Next Build Coming Up - 183 50w

[Raoul Duke]

Been sorting through the stuff one accumulates when fiddling with these electric guitar amps and figured out I have quite a bit of stock on hand to start a 183 two-holer. Been thinking about one for a while, but couldn’t find the motivation to sit down and go through the project until I realized how much of a head start I have.

Here’s the rough idea:

* 50 watt head
* Magnetic Components P-TM-50 Marshall type PT (bias coming off the HT)
* Mojo tone 3k4 Marshall type OT (left over from my JTM which got the Marstran RadioSpares OT)
* Precision Power Supply
* “Rock/Jazz” with PAB in the middle
* Two way Bright switch
* Pretty true to the documentation here on TAG
* AN chassis more than likely

I’m trying to take all my lessons learned from previous builds and approach this one with more forethought regarding component choice, board design, lead dress etc.

Started making and assembling some boards using leftover FR4, so they won’t all be the same color - which is fine by me. Also making my parts lists as I’ve done for other ODS builds and really have forgotten how labor-intensive just getting one of these builds organized is - but that’s part of the process - all of which I enjoy.

Here’s what I have so far with what’s on hand:

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I think I have most everything for the relay board as well; that’ll be tomorrow’s project.

Any notes, info, or anecdotes regarding 183 are welcome. Been reading everything I can find here about it and feel ready to embark on another ODS adventure, lol.

Stay tuned…

[Raoul Duke]

Ok, got my first question about this design. I see on the layout it specs the standard Fender-like 4 henry 90mA choke. Is this optimal for the circuit or more of a Dumble bench mark for choke value - regardless of the circuit?

Comparatively, I see that this value is pretty versatile and can fit a number of applications - just curious mostly.

Thanks!

[martin manning]

Good start! 4H 90 mA choke is the standard Fender 50 and 100W, Marshall tended to use larger inductances and 4-bolt mounting style, i.e. 5H 120 mA for 100W. I don't think the value is too critical.

[Raoul Duke]

Understood and thanks Martin!
It seems that 183 has had small changes throughout its life since Tony and Shad put together the layout and that a few folks on this board have been inside it (based on some of the posts I’ve read) and pointed out those changes. Nothing too big, but I wasn’t sure so thought I’d ask.

Decided to go with some solid core PTFE from Apex Jr for this build. They seem to have the best deal for such stuff. Just showed up today and looks pretty nice.

[Raoul Duke]

Yesterday’s progress:

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Last set of Hoffman relay boards - I knew I bought them for something; just didn’t know what at the time. Super adaptable, convenient, and well made.

Ordered my chassis yesterday - should see it tomorrow I’d reckon as Amp Nation is only about 60-ish miles north of me. Thinking of grey suede cab, black front panel with white piping. Too cold and snowy to drag the saws outside - so I have time to change my mind a few times, lol.

[Raoul Duke]

Random question:

Who was 183 originally built for? I figured I’d learn the whole story seeing how well documented it is but I still haven’t found that nugget.

Anybody?

[Raoul Duke]

Got some parts today and was able to complete the FET board and attempt biasing. Here’s what I got following the most updated FET guide in the files using a 2N3823 FET (because I had one on hand).

Looking for low Vd with 9k R1, I used the 9V power option and dialed the 10k pot down to 3.3v across the 10k Rd using a fresh 9V battery that measured 10.1V. Measured the pot and it read ~ 6.8k, so I installed a 5k1 Rs and tried the test again with a result of 4.5v.

I’m thinking I need a bigger resistor to get closer to 3.3v, but 5k1 seems higher than what I expected.

Is this because I used a different FET?

[martin manning]

Looking for low Vd with 9k R1, I used the 9V power option and dialed the 10k pot down to 3.3v across the 10k Rd using a fresh 9V battery that measured 10.1V. Measured the pot and it read ~ 6.8k, so I installed a 5k1 Rs and tried the test again with a result of 4.5v.

I’m thinking I need a bigger resistor to get closer to 3.3v, but 5k1 seems higher than what I expected.

Is this because I used a different FET?

JFETs are notoriously inconsistent in their biasing, which just comes down to variations in the manufacturing process. Per the FET bias guide, a 50% drop in voltage across the drain resistor will result approximately a center bias condition, Vdd/Vd = 2. A larger ratio, 2.8 say, will result in an off-center bias and more FET distortion.

If I understand correctly:

In your test with the pot at 6k8 you had 10.1/(10.1-3.3)=1.49

Right now with the 5k1 you have Vdd = 10.1 and Vd = 10.1 - 4.5 = 5.6, so Vdd/Vd = 10.1/(10.1-5.6) = 2.24

Not a bad place to start, but if you want more FET distortion you can decrease the 5k1.

[Raoul Duke]

Understood, thanks Martin - I was thinking I’d leave it and fine tune once it’s getting B+5. In every ODS I’ve built it seems like the FET always sounds a little better after some sound testing and tweaking; which I’d assume is how HAD likely approached it as well.

I understand what you mean about the FET manufacturing tolerances also - looking at my previous notes and reading others’ experiences, they seem to be all over the place. Luckily we have your bias methods to get us in the ball park!

Thanks again! Onward…

[wsaraceni]

what's the all in budget on something like this? im considering starting a build like this and I know im way in over my head but cant hurt to just jump in the deep end.

[GAStan]

what's the all in budget on something like this? im considering starting a build like this and I know im way in over my head but cant hurt to just jump in the deep end.

In my personal experience with 100 watt amps using chassis such as AN offers easily $1,000 to $1,500. Even more depending on things such as iron chosen or cabinet, current production or NOS, etc...

My suggestion is start by pricing major items such as iron, chassis and tubes. Then work on pricing smaller items such as components, pots, switches, knobs...these seemingly small items add up quickly. All of the online places allow you to populate a cart or basket free of charge so pricing the smaller items, while time consuming, isn't difficult.

[Raoul Duke]

My experience is pretty much as Glenn describes (and he gives great advice above) - the only variable for me is that as I’ve been focusing on this as my main “in door” hobby for the past few years; I’ve been able to accumulate stuff at value over time by keeping an eye out and planning way ahead.

The PT I’m using for this build is a good example. I bought it on the board here brand new from Taylor/Amp Nation a few months ago for a huge discount because he needed them out of his way. I knew a 183 or another Marshall build would hook me eventually - so I jumped on it.

Generally speaking the biggest costs are the transformers, chassis, and cabinet if you don’t do woodworking. Everything else is relatively inexpensive - although it does add up with the high parts count in a “D” style amp. In my opinion, you need good transformers - period. For a “D” clone (again, my opinion) the top notch quality and aesthetically accurate chassis you get from AN is well worth the cost. I got a couple from Erwin a few years ago and they were great as well if you’re in the EU. I also build my own cabs and boards because I enjoy doing it. Takes longer, but I find it rewarding - and I have the time.

[wsaraceni]

what's the all in budget on something like this? im considering starting a build like this and I know im way in over my head but cant hurt to just jump in the deep end.

In my personal experience with 100 watt amps using chassis such as AN offers easily $1,000 to $1,500. Even more depending on things such as iron chosen or cabinet, current production or NOS, etc...

My suggestion is start by pricing major items such as iron, chassis and tubes. Then work on pricing smaller items such as components, pots, switches, knobs...these seemingly small items add up quickly. All of the online places allow you to populate a cart or basket free of charge so pricing the smaller items, while time consuming, isn't difficult.

That’s definitely cheaper than what I thought. I do have to plan though. I found from my previous amp and pedal build experience that forgetting a few resistors and paying $20 for shipping. Or shipping from 10 different vendors is what kills the cost. I guess that seems realistic though because with AN chassis and board being $300. Transformers being $3-500. And chassis being a few hundred. The rest is prettt small.

[dbharris]

Agree with above. Cabinet and speaker(s) if you need them are also higher cost items.

-Dan

[Raoul Duke]

Speaking of chassis - got mine today and it’s fantastic. These Amplified Nation chassis really are very well done!
Now the figuring out begins. Marshall type transformers aren’t really “plug and play” in these chassis…

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I think I have 2 choices:

1. Adopt the Marshall JMP transformer configuration.

2. Get out the headphones and see where I end up.

Not sure which way I’ll go - guess I’ll sleep on it and decide tomorrow. What would you guys do?