Good projects for undersized power transformer

[Mick Bailey]

We tend to deal with amp tubes from a relatively modern era, and with a degree of standardisation. There are many older tubes from the 20s and 30s used in radios that have very low current ratings and odd voltages, such as the UX171A (71A) output triode (5v@0.25A and used in small modern-build hi-fi amps with high-efficiency folded horn speakers). Directly heated tubes need much less current to operate - many of my really old tubes operate at 'black heat'.

[Pixel]

Wow! My head is spinning after looking into all these possibilities.

Right now it seems the 5F1 with SS rectification could work. That would get around the weak 5V and also give a needed boost to the B+. This also works because I have a few SE output transformers kicking around. I like the 6V6 because I have a back-burner project to restore a nice Bogen PH10 pa amp which is PP 6V6GT.

On the other hand...the wife and kids would probably say they need me to have a lower power amp. So I will also look into 12AT7 and 6AQ5 single ended amps.

Thanks so much for all the help.

[Pixel]

Then we are back to determining if that 5v winding is really .4A (400ma) or really 4A. Clearly 600ma heater draw is more than 400ma. That precludes the 6X4 in my mind.


I don't know who your guy might be, but be aware you can find some guy on the internet to say most anything. I make speaker cones from Yeti hair myself. I was in the mountains when I found a dead one. I saw Himalayan there, and figured he didn't need his fur anymore...

Isn't the tone improved if you gather the hair during a solar eclipse from a virgin Yeti using a silver knife with fabric covered carbon composition handle while facing north and wearing a NOS hat made from oiled paper? Or maybe it was a teflon coated...

[Enzo]

No, that part is mere superstition.

[Mick Bailey]

One consideration is a 'Firefly' amp - nice range of gain and good tone, and it does clean up nicely.