Howdy! I'm new to the diyAudio forum, and I wanted some advice on building myself a general-purpose audio amplifier. I intend to use it with microphones, guitars, radios, etc.
The tubes I plan to use with this are the 12BA6 pentode as a driver, and the 35C5 pentode as a power output tube. I was going to pull a transformer from some old power supply to use as the output transformer. Any tips?
The tubes I plan to use with this are the 12BA6 pentode as a driver, and the 35C5 pentode as a power output tube. I was going to pull a transformer from some old power supply to use as the output transformer. Any tips?
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Your photo at the bottom right seems to be a portion of the power supply...Our protocol in this forum is to adhere to a policy of safety, this portion of the power supply is WITHOUT a transformer coming off the mains, and is unacceptable in design. Such older designs were rather unsafe & made for electrocutions long ago in common use...it seems a simple isolation transformer integrated into your schematic will work here.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
I've disassembled microwave transformers before....the laminations are welded up at the edges...I guess a grinder would open up its laminations OK, the primaries use rather thick wires, for its high current capacities...but its crude construction makes for a noisy operation. Maybe in low current conditions it is quiet. I'd get a suitable smaller roll of wire & wind up your own...you would have to count the turns anyway if you used the existing primary winding. You can reuse the existing bobbin. Lots of work for sure, but your current capacity is almost unlimited given the size of these transformers...worth a shot!.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
The resistor in series with the heaters will dissipate almost 15 watts. It better be big.
Safety First!
Prevent the "Surviving Spouse Syndrome"
And think of your kids too.
I am pretty sure someone in the Oregon Triode Society (Portland Metro Area) has an inexpensive power transformer they can part with.
Perhaps there is an inexpensive output transformer there too.
The Power Transformer protects your heart.
The Output Transformer is the Heart of the amplifier (Bad heart, bad sound, even if that is what is desired for a guitar amplifier).
Connecting the signal output of a Guitar, Microphone, or a Radio might expose people to the chance of shock.
By the way, I have seen as much as 8V difference between Neutral and Ground. Nothing that will shock, but it can smoke wire insulators and start a fire.
Fortunately the time I had that problem, all was turned off before any fire started; just ruined wire insulation.
I have seen houses where Neutral and Ground were swapped at the Wall Outlet. Ouch!
Murphy always takes over.
We hear less about shocks than we should, when the person involved does not live to tell the story.
'Nuff Said
I could let loose of a Hammond 125DSE single ended output transformer. 10k to 4, 8, 16 and 32; 5k to 4, 8, and 16; and 2.5k to 4 and 8 Ohm.
I have a power transformer, 300V-0V-300 Volt, with 6.3V @ 1Amp. Two diodes instead of one, and you get full wave, lower ripple B+.
A choke input filter could give nearly 270V B+. All my amplifiers are using 5 Henry chokes, I have some 20H chokes.
Or with a cap input filter, the B+ could approach 420V; a small cap before the choke could range lower than 420V, but higher than 270V.
There are lots of 6.3V tubes out there.
A 7591 only needs 0.8 amps at 6.3v, 1/2 of a 12A_7 dual triode only needs 0.15A at 6.3V.
I have 7591s, and 12A_7. I have lots of 5814 dual triodes, 1/2 side (one of tow filaments), takes less than 0.2 Amps.
Need more gain at the input, I am sure I have at least one 6AU6 (0.3A filament, that and a 7591 take 1.1A, OK because you are not going to use up the B+ rating of 120mA, so less heat in the transformer, and it is a true 120VAC primary, not the old 110, 115,, or 117V primary.
I need to downsize, and today is a good day to start.
Prevent the "Surviving Spouse Syndrome"
And think of your kids too.
I am pretty sure someone in the Oregon Triode Society (Portland Metro Area) has an inexpensive power transformer they can part with.
Perhaps there is an inexpensive output transformer there too.
The Power Transformer protects your heart.
The Output Transformer is the Heart of the amplifier (Bad heart, bad sound, even if that is what is desired for a guitar amplifier).
Connecting the signal output of a Guitar, Microphone, or a Radio might expose people to the chance of shock.
By the way, I have seen as much as 8V difference between Neutral and Ground. Nothing that will shock, but it can smoke wire insulators and start a fire.
Fortunately the time I had that problem, all was turned off before any fire started; just ruined wire insulation.
I have seen houses where Neutral and Ground were swapped at the Wall Outlet. Ouch!
Murphy always takes over.
We hear less about shocks than we should, when the person involved does not live to tell the story.
'Nuff Said
I could let loose of a Hammond 125DSE single ended output transformer. 10k to 4, 8, 16 and 32; 5k to 4, 8, and 16; and 2.5k to 4 and 8 Ohm.
I have a power transformer, 300V-0V-300 Volt, with 6.3V @ 1Amp. Two diodes instead of one, and you get full wave, lower ripple B+.
A choke input filter could give nearly 270V B+. All my amplifiers are using 5 Henry chokes, I have some 20H chokes.
Or with a cap input filter, the B+ could approach 420V; a small cap before the choke could range lower than 420V, but higher than 270V.
There are lots of 6.3V tubes out there.
A 7591 only needs 0.8 amps at 6.3v, 1/2 of a 12A_7 dual triode only needs 0.15A at 6.3V.
I have 7591s, and 12A_7. I have lots of 5814 dual triodes, 1/2 side (one of tow filaments), takes less than 0.2 Amps.
Need more gain at the input, I am sure I have at least one 6AU6 (0.3A filament, that and a 7591 take 1.1A, OK because you are not going to use up the B+ rating of 120mA, so less heat in the transformer, and it is a true 120VAC primary, not the old 110, 115,, or 117V primary.
I need to downsize, and today is a good day to start.
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This is not likely to end well. I would take advantage of the offers instead.
Not at all worth your time. Antek sells the cheapest tube amp power transformers. https://www.antekinc.com/power-transformers/