Metropoulos Forum

aw that sucks, R. - Is that from too much use @ low levels? ...guess you mean the light green resistor in the pic below.

like the sound of screwing the replacements down - no fkkn around - post some pix if you have any!

thnx for the info - really shaves of that fur-nonsense.

cheers,

J

zeeb wrote:aw that sucks, R. - Is that from too much use @ low levels? ...guess you mean the light green resistor in the pic below.

like the sound of screwing the replacements down - no fkkn around - post some pix if you have any!

thnx for the info - really shaves of that fur-nonsense.

cheers,

J

No, that the 160uF cap that's shorted out of the circut... I'm talking about the big effect resistor... on the other side of that shield plate, there's two effect resistors... next to the tranny... there's an 8 ohm/100w( big one ) and a 56ohm/25w (smaller one ) Keep an eye on the bigg one... that's the one that takes the heat ffrom the amp...
I don't have any pics, sorry...

....10-4. ah yeah the giant one. gotcha. am going to dive in and check that out. screw those wires in there.

thnx for the adv warning!

cheers,

J.

Hi Ralle

I have a PB on my bench for repair. As it turns out this cap, 150uf100v NP, has blown in this unit. Can't seem to find a replacement at the usual sources.

Just wanted to make sure I understand correctly that this mod is simply removing this cap and shorting across the terminals?
Everything else looks good, and the 2 high wattage resistors, measure correctly.

Thank in advance.

Harold

You don't have to remove the cap... simply shortcut the terminals... that'll put the cap and the choke out of the circut...
And you can allso remove ( remove, not shortcut ) that green 10 ohm resistor below the 150u cap... it works like a sort of ground shield against hum ( if there is any )... but it allso steels some of the signal to ground... and we don't want that

Appreciate it. I removed the cap anyway, as it had given up the magic smoke.

Thanks for you help!

Harold

I'm thinking about buying a used Power Brake and performing this mod, instead of getting an 8-Ohm THD Hotplate. I currently use a 16ohm Hotplate for my 1987 heads but have changed my rig to 2x12 cab 8ohm setup.

Is this mod designed to improve any reliability of the Power Brake, or is it just to improve the 'tone'. Also...is this mod designed to just improve the sound at very high attentuation, or does it sound better right across the range?

And what does the cap that you short actually do? What is it's purpose in the circuit and are there any risks to removing it in terms of affecting the intended function of the Power Brake?

A used Power Brake is much cheaper in the UK than a THD Hotplate but opinion is strongly divided on which unit sounds the best.

I heard a Power Brake is only good for 100W. Although I only have 50w NMV heads, would a cranked superlead be too much for a Power Brake?

Ralle wrote:I'm talking about the big effect resistor... on the other side of that shield plate, there's two effect resistors... next to the tranny... there's an 8 ohm/100w( big one ) and a 56ohm/25w (smaller one ) Keep an eye on the bigg one... that's the one that takes the heat ffrom the amp...
I don't have any pics, sorry...

You must mean this one? On mine, the wire is mechanically wrapped around the solder tag as well as being soldered. What is the best thing to do to reduce the risk of this problem?



Just looking over my newly purchased Power Brake now to familarise myself with the innards in case I want to do this mod. On mine, the cap that I would short out is silver, with no writing on it, and has some black goo on it, to presumbaly stabilise it from movement. The same goo is on the similar sized cap further back on the board.

Any warnings before I mod my Power Brake.

OK I read the thread, I don't want to blow any of my transformers. How many of you guys are still modding your PB this way with no issues?

The power brake is not the best attenuator out there, but I think it's the most fun to muck around with. The topology is simple enough to make it take whatever you can think of and still do it's job. Replacing that undersized riveted on load resistor on that internal plate was a PITA though. Had to remove crap and drill them out…(insert swearing here)…but that's not really part of the mod.

Anyway, this mod is quick and easy. It does in fact make the power brake sound a bit better, so it's worth it IMO. No issues with mine.

Hi all,

just tried this and like the result. It's actually a bit too much topend now though. So I was wondering if - instead of a wire - one could use a pot to bridge the blue cap instead. So the bypass could be dialled in gradually.

What value of pot would that have to be, anyone any idea?

Thaaanks

I have done the bridge of the two pins.

Wondering if it would be possible to use a pot to dial in the amount of bypass of the blue cap.

If I'd wanna try it, what pot values would make sense on this kind of circuit?

I used a 47 uf 50w resistor across the terminals to keep some of the treble adjustment in there. Works pretty well. Tried 33 and 68 too. 47 was my preferred.