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FDP Forum / Amp Mods, Repairs, and Projects / using a weber bias rite I have an odd question .

catnineblue

LA , Calif

I try my best
Oct 17th, 2016 08:15 PM   Edit   Profile   Print Topic   Search Topic

If an amp has either a 6V6 or 6L6 same base and we know pin 2 and pin 7 are the heaters and pin 1 and pin 6 not used , pin 3 plate , pin 4 screen pin 5 grid.

If one uses a grid stopper 1.5K pin 1 to pin 5 and a screen resister 470 ohm pin 6 to pin 4 you are basically inserting a resistance .

Since a weber bias probe reds plate pin 3 and cathode pin 8 through resistors to reflect in mV + mA cathode and plate mV=volts then are the two added resistors basically not seen ?

I know Euro uses mA for their bias tool so you use the mA scale on your DVOM instead of the 1 ohm resistor converting it or really dropping the voltage at your meter to safe levels.

Is one way better than the other ? I have only used Weber bias rite.

Hammond101
Contributing Member
*********

So. Cal. USA

Oct 18th, 2016 11:54 AM   Edit   Profile   Print Topic   Search Topic

The resistors(in the amp), the 470s anyway, are seen as the probe is reading the actual tube pin connected to the probe not the pin connected to the plate voltage. Kinda cool actually because in a simple tube swap/bias job you can notice a difference in plate voltage between tubes that may indicate drift or damage to a grid/plate resistor. (just one of many things that may indicate)

Either method works well, 1 ohm precision resistors or a probe with them built in. Same difference. I have I Bias Rite, the complete unit with meter and it works great. No resistors to solder in vintage amps and/or easier than doing a bunch of math using other methods. The tool has never let me down. It's quick and easy.



catnineblue

LA , Calif

I try my best
Oct 18th, 2016 12:46 PM   Edit   Profile   Print Topic   Search Topic

I just have on octal that is copper and only reads mV through the 1 ohm and the other have was when they offered a kit which has the white lead for plate voltage . I used a small plastic RS box and added a switch similar to the copper ones Weber makes so I can leave it plugged into the DVOM and read mV = mA and plate. I had one on each tube last time so I could tell what each tube read then swapped them to compare since the kit one reads a bit over 1 ohm yet both JJ 6V6s read the same plate and mA . I got them from AES as a matched pair along with a matched pair of EH 6V6 which I have not tried yet.

I have a Princeton AA964 without trem stuffed into a 77 music master bass amp chassis same size as a SF champ chassis. I used a Weber 5E3 eyelet board which fit's and has just enough eyelets to do that build. I always wanted to make a smaller eyelet board and somehow mount the filter caps like that larger deluxe had or even a cap can.

It's always worked well so I just leave it alone.

FDP Forum / Amp Mods, Repairs, and Projects / using a weber bias rite I have an odd question .




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