The Amp Garage

I'll put a 12AX7EH in there, but would it be desirable to lower the voltage on the cathode instead ?

Note the 2.4 V is more like the expected cathode voltage, and since they are tied together they should be identical. Crackling could be bad solder joints, or poor contact between tube pins and sockets. Poke around with a chopstick to look for sensitive areas. Note with 180 V on the cathode of V2, t...

Actually, that turned out to be faulty leads on my multimeter ! I ran out and got a new set, and all was well. I'd been repairing the old ones for several years, and it was long overdue.

They are, indeed, identical. I must have written it down wrong. I'm going to do a little chopsticking, and see if I can't chase down that crackle, but other that, it really sounds fantastic.
Thanks so much for the sage advice and direction.

If I get brave, I may post a clip or two.

I get sound, but there is a bit of a crackle. Actually, apart from the crackle, it's pretty stellar sounding.
Let me re-measure.

http://i.imgur.com/uAQNovi.jpg http://i.imgur.com/dHWjJOM.jpg Okay, now I'm getting better readings. Pins 3 and 4 are 412.8vDC and 411.6vDC on V4, and 411.0 vDC and 410.8 vDC on V5. V4 pin 8 = 37.7mvDC, and pin5 = -43.93vDC V5 pin 8 = 43.1mvDC, and pin 5 = -43.89mvDC On the preamp tubes, I'm gettin...

I reversed the (blue and brown) primaries, and it did eliminate the foghorn. Now I read -43 on pin 5 of each of the power tubes, but nothing on the resistor to ground off pin 8.
Also, all of the tone pots make a "whoosh" sound, like a presence control when rotated, this doesn't seem normal either.

With 6L6WGC's and GZ34 installed, I'm getting 430 to 432v DC on the filter caps, and 426v DC on V1, pins 1 & 6, 422, and 426 on pins 1 & 6, V2, and 423 and 421 on pins 1 & 6, V3. Upon firing it up after installing preamp tubes, it made a noise that made my wife exclaim (in faux British royalty accen...

So, I've installed a 25k linear bias pot, and replaced the 56k bias resistor. (First with a 27k, but it biased too cool, so I twisted two 10k's together, and that got me down into acceptable range, right around 41.5 mA. I'm going to spend a little bit of time tonight triple checking my connections a...

I have a fresh set of TAD 6L6GC's which are rated around 30W, as well as a GZ34 rectifier coming tomorrow. I think what I may do, in the meantime, is install a bias pot, to simplify things.

The OT I'm using has taps for 4,8, and 16ohm, but will be used with a 4 ohm load.

The tubes are Sovtek 6L6WGC/5881, and I'm getting 443 V on the plates.

I installed 1 ohm, 3 watt wirewound resistors from 1 & 8 to chassis on both power tubes, and now I'm getting 14.1mV on V4, and 12.4 mV on V5.

Right. Which leads me to a question. I've seen versions of this build where pins 1 and 8 are grounded directly to chassis, versions where just pin 8 grounded to chassis, and versions grounding through a 1 ohm resistor. Along with this is usually the advice "don't do it any other way, my way is best"...

I'm getting -56.9 V DC on V1, and -57.04 on V2. Measuring pin 5.

I don't have a way to adjust it. I decided to build it stock, and then once I was happy with it, maybe add test points and a bias pot.

With a 5U4G rectifier tube, I get the following :

Pin 5 = -59.2

Pin 4 = 475 V DC

Pin 3 = 477 V DC

Rect. Pin 8 = 479 V DC

Stby = 480 V DC