Power required for a Belton Brick reverb unit

[5thumbs]

Hi gang,
I just picked up one of the Belton Digilog Reverb Modules. I want to add it to my 5f2 Princeton Tweed build. It calls for 5v regulated power. Could I pull the power off of my rectifier heater or does it use DCV? What could I use to drop and regulate the correct voltage if i were to pull it off the power transformer? Any thoughts on the best way to implement this would be greatly appreciated!

Thanks ahead of time!
Tim

[Ken Moon]

If it says "5V regulated power", it probably requires 5VDC, not AC. I'm surprised the data sheet isn't more specific than that.

One easy way to get 5VDC is to tap off your 6.3VAC heaters - use a W005 (or similar) bridge rectifier, a 7805 regulator and a couple of caps (look on 7805 datasheet/application notes for values).

This web site has an example of how to use a 7805:

7805 Regulated +5V Power Supply

[Ken Moon]

I should have mentioned that the Reverb unit's data sheet should also say how much current the module uses - the W005/7805 circuit can handle up to about 1.5A with a good heatsink.

Here's a quick schematic - the 4700uF cap may not need to be that big, depending on how much ripple you can tolerate.



btw, Merlin's latest book on power supplies explains this and similar circuits in great detail, including good info on mounting and heat sinking, in case you're not used to using this type of component. He also includes regulated DC circuits that can supply more current than this one.

[5thumbs]

Thanks for the info Ken!

So I shouldn't use the 5V rectifier tap on the transformer with this?

Who is Merlin BTW?

Tim

[Ken Moon]

Merlin is Merlin Blencowe - MerlinB on here - he has 2 great books on tube amp design, and his latest is on power supplies (his website is full of good info too:

How to design valve guitar amplifiers

And no, you shouldn't use the 5VAC rectifier tap on your PT.

The 7805 (or any) regulator needs about 8 volts on the input to stabilize at 5v on the output.

The 6.3VAC, run through a bridge rectifier, will get about 1.4 times 6.3, or around 9VDC, which will work.

[5thumbs]

Thanks again Ken!
I appreciate you taking the time to explain this to me (I'm not the brightest bulb in the bunch! ha!)

Tim

[Bruce / Mission Amps]

He means not to use the 5v rectifier tube's filament lugs because there is very very high voltage DC on either lugs, 2 or 8 when the rectifier tube is conducting...
Also... if you use the amp's 6.3vac winding, say off of the pilot lamp assembly... what is the consequences of the filament winding being center tapped or having a virtual center tapped and referenced to ground, with respect to the new FWB's anodes being grounded?

[Steve Conner]

what is the consequences of the filament winding being center tapped or having a virtual center tapped and referenced to ground, with respect to the new FWB's anodes being grounded?

I don't know, but I can bet it involves a lot of magic smoke, almost as much as using the 5V rectifier winding would.

I tried running a digital reverb off the heater voltage, but never had much luck. The reverb module has a shared ground for signal and power, and there's no way (I know of) to ground it so that you cancel both heater hum in V1 and rectifier buzz in the reverb.

[Ken Moon]

Thanks for chiming in, guys

I thought he meant to use an unused 5V secondary - I can imagine bad things would happen if tapping 5V right off the tube rectifier!

So I was thinking more about the voltage requirements than the implementation - thanks again for catching that.

As far as the 6.3V winding, I'm having trouble visualizing what the effect of the artificial center-tap (or a center-tapped winding) would have when the lower side of the FWB is connected there.

The reverb module just needs a stable Vcc of 5V to operate - could the "ground" be floated or referenced somewhere else, to eliminate the problem?

I would just add a small tranny if I wanted to use one of those modules, but then again we're talking about a tweed Champ here, so not much extra room...

[J M Fahey]

You can't use a normally connected 6.3V filament secondary as shown, because the rectifier shorts each secondary half alternatively.
Lots of magic smoke.
You need another 6.3V winding, floating, (not connected to anything else), so you can ground safely the negative capacitor leg.
You *might* use a free 5V winding if available but I suspect you would not have enough "extra" voltage to drop through a typical 5V regulator.
Best bet would be to add somewhere a small unobtrusive 6.3V , 250mA transformer ; typical classic tube amps have a lot of real estate.
That reverb module can't use much more than 20/30 mA.
I *think* those Belton guys must have solved the digi-vs-analog grounding; they are big in their market and want to sell millions of them, I trust they did their homework.
Edit: I just noticed you are talking a Champ here.
Smaller than I thought, but, hey !!!, a "real" tank would take up a lot more space anyway .

[5thumbs]

Okay, this looks a lot more daunting than I thought! Besides the power, would I have to create some kind of op-amp drive and recovery circuit or is that imbedded in the Belton brick? And I thought this was going to be easy;-)

Thanks for all the help!

[Enzo]

DO you have the data sheet on the part? Doesn;t it have a sample circuit? Looks to me like apply power, and connect the in and out lines.