Pars

Happy Birthday!!!

Also, can you explain the choice between grounding the output transformers or connecting them to the cathode? I think I have the jumpers correct for the LED on the cathode, but I will need to double check them. As for your suggestion in post 305 regarding the higher CCS current and using the resistor to ground on the cathode rather than the LED(s), would you also recommend switching the transformer connection in conjunction with this? I'll have to go back thru this thread and the emails to find where you discussed this previously.

Listening-wise, I disliked the higher CCS bias, preferring the lower bias by quite a bit. I can perhaps understand the higher bias on Grados... and on rock. Amp is clearer on the lower bias with AKGs. Here are some measurements of various LED combos on the cathode LED: 2xRed L R Iled 12.6mA Vled 3.52Vdc 3.5Vdc Vplate 181.4Vdc 169.7Vdc rectangular blue Iled 12.6mA Vled 2.98Vdc 2.99Vdc Vplate 165.5Vdc 154.4Vdc blue Iled 12.6mA Vled 3.0Vdc 3.01Vdc Vplate 169.1Vdc 156.7Vdc

Fitz, I think the consensus was to stick with the 75 ohm original CCS. Doug threw a wrench in the works (it is his works, so I guess he can do that ) by suggesting another way of getting to the new 2.5-3V grid or cathode bias voltage by using the other CCS (56 ohms, or 221 || 75 ohms) and switching to the resistor grounded cathode jumper setting. See Doug's post 305 for more details. Currently I am playing around with the cathode LEDs (2x red and 1x blue) to try to get in the 2.5-3V range.

So is the 3.5V I am seeing too high? This is with the original 75 ohm CCS. I'll have to measure the plate voltage. I also tossed in a blue LED I have a bunch of and it was at ~3.2Vdc. And was it ever bright; made the mistake of putting my head right over it

Measurements were relative to ground. The schematic shows no direct connection to the cathode, but I suppose if the cathode is at +3.5Vdc and the grid floats? I would think the 1M resistor to gnd on the grid might have something to say about that but I dunno. If I measured relative to the cathode, it would show -3.5Vdc I would guess. The grid is connected to input jack->pot->resistor to gnd->series resistor->grid (pins 5 & 6).

^ Good idea! I'll be sure to check into it, though I'm not sure I could afford them. Then again, can I afford not to? BTW, the grid is only connected to the input (audio) and is at 0Vdc.

I put two of the red LEDs in series, and am getting 3.5Vdc in circuit. I'm guessing this may be a bit high up the curve? I will also try some blue LEDs I have. The red LEDs measured ~1.6Vdc on my meter's diode test each. I'll do both listening and RMAA on both the 2x Red and 1x Blue. The 3.5Vdc is on the LED stack or the cathode. I'll see what the grid is at.

I wonder if those would work in my Von Schweikerts, in place of the stock Vifa D25AG35? Hmmm.

Regarding the options for the production version, I like 6DJ8s/6922s, but had to LMAO when you posted the $400 pair of tubes link. I had a pair of those (actually 2) and liked them a lot. I sold one pair, the other was returned as one tube was microphonic... but I digress. For Option 3, would it be possible to place the tube socket patterns for both the 6DJ8 and 6J6 coincidental and let the bulider decide by which sockets they populated. I will confess to not looking at the socket patterns before asking this, and also not seeing what pin differences there are. Option 4 sounds interesting as well.

Which one? Hagerman's (marc's link), or Swenson's?

Kevin, Have you ever tried John Swenson's snubber across the xfrmr secondaries? Tube DIY Asylum - Different type of snubber - John Swenson - March 26, 2010 at 15:08:48

Happy Birthday!

Forgive the stupid question, but why does the LED impedance matter in this application? From your previous post, mu (38) * 40 ohms is 1520, added to an rp of 3500 = 5020 ohms. Two red LEDs in series, assuming 10 ohms, would be 20 * 38 = 760 + rp (3500) = 4260 ohms. Higher, but not huge? I'm sure I'm missing something here?

Have a great birthday Jim! Hopefully no students tuition-paying units will fuck it up

That is a balance pot, not balanced. Percy recommends using silver conductive grease on the shaft to rectify this. It works, but the grease is kinda pricey.

Have you plugged directly into one of the router ports via ethernet? Or directly into the modem's ethernet port to take the router out of the equation? Maybe you are being censored?

Happy Birthday, you slacker, you... !!!

My condolences to Todd and to the families. Terrible tragedy.

I was referring to the protecting the CRD from overvoltage with a zener trick.

Sounds like a Mike Elliot (Counterpoint) trick. Watch the CRD voltage limits... the 1N stuff is usually 100V, but the J5xx series is only 50V. Elliot uses a 91V zener for protection also.

I'm using a roll of Kester 44 that I got from work over 20 years ago. Works fine. I know Kester has an expiration date, but I wouldn't worry about it. One more way of selling more solder IMO.

Happy Birthday!

Oh goody! I can put blue LEDs in

Happy Birthday Deepak!