Ralle mod fixes Power Brake!

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zeeb
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Re: Ralle mod fixes Power Brake!

Post by zeeb » Sun Jul 18, 2010 11:26 pm

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. :twisted:

cheers,

J
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Ralle
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Re: Ralle mod fixes Power Brake!

Post by Ralle » Mon Jul 19, 2010 9:20 pm

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. :twisted:

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...

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zeeb
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Re: Ralle mod fixes Power Brake!

Post by zeeb » Tue Jul 20, 2010 9:45 am

....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.

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Re: Ralle mod fixes Power Brake!

Post by hdahs » Thu Apr 19, 2012 6:45 pm

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

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Ralle
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Re: Ralle mod fixes Power Brake!

Post by Ralle » Thu Apr 19, 2012 10:30 pm

You don't have to remove the cap... simply shortcut the terminals... that'll put the cap and the choke out of the circut... :wink:
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 :wink:

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Re: Ralle mod fixes Power Brake!

Post by hdahs » Fri Apr 20, 2012 12:40 am

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

Thanks for you help!

Harold

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Re: Ralle mod fixes Power Brake!

Post by OdgeUK » Mon May 14, 2012 2:59 am

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?
73 JMP 1987 w/LarMar
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Re: Ralle mod fixes Power Brake!

Post by OdgeUK » Thu May 31, 2012 11:33 am

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?

Image

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.

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73 JMP 1987 w/LarMar
78 JMP 1987
79 2104
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Marshall 1936 G12-65
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Re: Ralle mod fixes Power Brake!

Post by axeman » Tue Oct 23, 2012 11:32 pm

Any warnings before I mod my Power Brake.

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Re: Ralle mod fixes Power Brake!

Post by bobtec » Sun Oct 28, 2012 11:26 pm

:thumbsup:

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Re: Ralle mod fixes Power Brake!

Post by axeman » Fri Nov 02, 2012 7:14 am

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?

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Re: Ralle mod fixes Power Brake!

Post by ampSnob » Sat Nov 03, 2012 2:12 am

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.

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Re: Ralle mod fixes Power Brake!

Post by jaeger28 » Sun Jul 09, 2017 7:00 am

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
:rock:

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Re: Ralle mod fixes Power Brake!

Post by jaeger28 » Sun Jul 09, 2017 7:07 am

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?

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