Build Basics FAQ #3 : OUTPUT TRANSFORMERS!! ...and primary impedance

[@wakjob961]

I was just like you about ten years ago. Totally obsessed with this stuff. Morning noon & night it was all I thought about....modding, experimenting, theorizing, studying caps and resistors ect... I just watched my playing skills take a huge nosedive as my soldering skills went through the roof !!!

[@HeadfirstAmps]

Find time for both!

[@PhuketMyMac]

Thank you again Jason! So much to learn and you’re really helping. I might have said that already but you’re the Louis Rossmann of guitar tube amps!

[@russiangoose7053]

Please continue the build basics series! These videos are the most helpful ones I've seen!

[@HeadfirstAmps]

Glad you like them! What else would you like me to cover?

[@russiangoose7053]

@@HeadfirstAmps now that I look through your videos you've done most of what I could think of off the top of my head. Maybe you could cover lead dress and ground schemes? Or perhaps biasing in practice? Whatever you cover I just appreciate the knowledge you share!

[@PhuketMyMac]

@@russiangoose7053ground schemes would be a great one!

[@komorowski381]

Finally a video that made it understandable for me .Many thanks 🙏🏼

[@felinekaiju4517]

found useful?. I learnt something alright!. I'm glad that at 40 I'm understandinig concepts that would have fried my brain. I consider this Output tranformers for dummies!!. love it!.

[@TheFrozenDesert]

I am so glad I heard you on Tone Talk. Brilliant.

[@HeadfirstAmps]

Thanks!

[@lechstryzewski9350]

Yet another fantastic video Jason!! - The way you deliver the information makes it very easy to understand. Thanks man !!!

[@HeadfirstAmps]

Thanks Lech, that’s the goal for sure. Make it easy!

[@TopHatAmps-Guitars]

I love you too, Jason!!! My comment on this now 2 year old video… Two EL84’s at 390volt is in no way a normal/traditional arrangement. The design Max voltage on a 6BQ5/EL84 tube, in the RCA handbook etc. Is 300 volts. Many old guitar amps exceeded the tube makers directives… But Vox being the main purveyor of EL84’s, ran an AC15 at 315v and the AC30 at 330-5volt on plates. Marshall 18 watt ran somewhat higher…but nothing I’m aware of ran those tubes anywhere near 390volts. There are military versions of that basic tube that could possibly withstand that high of voltage on the plates!!! EL84’s are a freak of nature, relative to plate voltages…compared to 6v6, 6L6, EL34, other large 8 pin tubes. Marshalls and Voxes are two different realms. They have nearly nothing in common, as to power tube and power supply needs, imho.

[@andrewwilliams5042]

Great information / explanations, amp audio, production. Working my way back through the older videos.

[@NewReligion1954]

This was explained very well. Great video Jason. Thank you for all of the great support in our community. David Hopkins.

[@HeadfirstAmps]

Tnx David.

[@cheyneluke9330]

Fantastic thanks Jason!

[@marvelharris9540]

Fantastic job Jason!

[@LucasMastropasqua]

I still love revisiting your videos all the time, especially great as reference when I am working on something and need to refresh my memory. I was wondering, with a speaker load attached is there any way to measure the primary impedance, if for example you have an OT in an amp but don't know what specs are? The other question is if measuring the resistance of the primary should the resistance be equal on either side of the center tap?

[@schmolly75]

Marshall 100w uses four tubes and needs 1.700 ohms at primary. If your remove two tubes to get only 50W, the two tubes need 3.800 ohms at the primary. So if the 100w have a 16 ohms cab connected to the 16 ohms terminal output, to get 3.800 ohms with two tubes you only need to move the jack of the cab from the 16 ohms terminal to the 8 ohms terminal.

[@HeadfirstAmps]

Correct! It’s a useful additional point this.

[@BCEpedals]

This was so helpful!

[@danielsaturnino5715]

Thanks for sharing your knowledge :)

[@shredding51]

Great video! Think i have a OT going out on my jcm 800 2204

[@Toobzilla]

great content Jason, thanks!. i could never understand why the Jtm 45 which runs the same family of tubes as a 2x6l6, 5881 fender, not mentioning the direct copy of the 5f6a, runs a completely different spec OT. my homemade & fenders 5f6a calls for a correct 4300 ohm OT. the jtm45, around 8k, almost 2x the resistance. is there a non, *typical marshall* explanation for this?

[@HandWiredAmps]

The Origin 20 output transformer on my bench measures 5.4k Perhaps they decided to go with an impedance that's less efficient, as they only needed 20 watts, or, to fit better with the power scaling? Would have been a good question for Santiago's Q&A. Thanks for the video Jason!

[@HeadfirstAmps]

Yeah, as you drop the b+ voltage you’d increase the primary to keep the operating point optimal.

[@zabtej1645]

Can you really read the primary impedance off of the load lines? I have trouble finding the actual plate to plate values for my 6L6GC pair. But I did measure my old OT, and I have multiple selections for 8ohms, because my OT has 3 pairs of lugs. I have currently 7k5, 6k6, 3k7 and 3k3, all possible matches I can do for 8 Ohms. Any tips how to find primary load impedance for very high voltage of 520-530 V (will change the tubes for EL34 or KT88 later, the voltage is too much) on the 6L6GC?

[@ramilrodriguez8340]

Very nice. Do those formulas work with single ended amps?

[@HeadfirstAmps]

No, only push pull

[@freaksarise]

Hi Jason, when power scaling such as with the JCM 800 Studio Classic whereby the plate voltages are lowered to achieve the scaling, how does this affect the OT with respect to the equation (b+ voltage)2 / (plateDissipation X numOfTubes)? Thanks!

[@HeadfirstAmps]

It changes the performance for sure, they are so coldly biassed it's not an ideal operating point.

[@cobar5342]

Great video. I find this subject very difficult to grasp

[@Phantasm70]

What's your preference for output tap Jason, the least or greatest resistance?

[@HeadfirstAmps]

Makes no difference, as long as your negative feedback line is not connected to the speaker jack.

[@jpb962]

I know this is a tech video, and I thank you Jason for sharing your knowledge, I've learned a lot from your channel in the past year or so. But WTF JASON! I feel ripped off. I watched the whole video hoping that you would close it out with some a$$ kicking and face shredding on one of your amps!

[@HeadfirstAmps]

Hahaha, will keep this in mind!

[@GIBKEL]

God awful cliche… I won’t say it but I’ve got this Valco built Harmony 430-6973 output an it’s somewhat anemic. Old Jensen C10R pair, 12AX7 preamp. Slam a fuzz into it and it rips but you are still asking myself “Is that all?” Huge improvement in response when I actually got some black plates. Do nt know what to think. Maybe too much of the reverb/trem sucking the life. Not a build question-apologies.