5F1 - 180v on V1 pins 1&6 too high?

Discussion in 'Shock Brother's DIY Amps' started by doof, Dec 29, 2020.

Tags:
  1. doof

    doof Tele-Holic

    Posts:
    587
    Joined:
    Mar 27, 2011
    Location:
    Lethbridge, Alberta, Cana
    Hi everyone,
    I just put together a 5F1 using a Hammond 290AX PT and a Hammond 1760C OT. My voltages are within the 10% tolerance for the most part, except pins 1 & 6 on V1 are 185 and 181v respectively, so about 20 - 23% high. Is this high enough that I should worry? Or should I just shut up and enjoy the amp?

    Some other info, in case it's relevant:

    Rectifier: GE 5Y3GT (I also tried a couple RCA 5Y3GTs, and overall the voltages fluctuate in a range of about 10v)
    V1: RCA 12AX7 (Also tried a new Sovtek 12AX7 but my readings don't change)
    V2: Sylvania 6V6GT

    I originally used the 325-0-325 secondary leads on my PT, but my B+1 was right around 400v depending on which rectifier I used, so I changed over to the 275-0-275 secondary, and now my voltages read as follows:

    B+1: 350v
    B+2: 306v
    B+3: 269v

    V1 pin 1: 185v
    V1 pin 3: 1.26v
    V1 Pin 6: 181v
    V1 Pin 8: 1.25v

    V2 pin 3: 380v
    V2 pin 4: 307v
    V2 pin 8: 13.4v

    I'm reading 121 VAC at the wall.

    As mentioned, I'm overall pretty happy with those readings, and the amp sounds good. I haven't been able to try it out at high volume yet because I don't want to disturb the person that lives above me, but so far it sounds great. The only mods I did was to include an output impedance switch so I can choose between 4, 8, and 16 ohm speakers, and I swapped out the negative feedback resistor for a switchable potentiometer in series with a 1.5k resistor so I can go from 1.5k to about 54k resistance in the NFB loop (or disconnect it entirely). So I'm really just looking to make sure the 180 - 185v on pins 1 & 6 of the 12ax7 are nothing to worry about.

    Thanks for your time!
     
  2. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    40
    Posts:
    6,483
    Joined:
    Dec 3, 2005
    Location:
    CID
    About 180V is what I get on my 5F2A. I think you're in perfect shape, voltage-wise.
     
    Last edited: Dec 29, 2020
    doof and dan40 like this.
  3. doof

    doof Tele-Holic

    Posts:
    587
    Joined:
    Mar 27, 2011
    Location:
    Lethbridge, Alberta, Cana
    Thanks very much! That's good enough for me, I'm going to stop overthinking and play some guitar.
     
    ThermionicScott and Nickfl like this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.