The First 80uF Cap In A Rocket

[rp]

Question / Poll: there is no last word on the web, but I'd like to pick brains here regarding what you are all using for the first filter. As my intent is to build a Rocket in the hope to sell, I don't want it blowing Sino/Russian 5AR4s, and I don't intend to sell it with my small supply of Mullards.

Seeing how 80uF stresses the rectifier I'm thinking KF didn't just use what he had on hand but really wanted the Rocket to be extra stiff, but not solid state stiff, so he must have found some sweet spot with a 5AR4 with 80uF. I'm a bit worried that if I stray I'll just wind up with an AC30 clone.

My in progress Rocket is laid out for a 35mm radial can, hard to find an 80 that isn't a small photoflash, so 32+32 would make my life easy.

-Have builders here experienced a notable difference in feel and tone with 80uF vs say 64uF (32+32)?

-Have people using 80uF had modern rectifiers fail or been short lived?

-Which modern 5AR4s have you found to be most reliable and having the correct voltage drop?

Last thought, with electrolytics having +- 20% rating 80mf could be 100mf - that can't be good for the rectifier, no?

[martin manning]

Some good discussion on 5AR4's here: http://music-electronics-forum.com/t26515/

[rp]

Hey Martin, great link. I had noticed that real Mullards gave the same forward drop as a solid state plug-in thing, and others didn't, and thought it strange (though I was aware of the early '90s 4 pin fake 5AR4s). Now I know why.

This is good to know too as if I wind up a little high in my Rocket, and as I am in my Lightning (340V plates) I could maybe drop it just a touch with a GE 5AR4 or a Ruskie etc, rather than using a 5V4. Unfortunately nobody in that post mentioned how hard you can hit the Ruby with the first cap. Think I'll build my rocket w/o a standby. Unless someone here strongly endorses 80uF I'll probably go w/ 64uF and aim for reliability. If things break people will blame me not the Chinese.

[randalp3000]

My Mazerati GT uses an 80uF and took out at least one JJ 5ar4.

[martin manning]

RP, you should be pretty safe with the standby located after the reservoir as shown in the Rocket schematic. The current will come on gradually as the rectifier filament warms up.

[Colossal]

RP, my understanding and experience with overclocking a GZ34 is that it is ok, so long as the amp is not approaching or pulling max current under load. Under Voxy/Rocket conditions, a GZ34 with capacitive input is good for about 250mA so a Rocket is well below that. I think it's sensible to measure electrolytics given the typical +20% tolerance in manufacture. My last AC30/Rocket build I used 40uF and I didn't think it was too stiff or too soft. You would probably be just fine with 64uF. I might try that next time. FWIW, Dr. Z uses 40uF for the reservoir cap in his ZWreck. This choice may be in response to concern over rectifier tube reliability or feel, or both. That amp is more softly filtered. While I have a small stash of Mullards, I have been using Sovtek 5AR4s with good results and reliability. I much prefer the sound of them over JJ GZ34s.

[cap217]

RP, my understanding and experience with overclocking a GZ34 is that it is ok, so long as the amp is not approaching or pulling max current under load. Under Voxy/Rocket conditions, a GZ34 with capacitive input is good for about 250mA so a Rocket is well below that. I think it's sensible to measure electrolytics given the typical +20% tolerance in manufacture. My last AC30/Rocket build I used 40uF and I didn't think it was too stiff or too soft. You would probably be just fine with 64uF. I might try that next time. FWIW, Dr. Z uses 40uF for the reservoir cap in his ZWreck. This choice may be in response to concern over rectifier tube reliability or feel, or both. That amp is more softly filtered. While I have a small stash of Mullards, I have been using Sovtek 5AR4s with good results and reliability. I much prefer the sound of them over JJ GZ34s.

You prefer the sovtek over the JJ, why? What do you notice?

[Colossal]

You prefer the sovtek over the JJ, why? What do you notice?

The Sovtek has more depth to my ear. By depth I mean the quality that sounds like reverb without having reverb in the amp; the three dimensionalness of the tone. The JJ just seems more bland to me, not bad, just bland. It just did not have the same depth as the Sovtek nor does it have the same feel to me. Nothing beats a Mullard and I use it as the benchmark, but the Sovtek sounds really good for a new production tube. I have not had any failures either out of the box or prematurely while in service.

[tubedogsmith]

I like the Sovtek 5ar4's best of the newer stuff too. I know of three of my rocket type builds that have been running over ten years now with the same Sovtek rectifier tubes.

[Firestorm]

I like the Sovtek 5ar4's best of the newer stuff too. I know of three of my rocket type builds that have been running over ten years now with the same Sovtek rectifier tubes.

Anybody have experience with the latest Chinese crop?

[Blackburn]

I've been wondering about the TAD 5AR4, which is advertised as a good copy of the Valvo/Mullard GZ34. Who makes that one? Is that just another from New Sensor?

[Firestorm]

I've been wondering about the TAD 5AR4, which is advertised as a good copy of the Valvo/Mullard GZ34. Who makes that one? Is that just another from New Sensor?

I think it's Shuguang. That's the one I was wondering about.

[Turbojunkie]

After blowing 2 JJ GZ34's, looks like a smaller res cap would be the way to go. Allyn had posted to put the standby switch between the 2 40uf's? Trying to learn about all this.

But with me for now:
I read somewhere that Ken would only ship Rockets with Mullard GZ34's, specifically the ones with 4 notches on the sides of the metal...I put in an old 4 notch Mullard I have, having no problems since, and the amp sounds and feels better.

But I also am not using the standby switch for initial turn-on or final shut-down anymore...just for on/off when hot...I read in the Merlin book about inrush current in the amp, and started doing that, as my tubes were flashing blue when going from standby to on, which he said was bad news...do you all think this makes sense, or no?

Good Luck RP, I'm paying attention to see what works best for you.

TurboJunkie

[Mark]

I have to make this decision with my Rocket, I'm inclined to put the standby between the two 40uF caps. I can either turn standby and power on at the same time or I can turn power on and then the standby.

So i like having a choice, I'm inclined to agreed with Merlin in that the choke will try and kill the standby switch, this could take years, either way it is a poor design choice.

[rp]

According to the music-electronics-forum link from Martin, the Ruby is the closest to the GZ34, but that discussion was 2008. I didn't know Ruby was a manufacture I thought they were just a rebrander.

Colossal, how'd you find the voltage drop on the Sovtek, pretty much the same as a Mullard, i.e. very little?

They only ~80uf radial can I could find on the planet is this:

http://www.newark.com/cornell-dubilier/ ... Capacitors

cheap too, on sale! but maybe too much effort to deal with from Italy, right now I think I'll just go with 32+32. Half the time I feel KF used what he had on hand but here he must have had a good reason to use 80uF. The fact that he was so hard-core about supplying an already rare 4 tab Mullard reinforces this. Adding even a touch more bass and stiffness doesn't just add more bass and stiffness, it skews the whole tone and feel of the amp. He must have liked what he heard.