18Watt.com

Hey 18 watt family, I’m wondering your thoughts on something. I have a Soursound Choke going into my 18 watt build. Classic schematic values, B+ ect, but I’m using a choke in place of the 1.5k dropping resistor on el cap can. It’s a multi tap choke, one side is 7H@ 500R and the other is 10H @ 670R. In your experience with using a choke in this circuit, which value did you end up using? Wonder if I could put this on a switch… ?
Thanks !

Jason Patrick wrote: ↑

Tue 10/03/23 8:53 pm

Hey 18 watt family, I’m wondering your thoughts on something. I have a Soursound Choke going into my 18 watt build. Classic schematic values, B+ ect, but I’m using a choke in place of the 1.5k dropping resistor on el cap can. It’s a multi tap choke, one side is 7H@ 500R and the other is 10H @ 670R. In your experience with using a choke in this circuit, which value did you end up using? Wonder if I could put this on a switch… ?
Thanks !

I never use a choke in an 18 watt, but if I would I think I’d use the Hammond 194A or B

Anybody else…

Jason Patrick wrote: ↑

Wed 10/04/23 9:10 am

Anybody else…

You asked us about our experience, and the general consensus is that we do not use chokes in this circuit. No chokes, no NFB.

You're welcome to try it and see how it sounds. Historically the move was to reduce the H in the chokes used in similar circuits, and the choke Bieworm recommended is 4H, which is lower than yours, and the correct answer.

If you think your choke sounds awesome in the circuit, cool! Share a demo. If not, let us know what you didn't like about it.

JMPGuitars wrote: ↑

Wed 10/04/23 9:26 am

Jason Patrick wrote: ↑

Wed 10/04/23 9:10 am

Anybody else…

You asked us about our experience, and the general consensus is that we do not use chokes in this circuit. No chokes, no NFB.

You're welcome to try it and see how it sounds. Historically the move was to reduce the H in the chokes used in similar circuits, and the choke Bieworm recommended is 4H, which is lower than yours, and the correct answer.

If you think your choke sounds awesome in the circuit, cool! Share a demo. If not, let us know what you didn't like about it.

Huh, that’s odd since the the guy (Soursound) who wound the 18 watt set also wound this choke specifically for the set and highly recommended a using it. I’m sure he just didn’t pull those numbers out of thin air.

Imho the odd thing is that your guy decided to use a choke, while none of the others ever did. The classic 18 watt or Marshall 1974 is based on the Watkins Dominator, which is without any form of choke AFAIK

Bieworm wrote: ↑

Wed 10/04/23 10:43 am

Imho the odd thing is that your guy decided to use a choke, while none of the others ever did. The classic 18 watt or Marshall 1974 is based on the Watkins Dominator, which is without any form of choke AFAIK

Man you guys get testy about this choke thing lol. If you know Soursound, you would know the guy is a mad scientist when it comes to transformers. He just doesn’t do something for no reason regardless if it originally came with one or not. If it was a perfect circuit as is, then why so many mods. Anyways, back to the forbidden choke, it’s closer the 5H so I will first build it exactly as stock and then perhaps wire in the choke and see what’s what. Maybe put it on a switch. To quote Bryan when I asked

“Oh man I changed the core shim on that thing so many times. Also at first I was shooting for 3.3H and it ended up being closer to 5H in the end, but my meat brain kept saying 3H for like a week!

Red/black is prob what you want. Tighter, more attack and more transient forward. But try the black lead as well! It’s a little slower, thicker, more for the “I want my 18w to work like a jtm45”

Jason Patrick wrote: ↑

Wed 10/04/23 12:09 pm

Man you guys get testy about this choke thing lol. If you know Soursound, you would know the guy is a mad scientist when it comes to transformers. He just doesn’t do something for no reason regardless if it originally came with one or not. If it was a perfect circuit as is, then why so many mods. Anyways, back to the forbidden choke, it’s closer the 5H so I will first build it exactly as stock and then perhaps wire in the choke and see what’s what. Maybe put it on a switch. To quote Bryan when I asked

“Oh man I changed the core shim on that thing so many times. Also at first I was shooting for 3.3H and it ended up being closer to 5H in the end, but my meat brain kept saying 3H for like a week!

Red/black is prob what you want. Tighter, more attack and more transient forward. But try the black lead as well! It’s a little slower, thicker, more for the “I want my 18w to work like a jtm45”

Nobody is testy here, you're overreacting to the fact that chokes are not typically used in 18W amps. We're stating things factually, and you're reading into it defensively. There's no need for that. You're welcome here, and you're welcome to experiment however you like.

You can of course, as I mentioned above: try it and see if you like it. If you like it, cool! If not, okay.

A guy that makes transformers, sold you an extra piece. He likes them? Cool. It's all subjective. Maybe you'll agree with him, and maybe you won't. It's all good.

Experimentation and tweaking are highly encouraged.

Thanks,
Josh

I’d like to add to this..
Subjectively stated I find the circuit pretty spot on perfect. We just like to tinker and twist. We’re no “if it ain’t broken, don’t fix it” types.. we’re more the “what if we do this or that to it” guys
And I’m pretty curious too about the results with the chokes. Heck, why not? soursound may be onto something, although I’m more a sweet and spicy dude

I'm curious, is this choke feeding the screens, or is it part of a CLC filter for main B+ to the output tube anodes?

Jack

TriodeLuvr wrote: ↑

Wed 10/04/23 2:22 pm

I'm curious, is this choke feeding the screens, or is it part of a CLC filter for main B+ to the output tube anodes?

Jack

It will take the place of the 1.5k (r30) dropping resistor.

Jason Patrick wrote: ↑

Wed 10/04/23 4:37 pm

TriodeLuvr wrote: ↑

Wed 10/04/23 2:22 pm

I'm curious, is this choke feeding the screens, or is it part of a CLC filter for main B+ to the output tube anodes?

Jack

It will take the place of the 1.5k (r30) dropping resistor.

I know, you said that earlier. Not all the 18W schematics here have a 1.5KΩ resistor in the power supply. I found one after searching, but still don't know if it's the one you're using. That's why I asked.

files/JMPGuitars_18W_TMB_Modern_Classic_Schematic.pdf

Assuming this is it, the choke will improve the regulation of screen and preamp voltage. The former may or may not be important given that there are 1kΩ resistors in series with the screens anyway. If this forum has taught me anything, it's that the engineering principles that I typically apply to designing hi-fi gear are at least 50% irrelevant in guitar amps. The amps Josh and others here build are well vetted and likely difficult to improve. The choke probably won't hurt anything, but I tend to think it's probably unnecessary in the overall scheme of creating a good amp.

Jack

TriodeLuvr wrote: ↑

Wed 10/04/23 6:45 pm

Jason Patrick wrote: ↑

Wed 10/04/23 4:37 pm

TriodeLuvr wrote: ↑

Wed 10/04/23 2:22 pm

I'm curious, is this choke feeding the screens, or is it part of a CLC filter for main B+ to the output tube anodes?

Jack

It will take the place of the 1.5k (r30) dropping resistor.

I know, you said that earlier. Not all the 18W schematics here have a 1.5KΩ resistor in the power supply. I found one after searching, but still don't know if it's the one you're using. That's why I asked.

files/JMPGuitars_18W_TMB_Modern_Classic_Schematic.pdf

Assuming this is it, the choke will improve the regulation of screen and preamp voltage. The former may or may not be important given that there are 1kΩ resistors in series with the screens anyway. If this forum has taught me anything, it's that the engineering principles that I typically apply to designing hi-fi gear are at least 50% irrelevant in guitar amps. The amps Josh and others here build are well vetted and likely difficult to improve. The choke probably won't hurt anything, but I tend to think it's probably unnecessary in the overall scheme of creating a good amp.

Jack

I’m using this schematic more or less.

I see, that's a little different. The screens only have a single 100Ω, and that's a stopper for HF stability. Not sure it's a good idea to eliminate the 1.5K, considering it might provide some protection for the screens. Anyway, under these conditions, a choke will probably only affect high power tone, and even then, mostly on sustained output. That's an educated guess on my part though. The difference might be difficult to hear.

Jack