Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on December 09, 2023, 08:03:14 am

Title: Safety resistors on PPIMV - will they affect the frequency response ??
Post by: kagliostro on December 09, 2023, 08:03:14 am

Talking about PPIMV and the added safety resistors to prevent missing Bias Voltage if there is wiper loss of contact

we know that turning the shaft there is a modify in the frequency signal that starts from PI and arrive to G1 of the power tubes

I would like to know if the presence or not of the safety resistors (between wiper and G1 of power tubes) will modify the frequency responce somehow

Thanks

Franco

Title: Re: Safety resistors on PPIMV - will they affect the frequency response ??
Post by: d95err on December 09, 2023, 09:09:36 am

What type of PPIMV? What value safety resistors? What value pot? What value coupling caps? What type of phase inverter?

Title: Re: Safety resistors on PPIMV - will they affect the frequency response ??
Post by: kagliostro on December 09, 2023, 09:27:22 am

OK, the LarMar with 2.2M safety resistors 1M dual ganged pots

Coupling caps .... standard or KOC improved version

Franco

Title: Re: Safety resistors on PPIMV - will they affect the frequency response ??
Post by: pdf64 on December 09, 2023, 11:14:06 am

1M pot; a LarMar uses 220k or 250k stereo pot?

Title: Re: Safety resistors on PPIMV - will they affect the frequency response ??
Post by: kagliostro on December 09, 2023, 12:54:25 pm

I got confused remembering the Type 1 on The_Trainwreck_Pages

(https://robrobinette.com/images/Guitar/Trainwreck/Trainwreck_MV_Type1.png)

and used the name LarMar

Franco

Title: Re: Safety resistors on PPIMV - will they affect the frequency response ??
Post by: Ronquest on December 09, 2023, 01:44:35 pm

If the wiper looses contact, how will the bias voltage be lost?  Am I missing something?    You would only loose bias if your .1uF capacitor shorted and your volume pot wiper was turned down/off/short to ground.

The bias voltage (DC) is not going through the pots.

EDIT to add.  TYPE 2 PPIMV would loose bias if the wiper lost contact

Title: Re: Safety resistors on PPIMV - will they affect the frequency response ??
Post by: kagliostro on December 09, 2023, 02:23:50 pm

Right

I mixed too many memories together

(https://i.imgur.com/WEOBfxI.jpg)

(https://i.imgur.com/19UxR4H.jpg)

(https://i.imgur.com/glu45dH.jpg)

(https://i.imgur.com/QSikyep.jpg)

(https://i.imgur.com/SCRuU0R.gif)

(https://i.imgur.com/TvbO5Fn.gif)

(https://i.imgur.com/ovtnish.gif)

Franco