Satyrnine

Does anyone have any reading/data/thoughts of case temperature of the 15030/1's at various bias levels? I'm on temp less than ideal heatsinks, but direct mount with thermal paste. Getting about 50*C across the board after and hour or so with 30v supply and around 120ma bias. (Planning on 200ma once I'm on the dissipante sinks) Using a 4 channel thermocouple.

I'm going to put together a mouser BOM for the ubaltobaltube shortly, unless someone has one they could share?

A friend is at canjam right now and just sent me a photo of this beast there. Great work!

Well, the problem is I’m an idiot apparently. After going over the board carefully so many times, I came back to it after a breather and there it was, Q8 in backwards. I’m so sorry for wasting everyones time with this. 😫

Ack, I apologize simmconn, yes its the “ok” board. I’ve been wracking my brain on this and failed to recall you’d already pointed out that the OK is def not OK. Thank you for your help, will investigate there, makes perfect sense.

Without opamp, about 400ma 😬 The others are around 40ma as expected. I Just replaced all the output trannies, the input pair, and the ptza’s with as close matched parts as I could, no luck.

Trying to diagnose some excessive offset on one board. Likely culprit is unmatched N/P pairs I assume. I ordered 20x spare of each bc556 and bc546 but there's no way I can match these. 546's are all about 215hfe, and 556's are all about 120hfe. Same with ptza06 and ptza56, at least 50hfe difference between N and P types, but tight matching within their own type. I replaced the input pair and the ptza's with the closest hfe match I could find, helped offset ever so slightly, maybe 20ma. Should I be matching vbe instead of hfe? Sorry, tube guy learning the ropes.

It's possible, although my soldering skills are pretty developed. I like use Kester 186 liquid flux, Kester 44 60/40 solder and a decent Hakko Iron at 750*. Taught by a guy who helped make some electronic parts for the F117 fighter as a civilian contractor even. Everything is always nice and shiny and liquid looking. I wonder if like tubes, a tester only tells you a part of the picture. I've had numerous tubes test OK on a tester, but not in circuit.

Swapped all 15030/31’s and the bias issue is solved! Behaving nicely. I tested all the removed transistors with a cheap ebay tester and none tested “bad” but I realize thats a limited test. Thanks for the help all. I can finally try this beast in balanced mode! Still waiting on tube input boards from Dukei who had spares. Also need to wrap up dc connector details and order chassis yet.

I'm using a +/-30v grlv with common ground to power it. Tried it shared with a CFA2 as well as on it's own GRLV. I still get the noise both ways. Only way I don't get the noise is disconnecting cfa2 boards, powering only the protector board and headphones connected to it's outputs. I'm using onsemi 7812 and 7912, rated for 35v input and 1A. Relay is Omron G6A-234P-ST-US-DC12 which is 12v and ~17ma coil current. I'll check on heat, but seems if it was the issue, I'd get noise even without CFA boards connected, no? Thanks!

You're completely right, arbitrary to have a negative since I was just measuring drop across the resistors. Dukei recommended measuring drop across resistors vs voltages to ground. I mindlessly added the negatives when I was jotting it down, just a matter of probe position in this case. +10v is the proper voltage after the servo in this case. Thanks for the input, I'll investigate further. Sorry about the size. The resolution is decent, but on a phone or such device it may be tough. The schems I was jotting on were small, tried to keep everything visible. I def often write too small.

Yes, I've visually verified all parts, and ohmed out each resistor to verify. Checked for cold solder joints, polarity/orientation/etc. N's and P's in right spots. Good eye Pars! Yes, in that pic the two toasted output devices had the screws removed, I've since replaced with new official distributor parts. I do have spares, I'll just replace all the 15030/31's as you suggest. Those are easy as you say, esp with my new Hakko desoldering gun. Inputs to opamp would be the feed/sense from the output right? I should add, I have the amp working in SE mode now, with 120ma bias or so, and it absolutely blows my mind. Unreal power and slam, and the dynamics and detail are just wild. Raw dogging for now without protector board with my LCD-2's and LCD-X's.

Still haven't been able to test at below 30v, BUT I did find that if I have no CFA boards connected, just the protector board powered, I don't get any hum from headphones. I also built up a second board, and had same symptoms as first, so I'm guessing it doesn't like 30v.

I bit the bullet and took measurements of an OK and the "Hot Bias" CFA2 boards. Here is what I found: Test conditions: OK board biased to around 120ma, trimpot in middle-ish position. Hot bias board has trimpot all the way down, which gives about 100ma of bias. Ran from the same GRLV at 30v. Clearly the big difference is the output of the servo is showing 10v on OK board, and only .8v on hot bias board. Servos getting proper voltage on each board. I swapped in a known good chip, no difference. The 5k feeders after servo are showing dif drops between boards too. Can anyone give me some guidance on where to go from here?

I ended up using a spare 30v grlv to power the protector board separately. Same transformer. +/- 12v on pins 3/12, still had noise, but it was different sounding this time maybe. Less hf content? Maybe imagination. That mostly (?) rules out that it's somehow injecting the noise back through the grlv and through the cfas, but solidifies that it's happening at the protector board. I think. Suspecting overworking the 12v regs w 30v at this point. Wasn't able to test at lower input voltage because my bench supply isn't bipolar apparently. (I usually do tube stuff, rarely need a bipolar supply until now, hah!) I'm going to go through it and triple check values and get some more detailed readings.

I do have a bench supply, will def give that a shot and report back. I'll try it at 12v and 30v to see if there's any difference in behavior.

Will have to check the pins tmrw, but fwiw, spec sheet says the regs used max input voltage is 35v, so it is cutting it close. And yes, all unused input pins grounded. On delay is only a few seconds too. I'll triple check everything again asap.

I built a protector board up for this. When I connect it to one of the grlv set to 30v (also powering 2x CFA boards), it causes pretty bad high frequency noise on the outputs. Right now in SE mode, grounding negative inputs. I tried grounding two ways: 1) GRLV ground AND cfa output grounds all connected to protector board. (hf noise was present) 2) Only GRLV ground connected to protector, cfa output grounds and protector input ground connected to star ground. (hf noise was worse) When I remove the protector, cfa is dead quiet. I've read these can be used with 30v, but maybe I'm stressing 12v regs too much?

I built a protector board up for my 30v CFA. When I connect it to a grlv set to 30v (also powering 2x CFA boards), it causes pretty bad high frequency noise. Right now in SE mode, grounding negative inputs. Negative outputs not connected to anything. I tried grounding two ways: 1) GRLV ground AND cfa output grounds all connected to protector board. (hf noise was present) 2) Only GRLV ground connected to protector, cfa output grounds and protector input ground connected to star ground. (hf noise was worse) When I remove the protector, cfa is dead quiet. Thoughts?

Was going to go with switchcraft due to being less modular and worried about getting the right pins and all, but these are WAY cheaper than switchcraft too. Do you happen to know the right "pins" I'll need? I'd hate to order the wrong thing, and there are TONS of options with this line. Are locking nuts, plug housing, and everything but pins included with the connectors, or do those need to be sourced separately too? Doesn't seem clear. Datasheets show no accessories. Thanks! Also, does anyone have any guesses on what could be causing the spicy bias on the one board? I'd really hate to resort to shotgunning all the sand to try to find the culprit. I have a decent Hakko desoldering gun, but extensive rework sucks if avoidable. I'm going to go through and measure voltages across each resistor and compare to a working board.

Oh! Excellent, love both options! My main work is with instrument tube amps which often have a bit more real estate, so my probes are not so small. I think part of my issue is there was no good place to rest my arm/hand to stabilize as I probed, since this is all out on the table in spaghetti form currently.

Any reason I can't use this with a 30v balanced CFA2 if I plan on driving small speakers with it? It's rated for 1A, 2A max, and 30w at 8ohm is right at 2A. Thoughts?

Last CFA board has spicy bias. With bias pot all the way down, I get about 150ma across the 1R's. That can't be right. The rest needed to be set around middle to get any idle current at all. Rechecked my P's and N's, and resistor values. Any thoughts? Suspect the middle (bias driver?) 15030? 🤔 Edit: replaced the middle 15030 with a slightly lower hfe version, dropped minimum bias to 120ma or so, so not the culprit. And then I shorted legs with my probe again like an idiot and popped the "last" 30/31's again. You'd think I would have learned something. I need probes designed for this clearly. Here's latest chassis face design: The horizontal lines would be deep machined grooves.

Thank you! This is great to hear. Was concerned it may have taken out more, I will measure everything! The one blown 1R is currently about 250ohms, haha! Will replace both though, as they both got to warm.

Board 1) Butterfingered probing one of the 15030's trying to diagnose the high negative DC offset on this board. Shorted base to connector momentarily, 1R's went nuclear and started melting my probe tips within 1 sec. I powered down a second later, but I'm guessing I have some sand and resistors to replace now. Any suggestions on what to replace? Neat. Stupid mistake. Board 2) Remind me not to trust mouser to always get their parts picking correct. Could have been my mess up too I suppose. There was a 10k in place of a 10R near the input (R9 or R10) which I deduce was causing the LED's not to light. Replaced that resistor w correct value, LED's light and this board is now showing around 40mv offset without opamp and zero offset with opamp, which seems about right. Biased to low around 80ma for now, just had to adjust trimpot further. This board seems to be good to go. Indeed too much. Now that I messed this board up, may be replacing a bunch of sand anyway. I double checked my N's and P's and resistor values, and polarities before it went south, everything seemed to be in the right place.