Cary Rocket 88R bias setting with EL34 tubes?

You should contact Gerald Walsh @ Cary @ 919-355-0010 and ask about the bias and tubes. Sometimes their opinion varies from the manual. I had a V12R with EL34's that I liked (you could cook a burger on it) now I have a CAD 120s w KT88's. It's hooked up to an SLP98P and the sound is fantastic, and it runs much much cooler. Good luck.

Cary amps usually do not have one bias pot for each tube. Some of thier amps gang two tubes per pot, and some will gang 4 or on some older ones 6, tubes. So you have to start out with a matched pair, quad or sextet, and set them using one pot (per channel). I do not have the Rocket 88, but as I recall it has four tubes per side. 6550's are usually biased at 50ma per tube, 4x50 = 200ma. My Cary mono amps have two 6550's on each with a ganged bias pot and have a manual recommendation of 100ma.

Each type of power tube does have a different biasing requirement. So you would not bias small power tubes anywhere near the same lelvels of the larger ones. Exact bias setting though can be varied to the tonal expectations or longevity expectations of a user. Lower the bias setting and the tube may sound a bit cooler and last a lot longer, increasing the bias a bit will usually increase the sense of warmth and reduce its life. Increase it too much and you will really shorten the life span and increase the probibility of shorts/tube failure. Reduce the bias too much and you will create distortions etc.

I've usually biased EL34's (in my Cary, but other amps as well) at about 30 to 35ma per tube and it has worked fine. So if your Rocket 88 has four 6550's biased totally at 200ma, and you are in a hurry you can probably do this without a problem (ie not damage anything), but bottom line - you'll get a lot better and more specific recommendation if you talk to Cary.

Hope that helps a bit.

Thank you both for your responses.
Yes Newbee you're correct the Rocket 88R has one bias pot for the four output tubes.
I'll take your advise & email Cary directly, & post their recommendation for others who may have the same question.

Many thanks.

Interested in what you learn, Halo. I just bought this amp, pls post your findings.

Hi All,
This very quick response from Gerald @ Cary Audio Design.

John,

You may also bias EL34's to 200mA's DC for the CAD 808( Rocket 88). Cheers!!!

Gerald Walsh
Cary Audio Design
1020 Goodworth Dr.
Apex, NC 27539
919-355-0010 Ext.105
919-355-0013
www.caryaudio.com