Anderton '64 reissue JTM145 - any info?

[Ksandr]

about the sound: with more gain is fuzz. packackage started checking and realized that the fuzz appears after the second cascade. checked all the shoals in the Assembly and voltage is correct. I think that I accidentally ordered a transformer 150V on the anode winding. and I use the USSR tube 6n2p(12ax7) and 6n1p(12au7). what else had same problem?. (sorry for my bad english)

[cassoulet]

What schematic did you use? Matec's HTM1?
May be it is the 150V HT that is too low. What is your DC voltage at the power stage?

Have a look at the voltages on the attached picture. This will give you an idea.

[Ksandr]

i using last schem 01/07/2015 and add jtm45 tonestack. I made a mistake. on another transformer 150V. here 180V. so that's not the problem. voltage have approximately the same

[Matec]

Hello guys.

Many may have wanted to create your own amp 1W, but do not know if it will be good.

Here is a video and sample of axehack, who set up his own JTM1.

Link: https://www.youtube.com/watch?feature=p ... L4m4kCeHAE

The description is in TDPRI Forum at this link: http://www.tdpri.com/threads/jtm-1-clone.650255/

Enjoy!

Matec.

[yotool]

Has anyone measured the actual current draw from the main rectified 230 VDC bus?

I see that it is fused at 125MA, however I'd appreciate the actual current draw at idle and full power output.

The 12.6 VAC series-wired filament load is easy: 3*150MA = 450MA.

This may be considered a travesty, but I want to design a simple 100KHz switched-mode fly-back power supply to deliver the filament and High Voltage DC goods to this little bugger to keep the weight way down (like those new little inverter-based welders).

I couldn't find any generic efficiency numbers for a tube-based push-pull amplifier [of 1 Watt or so].

Thanks for the help.

[cassoulet]

If you take the voltages posted above, the idle current drawn by the output PP is about 20mA. Each triode in the preamp can be reckoned at about 1mA.

So that's 24 or 25 mA for idle. Don't know about peak. It probably doesn't change much for the preamp section and might increase a bit for the output section.

I'm also interested in this SMPS solution. Cheers.

[yotool]

Thanks for that info...

That then comes to 6 Watts or so at "Idle" (I assume that the PP current at idle is the static current used to avoid crossover distortion {aka fixed "bias" setting}...

Full load total MAs drawn would be great to know.

Since we are at maybe 12 Watts total, my thoughts are a small MolyPermalloy Powdered (MPP) toroid core crankin' at 100KHz in flyback-mode (only needs one silicon switching element) using either the Power Integrations or Fairchild "Simple Switchers" with the integrated High Voltage (rectified mains switching) MOSFET transistor (they are at war with each other over patent infringement right now which is interesting). Those completely integrated ICs save a big amount of parts count and support all of the standard power supply supervisory functions (current overload,under-voltage/over-voltage etc..).

This would also let you lower the B+ on-the-fly to see what effects that might have aka Eddie VanHalen's VARIAC on his plexi. ..not sure how that would apply to a 1 Watt'er like this though but it might be cool to try.

This would be a very small, ± 5% regulated AC/DC power module that would replace the standard relatively huge/heavy 50/60 Hz behemoth of yore... supplying all of the tube amp's DC power requirements...

[cassoulet]

Sounds interesting. Make sure it's not too noisy, though. SMPS are very noisy. Also, how do you plan to have your filaments powered? Use the same DC power section (before it is raised by switched mode for HT) or use a separate 12VDC?
The Eddy Van Halen trick might be good too. Ideally, it should lower down only the HT for the output PP tube while keeping the normal HT for preamp tubes. I figure that's how you would simulate a cranked amp.

[yotool]

Correct...

If I wanted to do the "brown sound" I'd have to use 2 separate flybacks and control circuits with one being a fixed 12.6 VDC to all of the filaments as you mention, as well as a fixed B+ for the preamp sections. The voltage to the filaments should remain the same as the Push-Pull power stage B+ is tweaked downward... although if Eddie just used a VARIAC on the mains input to his Plexi, he would have been varying everything simultaneously; but he was just experimenting in a now-famous way of course....

However, if I start without that added varying power section B+ complexity, I'd just have a separate secondary winding (many less turns of larger, or paralleled, because of skin-effect losses) on the flyback for the 12.6VDC circuit to power the tube filaments. The required "thermionic emission" from the filaments doesn't care about AC vs DC and DC is actually more noise/hum free (in theory which is why the series connected filaments is somewhat preferred as the EMI from the lower filament currents would also be lowered; of course proper wiring routes and twisted filament wiring which cancels the mag. fields can achieve the same).

With regard to the "noise" of a switcher (esp. a flyback) the noise is way up at 100KHz which is far beyond anything one could hear. That frequency also makes the physical size of the required magnetics "small", as the switching frequency and the required "magnetic volume" needed to transport "power" are inversely proportional. This is why the 60Hz AC power transformers are so "huge".

Magnetics; especially the power stuff, is pretty cool when you think about it. I've always been fascinated by it.

[Badside]

So did anyone ever figure out how the JTM145 offers two volume knobs?

It sounds QUITE different from the JTM1, I doubt it's just a JTM1 with a full tone stack.

Here's my theory: one of the designers gave some clues about the JTM1 and JCM1 on another forum, and one trick they used on the JCM1 is to have V2a driving the tone stack via MOSFET follower. The idea is that V2b is the actual phase inverter, V2a is just another gain stage and you CAN insert something in between.

Now, looking at that one gut shot picture of the JTM145, I can't seem to find a MOSFET (it could be on the front panel daughterboard, but there would need to be a B+ feed to it, which there doesn't seem to be), but you can definitely see that the traces going to the 3-wire connector for that daughterboard (CON4) all lead to and from V2, not V1.

So, there you go, that's my theory:
V1 is typical Plexi fashion (one bright, one normal, don't know at this point if they went full Normal/Lead setup or the shared cathode JTM45 config)
Each side drives a volume knob (one with a bright cap) feeding mixer resistors feeding V2a
Tone stack is inserted between V2a and V2b (replaces the 470k/560k voltage divider), negative feedback probably still inserted straight to V2b's grid.

This would technically have less gain than the stock JTM1 circuit. The JCM1 works around this by driving the tonestack with a MOSFET. However, bypassing V2a's cathode (not to mention the power tubes) could alleviate this.

I'm tempted to try and build one that way now.

[coldengray]

Was Smokebreak's layout ever updated to include switching, etc?

[Santi_]

Hi, I built my amplifier following the scheme of Matec, have also received his support by email, since I have no idea of electronics. I want to thank you for your help Matec.

My amp sounds great. I have a similar voltages and everything works fine.
The only thing I don't like is the sound at high volumes. It sounds with less definition and with some fuzz.I have to get a microphone and do some recordings.From what I read it seems to be a common thing.
I use Electro-Harmonix tubes. Tube Town-t30 toroidal and http://www.ampmaker.com/store/4W-push-p ... ormer.html


Anyway, I want to thank all the work you have done, although I don't understand many things that you speak here.

Cheers!

[10thTx]

I redrew the schematic posted on the 27th page in a manner that was easier for me to make sense of. Thought I'd post it here. Please compare it with the other one and look for errors on what I've posted.

IF there are discrepencies between the schematic and layout, please refer to the schematic that Matec provided as the proven design.

With respect, 10thtx


I've added a version that has TMB tone stack for your consideration. Haven't built this, so it's an unproven DRAFT version.

EDIT: Please read Matec's post directly following this post. I changed the 560k back to 56k & added the 1M and .02 parts in the NFB. Refer to earlier in thread on this
same page 27 for voltage values on components.

[Matec]

Hello.

It's great that people make their own layouts.
The schematics too. They always tell me that my schemes are confusing, but I relied on PCBs to form the groups of components. There is no problem in reissuing.

Just do not remove information, such as the working voltage of the capacitors, or the power allowed to the resistors.

The layout has small errors. The value of the resistor in turret 21 is 56k, not 560k. They are not included in layout R15 and C11, which are part of the NFB. Also the source components are not indicated, nor the power attenuator of 1W / 0.1W.

As for the tone stack is at the discretion of anyone who wants to make the circuit. I even preferred the full tone stack, with bass, mid and treble.

Cheers

[10thTx]

Matec,

Thank you for your post and the generous sharing of information. I have edited my layout and schematic to reflect several of your suggestions.

With respect, 10thtx