Lets Build a Guitar Amplifier - Part 4 - Output transformer mistake and explination
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- čas přidán 11. 09. 2024
- Moral of the story; you can't use a push-pull output transformer in a single ended amp! Good info for anyone who wants to build an amp from scratch.
Don’t apologize. Making a mistake and fixing it is so more educational that getting it right and never knowing why. I’m quite new to electronics and learned a lot from that mistake.
The obseration of using air gaps to decrease the magnetization is correct. However. The air gap equivalent with some non-permeability material is not introduced between the laminates in the laminate direction. That would only decrease the effective cross section.
The air gap equivalent is achived by stacking all the E laminates in the same direction and all the I laminates into a bar. Then a small sheet of some non-permeability material is inserted between the E stack and the I bar. This increases the "magnetic resistanstance" of the core.
The video shows the stack having the E I orientation switched every three laminates. This is just convenience. Sufficient symmetry is obtained. Best would of course be to switch the orientation every next laminate.
I made a blunder myself claiming that superregenerative receivers are not slope detectors detecting FM. The fact is that they are with FM.
Come on, come on let's work together😄... And we can all learn from each others mistakes this is good stuff
a Cold cathode preamp stage intentionaly clips one side of the signal. This is my favorite type of distortion for guitar amps.
Tony, I thought I new a thing or two about tube amps, but I would have made the exact same error as you made. I just never thought of permeability and the two out-of-phase primaries. Please don't beat yourself up. I have learned so much from your videos. Happy Holidays, Jeff WA3PBK
Interesting. I never knew where was a difference between singe-ended and push-pull transformers! maybe it'd be easier just to go with push-pull. You still have plenty of room for another KT-88 and phase-inverter :)
Hey guys I’m building a amp I have 3 jj el34 that’s 450 for each right so that’s a 1800 volts what output transformer should I go for
Hello I have an indirectly related question I have a Yamaha B 100 - 115 III bass amp I had unplugged the speaker and forgot to plug it back in and then went to plug in a bass I believe that I blew out the output Transformer the headphone jack still works but nothing comes out the speaker now are you able to confirm this based on the scenario? Thank you very much for your input.
Laminations are usually (silicon) steel, not iron. Silicon steel has much higher electrical resistance than iron, and less magnetic
hysteresis, both being advantages for reduced losses. Specialist alloys are probably used for single-ended transformers to increase linearity with a DC current offset (ie a DC magnetic flux burden)
The gap limits the permeability of the core, which reduces the low end response, but increases the amp-turns before saturation,
and also stabilizes the properties of the core across temperature changes.
Hi. Did you ever got the right transformer? Finished the project?
Does it go both ways? Could one use a single ended OT in a push-pull amp?
No. A single-ended transformer only has a single winding on the primary without the necessary center tap for push-pull. The permeability of the core is also different. Each transformer type can only be used for its intended purpose, as I found out the hard way!
xraytonyb Super. Thanks to you I won't have to try and fail myself. Thank you for your super fast reply and keep up the good work.
Great vid. So just to recap, transformers for single ended design have air gap?
Yes. The core of a transformer is made up of thin laminations of ferrous material, all sandwiched together. The thickness and alloy of each lamination affects the flow of eddy currents in the core, as well as the saturation point. By adding a non-ferrous "shim" (mica, plastic etc.) between each lamination layer, it breaks up the eddy currents and raises the saturation point of the core by adding an insulating air gap. This is necessary to prevent the core from saturating and magnetizing when you apply the DC idle current in one direction only, as you do with a single-ended output section.
That chassis is huge for that amp
Don't apologize. This 'mishap' revealed a fact I did not know before.
I thought you need caps to block the DC to the output transformer..........no?
ToBeOrNotToBe have a look at most schematics. You’ll have AC going to some sort of rectifier then to some filter caps that smooth out the ripple. Notice that preamp tubes always have the most filtered DC possible, with their DC B+ to their plates coming from the 2nd or 3rd node from the power supply. Power tubes done require as much filtering, so you can often get away with DC from the rectifier through one filter section of the power supply, with further smoothing from the output transformer centre tap splitting to each plate. The output transformer acts like a choke in regards to a rectified B+ supply.
On the output screens you need a .05 -0.02 coupling capacitor that’s about it on the tube to the trans
I previously made a comment about a laminated transformer not needing the air gap. I was incorrect and deleted my previous comment. As I sit here with my foot in my mouth. :-P Tony and Hammond transformer are correct, Tinkerham was wrong and stands corrected.
No problem! I originally tried to go online and find some info about this and quickly found out how little info there is. Only after a lot of research and going back to my college transformer class over 30 years ago was I able to figure this out. I thought this video would help others so that they wouldn't end up making the same mistake I did.
Thanks so much for watching!
Yep, I watched part 4. You need a nice open back box for that speaker! Congratulations on a successful project completion. BTW, I like the home built guitar!
Hi. Did you ever got the right transformer? Finished the project?