Well… it's been a long time since i didn't build anything (4 years) and an old radio came to my hands not working, but the tubes and transformer were OK.. so i decided to make a small guitar amp..
The radio was an old Biennophone Crans Mod. 47HL.. a 50's radio. the best schematic that i found is barely readable.
It's ECL86 based.
Than i found a schematic for a ECL86 Small single ended Guitar tube amp on the Web: (here is the link for the original project: http://licho.rowerpower.org/gitara/foxtrot/)
My problem is… My OT have 3 taps on Primary side one is the B+, another going to ECL86 Pin6, and another one to Pin3... (i made my best to make more readable scheme)
Well.. after thinking i don't know what to do.. i'm wire it like the original…? can i suppress the wire going to Pin3? or buy another OT (the ultimate solution)
The amp is almost done.. the only part missing is those connections.
That's not single-ended ultralinear. The screen is fully bypassed with a 50µF filter cap. That primary tap is just being used as a choke. Lot's of small consumer products from that era did the same.
An ultra-linear transformer has a connection to the plate at one end, the HT at the other end, and a tap somewhere in the neighborhood of 40% of the winding for the screen grid. The OT in the 47HL schematic is not ultra-linear. This one is connected to the plate on one end, the HT on a tap somewhere closer to the center of the winding, and the opposite end of the winding goes to the screen grid. I don't remember the name for this config but it essentially uses the section of the OT between the HT and the screen grid as an inductor for filtering. I've seen it discussed elsewhere on the internet, i'll see if I can dig something more informative up.
sluckey wrote: ↑Thu Sep 26, 2019 3:26 pm
That's not single-ended ultralinear. The screen is fully bypassed with a 50µF filter cap. That primary tap is just being used as a choke. Lot's of small consumer products from that era did the same.
Apologies. That's correct. Should scan schematics more, and more carefully, before tossing off responses.
The other info I'd seen before about this type of OT was a) on a hi-fi stereo forum, so the technical details were sparse, and b) may have been specific to the transformers I had on hand. The one important detail was that the screen tap on this transformer was in the neighborhood of 5-10% of the winding, and not the 40% that's useful as an ultralinear tap. Your OT may vary.
nworbetan wrote: ↑Thu Sep 26, 2019 5:45 pm
The other info I'd seen before about this type of OT was a) on a hi-fi stereo forum, so the technical details were sparse, and b) may have been specific to the transformers I had on hand. The one important detail was that the screen tap on this transformer was in the neighborhood of 5-10% of the winding, and not the 40% that's useful as an ultralinear tap. Your OT may vary.
Thanks for all of you that gave me tips… did a lot of reading.. and it looks like a UL type BUT I measured.. between B+ tap and one side i have 310 Ohms to the other tap it has 12,5 Ohms.. total between outer taps ~322 Ohms.. a little like yours, mine is about 4%.. not 40%..
I think i'm gonna wire it like the original, i don't want to buy another OT for now, maybe later.. it sounded good when i tried it (did some basic mods on preamp to guitar use to test it..)
What started with simple mods came to new chassi, full Marshall type preamp and some other things..
The tail end of the transformer bucks some of the hum in the amplifier. Just connect to the center tap (which is not at the center ) and it will work like any other SE OT.
It lives!!!! The clean is beautiful.. the OD need some tuning.. way to hot and a notch bright, need some fatness, maybe reduce the pots value.. maybe is the low volume that i've tried.. need to implement Rob Robinette 10% power switch and the NFB.
printer2 wrote: ↑Fri Sep 27, 2019 11:50 pm
The tail end of the transformer bucks some of the hum in the amplifier. Just connect to the center tap (which is not at the center ) and it will work like any other SE OT.
I made the chassis myself... 23,5cm x 12cm x 4 cm. The knobs are ones I had here around.
It has footswitching, I also modded the gain structure (distortion) and volume (Gain)… and some other features.. Need to decide what mods to do to the timbre, but i must wait untill i can plug it to a real cab.. until now i only tried it plugged to a 10" gold back from a marshall cheap combo (not the best speaker). I have a WTS ET-65 and a Cannabis Rex in my storage room but want a V30 for this amp.
Moved the Power and standby switch to the back since the AC was running along with ground wires. Need also to rewire the main ground to the back of transformer (green), and shorten the AC wires (yellow).
Now need some faceplates and a head cab.
) and it will work like any other SE OT.
