Is there any merit in replacing the rectifier tube?

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Re: Is there any merit in replacing the rectifier tube?

Postby Grog on Tue Feb 24, 2009 10:20 am

I changed mine to Watford Valves Harma brand as I thought the rectifier might be going west, turned out to something else entirely, so I still have the Sovtek as a spare. Some say there is nothing is affected tonally changed by using a tube or not, but I read that Steve Grindod returned to tube rectification for its tonal qualities in the CC range, so maybe there's something in that. Replacing with a copper cap sort goes against the design idea, but I suppose whether to use a good quality tube or copper cap is down to personal choice at the end of the day.
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Re: Is there any merit in replacing the rectifier tube?

Postby OldSchoolDave on Tue Feb 24, 2009 1:02 pm

Mr. dB wrote:Copper Caps coming apart seems to be a common complaint.


Weber site wrote:While the filament and coating on the cathode of a tube rectifier are destined to eventual failure, a Copper Cap will last the lifetime of the amp when used properly.


Two conflicting statements :?: . So, they last a lifetime if they don't come apart?

Just bought a couple of CC's for experimentation. Now, I'm wondering if that was wise...

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Re: Is there any merit in replacing the rectifier tube?

Postby AirykB on Tue Feb 24, 2009 5:24 pm

From what I understand, a coppercap emulates a tube/valve with solidstate parts. The usual difference between a tube rectifier and solid state in an AC30 is that there's a bit more sag/compression with the tube. (just for clarification. not sure if everyone on this thread knew this...)

As far as heat reduction goes, there was no difference with the coppercap over a tube. (I actually couldn't tell any difference at all.)
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Re: Is there any merit in replacing the rectifier tube?

Postby Frankie Sixxxgun on Tue Feb 24, 2009 5:31 pm

Is a 5AR4 even getting taxed enough to sag in an AC30?
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Re: Is there any merit in replacing the rectifier tube?

Postby Grog on Tue Feb 24, 2009 5:39 pm

Frankie I think yuo're right. As I understand it the GZ34/5AR4 is up to it, so you will experience very little if any sag effect with an AC30.
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Re: Is there any merit in replacing the rectifier tube?

Postby AirykB on Tue Feb 24, 2009 5:55 pm

No it's certainly there. If you've ever played a 70s or Rose Morris AC30, you'll notice a difference in the feel of it. It's a little more noticeable when you jumper channels, but the difference isn't that huge.

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Re: Is there any merit in replacing the rectifier tube?

Postby jcs on Fri Feb 27, 2009 1:50 am

theres a reason mullard and amperex gz34 are getting pricier, they are great tubes that are in high demand.

there is no better gz34 on the planet and for the folks that can afford it $90-100 for a good used one that tests new is cheaper in the long run.

i rarely ever hear of a mullard-amperex gz34 failing.

i also like the 'feel and response' of mullard gz34 in my 63 tremolux and 66 princeton over any other gz34 i have tried,the usa 5ar4 a close second.
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Re: Is there any merit in replacing the rectifier tube?

Postby Scott S on Fri Feb 27, 2009 3:45 am

Frankie Sixxxgun wrote:Is a 5AR4 even getting taxed enough to sag in an AC30?


It *is* getting taxed in there. According to the schematic, the AC30 is drawing about 206mA at idle, 256mA at full power. That's just over the 5AR4's rated max of 250mA! The reason you don't hear much sag is that the voltage only drops about 10V from idle to full power...

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Re: Is there any merit in replacing the rectifier tube?

Postby P-Dawg on Fri Feb 27, 2009 4:01 am

AirykB wrote:From what I understand, a coppercap emulates a tube/valve with solidstate parts. The usual difference between a tube rectifier and solid state in an AC30 is that there's a bit more sag/compression with the tube. (just for clarification. not sure if everyone on this thread knew this...)

As far as heat reduction goes, there was no difference with the coppercap over a tube. (I actually couldn't tell any difference at all.)


I've just done a measured comparo with a lab grade Fluke digital thermometer on a relatively new (2 months old) AC30CC2 and I'm showing about a 20 degree drop in internal temperature when using a Sovtek SSR solid state rectifier as compared to a JJ GZ34. Conversely, removing the baffle that keeps the beer off the EL84s did not produce much of a heat reduction.
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Re: Is there any merit in replacing the rectifier tube?

Postby Frankie Sixxxgun on Fri Feb 27, 2009 4:25 am

So you're saying put the baffle on and get a solid state rec replacement? What about the Weber Copper Cap?
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Re: Is there any merit in replacing the rectifier tube?

Postby AirykB on Fri Feb 27, 2009 7:32 am

Mine's a JMI spec AC30, and I can't tell any difference heat wise. Perhaps there's some difference in operation between the CCs and the old ones?

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Re: Is there any merit in replacing the rectifier tube?

Postby AC50 on Fri Feb 27, 2009 10:36 am

Frankie Sixxxgun wrote:
Mr. dB wrote:I'd let the present rectifier run its course. When it finally fails, whether it's next month, next year, or five years from now, then consider finding a NOS one 'cause a healthy Mullard GZ34 will last for decades.

Oh, and have a spare on hand in case of sudden failure at a gig. Cheapo spare is fine.


Should I just suck it up now and put a Copper Cap in it?


I did.
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Re: Is there any merit in replacing the rectifier tube?

Postby AC50 on Fri Feb 27, 2009 10:43 am

AirykB wrote:Mine's a JMI spec AC30, and I can't tell any difference heat wise. Perhaps there's some difference in operation between the CCs and the old ones?

Eric


There are more tubes in a JMI, producing more heat. As far as I can tell, heat is no real problem with the AC30CC. You also don't have wax-insulated transformers, literally melting down in the CC.
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Re: Is there any merit in replacing the rectifier tube?

Postby blackba on Fri Feb 27, 2009 2:12 pm

The Rectifier tubes are known to not last too long in the AC30CC amps, so I would personally replace the rectifier. I went with a JJ GZ34. I just don't trust the Sovtek rectifier.

Ironically it was the stock EH EL84's that ended up failing, but the JJ GZ34 was fine.
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Re: Is there any merit in replacing the rectifier tube?

Postby Frankie Sixxxgun on Fri Feb 27, 2009 3:29 pm

AC50 wrote:
Frankie Sixxxgun wrote:
Mr. dB wrote:I'd let the present rectifier run its course. When it finally fails, whether it's next month, next year, or five years from now, then consider finding a NOS one 'cause a healthy Mullard GZ34 will last for decades.

Oh, and have a spare on hand in case of sudden failure at a gig. Cheapo spare is fine.


Should I just suck it up now and put a Copper Cap in it?


I did.


Any tonal difference in doing so? Did you go with any B+ reducing?
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