Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Dallas on March 27, 2011, 07:03:12 pm
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Big beautiful torroid transformer, 120V in 120V out with two 24V taps.
I know its not an ideal transformer but I'd like to use it as a starting point if possible. Any tubes that would work off 120V?
Just a project for fun and to learn about tube amp circuits. Don't want to spend much and want to use "found parts" where possible, just because I get a kick out of it. I also found a couple of 8-ohm 10" speakers.
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That's not exactly ideal for tube applications, but it possibly could be worked into something. 1st off you have no filament winding. Filaments could be heated using a separate 6.3V transformer. What is the current rating for the secondary 120V? Are the 2x 24V taps are winding, and what are their current ratings? Almost all of your popular geetar circuits run at much higher voltages. If you have enough available current, you could have a voltage doubler or tripler off the 120V secondary and get a more desirable B+. Some tubes such as the 6DJ8 can be made plenty happy enough at 100ish volts.
Seeing how this is your first post here (and welcome to the forum BTW) I will ass*u*me you are new to tube amps. If this is the case, you're gonna end up money ahead starting with a simple known kick butt project such as the Stout vs. creating obstacles for yourself such as working around a less than ideal transformer.
Can your transformer be used in a tube app? Probably. Is it an ideal building block. No.
-Richard
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Welcome to the forum Dallas,
Give a quick post in the Introductions thread an let us get to know you a bit.
I love found stuff, especially transformers.
Depending on its physical size, I think you may have a good transformer for a preamp project.
Ray
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Thanks for the warm welcome and replies.
The tag says something close to this:
Primary: 240V / 120V
Secondary: 120V 450VA, 2 x 24V 240VA
There are four wires on the input (red, orange, black, brown) and 6 wires on the output. After testing continuity on the windings we put 120V to the primary and measured 122V, 25V and 25V on the secondary.
I'll take a look at the 6DJ8 tube and the Stout project. Meanwhile, I've got a bunch of old equipment in our "bone yard" at work that I can eyeball for transformers.
Just got my first geetar amp (Super Champ XD) and thought it would be fun to learn about tube amps. I've got a long way to go but this is a good place to learn and get advice. I've done minor projects in the past like building a 12v DC charger using a full-wave rectifier and current limiter. Also built a circuit that uses parallel port from a computer to control reed relays that control motors on a telescope mount. Just to give you an idea of my limited skills and experience.
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ok, what is seems like you have is:
1 sec. @ 120V @ 3.75A.
if you parallel the 2 24V secondaries you'll get 3.5A if you run them in series (48V) you'll get 1/2 that or 1.75A. or, run them independently as 2 individual 24V windings rated @ 1.75A EACH.
attached is a schematic of possible PS scenario using a doubler and several series stringed filaments examples.
1) in a series filament string you can use different types of tubes with the same voltage rating, however, the sum of the each tube filament voltages must add up to 24V, AND the tubes must have the same filament current draw rating.
2) you can also use different voltage tubes in the string as long as the tube filament voltages add up to 24V AND the current draw rating of each tube MUST be the same.
http://tubedata.milbert.com/sheets/093/1/12AX7.pdf
http://tubedata.milbert.com/sheets/093/1/12AU7A.pdf
http://tubedata.milbert.com/sheets/093/1/12AT7.pdf
http://tubedata.milbert.com/sheets/106/1/12BZ7.pdf
http://tubedata.milbert.com/sheets/093/6/6AV6.pdf
http://tubedata.milbert.com/sheets/093/6/6V6GT.pdf
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The total rating of that toroid is 690VA. :huh: It must be a big'un.
It's probably not suitable for a first amplifier build, but could be used very effectively in a higher-powered unit.
If the heaters were supplied from a separate transformer, the two 24 volt windings could be added in series with the 120 volt secondary. Using a voltage doubler, the B+ would then be a very useful 470 volts.
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could be used very effectively in a higher-powered unit.
agreed - i sim'd with 6V6 anyway.
heaters were supplied from a separate transformer...
i'm cheap - see attached. :icon_biggrin:
fig. 3 seems optimum???
EDIT: new schematic - fixed?
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Figures 2, 3 and 4 all have secondaries short circuited by one of the rectifier diodes!
You can use the 24 volt secondaries for heaters if they are left floating above earth - but the maximum heater-cathode voltages are then grossly exceeded.
I'm cheap too, :icon_biggrin: so I've looked into most of these ideas, and there's still no such thing as a free lunch. :sad:
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so I've looked into most of these ideas, and there's still no such thing as a free lunch.
oops! it was late - i didn't even consider the whole secondary; one of the problems of cut and paste and exhaustion.
i uploaded changes i think will work.
--DL
EDIT: bit then again maybe not - in Fig.2 & Fig. 3 the filaments will be floating @ ~~1/2 B+ - maybe bad news.... Fig. 4 is what i'd go with.
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Those schematics are much appreciated. I printed the last one to study and contemplate.
In the end this transformer will probably go back to the bone yard. Sifted through the bone yard today but all the transformers step down to 10, 12 or 24 volts. Beginning to realize these transformers are rare in modern equipment.