• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Powering tubes without transformers

Jared Houseman

Jared Houseman

Jul 5, 2018
738
793
#1
Is there any good ways to build tube amps without transformers? Im interested in building some small practice size tube amps just for fun but the costs of transformers are prohibitively high.

I know there are power supplies that can power tubes but I don't know if they are any good or if they are noisy. Can anyone point me in the right direction
 
#3
Jared Houseman said:
Is there any good ways to build tube amps without transformers? Im interested in building some small practice size tube amps just for fun but the costs of transformers are prohibitively high.

I know there are power supplies that can power tubes but I don't know if they are any good or if they are noisy. Can anyone point me in the right direction
Click to expand...

My guess is the biggest obstacle is impedance matching between the tubes and speakers. A transformer is used to match the high impedance of the tubes to the low impedance of a speaker.

I found a page the details different topologies for transformerless tube output sections, but there is probably some good reasons why they are not common.
Output Transformerless Amplifiers

It's definitely possible to build tubes amps without a traditional power supply. Take a look at the Peavey VB2 and VB3 which use switch mode power supplies. The VB3 was rated for 300W at weighed 37lbs. I believe both amps still use both a power transformer and output transformer though.

Feeding the tubes heaters might also be problematic. The voltage is only 6.3V but the current requirement is typically pretty high, for example 0.9A for a single 6L6GC
 
#4
I am building a tube tester using regulated power supplies (which take up about 7-8 rack spaces), but even these have transformers. Then, as mentioned is the output side... you might try asking over in antiqueradios.com forum. The people there really know their stuff and offered me some good advice. However, they don't suffer fools...
 
  • Like
Reactions: Wasnex
#5
Jared Houseman said:
Is there any good ways to build tube amps without transformers? Im interested in building some small practice size tube amps just for fun but the costs of transformers are prohibitively high.

I know there are power supplies that can power tubes but I don't know if they are any good or if they are noisy. Can anyone point me in the right direction
Click to expand...

You can find a wide variety of used transformers on eBay. You just need to know what you are looking for. Don't forget about the cost of a chassis, passive components (resistors, caps, pots, switches, speaker & input jacks, etc.) and tubes. If you haven't done something like this before, you'll find the learning curve to be pretty steep. A kit is a much easier way to get this background.
 
  • Like
Reactions: Wasnex
#6
AstroSonic said:
You can find a wide variety of used transformers on eBay. You just need to know what you are looking for. Don't forget about the cost of a chassis, passive components (resistors, caps, pots, switches, speaker & input jacks, etc.) and tubes. If you haven't done something like this before, you'll find the learning curve to be pretty steep. A kit is a much easier way to get this background.
Click to expand...
The parts are the easy part, I suspect that a transformerless design may be more than a wee bit challenging... even for an experienced designer.

I don’t know any transformerless kits even remotely suitable for bass guitar.
 
  • Like
Reactions: BassmanPaul, AstroSonic and Wasnex
#8
That makes a lot more sense.

In the DIY world, there are a lot of really goofy parts and PCBs offered that in many cases are terrible designs. Also, many do not have any kind of safety approvals and can not pass any kind of global safety approvals.

A common theme of these goofy designs is that they make no sense to professional designers and engineers, and usually do not function the way the "designer" explains it. Surprisingly often they don't even function nearly as well as simpler, more straight forward, more conventional designs. In other words, smoke, mirrors, esoterica and snake oil all come to mind. It's especially bad in the DIY hi-fi world. Even the real designers in that world cringe at some of what's marketed as "high end".
 
  • Like
Reactions: Garret Graves, BassmanPaul and AstroSonic
#9
agedhorse said:
The parts are the easy part, I suspect that a transformerless design may be more than a wee bit challenging... even for an experienced designer.

I don’t know any transformerless kits even remotely suitable for bass guitar.
Click to expand...

I assumed that the OP would be working from a schematic and layout diagram. I suspect that many players would actually want an output transformer because of the saturation impact on the sound.
 
#11
Jared Houseman said:
Is there any good ways to build tube amps without transformers? Im interested in building some small practice size tube amps just for fun but the costs of transformers are prohibitively high.

I know there are power supplies that can power tubes but I don't know if they are any good or if they are noisy. Can anyone point me in the right direction
Click to expand...
Is your name Julius, perchance or related to anyone named Julius?
 
#12
There are relatively low power power supply circuits that use rectified line voltage, but these are lethal grade dangerous, and I hesitate to even mention them. A transformer is cheap compared to lawsuits and/or funerals.

To drive a speaker, you are pretty much relegated to using an output transformer.

Based on the questions you're asking, you sound like a beginner hobbyist. I would respectfully suggest you learn some electronic safety first, and start off with some simple, solid state low voltage circuits before you start toying with dangerous voltages.
 
  • Like
Reactions: S-Bigbottom, delta7fred and agedhorse
#13
Jared Houseman said:
Is there any good ways to build tube amps without transformers? Im interested in building some small practice size tube amps just for fun but the costs of transformers are prohibitively high.

I know there are power supplies that can power tubes but I don't know if they are any good or if they are noisy. Can anyone point me in the right direction
Click to expand...

If you are really determined to build a output transformer less amplifier, do a google search on Julius Futterman, and Transcendent Sound OTL amplifiers. None of these circuits are economical to build. They usually involve the use of several output tubes run in parallel to bring the output impedance into a usable range and to get a usable amount of power. They are also known for being unreliable.
 
#14
AstroSonic said:
If you are really determined to build a output transformer less amplifier, do a google search on Julius Futterman, and Transcendent Sound OTL amplifiers. None of these circuits are economical to build. They usually involve the use of several output tubes run in parallel to bring the output impedance into a usable range and to get a usable amount of power. They are also known for being unreliable.
Click to expand...
Note that they still require a power transformer to provide isolation for safety purposes.

The OTL topologies aren't just unreliable, they also struggle with delivering adequate power levels required for (most) bass guitar applications.

I have designed several (output) transformerless power amps over the years, so far I have not been able to achieve what I would consider even barely adequate performance unless using many output tubes (and some unconventional circuit elements). At that point, for equivalent power it's less expensive and takes up less real estate than just using an output transformer.
 
  • Like
Reactions: AstroSonic and byacey
#15
AstroSonic said:
If you are really determined to build a output transformer less amplifier, do a google search on Julius Futterman, and Transcendent Sound OTL amplifiers. None of these circuits are economical to build. They usually involve the use of several output tubes run in parallel to bring the output impedance into a usable range and to get a usable amount of power. They are also known for being unreliable.
Click to expand...
These designs are far below the point of diminishing returns; I can't think of any advantage they may have over conventional designs.
 
  • Like
Reactions: agedhorse
#18
agedhorse said:
Note that they still require a power transformer to provide isolation for safety purposes.

The OTL topologies aren't just unreliable, they also struggle with delivering adequate power levels required for (most) bass guitar applications.

I have designed several (output) transformerless power amps over the years, so far I have not been able to achieve what I would consider even barely adequate performance unless using many output tubes (and some unconventional circuit elements). At that point, for equivalent power it's less expensive and takes up less real estate than just using an output transformer.
Click to expand...

All true. By this point, the OP should realize that these designs are unreliable, expensive and wildly impractical for bass guitar amplification.
 
  • Like
Reactions: BassmanPaul, byacey, S-Bigbottom and 1 other person
#19
I was just scanning through my Mullard book and came across an amplifier design for aC/DC used from the UK mains supply of 240V. Interesting but certainly nothing I'd use for bass!

I've seen designs for OPT less amplifiers. You see a lot of 'out there' amplifier prototypes in school. Interesting but not really practical! LOL
 

Latest posts

Top Bottom
Back