How does one determine what type of transformers are used?

[ToneMerc]

I'm just going to throw this out there about the KT66. There's a lot info abound about the impedence that the KT66 should be run at. Most of it's based on the mistake that Marshall made using those surplus Radiospares output transformers in the JTM45. Many people have it burned into their mind that the KT66 should be run at either a 6.6k or 8k impedence. However, this mismatch just happens to sound good. At the same time the KT66 sounds damn good at 3.4k, particularly with the 50W Marshall transfomer than has the buried 100V tap.

The nice thing about this game is that; what you are looking to do you has already been done before, so it doesn't take a great technical exercise to do this. I do have the questions though.........

1. Why exactly the KT66 and not the 6L6?
2. How did you determine 30 watts?
3. What output section topology, single ended or push-pull?

I say all this to say, don't get too hung up on discrete technical concepts when you haven't first determined your needs or have an idea what you hear in your head.



TM

[M Fowler]

The KT66 sound good with Dynaco A-470-S at 4k3 as well.

Mark

[rdjones]

If any of you have suggestions for reading material that I should look into for getting more information on this subject I would appreciate that very much.

If you want to go back to the ancient scrolls, The "RDH".
RCA Radiotron Designer's Handbook.

[DocRocz]

I have picked up two books one of which was suggested here.
I picked up the book Designing Tube Preamps For Guitar and Bass By Merlin Blencowe and Valve Amplifiers By Morgan Jones.

Does anyone have any feedback on the second book by Morgan Jones, as the first book was suggested by surfsup?

[DocRocz]

The nice thing about this game is that; what you are looking to do you has already been done before, so it doesn't take a great technical exercise to do this. I do have the questions though.........

1. Why exactly the KT66 and not the 6L6?
2. How did you determine 30 watts?
3. What output section topology, single ended or push-pull?

The answer is simple:
Reeves Custom 30 MK II.

Another level of input that I got for the KT66 was from this review on the KT66 tube.

Also back in the day I had a Marshall Major that ran KT88's and it was to harsh. When I discussed this with my tech he said if I didn't have an aversion to rewiring it to take another tube it would have a a smoothing effect. The process worked very well. In case you're wondering the tube the head was rewired for were 6550's.

[DocRocz]

If you want to go back to the ancient scrolls, The "RDH".
RCA Radiotron Designer's Handbook.

I did a search and found this site:"Technical Books Online"
They have the Radiotron Designer's Handbook and lots of others to download.

[David Root]

+1 on the observations about the KT66 at various primary impedances, it's all true.

The KT66 is a British 6L6GC with higher current capability and a flatter frequency response, no scooped mids compared to the typical 6L6GC (if there is such a thing). More of an audio tube really, by design. So you can do a pair with a 4K primary OT, just like a Fender. It won't sound like a Fender, especially if you use Marshall iron.

The JTM45 should not have worked, on paper, but it does. To this day I don't know if anyone has figured out why Marshall used that 8K primary, I don't.

[ToneMerc]

+1 on the observations about the KT66 at various primary impedances, it's all true.

The KT66 is a British 6L6GC with higher current capability and a flatter frequency response, no scooped mids compared to the typical 6L6GC (if there is such a thing). More of an audio tube really, by design. So you can do a pair with a 4K primary OT, just like a Fender. It won't sound like a Fender, especially if you use Marshall iron.

The JTM45 should not have worked, on paper, but it does. To this day I don't know if anyone has figured out why Marshall used that 8K primary, I don't.

David, I found this which is good reading. Makes you wonder if the Marshall folks just goofed up plotting the load lines.

Mhttp://www.audioxpress.com/resource/audioclass/ga100ac.pdf

TM