Thanks for chiming in rooster. As Phil says this is wired for 240v.
Regarding the 5.3vac reading at the filaments I don’t have taps for a rectifier, I’m theorising that the lamp limiter reduced the voltage here, in line with Martin Manning’s earlier comment on reduced voltages with a 60w bulb, or I have a faulty PT.
I’ve no variac here (mental note to acquire a variac asap) so the lamp limiter was engaged to quickly test the PT, thanks for your note on best practice.
The layout I am following (TW Express Layout RLW 1. suggests wiring the AC to the top lugs of the switch but your suggestion makes sense as it will keep those ac line closer to the chassis.
? Your PT schematic shows a rectifier tap. Is this not the PT you have?
Also, then for 240 you need to have the Black wire attached to one switch lug, the White wire joined to the Black/White wire (solder together and shrink wrapped or joined to an non-grounded chassis lug somewhere nearby), and then the White/Black wire to the parallel lug on the switch. The AC will be Black wire to fuse, then to the lower switch lug (below the Black PT wire), and the White wire to the parallel lug on the switch below the White/Black wire.
This gives you a full AC disconnect like Marshall used. The lamp has to be 240 or you could use a 6.3 volt version and tie it to your filament source.
Last edited by rooster on Mon Mar 26, 2018 7:35 am, edited 3 times in total.
Most people stall out when fixing a mistake that they've made. Why?
Alright. When I check a raw PT, BTW, I prep the primary side (120/240 in your case) and - not even attached to a chassis but sitting on a wooden bench - attach an AC pigtail with wire twists and plug this into a switchable fused power strip, attach my volt meter leads (using clip leads) set to the appropriate range AC/DC, etc., and throw the switch on the power strip. When I have a reading on the secondary that I like I turn things off, reattach the leads to another secondary tap, measure it, etc.
The key here is to isolate the secondary leads that you are not measuring so they do not touch anything that would cause pain. Use either a small twist cap or tape. I know it must seem cavalier but it is always better to check a PT out this way because first off, the voltage is not stored in a cap, and - more importantly - if the PT is not potted correctly and it is a humming devil device, you do not want to build the amp and then find this out. In fact, if you build the amp around a noisy PT, you may find yourself investigating all sorts of things that have nothing to do with the noisy PT. Been there, and it was a good brand.
Most people stall out when fixing a mistake that they've made. Why?
suggests wiring the AC to the top lugs of the switch but your suggestion makes sense as it will keep those ac line closer to the chassis.