Anderton '64 reissue JTM145 - any info?

[Smokebreak]

I'm wiring the OT and NFB, and for now I'm just going straight 8ohm jack. I'll worry bout the .1W switching and 16ohm tap later.

I was wiring 1M/22n, then realized Matec has it coming off the 16 tap, so I was going to reduce that to 470K/47n, then I realized in the original scheme, Matec has 400K/47n in parenthesis.

Matec, can you explain your thoughts here?

[Matec]

My OT has only output 4Ohms. So the resistor is 1/2 of the value and the capacitor 2x. (470k and 47nF). If you use the output 8Ohms to make the feedback resistor value will have ~ 0.7x (680k), and ~ 1.4x capacitor (33nF).

This will keep the gain of power by similar amounts.

The value of 400k were adjustments I've been doing, should not have been placed in the scheme (sorry).

I can not now modify the schema on that page, since Google does not respond well to this, taking the schema search. (Has this happened). In time I will making new posts to go to correcting these details.

[Smokebreak]

Thanks for the clarification Matec. I was thinking from 16>8 would be half, but of course it's not linear. My OT theory/understanding is pretty awful But it's getting better.

So I'm using OT with no centertap, and just had it in my head that I'd tie one side of the heaters to the 12AU7 cathode, but neglected the fact that there's not going to be much DC elevation there. So, I wired two 100ohms in, and just tied them to the cathode.
What do you guys think is the best bet here? I could ground them, but I figured even a little DC elevation is better than none?

[roberto]

The voltage on the secondary of an OT is multiplied by 1,41 every time you double the impedance of the tap.

This is because the power is constant, while the impedance changes, but the power is squared voltage divided by impedance. That's the reason of the 1,41 = sqrt(2) factor.

[Matec]

So I'm using OT with no centertap, and just had it in my head that I'd tie one side of the heaters to the 12AU7 cathode, but neglected the fact that there's not going to be much DC elevation there. So, I wired two 100ohms in, and just tied them to the cathode.
What do you guys think is the best bet here? I could ground them, but I figured even a little DC elevation is better than none?

Forgive my poor knowledge of the language. Do not understand the content of those sentences.

Explain each subject separately. Please.
---------------------------------------------------------

Ops. I understand now, you are referring to the PT and the heater circuit.

The Marshalls do not have these resistors, I put them to avoid some noise. In my amp they are grounded. There is no noise. You can try putting connected to the cathode.

[Smokebreak]

No problem, Matec.

I meant that I have a PT that has no centertap for the heater windings.
I'm sorry, I said "OT" at first .
I'm trying to reduce hum, and I'm wondering if the best way is :

1. two 100ohm resistors from each side of the winding, to ground
2. two 100ohm resistors from each side of the winding to the cathode of the 12AU7
3. one side of the heaters straight to the cathode of 12AU7

Originally, I thought #3 would work, but I forgot that there isn't much DC elevation there.
Right now, I've got it wired like #2.

I was curious what you guys thought. Hopefully I'll fire it up soon and we'll see.

Your English is good. Mine can be very bad.

[Matec]

I could understand, and I answered in the previous post. Options 1 and 2 are good.

I put 2 resistors of 270ohms in my mounting, but 100ohms is good.

With the guitar volume being closed, not hear any noise.

The voltage to the heaters is 12v?

[Smokebreak]

I've got 6.3V

[Matec]

So, 100ohms resistors are best.

[Matec]

I feel I should thank to Roberto for having created this topic. And to better complement my answers, I do not know if even be clear.
Thank you Roberto!

[Smokebreak]

Indeed! I wasn't even aware of these amps until this thread.

I finished up the amp today, and everything is working. "1W" is indeed too loud for an apartment. The .1W setting works as advertised, and my wife even said "If you were in the other room, that would be perfect". haha.

The amp sounds pretty good, and here is a clip :
https://soundcloud.com/jeremyslemenda/jtm1-5-2

This is with the .1W setting, which doesn't sound quite as good as the full power setting. The first part is with the gain on 4, then 7, then 10. At the end I backed off the guitar volume to demonstrate how it cleans up. Tone controls at noon, with bass backed off a little

My only issue is that there is a little nasty fizz/buzz behind the notes, which you can hear in the clips. The 1st two 12AU7s I tried made this effect much worse, and I remember them being problematic in the vibrato section of another build. So this is my last "good" 12AU7, and it sounds much better than the others. But, I've still got a little buzz.

The gain on 10 is a little too much, and kinda harsh, too. It sounds like either the PI or the 12AU7 is getting pushed too hard.

The amps is very,very quiet even full power and full gain.

Suggestions are welcome.

I'm going to try a few things :
Put a larger stopper at the grid of the cathodyne, as per Merlin
Increase 12AU7 grid stoppers
Find another 12AU7

My B+ is 263, cathode at 9.4V

The Hammond PT I'm using, rated 190-0-190, is putting out 202-0-202, and that's with the 125V taps, but I believe my voltages are OK.

[cbass]

That sounds really good.Nice job buddy

[Matec]

Congratulations on your work. This amp was assembled in record time and is apparently perfect.
I did not notice the noise you mentioned. Maybe the recording does not show all the details, but it seemed good to me. (I'm extremly suspect to opine).
The voltages you mentioned are somewhat taller than my amp, but are within 10% tolerance which is reasonable. If you notice serious problems let me know.

Enjoy

Matec

[Matec]

Yes, after listening to 5 times the sound sample I identified the noise.

Suggestions.

I remembered something that is important. If noise or whistles occur in the sound, perhaps the feedback is positive, rather than negative. In this case, the inversion of taps of the primary OT be attempted.

Matec

[mhartman]

That looks awesome. Nice work!