Replaced the dinky volume knob with this. More better? Thanks for the idea ... Craig.
Think I know why the wiring got switched in the shed. I have this thing with switching things, oddly it's usually the basic things that get mixed up while the more complicated stuff remains relatively unaffected. It's something I've always had to keep an eye on that forces me to double check my work, and redo a lot of it.
Pointer was made with a blowtorch and piece of SS welding rod. Couldn't find any small diameter long length set screws that would work so used a couple bronze looking wood screws and cut the points off
Plugged it in, no tubes yet. It appears boy was somewhat disappointed there was no smoke, nothing blew up, and I didn't get electrocuted. Thought I'd post finding first.
Yep that sounds right. Next I'd just install the EZ81 rectifier tube and then power it up. You'll see the B+ come up as the tube warms up. Without the triode tube installed your B+ will reach a value quite a bit higher than your target 250Vdc, that's normal and ok. When you install the triode tube you will put a load on the power supply and the forward voltage drop across the EZ81 will increase as well as the voltage drop across the C-L-C choke, resulting in a lower B+. Same with the heater voltage. Right now with no tubes installed the transformer is unloaded and giving you 3.4 + 3.4 = 6.8 Vac. With both tubes installed it should drop closer to the target 6.3 Vac.
And just so you can sleep good tonight, with tube circuits like this one, hitting exact voltages isn't super critical. Generally the rule of thumb is only +/- 10% !
So if your B+ voltage with both tubes installed ends up measuring somewhere between 225 and 275 Vdc you're good. Same with the filament (heater) voltage... if it ends up between 5.8 to 6.9 your tubes won't explode in your face or die in 6 months.
B+ started around 281Vdc and after ~4 minutes 280Vdc. Didn't check heater voltage. Will the B+ change once a load is hooked up? After measuring our household AC voltage, 124volts, I did use the 120volt input of the transformer instead of the 115 input.
B+ started around 281Vdc and after ~4 minutes 280Vdc. Didn't check heater voltage. Will the B+ change once a load is hooked up? After measuring our household AC voltage, 124volts, I did use the 120volt input of the transformer instead of the 115 input.
There is a load of sorts - the pot on the output. Depending on the input impedance of your amp, your B+ may come down a bit since it will be in parallel with the pot. It also might change depending on the particular tube. You're 30v higher than spec, but in the tube world, 10% fluctuation can be considered normal in some designs. So you're actually not that far off. You might want to measure the voltage drop across the cathode resistors to see if the tubes are biased correctly.
There is a load of sorts - the pot on the output. Depending on the input impedance of your amp, your B+ may come down a bit since it will be in parallel with the pot. It also might change depending on the particular tube. You're 30v higher than spec, but in the tube world, 10% fluctuation can be considered normal in some designs. So you're actually not that far off. You might want to measure the voltage drop across the cathode resistors to see if the tubes are biased correctly.
The designer was shooting for 257dvc so that is just inside his 10%. Check that to ground?
In this case it's even easier - in that article they are calculating plate dissipation for output tubes. For the 4S, he gives you the voltage you should see from the cathode to ground for each tube type in the charts. If you're running a 12AX7, it should be -1.16v. 12AU7 - 2.2v. I'm betting you're pretty close.
What tube was the Fender, couldn't find the number on it? An article did mention that Fender likes to run a lot of plate voltage on their tubes so maybe it's built a little tougher than normal.
Catchode to ground 1.1v. after ~1 minute of warmup, 280vdc to plate, 6.6vac to heater.
Might mate this with a cheap amp and speaker today and see what happens.
Cathode voltage is nearly spot on. B+ of 280 (I'm assuming you are measuring B+ before the 100K resistors, not the voltage to pin 1 or 6?) is a little high but I just read that Fender routinely ran 12AX7s with a plate voltage (that's after the plate resistor) of 380v on their tremolo driver stage, so you should be fine.
I think B+ was measured before the resistors. I can do it again to be sure.
That link was similar to other links that mentioned Fender liked running plate voltages above spec.
We went out to the shed with one of those cheap tri-path chip amps and intended to hook that to a pair 2" bmrs' that used to be in a soundbar. Searched for push-clips forever so we didn't have to solder to the driver, wound up soldering anyway. Then it was time for supper.
Then time for Venom.
Holy $hit. Maybe some of you seen the Gradientaxp/Peerlessda25bg/sd215a build, well they've been my mains for a while (even though I can no longer connect to the minidsp -thanks PE). The sd215 doesn't quite keep up with the mid/tweet but take some of the burden off them with a pair of 18" IBs tho and damn! Impressed the hell out of me how clean they sounded to extreme levels.
Really need to mover further into the country where there are no neighbors.
How's the noise floor? That Fender tube has been sitting in box of used tubes for over 20 years. I don't even remember who gave it to me. I wasn't sure if it would behave itself in hifi equipment.
Initial impressions with Fender branded tube (12ax7?) as compared to long time stable Aune x1 dac/pre.
Spotify>Aune x1 used as dac>tube pre>minidsp>Acurus a200x3>Gradient axp06/Peerlessda25bg/sd215.
With volume at 0 and my ear about 6" away from the tweeter I can hear a little tweety bird in there.
Volume seemed to increase after several minutes listening. Are the tubes coming up to temp or did I imagine this?
Billie Ellish You should see me in a crown has some hash on top of her voice. Not as clear or as clearly outlined on stage. Voice sounds more real but is feathered into the soundstage. Not as well defined. Before you could pinpoint her, now you point towards her.
Steve Aoki remix Spoonman; Bass is fine, tight and deep, maybe more full. Hard to tell as I made a recent change in the minidsp and now can't go back to where it had been for several months prior (thanks PE). The problem with active dsp, always messing with it.
Upper treble seems boosted (could be related to recent dsp change) ... and oddly, maybe more delicate?
Charm City Devils Man of constant sorrow; Upper range vocals and maybe lower treble seem to stick out, feels more congested in that range.
Oddly enough sound releases from speakers better and the soundstage just seems to be there, definitely better depth front to back. Back of stage used to have a fairly distinct stop at the back wall, now it's a soft stop with sounds supporting it from behind. Stage is definitely deeper. As a whole, the soundstage is more an organic whole, not layered at all, just there. I'm mixed up here, hard to describe. The paint the picture is painted onto is not as black but the picture feels more real???
These are initial impression and subject to complete reversal as I switch back and forth between gear and music.
Great to hear everything is working! It's a great accomplishment to have your first tube project fire up and make music. Let the tube-rolling begin
Your comments about the the sonics are very similar to what I noticed a few weeks ago when I pulled out one of my Dynaco ST-70 amps. It was obvious the highs were not as accurate as most of my SS amps, but I was definitely hearing more depth from those tubes. You are spot on - it just sounded more organic. I almost couldn't stop listening, pissing off my wife when she had to yell twice (maybe more?) to come up for dinner.
It could be the difference in input impedance for each amp. Since the pot is on the output, that impedance may have greater effect on how much signal (voltage) the circuit can deliver to a given amp. I would be curious if anyone on their forum has tried it with pot at the input.
Fella on one of the car forums asked about finding some 7868 tubes for his vintage gear. No problem, looks like EH is making them now. Which led on a bit of searching about Electro-Harmonix, aka the New Sensor Corp. It appears they manufacture a whole lotta tubes at their Xpo-Pul factory in Saratov, Russia; Gold Lion, EH, Sovtek, Tung-Sol, Svetlana, and Mullard to name a few. There's a rather large price swing between those brands. Other than price, is there really a difference between them? I've read many a 'golden ear' reviewers gush over a certain brand tube.
Then there's JJ/Tesla out of Czechoslovakia.
Winged C aka JSC Svetlana out of St. Petersburg, Russia.
Wish I could give you some insight. I've never used any of the Russian/Chinese/Czech small signal tubes besides the 6n1p and ef86. Neither of those will work in this design as-is. I did read positive comments about the EH 12ax7 a while back, but I don't remember the site or author. It's also tough to sift through user reviews since these tubes are used in so many guitar amps.
12at7 Raytheon ... notes as jotted on paper while trying to listen;
one side of tube looks to glow brighter than other, bias? Not much difference in volume knob vs 12ax7.
Billie Ellish - bass not as deep- voice nice, more bite to it- more real-more body-she's just there between the speakers and a little behind the rear wall-vocals seem further back in general-the hash that was there on voice gone and now clearer-less detail
Spoonman - yep, bass not as strong or deep-good mids-upper most treble soft-not analytical-don't think this tube pulls all the detail out of the recording but it sure makes it sound good
Man of Constant Sorrow - deep smooth organic soundstage-bass not as strong-nice upper vocals-lower male vocals loose some chestiness but from there up nice nice-lower treble clean-easier to pick out individual voices-highs bit soft-background blacker
Peppery Man - Wow just wow! big smile
12at7 vs 12ax7 vs Aune x1 dac/pre
overall 12at7 not quite as dynamic as 12ax7, neither dynamic as the Aune dac/pre.-Aune more analytical than either tube-fly$hit out of pepper difference-Aune=everything clearly laid out bare naked as is. Tubes more organic music as a whole. Suspect 12at7 freq response not as linear as 12ax7.
12ax7=more bass, better rhythm (bass?)-more treble-better dynamics-more detail-nice piano vs 12at7.
12at7= nice mid-nice vocals-vocals feel more detailed but the other stuff is less detailed-I mean really nice voice-Like wow nice. Like magic on certain pieces of work.
Comments
Are you ready to plug it in yet? That's always the exciting/scary part in a tube project.
So if your B+ voltage with both tubes installed ends up measuring somewhere between 225 and 275 Vdc you're good. Same with the filament (heater) voltage... if it ends up between 5.8 to 6.9 your tubes won't explode in your face or die in 6 months.
After reading this I'm wondering if it might be better to run a tube with less gain once you have everything buttoned up.
Your comments about the the sonics are very similar to what I noticed a few weeks ago when I pulled out one of my Dynaco ST-70 amps. It was obvious the highs were not as accurate as most of my SS amps, but I was definitely hearing more depth from those tubes. You are spot on - it just sounded more organic. I almost couldn't stop listening, pissing off my wife when she had to yell twice (maybe more?) to come up for dinner.