Question about LPTT dual rectifier 5V filament power

[T Wilcox]

Hey guys! I am currently building a low power tweed twin and using a PT with only 3amps available on the 5V tap. The amp uses 2 5U4G rectifiers that consume a total of 6 amps. I also have another 5V 3amp classictone trannie. Was thinking I could use the PT to power one rectifier and the other classictone to power the 2nd rectifier.
The problem is I see the HT tap on the 2nd rectifier is the same pin (pin 8 ) that is also fed by one leg the 5v and is in parallel with the 1st rectifier
So in other words can I use the 2 separate 5volt sources for the 2 rectifiers or will that cause some kind of problem?
I am aware that I could just abandon one rectifier and use a gz34 tube instead of the 5u4 but I wanted to build it somewhat accurate to the originals
I'm sure my question is clear as mud but I would appreciate any feedback
Thanks!

[martin manning]

You can power the two 5U4G filaments from different sources and connect the pin 8's together. I would match the phase of the 5VAC sources so it's as if they are powered from the same PT, and be aware that the 5V winding is DC biased up to the B+ level. Your 5VAC transformer should have enough insulation to handle that.

[sluckey]

A single 5U4 or GZ34 will power that amp just fine. And it would be much closer to the original than adding another transformer.

[martin manning]

I would think that two 5U4G's in parallel would have something close to a GZ34's voltage drop, so one GZ34 may be closer to the original than one 5U4G, and it would run a lot cooler.

[T Wilcox]

You can power the two 5U4G filaments from different sources and connect the pin 8's together. I would match the phase of the 5VAC sources so it's as if they are powered from the same PT, and be aware that the 5V winding is DC biased up to the B+ level. Your 5VAC transformer should have enough insulation to handle that.

Hey Martin, Thanks for your reply! How would you suggest matching the phases for the 5vac sources?

[martin manning]

You could temporarily connect the two in series (with no other connections) and measure the result with your meter. If you get something close to 10VAC, then the phase is the same. Connect to pins 8 and 2 of the two rectifiers as shown. Pin 8's will be joined and connect to the reservoir capacitor. If you get something close to zero, they are out of phase. Swap one pair of leads.

[T Wilcox]

You could temporarily connect the two in series (with no other connections) and measure the result with your meter. If you get something close to 10VAC, then the phase is the same. Connect to pins 8 and 2 of the two rectifiers as shown. Pin 8's will be joined and connect to the reservoir capacitor. If you get something close to zero, they are out of phase. Swap one pair of leads.

Man I would not have thought to do that but it makes complete sense! Thank you so much Martin!

[didit]

Do what Leo would do, and use a 5AR4 as suggested.

Best .. Ian

[T Wilcox]

Do what Leo would do, and use a 5AR4 as suggested.

Best .. Ian

I plan on trying that out as well! Thanks for the suggestion!