My 50 watt #183 with footswitchable FET build.

[martin manning]

You could wire a DPDT OD panel switch to interrupt the FET relay's internal ground path and get the same result without the foot switch. Another option would be to reverse the OD relay state for OD mode, and run the FET relay ground through the OD relay ground. Then you could add a switch to enable/disable FET boost in OD if desired.

[Matt J]

Ok... Here comes the fun part, "Diagnosing what's gone wrong"....

Finished up the OD relay and the heaters. Went through a test power up with my current limiter and a dummy load. Everything dimmed properly and there were no pops, sparks, or smoke. Ran it without the limiter and everything seemed ok. Voltages were their proper range and everything appeared well.

Hooked up this speaker and this is where the fun began. Switching from Standby to Operate results in an extremely loud BBBBBBBBBBRNNNNNNNNNNNNNN noise that doesn't seem affected by at all by any of the volume or other controls.

Could this possibly be the OT secondaries? Time to start double checking everything again....

- Matt J.

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[stelligan]

Hooked up this speaker and this is where the fun began. Switching from Standby to Operate results in an extremely loud BBBBBBBBBBRNNNNNNNNNNNNNN noise that doesn't seem affected by at all by any of the volume or other controls.

Could this possibly be the OT secondaries?

That would be a place to start. Usually more of a "squeal" or "shriek", in my limited experience. Only will take a quick second to prove. You might also check that your FET circuit is not engaged - my experience is even more limited there as I don't build them in.....

[Matt J]

Update:

IT'S ALIVE!

I was the OT secondaries after all. I switched them around and now it works as it should!

Quick observations:
- Engaging the PAB doesn't result any in a volume or tone boost. The volume drops and it cuts out most of the bass, so it becomes very thin sounding.
- The presence control has very little sweep to it, which really doesn't bother me at this point.
- I can't really make a judgement on the FET yet since I've never worked with one before. I'm going to have to play with it some more before I can really wrap my head around it. Your tone doesn't really get dirty as you turn up the trimmer, but it certainly adds life and volume to your signal.
- The OD has PLENTY of gain on tap. You can get near Marshall levels with those 250k controls, but you gotta be careful with it. It quickly becomes very noisy with lots of hum if you push that OD tube too hard. I've got the trimmer set at 22K per the original 183. I'll play with that later. (Any tips?) Any suggestions on a top quality OD tube to eventually try for V2 after the amp has some more burn in time would be appreciated too!
- You really need to have the bright switched engaged on either of the bright caps or it can sound a little flat.

I'm going to finish tidying up the wiring tomorrow morning and work on the OD and PI balance trimmers. Then I'll install it in the cab and try it at higher volumes outside so I don't blow out my windows! Still lots more to do!!

- Matt J.

[norburybrook]

the PAB should give you a volume boost so something's wrong there.


the FET is a crystal clean boost so it doesn't OD in itself it will just push V1 harder. If you want a bit of grit then have your volume set at about 2 O clock and the FET gain at 12 o clock or higher and it will give you a bit of 'hair' when you dig in.


the Presence is fairly subtle so don't worry about that. I quite like the accent switch on the earlier models it's either full on or fully off it's still a subtle thing though.



M

[norburybrook]

There’s a much easier way: Just run the ground path for the FET switch through the unused side of the (SPDT) OD switch in the footswitch. When OD is on, FET boost is inactive.

Martin,

could you draw that on here please? I'm not exactly sure what you mean.

3 switch footswitch wiring.bmp

here's what I think you mean.

3 switch footswitch wiring-no FET on OD.bmp

M

[martin manning]

Edit: Here's a version using SPDT switch as I had originally imagined:

[Matt J]

Here is how I wired the PAB switch. Anyone notice anything amiss?
- Matt J.

PAB Wiring 1.jpg

PAB Wiring 2.jpg

PAB Wiring 3.jpg

[norburybrook]

Almost. Like this:

thank you I'll give that a go.

Matt sorry to derail your thread. Actually as you've done the same i suppose it's useful to you too.


M

[Matt J]

Almost. Like this:

thank you I'll give that a go.

Matt sorry to derail your thread. Actually as you've done the same i suppose it's useful to you too.


M

No problem!! I think it's great that information on that topic is being discussed and shared!
Please feel free to post more on the FET topic if you want! Once I get the PAB issue fixed and spend some more time tweaking the amp, I might implement you or Martin's FET switching designs!

- Matt J.

[norburybrook]

Here is how I wired the PAB switch. Anyone notice anything amiss?
- Matt J.

PAB Wiring 1.jpg
PAB Wiring 2.jpg
PAB Wiring 3.jpg

I've never had the PAB on the jazz/rock switch so can't help sorry. Is that a #183 thing?


M

[norburybrook]

you're missing a jumper between the bottom right and center left on the DPDT switch.

actually your jumper is on the wrong pins.

Mat J switch.jpg

M

[Matt J]

you're missing a jumper between the bottom right and center left on the DPDT switch.

actually your jumper is on the wrong pins.
Mat J switch.jpg




M

Thanks M!

I've seen how the R/J switch is wired like that in the original #183 layout, but I've seen other builds that use a method like I have done. Could there be anything else I'm over looking?

- Matt J.

[norburybrook]

you're missing a jumper between the bottom right and center left on the DPDT switch.

actually your jumper is on the wrong pins.
Mat J switch.jpg




M

Thanks M!

I've seen how the R/J switch is wired like that in the original #183 layout, but I've seen other builds that use a method like I have done. Could there be anything else I'm over looking?

- Matt J.

Yes they're wired similar to how you did it because there's no Center off I would presume.

Check you have your bass and mid pot wiring correct as well, I've had the wrong wires from the board going to the wrong pots in the past with the bass and middle and it had a similar effect to what you described.

M

Sent from my Nexus 6 using Tapatalk

[Matt J]

I rewired the R/J switch to match the original #183 layout. I noticed on it that the lead from the bass cap to the switch attaches at the same solder point as the wire going to the bass pot. That's how I have wired mine.

The volume drop is no longer there, but it still doesn't seem that the PAB function is working. There's no change in volume or tone at all. I might have erred in using an On-Off-On switch in the first place and may just have to pull the whole thing out and replace it with an On-On switch.

Also, the FET now seems to be backwards. There's a volume drop when it is engaged. It's working, you can tell since the FET gain pot works, but switching it on just cuts out at least a third of your volume.

- Matt J.