Help with LP70S

[Briz Vegaas]

Hi guys, who know their tube amps?

Just turned on my LP70S and the right hand tube in the little bay at the front does a light show from its base. Bright and flickering like its arching or something. No sound or noise from the amp. I switched it off then on again a minute later and it did the same thing so it went straight back off.

Is this a failed tube pure and simple?

Yours in depressing silence

briz.

[analog brother]

yep, sounds like tube is gone.
replace and try again.
if still does it, problem is amp.

[ronenash]

Its definitely a tube problem. Some 6922 can't take the B+ voltage used in CJ amps. The flashing will stop once the tubes warm up but the tube will not last long if it does this. Are you using NOS tubes? I have never seen this with the EH tubes that are supplied by CJ?

I have seen it happen with amperex tubes in the past.

[Puma Cat]

Ron is right, there are some tubes that the LP70S just does not get along with. I'm using Ediswan 6922s in my amp with no problem, but had issues with other variants of 6922 back when I first got the amp.

[Briz Vegaas]

Thanks guys. My dealer in Brisbane has recommended that it needs to come in for a check up so that's what I will do. David at Caxton Audio is a bit of a guru, having designed and sold his own amps in the past. That's enough plugging for now. Let's hope it is just a tube, or that there hasn't been subsequent problems as a result of the tube failure.

It's times like this you wish the amp was a little lighter.

[ronenash]

Originally Posted by Briz Vegaas

Thanks guys. My dealer in Brisbane has recommended that it needs to come in for a check up so that's what I will do. David at Caxton Audio is a bit of a guru, having designed and sold his own amps in the past. That's enough plugging for now. Let's hope it is just a tube, or that there hasn't been subsequent problems as a result of the tube failure.

It's times like this you wish the amp was a little lighter.

I would not bother sending it in before putting in the tubes that came with the amp. I am confident it will work flawlessly.

[Briz Vegaas]

It was a store demo. Only the amp came with the amp. It had been around a long time. I will probably replace the set rather than just one of the 6922s, keep the good ones as backup spares. The 120s were new when I got the amp last year ( so apart from the tubes this should be under warranty). So, how does one know when buying tubes that they are in fact new. Lots of them are sold over the net.

I wondered that about cartridges as well. I bought a "new" never installed Dynavecter Karat D17 from a fellow audiophile in Sydney ( picking up from the post office tomorrow). In this case the seller is a website forum moderator so you think the risk is low but how would you know the item didn't have 500 hours on it once the box is opened Just to check it was ok. I would think the cart would have screw marks on it if installed but otherwise it's trust of some one you have never met. Tubes would be harder still. Mind you, a dealer could sell you used stuff as well, it's not always easy to tell.

I digress. Just having a paranoid moment. Although, did you know that your dog is far less likely to follow commands in the dark. It knows that humans can't see in low light and takes advantage of the fact. ( it's why I like cats a little more, you know that are being selfish.....but mine still seem to come when called....most times.....there are snacks or scratches to be had after all). Just because you are paranoid does not mean you aren't being followed. :-)

[ronenash]

Avoid eBay and buy from reputable dealers. upscale and partconnexion come to mind. We will pay more per tube but at the end of the day it will cost less since you will have 100% success.

[CJinSC]

Originally Posted by ronenash

Avoid eBay and buy from reputable dealers. upscale and partconnexion come to mind. We will pay more per tube but at the end of the day it will cost less since you will have 100% success.

I've had good luck with Upscale Audio as well.

[Briz Vegaas]

Well, better safe than sorry......but it was just a tube.

One thing to share. If you have a suspect tube don't swap tubes like you would swap speaker cables to diagnose a fault. If the bad tube has taken out circuits and you swap it with another one ( ie not with a spare one), you will just blow more more circuits where you put the faulty one. Apparently people do it without really thinking it through. Obvious when you think about it, but apparently it's not uncommon.

I didn't, but I'm a cautious newbie. A bit more arrogance and I might have done it as I did not have a spare.