I use older transformers from battery chargers and you will also find that a lot of these transformers are center tapped at your 6.3 volts you need for tube radio 6 volt filament. for 5 volt filament I use old VCR transformer. This is why I take old unwanted electronics from friends at work. You never know what reusable parts you will find inside them.
Another alternative would be an Antek toroidal transformer. For $29 you can get a transformer with a range of secondary voltages plus two 6.3V secondaries as well. For not a lot more you can get a 100Va unitgood for something around 20W output. I've used these transofrmers on a half a dozen projects. they also have transformers with a 5 volt winding as well.
Here's a 2-birds with one stone solution for getting both high voltage and getting your filament voltage: You get 2 transformers: 120V-12V (this is your filament supply). You then connect the secondary of a 120V-6V transformer to the secondary of the first transformer. So it goes kind of like this: 120V -> 12V -> 6V (12V) -> 120V (240V). Does that makes sense? So you're putting 120V in one side, you're getting 12V after the first transformer and then you're getting 240V after the second transformer.. You can use different secondary voltages on the second transformer to get different voltages. You can use a 120V to 9V, for example, to get 180V after the second transformer. I used to get old tube stuff off of craigslist. I think maybe it got more popular since I was doing that, but I was getting old Hammond organs (and Conn and Baldwin) for peanuts, sometimes free. I'd strip them for parts. But you'd get a complete tube amp. The Hammonds are particularly excellent for making making guitar amps. I had both L100 series and M3 series amps. Anyway, if you can find that stuff on Craigslist, it's a great way to get free parts. The only down side is getting rid of the organ body. My cousin owned a restaurant at the time and he'd let me dump them in his restaurant's dumpster.
I've used the N68X for a couple amp designs using series filament tubes (fused wall power for filaments and the N68X for B+). It works great and 240V will rectify to about 330V, depending on the current draw. Another alternative for filaments is a 12V center tapped transformer,, not uncommon on solid state electronics. Your 12A*7 tubes can use the full transformer voltage swing, and 6V output tubes can each take a leg and the center tap.
Simple and Stylish in its 2-tone Green and white housing with a sound that will definitely please the neighbours...I bet it would sound "Cosmic" with an Alnico P10r type speaker...in a matching 2-tone green and white cabinet, like a Sci-fi mini stack!
Another good option is something like what the peeps from the Brazilian forum Handmades did with their Camine HB-1, HB-2, and other such projects, where they use a 30v+30v transformer to get 60vAC, and run that through a voltage doubler to get 145v DC. It also powers the filaments from the 30vAC center tap (where they're wired in series). There's also many projects from the website OzValves where they use voltage multipliers to get B+ voltages.
HI Terry , Im in the Uk, i built an amp Standel 25L15 years ago, but now got problems, its the transformer 350-350, etc..... But its the 6.3V with the Center Tap connected and its a dead short to ground, (both 6.3v wires) unground Center Tap, no short to both 6.3v wires. Many thanks Richard
Now thats freaking cool. Now I need to dig through the shop and see what I could put one of those in. Maybe a Benton Harbor, Mi 1960's green thing??Hmmm....
Good info there Terry. Thanks for the tips! Those are very affordable! And honestly, this is one of the reasons I haven't made a homebrew amp yet. Transformer costs. Also good tip on the preamp tubes! I figured there was a comparable single triode to the 12AX7. =) Awesome.
I would probably turn the output transformer 90 degrees from the power transformer to reduce the possibility of magnetic coupling, but other than that, a nice build.
Another option is control transformers. They are usually used to step down 480 or 240 to 120 but you can reverse feed then and they are cheap, I got a bunch free working as an electrician.
Very interesting! The Princeton reverb puts out 12 watts and it's original power transformer was only about 70mA ..... Will this alternative power push pull 6v6s with 4 12ax7s if you bump up the filament transformer to 2.2 amps? With the lower supply voltage(240 vs 320) and a SS rectifier will it make 10 watts?
Hola amigo, vi en otro video que enseñas a probar transformadores para single ended para determinar la corriente de trabajo bajo carga, mi pregunta es siempre se prueban con carga de 10k 10w? O depende de la valvula? Quiero probar un pentodo de salida en single ended EL34, muy buenos y educativos tus videos, saludos desde Chile.
Hi terry from down under . I watch you RU-vid channel all the time and its a very cool channel . I have a Johnson Viking 2 with the 122 vfo. Would it be possible to give me some advise ? When I load up the JV2 with vfo on the 160,80,40 band switch I get harmonics on 20 meters and 10 All other band allocations are fine no harmonics for example if I load the JV2 up on 40meter on the 40,20,15,10 allocation no issue with harmonics at all, This is the same with the 40 and 80 fix crystals no harmonics In your experience have you seen this behavior before? . and if so would you give me a clue onto were to start looking in the vfo .? Thank you for your time. Below is a photo of my Johnson Viking 2 Andrew
What about a solution for modulation transformers? If I'm looking to build a mid-to-high power plate modulated transmitter, there's a definite shortage of modulation iron aside from cannibalizing a radio to get the iron out of it
Thank you So much Terry for that information. I took a break from building for a little while and in that short time I can’t believe how much transformers went up. Our options in HIFI Outputs are nearly none. A pair of Edocrs I bought for under 30 a few years back are over 60 now. The last small wattage amp I built for my garage using 6DN7s(Mike Frieda’s schematic) I wound up using those PT-31’s. Inexpensive but sound great to my 55 year old ears. Any thoughts on output manufacturers out there for alternatives?
I'm a 56yr young gentleman from Ohio & I have an old JVC receiver that pops the fuse just like the Realistic receiver you repaired 4yrs ago. I'd like to have it repaired 😢 would you please accept the task? I look forward to your reply🙏🏼
Yes, if the transformer lines up with the high voltage required. You can use the main power tranny in the Regency MR-10 receiver. It is around 400vac CT. Then use the cabinet for the retro look!
It's all a question of volts and amps. So, assume you're looking at an old tube radio at the swap meet and wondering whether the trannies will work for you, and of course, all you can do is to make an educated guess. That is, if it HAS trannies...many AM radios do not, they fetch their B+ direct from the AC line. No goodsky. But you will find that it's often the case that an old radio will not make more then 200-225 volts. And yes, you can make a low-power 2-3 watt amp with that with a solid state bridge rectifier, but not even a genuine Fender Champ which wants 325 or so volts despite the low power rating. Probably the radio output transformer is a piddly little thing designed to drive a 4" cheesy speaker, or maybe it's even the field coil on the speaker! Yikes! Not that great. The snarls come in when you try to make a push-pull 10-20-50 watt amp. For that, you are gonna need 350+ or even 450 volts on your 6V6 or 6L6 plates and that you won't find that in a radio receiver. In an old TV set, yes, you definitely can. The truly useless (except for the cabinetry and/or chassis) flea market stuff is in old tube VIDEO equipment. Wideband amplifiers, distribution amplifiers. It usually looks pretty good and is generally well built, but remember, the old NTSC video signal was a 1-volt peak-to-peak affair and did not have to drive any appreciable current. So you take the trannies out of that gear and you will find that the power supply makes only 100 or so volts, the tubes run at 80-90 plate volts and the trannies are completely useless. That's because the thing only has to swing 1 volt on the output! Oh, and by the way, on that kind of old tube video gear, you may not even be able to physically fit a 6V6 or a 5Y3 inside the thing because it was built to be slim and trim and the cage for the chassis isn't tall enough to fit an octal tube! Ask me how I know!!
You clearly demonstrated that it works which is fantastic, however, I am just wondering something, you said the 120v Red wires are the line, but looking at the Datasheet it clearly says that the black, yellow/black, Green/black/red/ and the black are the power in and the Reds and white are the outputs, do you forsee any long term use issues? are both sides the same wire gauges and or ohms turn ratio?
Hello, In this application it works great, Thats why I made sure to test & show a demo. I have built these for years, Never a complaint or report of failure.
@@d-labelectronics Sweet! Thank you Terry for this and everything else you do for the DIY Small Tube Amps community. We all appreciate you man. Thumbs up!
These are harder to come by. You must know what you want specifically and look for something near that as surplus. I found a deal on these rather small transformers, about 1/2 the size of a Hammond 125 and I got like 20 of them for around $3 a piece including shipping! They work fantastic for little 6AQ5/6V6/EL84/EL86 PP Output transformers. Around 10W Output is the max you can run on 1 of these. I've still got a number of them lying around in my shop waiting for me to start tinkering around again.
