Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on February 26, 2024, 03:57:46 am

Title: BIAS measurement method - a question
Post by: kagliostro on February 26, 2024, 03:57:46 am
I would like to know if by using the method of the resistor in series with the anode voltage and two resistors in series with the connection wires of the instrument it is possible to prevent the anode voltage from reaching the front panel or if this solution is not possible to put it in practice

Thanks

Franco
Title: Re: BIAS measurement method - a question
Post by: Latole on February 26, 2024, 05:03:44 am
It would be much simpler to use the tried-and-tested and safe method of putting a 1 ohm resistor ( on red ) on each tube cathode connected to ground .

Resistors you can even leave in place once the bias is over, which will be useful for the next bias.

Title: Re: BIAS measurement method - a question
Post by: pdf64 on February 26, 2024, 06:09:53 am
Current sensing resistors and test points in an output valve anode circuit seems like a recipe for terrible lead dress.
Title: Re: BIAS measurement method - a question
Post by: acheld on February 26, 2024, 09:36:29 am
This would be no more than a gimmick, IMO, but you certainly could place a Hall effect current sensor at your test point,  with the meter in the front panel.   

The sensor is not directly "in circuit," and thus does not bring high voltage to the front panel.   Not sure if there are inexpensive (and accurate) ammeters in the milliamp range, but it could be done safely and without screwing up your signal path.

A lot of trouble for not much benefit.   
Title: Re: BIAS measurement method - a question
Post by: WimWalther on February 26, 2024, 10:10:51 am
Not sure if there are inexpensive (and accurate) ammeters in the milliamp range (...)

Many ammeters are actually mA or even uA meters, with parallel current shunts added for reading higher ranges.