grid stoppers in BH kits

Larpy · 367

0 Members and 1 Guest are viewing this topic.

Offline Larpy

  • Full Member
  • ***
    • Posts: 211
on: January 25, 2021, 07:45:30 AM
Over the past 15 or so years, I've built a half dozen Bottlehead kits:  a FPIII, an Extended FPIII (twice), a Mainline, a Kaiju, and now an Eros.  I've noticed that the FPIII used carbon film 220Ω grid stoppers, but the Kaiju and Eros use 90.9Ω metal film grid stoppers.

So here's a question for Doc, PJ, and/or PB:  is the 90.9Ω value based on specific circuit design or is it an inventory decision (using a non-critical value common to as many different kits as possible to keep inventory smaller)?  And why the change from carbon film to metal film?

Were I to replace the 90.9Ω grid stoppers in my Kaiju and/or Eros with carbon film 220Ω Rikens that I stocked up on back in the day, would I be overlooking something important about the value and composition of the stock resistors?
« Last Edit: January 25, 2021, 09:05:08 AM by Larpy »

Larry


Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19369
Reply #1 on: January 25, 2021, 08:19:24 AM
The FP-III used carbon composition resistors.  They are technically the best overall choice for the grid stopper position, but the resistors themselves are a bit delicate and can break easily, so we have switched to either metal film or carbon film.   The choice today depends primarily on how long the leads need to be to reach in the circuit. 

Sure, you can put 220 ohm Riken resistors in if you'd like.  I think that would be a tremendous waste of money, but if you have them sitting around you may as well use them!

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man