Pars

Happy Birthday to the motley lot of yez!

Agreed on temp... 55-60 deg. C seems fine. When they get up to 70 I start getting concerned. Once I put the top on, I may need to do something. The power transformer does not feel warm or measure above 35 or so. I may use the heatsink for the top over the BJT area instead.

Thanks Tom. Is there an optimal voltage, or does higher = better in this case (measured at PR / PL to ground)?

I thought these tubes were matched? As for increasing the bias, while I was running RMAA, the temps on the BJTs were ~60 deg C. The voltage regulator was around 55 deg C, heatsink was uncomfortable to touch, but case wasn't hot anywhere I felt (top is not on or drilled currently). It's no problem for me to replace the 75 ohm resistors, though I'll have to see what I have laying around. Off the top of my head, I have some ratshack carbons (I think) from a variety pack I may have some RN60s or something around also, or as you say, I can parallel something. I could put 100 ohm pots in also, but since this isn't intended to be a play amp, probably not. Again, if anyone needs another end panel or two, you can have them. Out of the US I might have to charge postage, but free otherwise.

I started running RMAA on the amp tonight. There does seem to be a channel imbalance with the higher bias tube having a slightly higher output. The delta appears to be greater at low impedance. I have a load box (Amb's design) that I was using, but also ran unloaded measurements. I am using an M-Audio Firewire Audiophile box for the test. I was adjusting the input levels (I assume coming out of the amp) with the M-Audio control panel and had to compensate for the level imbalance. Not sure whether I should do that or just lock them at an equal position. The CCS 75 ohm resistors are Draloric 0.5%, but I did not measure or match these. I'll take some voltage measurements of the drops across the L and R, as well as the LED voltages tomorrow. I'll try to pdf the RMAA test results and post tomorrow also.

Also, I got some extra end panels, so if anyone wants one for redos, let me know.

Is there any particular heatsink grease anyone would recommend? I used a silpad on the regulator, but only had some really old ratshack thermal grease for the BJTs. Arctic Silver? Other?

Thanks, that is helpful. It has probably been stated in the thread already, but which switch position is which? If from the schematic, pin 1/4 of the switch should be the higher impedance and pin 3/6 the lower? For this amp, is it 300 ohm and 32 ohm taps?

Thanks Nate. I'll run RMAA on it, and also some test tones and look with joe scope to see how things are doing. I would certainly expect sand state to be better than this j/k

Doug (or anyone): Will the bias imbalance between channels that I am noticing at PL/PR have any negative effects on performance? I am guessing that a better matched tube pair is the only way to fix this? Or is it a non-issue?

Congrats on the mill usage and on the job switch proceeding as planned Nate. I'm sure that was a bit odd on Thursday. Vicki: glad that the NSAID is working; that is good news. When I was going thru my hip(s), I was taking diclofenac sodium, and it helped, but wasn't what I would call awesome. I looked into resurfacing but my ortho recommended against it; these things seem to come into/fall out of favor. And Brent, congrats on the job.

Regarding the voltage imbalance between PR and PL that I was seeing (130Vdc vs. 112Vdc): I swapped tubes and it moved with the tubes, and stayed the same voltage-wise, so I guess I can conclude that it is the tube matching and not CCS matching causing this. I guess I can also conclude that the amp is working correctly? I'll finish casing it and go from there. BTW, I was missing one of the feet for the case, but I guess I can find something else that will work fine.

That is kinda what I did on mine, though your suggestion to mount the components to the panel first is a good one... why didn't I think of that Oh wait, I didn't have the panel cutout yet. BTW, I may come up with some extra panels if anyone needs an extra one. I'll let you know if these magically appear or not.

^ too long (the case, that is)

Marc: I drilled the front panel tonight. The pot and the jack positions are fine, including the antirotate nub. The switch was a little high (template) compared to the actual switch. If I were to do it over, I would make a slot (vertical) for the toggle only to come thru. The switch sits back so the barrel of the switch does not stick thru or touch the front panel. On the rear, I haven't had a problem with the RCA jack screw versus the IEC screws, but I haven't put them both in yet. Hmmm, will have to take a look. By eye, it appears that the case is pretty much 2x the thickness of the plastic end spacers too short. I will need a washer behind the jack and the pot. Better as Kevin said to slide the PCB all the way back so the RCA jacks fit properly. OK. I didn't do any matching. Voltage moved with the tube, so I guess it is what it is. I replaced the heatsinks with some extras from my Gilmore V2 build. Mouser 532-563002B00. I mounted them upside down, and will cut the tabs off. BJTs were running around 50-51

Got the amp built and casing partially done (back panel). I tried to move all panel components as far forward or backward as the case may be in order to compensate for the case length, including partially straightening the pot pins to move it forward a bit. Same with the switch. The RCA jack on the template seems slightly high, though it could very well be my placement of the template on the panel MJEs are running around 70

Amb has some in his store.

But then it would be burn out, and wouldn't qualify...

Mouser 512-ISL9R860PF2 ISL9R860PF2 Fairchild Semiconductor Rectifiers These are the Stealth rectifiers that I have used. TO-220F package.

Yeah, that would work. Probably just one shorter nylon screw and nut on the end diode would suffice. What might work better would be to use some fullpak diodes, which are insulated. The MUR series doesn't offer them other than the MURF860G. I've used some Fairchild Stealth diodes from Mouser before in a sigma22 (the one on my dynahi) which use this package. Most layouts don't put these diode packages in back to back, but keep the orientation the same (sigma22 for example). Just pointing out a potential problem once these kits are released into the wild, as I could easily bend the two into contact with each other, intentionally or not. Because of the heat issues, there is also more likelihood of peeps running these without the tops on, so more chances of fingers getting in there.

Oh... you're supposed to use solder on these? With heat? Seriously, for the production run or whatever, this could be a concern. If someone can f something up, they will. Poking around on the board, etc., they could be bent into contact with one another. The caps protect them somewhat.

Mike, my condolences. Me: heat turning up on project at work, but it will be done in a week. Have gone riding (bike) every night after work for 20-30 mins (5-8 miles). Up to averaging 16 to 18 mph, but bike path can slow things down. Have to be mindful of the kids, walkers, joggers, etc. I'm sure this is not up to Chris' (dreadhead) standards Haven't seen him around here for a bit, hope all is ok.

My brother brought the rest of the parts over yesterday, so I got started on building this. Looking at the MUR810s, I assume that the tabs of D5 and D6 touching each other would not be a welcome occurrence? Anyone do anything to safeguard against this happening?

Fortunately I never even saw the red vodka, not that I would have had any... Beer or red vodka... hmmm, tough decision

That reminds me. I wanted to meet Pete Millet at CJ, but never did. CanFest, not so much.