View Full Version : Replacing valves

Iain Sinclair
03-05-2008, 21:03
Right, that's enough banter, now for a serious question.

I have a suspicion that one or more valves on my power amp needs replacing. On one channel, on some CDs, there's a sort of 'rustling paper' noise in the background. It's not there when I listen on headphones.

Now, as far as bits of amps are concerned, I am about as clueless a n00b as it's possible to imagine. I have just enough sense not to poke about inside high voltage equipment, but that's my limit.

So my questions are thus:

1) Does this sound like an early symptom of valve failure?
2) If so, how easy is it to source and fit replacements (I understand there's a process called 'biasing' but don't know what's involved)
3) Or would I be better off getting someone competent to do the work for me?

Any advice welcome.

Ali Tait
03-05-2008, 21:29
Hi Iain,
It could be a dodgy valve,but sounds like it could also be a capacitor or resistor going u/s.What amps are they,and what's the valve line-up? A good way to check valves is to swap one valve pair at a time between channels and see if the fault follows the valve i.e. the noise comes out of the other speaker.Switch off between changes! If,when you've tried this with all the valves and the noise still stays on the same channel,then it's something else. Also,how long have you had the amps? Do you have an idea of how many hours the valves have done? They don't last forever,and you will get degredation in the sound over time,but this can be quite gradual so not very noticable.If it is a valve,replacements are readily available from a variety of sources.I'll advise some good places when I know what valves you are using.Biasing is easy if you have a multimeter,or are there mA meters on the amps?


03-05-2008, 21:33
Could also be grubby valve pins.

Ali Tait
03-05-2008, 21:43
Yep,good point Al.

Iain Sinclair
04-05-2008, 15:29
Right, facts as I know them:

The amp is a Border Patrol 300B SE. It has two large 300B valves; four small EZ80 valves and one middle-sized valve with illegible writing on it. I bought the amp 3 years ago, but I believe it dates from around 1995. The previous owner replaced some of the valves; I have an email somewhere with the details of exactly which replaced and when and will try and track that down.

No dials of any kind on the amp; just an on/off switch.

I'll try swapping the valves around and cleaning the pins and will report back.

Thanks for the suggestions - keep 'em coming!

04-05-2008, 17:32
I would suggest being wary of swapping valves about if you are unsure what they are. As far as i can tell the valves are:

"The amplifier is by its very nature very simple; a 13D3 input valve is capacitor coupled to the E182CC which uses an inter stage transformer to drive the 300B output tube. ...

The large aluminium case contains three separate valve rectified choke input filter supplies. A GZ37 is used to supply HT to the output stage, while two EZ80's provide HT to the input driver and negative bias to the output stage"

After three years depending on the amount of use its had, the 300b's may be getting a little past their best, but that would normally not produce 'rustling paper' noise, but its possible.

I think, but am not certain that the amp in question uses cathode bias, so wont need the bias setting manually.

pure sound
04-05-2008, 18:54
I'm not sure it'll be cathode bias but ask the man himself


04-05-2008, 19:33
Good point, the text I posted did mention negative bias, so maybe not :-)

Ali Tait
04-05-2008, 19:56
Whereabouts in the world are you Iain? Perhaps you are not too far from someone who could render assistance.