Initial Impedances

[pro_crip]

Okay, I got my amp all screwed and wired together (thanks ashok). The feedback was set at 16.3K since I'm using a 4 ohm tap (I hope that's right) and all pin 3's measured around 400 ohms so initial bias is okay. Now, I can't adjust the bias or check the pin voltages yet because I'm hesitant about plugging 'er in. I've never done anything like this before and I'm afraid I did something completely wrong and the amp is gonna blow up when I turn it on. So I decided to ohm it out (at least that's what the instructions say to do). I've got a hammond 270hx pt and hammond 1650f opt's and a 100k volume pot with all connections made. Here are the numbers I got, if someone could tell me I'm on the right track (or any track for that matter), I'd be eternally grateful. TIA.

J1
1: 28.3 ohm 2: 31 ohm 3: 2.4M 4: 2.4M 5: .3 ohm 6:.3 ohm 7: 50.4 ohm
8: 50.4 ohm 9: overload 10: overload

J2
1: 2.4M 2: 1.6M 3: .4 ohm

J3
1: 6.4M 2: 5.5M 3: 16.3K

J4
1: 3.9M 2: 3.5M 3: 16.3K

J5
1: 1.5M 2: 1.4M 3: .4 ohm

J6 (volume turned all the way up)
1: 92.5K 2: .4 ohm

J7 (volume turned all the way up)
1: 96.1K 2: .4 ohm

[Shannon Parks]

Hi pro_crip,

All your impedances look good. On the money. Lastly, you could ohm out the two prongs of your AC cord testing your on/off switch and also removing the fuse (to insure proper wiring). In 'off' position or fuseless, you'd have an open. Resistance will otherwise be over a 100 ohms (because of the IRCL).

The feedback was set at 16.3K since I'm using a 4 ohm tap (I hope that's right)

Technically speaking, a 8 ohm tap would be 27K divided by 1.414 and the 4 ohm tap is 27K divided by 2 - add 1.3K to both of these when measuring from J4-3 & J3-3 due to the cathode resistor of V1. So 4 ohm feedback setting would be 14.8K. Just leave it where it's at, though. You won't miss the extra NFB.

Even further technically speaking, the cap gets adjusted as well (multiplied instead of divided, though). But I wouldn't worry about subbing a 50 or 60pF cap - Hafler's screen feedback gives a large degree of stability.

Shannon