From james_eaton@btopenworld.com Tue Mar 26 07:25:03 2013
Subject:Re: Converting a 147 amp to 122 negative feedback standard - earlier distorsion

Hi Frederick,

I'm guessing you didn't change the 56k/1nF feedback network as you'd then need a 7 pole switch, otherwise I think you only need 3?
- 2 x two-way to swap each cathode to either secondary (147) or 200uF/150R (122);
- 1 x two-way to swap secondary CT to ground or 200uF/150R
If you swap the other components you need in addition (since the the feedback network for the 122 has 5nF to ground):
- 2 x two-way to swap the control grid between 390K and 1nF
- 2 x two-way to swap the anode between 5nF and 56K

I suspect it is possible to introduce some nasty oscillation if a switch was used without proper dressing, although I've heard it has been done before. Some kind of plug might be a safer alternative.

Cheers
James