How to know when your 300b's need replaceing

[LGarfirth]

Hi, I have a pair of WAD 300b PSE monoblocks that I built a couple of years ago. I have noticed the volume has dropped and although they still sound lovely I now have to turn the pre-amp up much louder than I used to.

I have replaced the two small valves on the front end but this hasn't corrected the volume.

How can I test the 300b's to see if they need to be replaced without a valve tester.

Just in case you want to know

- All heaters are powered DC
300b's are JJ been running 8 hours a day for about 2 years

[John Caswell]

Hi LGarfirth,
Well 8 hrs a day for 2 years at say 5 days a week = 4160 hours so I would guess well worn out and at 7 days a week = 5840 hours so I would change them.
Conditions vary considerably of course but a good average is 2000-2500 hours before replacement. It may of course be the 5U4G rectifier valves also, but there you can at least measure the HT line
Unfortunately the only way to check the 300Bs is on a valve tester.

Regards

John aka Dr John

[LGarfirth]

Thanks for the reply.

I will check the HT's and report back.

Also I will attempt to get a valve tester off EBay although I haven't a clue how to use one.

I have noticed some articles claiming DC heaters on 300b's can also reduce the life - is this true.

[Greg.]

It might be worth posting or adding to your profile where abouts you are. There might be someone around the corner with a valve tester happy to help you out.

Best wishes,

Greg

[Darren D]

Originally Posted by LGarfirth

Thanks for the reply.

I will check the HT's and report back.

Also I will attempt to get a valve tester off EBay although I haven't a clue how to use one.

I have noticed some articles claiming DC heaters on 300b's can also reduce the life - is this true.

You have a valve tester, it's called your amp!

Measure it's dissipation, the more worn it is the less current it will draw.

You can work this out from either the load resistance ( output transformer ) or the cathode resistor (if it has one). Cathode is prob easier.

[pre65]

Hi-now i have got the "hum" on my 300b se down to a respectable level i have decided to try a pair of the "gold" ones on e-bay.

http://cgi.ebay.co.uk/ws/eBayISAPI.d...e=STRK:MEWN:IT

i will try these before making a firm decision on the Rankin 45 DC CC.


Philip

[andrew ivimey]

Hear hear Darren.

And Philip 300bs and 45s really are as different as chalk and cheese. I agree with everyone else though that EH GGs really are worth their money.

[prince of darkness]

That seems a great bargain, but I notice this same seller is slightly cheaper if you pay in Euro's.

http://cgi.ebay.co.uk/NEW-Electro-Ha...QQcmdZViewItem

[david counter]

I agree Andrew,

300bs were a phase I had to go through before I discovered 2A3s and 45s

[pre65]

Hi-as i already have the amp i might as well see what it is capable of !

Philip