DirtyErnie

Now we're getting somewhere good, at least the bass player in me thinks so. That's about the size of a 2x12" cabinet, maybe a small 2x15", and might stack up well. What is the efficiency of your New center, in the 1w/1m numbers? I have an addiction to vacuum tubes, which can make it hard to keep up. Great discussion, thank you all.

^^ Both amps claiming to be waaay out on the flat part of the curve. How much resistance between there and the driver itself? Or even to the inputs at the crossover? What's the actual delivered damping factor? Probably way less than 3K. Either way, I'm jealous and I want one of those. 😁

I've come to understand negative feedback as an Error Correction, and the fewer errors it has to correct, the better. Damping factor? Just need 'enough', and your cables degrade it. Functionally, it's a log curve, amps that claim to be out in the flat part usually end up on the curved part after speakers and cables are hooked up, and beauty is in the ear of the beholder. Aren't the Subjective Art Hobbies fun?

I think that talk started in the world of P.A. systems and low-efficiency HiFi. If you're smacking speakers with high power for long periods, distortion frequencies up into the ultrasonic range might cook your tweeters. Really isn't a concern with high efficiency horns, and low power amplifiers. Distortion products tend to be lower order, and likely lower frequency in the low power world.

Those compression/port plugs are beautiful.

"A man's got to know his limitations." Detective Harry Callihan, SFPD

So does mine, but you have to go a few steps father to make the surgical changes and flatten impedance where it needs to be flattened.

It may be a better approach to analyze the crossover and find out which components are responsible for causing the impedance variations in the first place, and then apply targeted corrections there.

Definitely get the electrolytics out of there. When they go bad, high ESR, the crossover starts pushing too much mid/high info through the woofers. That can really make a mess of things when all 3 drivers are trying to reproduce the same frequencies. The electrolytics are in the shunt and LCR positions, so just about any film cap should be a huge improvement. The series-pass caps in the tweeter section are much more critical for quality. I'm taking the easy way out and letting a Sony receiver auto-calibrate my speakers (after xover rebuild). The amp is definitely the weak link in the chain, but convenient and toddler-proof.

^^^ This. Even better, only do one section of one speaker at a time. I did that method on a set of KG2.5's several years ago. The biggest difference was in replacing the bipolar electrolytics; speakers were surprisingly congested and flat before that move. Used ERSE poly's there, and a Crites kit for the rest. The other caps, the titanium domes were nice improvements, but swapping the old bipolars was mandatory to get the crossovers working right. I could have stopped there and been happy... ...but that's not what this hobby is about for me.

Just went through something similar in a JBL unit. Short version: chassis was made of Aluminum, which oxidized, and increases resistance in the ground paths. Fix for my unit was to take the amp out, open it up, and get some "conduction improver paste/grease" where boards meet chassis and chassis meet brackets.

@slovell , any updates on your toe-in?

For me it's all about the flux. A syringe of 'chipquick' changed my whole game for the better. There's so much control, and so little waste, I'm not feeling at all bad about it costing $12. The joints are beautiful.

Are we prepared to talk about the moon?

Maybe. If my brain's not broken tonight, I though high screen voltage was harder on tube life than high plate voltage.

18 might well be fine if you run your power cables to the 'lows' input and jump 18awg from there up. Highs take a lot less power.

But how does it SOUND?

Ultimately, the only thing that matters is what sounds best with your speakers, room, and ears. "If it measures good, and sounds good, it is good. If it measures good, and sounds bad, you've measured the wrong thing." ~ H.H. Scott

Take them home, wipe the wood down with Lemon Oil, plug in, and go. They really don't need much attention, especially if you're going to bi-amp. If you have a bristle brush attachment for the vacuum cleaner, that might be good in the grilles. Piano and acoustic guitars will blow you away.

EL84 400v plates, 300v screens, 20 watts. Pick up an old Scott and fix it, or just the transformers. Or just the schematic for the power amp and build. They're simple and sound great.

John nailed it. Between cables, crossovers, and negative feedback, the laboratory-measurable differences go away and we're left with "What do YOUR ears like?"

After the first round of mods, I was hearing things I'd never heard before in movies I was quite familiar with, and 60's vintage music was amazing. Probably something about being recorded with tube consoles, and being played on a tube amp. Axis: Bold as Love was nearly a perfect experience. This was on a pair of upgraded KG 2.5's and a JBL 12" active sub box coming out the 'center' channel.

Got some holiday-season Funemployment time on my hands, so it's time to get the lab sorted out and working better. First order of business: music. Had the 222c running as the main amp upstairs for a while, then marriage and kids decided on simpler things that don't burn small hands. Also, it popped a JJ rectifier and always buzzed after, kinda helps the decision. I'll add a pic and more after I get on the computer, cell phone pix are too big to attach... More: Looks like it's time to replace the screen bypass caps on the 6GH8's, one finally went way off spec. Pretty sure I've heard these are prone to failure. There's one more failed cap in the phono stage, but since it's under everything AND I don't use the phono stage, it gets to just hang out and be failed. Previous repairs & mods: Replaced the two positive-voltage cap cans with JJ equivalents. Although the main HV cap is a 40-20-20-20. Currently, there's a small 10uf-500v as the first cap after the rectifier, then an 80-ohm resistor, then 60uf of that cap feeding the output transformer center taps. Not sure what difference that made, but things seem to be OK. 10UF should be easy on a GZ34. I added a tag board (barely visible, upper left) with some trimpots to get independent bias voltage adjustments on each channel. Screen Grid voltage was about 390 at first, way too high. Swapped out the 1.2K series resistor for a 3K, working with the stock 8K shunt resistor as a voltage divider for the screens. Added another 10uf - 500v cap to bypass the 8K to ground and add a little filtering at that node. With the original Telefunkens in one channel (I have all four, but the screen pin busted off one of them. Yes, I could cry...) it sounded amazing stock, but with what tubes are available at my budget point (JJ), there was a harshness. With screen voltage closer to 300v, the JJ's sound very nice. I'm a firm believer that load impedance and screen voltages should match for best sound, and 390v had the JJ's WAY off their map. Then there's the standard 'replace the selenium rectifier with a silicon bridge and adjust the series resistor after it' for the pre-amp tubes heater supply and output bias voltage. Also swapped out the original driver-to-output caps with russian Paper-in-oil types, but made sure to wrap them in heat-shrink to keep their steel bodies from shorting out the insides of my amp. Planned: I'm intending to add a little outboard input & volume box to direct feed the power amps through a pair of RCA jacks I'll install somewhere on it, I think I found a place right behind the volume knob that should work. Maybe I'll build a cabinet for it some day. That's another thing my 20-year-old self did that I don't want to talk about 22 years later...

Mr. Warren, this is absolutely brilliant.

I can't imagine four tweeters and eight mids in an array like that sounding better than a single-point horn mid/high driver with symmetrical woofers. No matter how hard they math it, an array is always going to have artifacts somewhere. Glad to see the Epics on good stands. It's giving me ideas.