why most amps don't like a short circuit at the output. Rail voltage has nothing to do with anything.

Great story! I don't know if kids have laser tag anymore but it would be fun to play laser tag in a dark house with those headlamps on! I got a ball for my dog that you could record an audio track onto it and when the ball was bounced or chewed it would blast out the recording. My dog freaks out over birds (especially crows) and so I recorded "GET THE BIRDS!" She went bonkers over that thing!! When she got it in her mouth and chewed it it would scream "GET THE BIRDS!" and she would drop it all freaked out but then continue to attack it anyway. Hours of fun there. No literally only hours, it was destroyed but hysterical while it lasted.

I am very surprised nobody picked up on no grid stoppers on the schematic.........they are on the tube socket just not in the schematic I used as big as I felt comfortable on the EL34 to try and cut down on grid current during overloading. Also it's a high transconductance tube.

Hey Jim! Yes R8 was the original feedback resistor which included the output transformer in the loop (not power transformer). And yes R9 was also removed. In the revised schematic the new feedback resistor is the R9, 220K. I guess we can call it "Inverse-Voltage Feedback for adjustment of tube impedance". Strapping the EL34 as a triode lowers it's plate resistance to about 950, adding the amount of feedback I did lowers it further to 500. Not too shabby The "trade secret" is a capacitor that isn't in the schematic.

Hello Maynard, 500Hz square wave looks great! I added a "trade secret" to help with the square wave response (It's just a 1nF 1kV cap from the EL34 plate to ground). I was going to hook it back up and do more testing so I will try and get some pics. I can never get good pictures of my analog scope with my phone, it's a tektronix 465. I am sure all analog scopes are the same, just like trying to take pictures of old TV sets and computer monitors. I usually take snapshots using my digital scope on my computer and upload them that way but the digital filters cause ringing on square waves so it's pointless hooking it up the the computer for that. I will try and get some pics up next time it's on the bench. It shouldn't be too much more work to add the .015uF cap in series with the feedback resistor, if I have one....I might only have .01uF laying around. As far as the overshoot with the transformer in the feedback loop I believe it was at 200Hz square waves, this was days ago so don't hold me to that data.

Not sure if anyone is still interested in this but Jim sent me the amp and I will share my progress. Here is the actual schematic. I was fairly close with original schematic that I made from just looking at the pictures. First on the bench I could only get about 2 watts out of it. EL34 Vp=270, much lower than I had thought, something must be wrong. With the rectifier out I get 317-0-317 w/ 125 ohms winding resistance end to end. I should have much higher B+. Swapped out the rectifier and sure enough the voltage came up to where it should be. Now measuring about 4.5 watts out @ 6% THD! Hooked it up to some speakers and the sound wasn't too bad, just not a lot of clarity and sound staging. I now turn my attention to the why the heck they have the output stage wired like this, doesn't matter Jim has asked to go for Triode mode. I snipped the ultra linear taps and wired in a couple 150 ohm resistors from plate to grid 2. I had some overshooting during square wave testing which was helped via a lead comp cap. Power out is down to under 4 watts. I listened to it like this, and it was better. Now I have changed the feedback entirely, Power is down to 3.5 watts BUT THD is down to 1% at full clean output. The sound staging is good now and much better clarity, sounds like a much tighter amp. Here is the current schematic. I plan to do a few "tweaks" on Monday and see if I can't tighten her up and get it even more accurate. I like accurate, when I got the amp it sounded colored and slightly boomy, not anymore.

I don't want to start a thread about capacitors. He started a thread about his amps being built and posted pictures of them, I am commenting on the pictures. How is me saying expensive caps are snake oil offensive, it's my opinion, take it or leave it. Agree to disagree, or discuss them. Isn't the point of this forum to discuss tube amps? I do know there is no advertising (supposedly) on this forum which this and pretty much all of toolshedmatt's threads are. Give me a break.

You are the one who opened up this thread for the whole world to see and comment on. From experience and knowledge my "opinion" is that $150 for a 1uF 630V capacitor is crazy talk and is what hikes the price of these amps up. Sorry just an observation. I always find that the folks who choose to use these snake oil parts in their build blindly think because they cost more they are better, but they fail to explain technically why they are better and how they will improve their amp. I usually see some generic comment like "I found no other capacitor that sounded as good in the amp when testing". Golden ear syndrome all over again. You may just have a lot of money and your only cause for using these sort of capacitors is that they are expensive and you don't care, now that is a reasonable answer I can accept.

Oh god snake oil capacitors, I forgot why these amps are so expensive.

Another beautiful layout Maynard!! I had a fun idea I would like to run by you. Instead of running the 60FX5 how about a cool looking 25 watt bulb? It should fit the 600 ohm requirement and will only burn at 6 watts so it won't be too bright, it should glow a dull orange like in the picture. https://www.1000bulbs.com/product/96743/PLT-000601.html?utm_source=SmartFeedGoogleBase&utm_medium=Shopping&utm_term=PLT-000601&utm_content=Candelabra+Light+Bulbs&utm_campaign=SmartFeedGoogleBaseShopping&gclid=Cj0KEQiA4qSzBRCq1-iLhZ6Vsc0BEiQA1qt-zso1i3SpdnkCk8ccOInUsXJHJPrTOSHGMPzOW6N-WicaAq8a8P8HAQ

https://www.youtube.com/watch?v=bE6X72GD3ug

I am fairly certain you can live off Ketchup and nothing else, it provides all essential vitamins, minerals, and protein a body needs. It's the perfect food.

Good luck!!! Fallout 4 is off the hook!!!

Your killing me here!!!! Only about 40 minutes from me but I don't have the room or the $$ for them. Someday the stars will align for me.

I highly doubt you can talk them into replacing any capacitors that haven't failed for free under warranty. Good luck!

My dog is a turkey.

Those holes are probably for the "can" style capacitors.

Service industry? It's non-existent. We live in a throwaway world.

My last push pull amps I used a good amount of feedback, 20db. I ended up adding a Lag compensation network at the plate of the input stage to improve performance. Here is a good article on calculating the compensation networks: http://www.angelfire.com/electronic/funwithtubes/Amp-Compensation.html