1 watt amp

[Bieworm]

On the schematic the cathode of V1a has a bypassed bias resistor that's parallelled with an RC.. is that something that is applied more often?

Some type of frequency contouring. Would you like me to run a simulation on it? I could post a graph of the response it creates.

Jack

Would be nice.. yes

Marshall 1 watt amp revised JTM1.gif

The circuit attached to the mains power inlet ground.. is that a noise filtering system? I am using a filtered IEC plug, so I reckon it's obsolete?

[TriodeLuvr]

I had a discussion yesterday on a different forum regarding that ground network. It's intended to break ground loops caused by the parallel currents in the house (earth) grounding system. Personally, I think it's a bad idea, and I don't quite understand how it would be beneficial in a system with only one component, such as a guitar amp. Anyway, there's a brief description of a similar network here:

https://www.tubecad.com/2017/09/blog0397.htm

Jack

[TriodeLuvr]

Here's the sim of the JTM1 input circuit. Be sure to consider the scale on the left when viewing the plot. The contour is very mild, not sure why they even bothered. Note that the shallow rolloff above 10K is the result of the 100pF cap from anode to cathode. It's mostly an ultrasonic filter.

Jack

[Daviedawg]

"Did you work with the Matec Schematic?" Bieworm.

If that is the schematic you posted above, then yes. I have looked through my stuff on it. I had a notion that I had made changes but that must have been something else because it worked as drawn as far as my notes say. It is fitted with an Ampmaker OT and toroidal PT and three NOS Brimars.

The guy is still using it as his home amp.

Dd

[Daviedawg]

"The circuit attached to the mains power inlet ground".

There was discussion of that on the site where I found the schematic. I did not incorporate it in my build.

Dd

[Bieworm]

"The circuit attached to the mains power inlet ground".

There was discussion of that on the site where I found the schematic. I did not incorporate it in my build.

Dd

I don't intend to either. I just gonna use a 10A filtered IEC plug as I always do.

[Bieworm]

Here's the sim of the JTM1 input circuit. Be sure to consider the scale on the left when viewing the plot. The contour is very mild, not sure why they even bothered. Note that the shallow rolloff above 10K is the result of the 100pF cap from anode to cathode. It's mostly an ultrasonic filter.

Jack

Fwiw I will just follow the schematic and see from there. It's just 2 components extra.. couldn't hurt things either.
Thanks Jack

[zaphod_phil]

Push-pull 6AK6s will give considerably more than 1W. That's what a single one in single-ended Class A pushes out. However you could try running a pair in a "self-split" power amp, as used in the Heavy Watter and also the Powerman design - http://www.harmonicappliances.com/power ... erman.html. Self-split is a kind of inefficient pseudo- P-P, which provides very little more output power than SE Class A. So that should get you into about the right ball park.

[Bieworm]

Push-pull 6AK6s will give considerably more than 1W. That's what a single one in single-ended Class A pushes out. However you could try running a pair in a "self-split" power amp, as used in the Heavy Watter and also the Powerman design - http://www.harmonicappliances.com/power ... erman.html. Self-split is a kind of inefficient pseudo- P-P, which provides very little more output power than SE Class A. So that should get you into about the right ball park.

Thanks ZP!! But the fellow who wants the amp has his mind on the JTM1. So I will have to build that one. I'll score some info on it the next few days and start gathering the parts. Maybe I will be nagging and crying after that build.. lol.

[TriodeLuvr]

The 1W concept makes me wonder - does anyone make a low output speaker/cabinet to reduce loudness, rather than relying on resistive attenuation for home use? I'm thinking about a nearly sealed enclosure with lots of dampening material on both sides of the speaker.

Jack

[Bieworm]

The 1W concept makes me wonder - does anyone make a low output speaker/cabinet to reduce loudness, rather than relying on resistive attenuation for home use? I'm thinking about a nearly sealed enclosure with lots of dampening material on both sides of the speaker.

Jack

Owww yet another angle.. try the eminence reignmaker for speaker attenuation. I have one.. works great. Reduces to 9dB less

[zaphod_phil]

I have yet to see a complete schematic for the JTM1. Has your friend heard one in real life? What is he actually looking for, just a 1W amp with a generic Marshall vibe?
On the subject of self-split power amps using pentodes, check out the Pentotron for an example- http://harmonicappliances.com/pentotron/pentotron.html

OK, I just found a JTM1 schematic - http://musiciansroadhouse.com/download/ ... 0b61774c60 Unfortunately, it uses a 12AU7 for the power stage, but could probably be modified to use 6AU6 pentodes to more closely approximate the EL34 sound
You could substitute in the SuperLite TMB's preamp to get you closer to a real Marshall vibe.

[zaphod_phil]

The 1W concept makes me wonder - does anyone make a low output speaker/cabinet to reduce loudness, rather than relying on resistive attenuation for home use? I'm thinking about a nearly sealed enclosure with lots of dampening material on both sides of the speaker.

Jack

Owww yet another angle.. try the eminence reignmaker for speaker attenuation. I have one.. works great. Reduces to 9dB less

Cool suggestion! I personally recommend using a VVR to scale the power amp and PI rail voltages. That works real well.

[TriodeLuvr]

Good ideas, thanks. Wasn't aware of the Reignmaker.

Jack

[Bieworm]

I have yet to see a complete schematic for the JTM1. Has your friend heard one in real life? What is he actually looking for, just a 1W amp with a generic Marshall vibe?
On the subject of self-split power amps using pentodes, check out the Pentotron for an example- http://harmonicappliances.com/pentotron/pentotron.html

OK, I just found a JTM1 schematic - http://musiciansroadhouse.com/download/ ... 0b61774c60 Unfortunately, it uses a 12AU7 for the power stage, but could probably be modified to use 6AU6 pentodes to more closely approximate the EL34 sound
You could substitute in the SuperLite TMB's preamp to get you closer to a real Marshall vibe.

His current amps are a Cornford Harlequin and a 57 custom champ. I think the superlite TMB is an excellent choice, matched with the 1W power amp. I personally recommend the Tremolo TMB Reverb in a 1W package... I will build one for sure. But if you hear this video I bet you're blown away by the JTM1 too:
https://youtu.be/FIQQDHa7qTk

[Bieworm]

Good ideas, thanks. Wasn't aware of the Reignmaker.

Jack

I have a NOS GE 5814A ... good tube for the 12AU7 purpose, no? Supposes to be great quality?

[Bieworm]

I have yet to see a complete schematic for the JTM1. Has your friend heard one in real life? What is he actually looking for, just a 1W amp with a generic Marshall vibe?
On the subject of self-split power amps using pentodes, check out the Pentotron for an example- http://harmonicappliances.com/pentotron/pentotron.html

OK, I just found a JTM1 schematic - http://musiciansroadhouse.com/download/ ... 0b61774c60 Unfortunately, it uses a 12AU7 for the power stage, but could probably be modified to use 6AU6 pentodes to more closely approximate the EL34 sound
You could substitute in the SuperLite TMB's preamp to get you closer to a real Marshall vibe.

Correct me if I'm wrong, but the JTM1 is a full house of components compared to the superlite TMB. Caps and resitors and caps and caps... looks like a lot , maybe too much?
I'm also really interested in that what you suggested. The superlite TMB coupled to the 6AU6 power stage. Are there any examples of a +- 1W amp with that power stage? OT type or specs.. I was planning on using the Hammond 125A which has various primary options?

[TriodeLuvr]

nada aqui

[TriodeLuvr]

Good ideas, thanks. Wasn't aware of the Reignmaker.

Jack

I have a NOS GE 5814A ... good tube for the 12AU7 purpose, no? Supposes to be great quality?

The 5814 is a "reliable version of type 12AU7." The 5814A is additionally "tested for military use." You should be aware that the heater-cathode rating of these tubes is 100V, half the rating of type 12AU7. That would be important to keep in mind if the tube is used as a cathode follower or cathodyne splitter. Other than that, it looks very good!

Jack

[Bieworm]

Off topic.. but building a new tele. Got a thinline body on order. Here's the neck..well headstock with the gold logo.

20210506_225341.jpg