Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Captain chunkulus on May 11, 2021, 09:48:07 am

Title: Carvin v3 biasing question.
Post by: Captain chunkulus on May 11, 2021, 09:48:07 am

So I've watched all the video info as well as downloaded the instructions from carvin about how to bias this amp. I have biased many amps and built a few  but this ones got me stumped. Maybe I'm just missing something but it says to bias it at 100ma dc, however I can only get it to read A.C. ma. It does not have 1 ohm resitors and there isn't an easy way to add them or I would just do it that way.  Euro tubes has a video but it doesn't help because I'm only getting a.c. milli amps not. Dc milli amps. I don't currently have a bias prob so what am i missing?

Title: Re: Carvin v3 biasing question.
Post by: sluckey on May 11, 2021, 09:56:54 am

Maybe you could post the schematic and bias instructions. Then we may be able to offer suggestions.

Title: Re: Carvin v3 biasing question.
Post by: Captain chunkulus on May 11, 2021, 11:21:44 am

Bias instructions.

Title: Re: Carvin v3 biasing question.
Post by: Captain chunkulus on May 11, 2021, 11:34:58 am

Schematic.

Title: Re: Carvin v3 biasing question.
Post by: shooter on May 11, 2021, 12:56:32 pm

did you connect like step 8 pic2, red closest to you, black behind?
I couldn't find "DC" milliamps in the directions, just "100 milliamps" no ac/dc reference

Title: Re: Carvin v3 biasing question.
Post by: sluckey on May 11, 2021, 02:04:40 pm

You're connecting the meter across the STBY switch. LEAVE THE STBY SWITCH IN STANDBY MODE! Be sure to use the correct probe jacks for measuring mA current. Set meter to measure DC milliamperes. You are measuring the B+ current for the entire amplifier. Adjust the bias for 100mA. Sounds very straightforward to me. What make and model is your meter? It could be that your meter is not happy trying to measure 100mA DC current when there is several volts AC ripple present. Carvin's manual is using a cheap Tenma meter.

Title: Re: Carvin v3 biasing question.
Post by: Captain chunkulus on May 11, 2021, 04:07:34 pm

What the pc board says.

Title: Re: Carvin v3 biasing question.
Post by: Captain chunkulus on May 11, 2021, 04:12:11 pm

My meter.

Title: Re: Carvin v3 biasing question.
Post by: Captain chunkulus on May 11, 2021, 04:20:37 pm

I attached 1 lead to one side of the standby switch and the other lead to the other side of the standby switch.  Basicly as I understand it the amp turns on through the meter. The standby switch is located after rectification so Dc? A.c.? Im not getting any dc readings like what's printed on the board. I get a.c. in milli amps but not dc.

Title: Re: Carvin v3 biasing question.
Post by: sluckey on May 11, 2021, 04:29:00 pm

Your meter must be set like this with the probes connected as indicated...

Title: Re: Carvin v3 biasing question.
Post by: Captain chunkulus on May 11, 2021, 04:35:58 pm

I'll give it a shot when I get home. I knew it was personal error some how.

Title: Re: Carvin v3 biasing question.
Post by: PRR on May 11, 2021, 05:05:09 pm

RTFM (https://www.myflukestore.com/pdfs/cache/www.myflukestore.com/fluke/multimeter/179_efsp/manual/fluke_179_efsp_multimeter_manual.pdf)