Rocker 30 "Cathode Resistor" mod.

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WALKEN
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Rocker 30 "Cathode Resistor" mod.

Post by WALKEN » Sun Sep 18, 2016 5:37 pm

I have 2 rocker 30 heads and have been thinking about swapping out the cathode resistors to (470ohm/6watts) but can't seem to locate these resistors in 6watts?

Also, has anyone done this and if so have you tried using 6550's? My old jcm800 2210 came stock with 7025's and 6550's (GT) and the sound was beautiful to me. Just curious how it would sound in the rocker 30.

Any real information would be wonderful, thank you.

jontheid
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Re: Rocker 30 "Cathode Resistor" mod.

Post by jontheid » Sun Sep 18, 2016 8:42 pm

Why not use 7 watt 470 Ohm resistors then?
These are readily available.
Having cathode resistors with more power handling capability is not going to be a problem.

WALKEN
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Re: Rocker 30 "Cathode Resistor" mod.

Post by WALKEN » Sun Sep 18, 2016 10:18 pm

Ade Emsley suggests 6watts

"KT88`s will work in a Rocker 30 head but they wont fit in a combo as they will hit the speaker! You will also need to change the cathode resistors from 330ohm and 270ohm 4W to 470ohm and 470ohm 6W!
The Rocker 30 head will then run on KT88/KT66/6L6/5881/6550 with slightly different power and tone!"

Hence why I'm seeking out 6watts. Maybe there is a reason why?

jontheid
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Re: Rocker 30 "Cathode Resistor" mod.

Post by jontheid » Sun Sep 18, 2016 10:57 pm

The important thing to remember is that a 7 watt 470 ohm resistor will behave in exactly the same way as a 6 watt 470 ohm resistor in the Rocker 30. It can just handle dissipating one extra watt of power. You could put a 50 watt 470 Ohm resistor in and it would behave the same.

Wattage ratings for resistors are merely an indication of the power they can dissipate. The power dissipated by a resistor with a d.c. voltage across it (such as the voltage across the cathode resistor) is volts squared x resistance.

Ade has recommended using higher-power 470 ohm resistors (higher than the standard 4 watts) as presumably when using KT88s the cathode resistors will dissipate more than 4 watts, and less than 6 watts.

Hope this helps,

Jon

ps you are in the enviable position of being able to modify one Rocker and compare it to the other, unmodded one!

Jondog
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Re: Rocker 30 "Cathode Resistor" mod.

Post by Jondog » Mon Sep 19, 2016 12:43 am

Just go with 5 watt resistors.
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WALKEN
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Re: Rocker 30 "Cathode Resistor" mod.

Post by WALKEN » Mon Sep 19, 2016 1:02 am

"ps you are in the enviable position of being able to modify one Rocker and compare it to the other, unmodded one!"

I suppose. I guess I should mod the "non" limited edition one for the sake of originality. They are both in brand new condition bought by me from Humbucker music years back. Funny thing is I loved them when I first got them but ever since I got my Radial plexitube I just get bored playing through the rocker30..

Maybe I am more of a Marshall tone person after all? Its almost like the Rocker becomes fatiguing to my ears. It has this low/mid range snarl/attack rather than a sharp bite if that makes any sense?

I guess the goal is to replace the El34's with 6550 to clean up the natural channel and try the plexitube in front of it.

fiveightandten
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Re: Rocker 30 "Cathode Resistor" mod.

Post by fiveightandten » Mon Sep 19, 2016 9:13 pm

The Rocker 30 isn't going to sound like a Marshall if you put 6550s in it. It's a completely different amp. You have 2 of them. Rather than modding them, I would suggest selling one and using the money to buy the amp you do want. It sounds like that's a Marshall.

And if you must mod the amp, i'd recommend getting someone to help you that is familiar with this. I don't mean any offense, but it sounds like you don't really have experience with working inside an amp. In a PCB amp like this, replacing the cathode resistors is actually a pretty big job. As others have said, you can use a 7W, or even get away with a 5W. But you need to use something that's physically the correct size for the lead spacing on the PCB. These big resistors get hot, so you can't lay it directly on the board, and they're heavy, so you shouldn't just throw a huge one in there with the leads bent in all sorts of directions to get it to fit.

Also, don't forget that the primary impedance for the output transformer is designed for EL34's, not 6550's.

-Nick
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WALKEN
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Re: Rocker 30 "Cathode Resistor" mod.

Post by WALKEN » Wed Sep 21, 2016 6:05 pm

Nick,

your making a whole lotta sense buddy :)

I don't even know what I should sell them for? I bought them both as I said from Humbucker music, the white limited 2009 was $1450 and the straight up orange tolex one was $1250. They have never left my house and pretty much have been in their original boxes in a controlled smoke free climate not being used. I take the orange one out from time to time to a/b other amps. But as I said the radial tone bone is where its at for me, I can shape the tone I want at will hence I can mock the R30 and blind fold you and you'd be none the wiser.

I have read somewhere not to discuss selling on this forum, but the Rocker 30 is discontinued so I believe that means fair game to discuss prices etc?

Your probably right though, I should just leave well enough alone, just trying to justify keeping them. I owned plenty of amps over my 39 years of playing guitar and I will admit the Rocker 30 does have a great tone!

Edit, holy smokes Nick I just noticed your in CT, so am I, wow small world.

fiveightandten
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Re: Rocker 30 "Cathode Resistor" mod.

Post by fiveightandten » Wed Sep 21, 2016 8:47 pm

WALKEN wrote:Nick,

your making a whole lotta sense buddy :)

I don't even know what I should sell them for? I bought them both as I said from Humbucker music, the white limited 2009 was $1450 and the straight up orange tolex one was $1250. They have never left my house and pretty much have been in their original boxes in a controlled smoke free climate not being used. I take the orange one out from time to time to a/b other amps. But as I said the radial tone bone is where its at for me, I can shape the tone I want at will hence I can mock the R30 and blind fold you and you'd be none the wiser.

I have read somewhere not to discuss selling on this forum, but the Rocker 30 is discontinued so I believe that means fair game to discuss prices etc?

Your probably right though, I should just leave well enough alone, just trying to justify keeping them. I owned plenty of amps over my 39 years of playing guitar and I will admit the Rocker 30 does have a great tone!

Edit, holy smokes Nick I just noticed your in CT, so am I, wow small world.
Small world indeed!

Yeah, I wouldn't mod it. If you only had one, I could see it being justified. But based on what you're saying, i'd bet that you'd mod it and still not quite be happy with it. Then you'd have money into a modded amp, and have to spend money again bringing it back to stock, or trying to sell a modded amp (greatly reduced buying demographic).

If you google pictures of "Orange Rocker 30 chassis", you can have a look at what's entailed. The entire circuit board needs to come up to replace the cathode resistors. All the pots and jacks need to be unscrewed, the wires with push on connectors need to be labelled and removed, and the PCB standoffs need to be unscrewed. Then the board can be carefully lifted up. Personally, I don't like messing with these things. The PCBs aren't *that* nice, and there is a finite amount of times you can flow solders on a given point before the trace starts to fall apart. Then things become a real pain. That's just my opinion though. Maybe someone can surmise some good logic behind modding it. Haha. In my book, there are TONS of great amps accessible to everyone these days. If you have something that you're not bonding with, move on to the next thing and try again.

Anyways. I sent you a PM with some selling data from eBay and Reverb. Based on your description, i'd say either one of your amps would be valued at the top of the market. Though i'd keep the white one, as it sounds like you may be partial to that one. I may very well be interested in buying one of them from you.

-Nick
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WALKEN
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Re: Rocker 30 "Cathode Resistor" mod.

Post by WALKEN » Wed Sep 21, 2016 10:02 pm

Thanks Nick for the valuable information. I'm not afraid to tinker around but as you put it, its not as easy as just unsoldering a couple resistors and soldering them back in. I guess they will sit in the boxes unless someone wants them?

Jondog
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Re: Rocker 30 "Cathode Resistor" mod.

Post by Jondog » Thu Sep 22, 2016 1:45 am

Could always try KT77 or 6CA7's. I really liked 6CA7s in the rocker.
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WALKEN
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Re: Rocker 30 "Cathode Resistor" mod.

Post by WALKEN » Thu Sep 22, 2016 1:54 am

Jondog wrote:Could always try KT77 or 6CA7's. I really liked 6CA7s in the rocker.
This is true. How was the tonal difference in your words?

Jondog
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Re: Rocker 30 "Cathode Resistor" mod.

Post by Jondog » Thu Sep 22, 2016 2:43 am

6CA7s have a bit more lows and highs or less mids, rounder/fuller. Not like a 6L6 though, still in the EL34 range.The KT77s I tried once, didn't use very much. I don't recall much of the detail other than thinking they were kind of neutral sounding.
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Re: Rocker 30 "Cathode Resistor" mod.

Post by WALKEN » Fri Sep 23, 2016 1:30 am

Jondog wrote:6CA7s have a bit more lows and highs or less mids, rounder/fuller. Not like a 6L6 though, still in the EL34 range.The KT77s I tried once, didn't use very much. I don't recall much of the detail other than thinking they were kind of neutral sounding.

Ade Emsley mentions that the 6ca7 is a military grade el34, not sure if he is correct or not? I'm glad I inquired about this mod as Nick pretty much summed it up for me, better off leaving them alone. In fact I'm just going to give them to Nick, lol :D Seriously though whoever ends up with these 2 amps will be happy as they are as near to brand new as you can get without buying brand new.

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Re: Rocker 30 "Cathode Resistor" mod.

Post by Stymie13 » Sat Sep 24, 2016 2:06 pm

I put KT88s in my R30 a couple years back and love it. I'm sure there's an older post with photos somewhere on the forum. I went with 10W cathode resistors which were tricky to fit onto the board but I had the amp disassembled to install a 50W output transformer anyway. While more dynamic and clearer, even with KT88s and the Plexi-style OT, it still sounds and feels like a Rocker 30. Neither the tubes nor tranny changed the actual voicing of the amp.
Rocker 30
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