Amp Trans Alternative

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Jmay
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Amp Trans Alternative

Post by Jmay »

Hey guys I'm not the sharpest guy with circuit design, so I have what may seem like a foolish question :D

I've been thinking about maybe starting on a tube amp project, probably something like the 18 watt lite. The issue I have is dang besides a decent speaker for the cab the power transformer for the head is one of the biggest cost.

I don't want to sound like a cheapskate but man I was wondering is there a cheaper option? What about a full wave voltage doubler circuit?
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colossal
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Re: Amp Trans Alternative

Post by colossal »

In my experience and opinion, anything worth doing, is worth doing right. The 18W Lite IIb is a spectacular amp, when built correctly. Getting the voltages right is a very important piece in the equation. I would not cut corners or mess with the "formula", especially if you are a first-time and/or inexperienced builder. I would save my cash and get the correct power and output transformer, once, and from the start. I would look at GDS, Heyboer, or Mercury for transformers. Second, the speaker choice is important, but this will depend on what sound you want, the efficiency, and the style of music you play. You can find deals for Celestions and other speakers on Reverb, saving some money there.
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Jmay
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Re: Amp Trans Alternative

Post by Jmay »

Yeah you're right & thanks that is sound advice. I was curious though about a full wave doubler circuit & if anyone had ever tinkered with it in that type of application.

My thought was I guess if one was to try it the cost & effort would be minimal in the event it didn't work out it wouldn't be much of a problem to remove the circuit and install a proper trans. If it did turn out satisfactory then that's something new in your arsenal for the future.

I'm not always purists I admit (no disrespect intended to those who are) & sometimes ponder on not so traditional possibilities. The cat was curious so he asked :lol:
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colossal
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Re: Amp Trans Alternative

Post by colossal »

I personally have not tried a doubler circuit with a Lite II amp. There is no reason you couldn't, if you have a transformer that is suited for it and might fit the application; supplying adequate current and achieving the target rectified voltage (~350VDC). As you said, if it didn't work out, you could install the correct transformer. It's your build, so you are only limited to constraints set for you, like budget, requirements for vintage accuracy, etc.
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katopan
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Re: Amp Trans Alternative

Post by katopan »

I've built a couple of amps with doubler or quadrupler power supplies for the HT. They work a treat! The only trouble is normally, especially for an amp that isn't low power, you need a separate transformer for the heaters.
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Jmay
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Re: Amp Trans Alternative

Post by Jmay »

Katopan if you don't mind me asking what voltages are you working with on your voltage multipliers input / output?
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katopan
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Re: Amp Trans Alternative

Post by katopan »

On the bigger one it has two 30VAC transformers in series for 60VAC into a quadrupler. Gave 310VDC out for the B+. Needed a separate transformer for the heaters, so including the OT that's four bits of iron, but all cheap LV for the supplies and a P.A. line transformer for the OT. That amp runs a pair of cathode biased 6V6s into the OT set for 8K and gave about 11W clean output.

Some other guys have found higher output CT transformers that can supply the quadupler by itself for that sort of size amp. That means 3 transformers (HT, heaters and OT) instead of 4.

I also used a quadrupler on a subminiature build of an 18 Watt Superlite many years ago. That used a single 30VAC multitap transformer into a quadrupler for 160VDC B+. Also, because the valves could handle elevated heaters up at half the B+. It's only a 2W amp so I could derive the 6.3VAC heater supply from the same transformer that supplied the quadrupler.

Lastly I had a test chassis build where I was playing around with 6F4P and 6F3P single ended amps. That had the 30VAC transformer feeding an octupler (lots of caps) for about 300V B+. That one had a separate heater transformer.

The multiplying rectifiers work well. You do need a reasonable amount of capacitance though compared to normal, 470uF at each point is good. But they don't need to have as high voltage rating because of the split nature of the supply. So you need more caps, but they can be cheaper. Think that through because the price of the caps can chew up all the savings you made in the cheaper transformer.
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crgfrench
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Re: Amp Trans Alternative

Post by crgfrench »

Could you share a circuit diagram or schematic of the doubler/quadruplers you're describing?
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katopan
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Re: Amp Trans Alternative

Post by katopan »

You'll find info all over the place on quadruplers.

OzValveAmps info -
https://ozvalveamps.org/ava100/ava100project.html
https://ozvalveamps.org/ava100/ava100psu.html

My harp amp -
https://ozvalveamps.org/ava100/ava100harp.html
https://sites.google.com/site/chosenaud ... hedforharp

My submini version of the 18 Watt Superlite TMB -
https://sites.google.com/site/chosenaud ... otscreamer

I wasn't sure if I still have a schematic of my octupler, but found it -
https://sites.google.com/site/chosenaud ... n7pushpull
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Jmay
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Re: Amp Trans Alternative

Post by Jmay »

Awesome thanks for you sharing that stuff awesome 👍
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crgfrench
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Re: Amp Trans Alternative

Post by crgfrench »

The regular PT is only $84 from Mojotone?
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Jmay
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Re: Amp Trans Alternative

Post by Jmay »

crgfrench wrote:
Sun 05/24/20 9:34 pm
The regular PT is only $84 from Mojotone?
Yeah I hear you, but I guess I was just curious about the application of voltage multipliers in amps vs trans.

Voltage doublers are used in all sorts of items these days. I Honestly have never seen them in any amplifier schematics until the gentleman above posted some of his drawings.

I’m no deep thinker by any means but I know sometimes we as humans keep doing things just because we’ve seen them done that way for many years. I was just trying to think if you could save a few dollars & achieve satisfactory results why not? For all I know the concept maybe terrible in this application, but that is the reason for the question to as ask the collective.
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Re: Amp Trans Alternative

Post by crgfrench »

Understood-- that was my logic in exploring toroids too.
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Jmay
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Re: Amp Trans Alternative

Post by Jmay »

Crgfrench I have heard of people using toroids trans in amps but was never sure what all the benefits were. What have you found to be the main benefits of the toroids?
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