Premier 4 tube selection and bias

[sjbellers]

I have inherited a CJ Premier 4 power amp, a PV4, Tiel CS 3.5 speakers and a Sonograph 3 turntable. I have an issue with the Premier 4. The left channel has all (4) USA made 6CA7 /EL34 fat bottle tubes and the right channel has a mix of (2) USA 6CA7 /EL34 tubes and Electroharmanix El34 tubes. I want to replace the right channel tubes, so they are all the same model tubes, but I don't know what to install. I've read that the USA tubes marked with 6CA7/EL34 are really EL34 Pentode tubes that were manufactured with dual markings because they are electrically interchangeable with either the EL34 or the 6CA7 tubes. The 6CA7/EL34's are fat bottle tubes, and looking at the tube wrapper internals, they resemble the EL34 tubes instead of the beam focusing 6CA7 tetrode tubes. I was hoping someone with experience could shed some light on this for me. Last week one of the EL 34 Electroharmanix tubes lost a filament and I replaced it with a spare EL34EH.
I set the bias on all tubes per the instruction manual where the Bias LED indicators would barely stay off at amp idle. I measured the Bias current and all tubes would draw 48 - 50Ma at Idle. I'd love to know if this is a typical current for these tubes. I have some electronic experience, at least enough not to get shocked or smoke the amp through stupidity, but I feel I really could use some help on this. C-J won't return calls or answer emails, so I feel all alone on this issue.
By the way the sound system is great, the sound it clear and realistic, so much so I close my eyes and swear Stevie Ray Vaughn is playing right in front of me.
- Regards, Steve B

[AnotherJohnson]

I think 50 mA sounds about right.

Why replace the tubes if it sounds great? This is not a good time to be in the tube market.

You’re right about not getting info from CJ. It’s pretty much a one man show, and that man is as busy as a one armed wallpaper hanger. It is his policy not to share technical information … he protects it from DIYers and unknown technicians, both domestic and foreign.

From CJ’s web site

IMG_0606.jpeg (37.7 KiB) Viewed 716 times

Replacement Tube Set RTPR4
V1 & V2: 5751 | V3 & V4: 6FQ7/6CG7 | V5-V12: EL34

[sjbellers]

Thank you for the response.
Normally I'd agree with the idea of 'if it ain't broke don't fix it' but I've had problems with the Electroharmanix EL34's that were installed in the right channel. A month ago V6 shorted and took the plate fuse with it. The man I inherited this system from had some spare EL34EH's so I replaced the offending tube. Fortunately, the man had also bequeathed me tube tester so finding the bad tube was easy. I replaced the tube with a spare and everything worked except the new tube would not bias down. I cranked the bias pot to its minimum position and still could not get the V6 bias LED to extinguish with the amp idling. So I replaced that tube with my last spare. This tube did bias correctly, but now I have no spares and a distrust of the Electroharmanix EL34EH brand, or at least that production run of tubes. I wish I could identify the 6CA7/EL34 USA tubes so I can try to locate this model tube. they are fairly old but appear to be really reliable. I wish I could identify if they are really 6CA7 or EL34 so I could decide what the tube characteristics were so that I could buy more of that model.
Also, since I measured all V5-12 power tubes idle bias current at 48-50ma I'd like to find if any other CJ owner member has similar current measurements. I really appreciated your info that 50Ma is probably alright. This is the type of tribal knowledge I find invaluable. I know from the Electroharmanix tube data sheet that max bias current is listed at 100 Ma, therefore my readings are probably alright with some headroom for bias to increase as power output increases, but is will 50Ma support long tube life?

[AnotherJohnson]

Premier 4 celebrates its 40th birthday this year (if I remember correctly).

I think you can take 50 to the bank … it’s surely not more than 56. 50 sounds right for that amp and those tubes.

You’re chasing a ghost trying to figure out the perfect OEM tube set. In the present market you’ll be lucky to find whatever you can. That doesn’t mean the quest might not be fun. If you want to chase down old CJ specs and parts, you’re definitely among comrades in arms.

Good luck. Maybe one of the guys who enjoys restorations will chime in.

[Tommd]

Hello sjbellers, I am also a proud owner of the Premier four; a great amp! I have both tubes the GE 6ca7 and the Tundsol el34b. First, always use the same tubes in the left and right channels. As far as I'm concerned, the Tungsol el34b or the TAD el 34 is by far the most beautiful tube. And above all enjoy the music!

[Tommd]

Keep in mind that after more than 40 years of loyal service, your power capacitors only measure half of their capacity. New and heavier capacitors give an enormous sound boost.

[Tommd]

Hello sjbellers, I am also a proud owner of the Premier four; a great amp! I have both tubes the GE 6ca7 and the Tundsol el34b. First, always use the same tubes in the left and right channels. As far as I'm concerned, the Tungsol el34b or the TAD el 34 is by far the most beautiful tube. And above all enjoy the music!

[sjbellers]

Tommd and Another Johnson - Thank you for the info. Currently my right channel is a mix of (2)EL34EH's at V10 and V12 and (2) USA 6CA7/EL34's at V6 and V8. That way the same tubes are looped into a push-pull arrangement. I can't tell the difference between the left and right channels sound making A/B comparison. I took great pains to match the Bias currents, so I don't think I can damage the amp. At this point I think I'll just put the cage back on the top of the amp and listen to some old Vince Gauraldi records. Again, thank you for the responses.

[SolderSlinger]

Another Johnson is correct, EL34 is 50ma. I had a Premier 4 a number of years ago and it had NOS Mullard EL34 tubes. Never had an issue with tube failure. Concerning tube suppliers, I've purchased tubes from well regarded suppliers and can recommend Parts Connextion located in Canada. They have a sale a couple of times per year.