Noob Valve Amp Ownership Questions

[Figlet108]

I'm a complete noob to valve amps. I bought some EAR509s from potatoha on here last June and since then I've just had them in my main system, played them every day and loved every minute with them. I haven't given a second thought to the fact they are valves.

However, now I want to understand more about ownership and maintenance.

The 2 first questions are:
1) How do I know when to replace the valves?
2) How do I know if the amps need re-biasing or just a general service

Thanks

[anthonyTD]

hi Jason,
As valves age, they tend to lose their edge, start sounding a bit soft etc, but you only tend to notice this when you have replaced the old ones with a fresh set because the degradation is so slow in some cases. Some people believe in leaving things alone until they are forced into a repair etc,preventative maintenance is preferred as most often, a potential fault can be picked up in a routine service before it happens.
Hope this helps.
I'm a complete noob to valve amps. I bought some EAR509s from potatoha on here last June and since then I've just had them in my main system, played them every day and loved every minute with them. I haven't given a second thought to the fact they are valves.

However, now I want to understand more about ownership and maintenance.

The 2 first questions are:
1) How do I know when to replace the valves?
2) How do I know if the amps need re-biasing or just a general service

Thanks

[Figlet108]

Thanks Anthony. Preventative maintenance rather than reactive does make sense.
But at what intervals and at what costs? I think the last time these 509s had a service was in 2003, and I'm not sure the valves have ever been replaced...

Is there a way to measure how much 'juice' is left in a valve?

[Firebottle]

Hi Jason,

As far as how much 'juice 'is left you really need a valve tester. A few folks have got them, me excluded, they are generally large and not cheap.

If the gear is well designed the valves should be operating well within their maximum ratings, in which case they will last for years before requiring replacement.
The typical failure modes are:
The heater goes open circuit, i.e. the valve doesn't light up, end of operation.

The valve gets 'leaky', either the vacuum goes a little soft or residual gases are released from the internal pieces that make up the valve. You might get a little blue glow from ionisation in this case, and eventually the heater will loose its emissivity due to contamination by the released gases. In extreme cases the silvering at the top of the valve (the getter) will start to go white, this shows the valve is shot. Before this happens the valve can also start to draw grid current, not usually a desirable thing, which can upset the normal biasing of the valve. I have just repaired an amp with a leaky valve, the output transformer was also faulty, probably due to the failing valve.

Lower emission from the heater, usually due to age, more than likely with increased distortion in an audio application due to the operating point being way off by his time.

If you have a means to measure the output power the time for valve replacement is when it starts to drop significantly. This also could apply to the re-biasing question.
A lot of valve circuitry is what is referred to as auto biased, usually just a resistor, with or without a decoupling capacitor across, in the cathode circuit.
This develops a voltage that makes the cathode more positive than the grid, or from the grids perspective it is negative with respect to the cathode. All valve data sheets show graphs of the negative grid bias against other operating parameters.

Re-biasing is usually only required if you change the valves in a circuit that doesn't use auto bias. Normally in this case the negative bias voltage is generated separately in the power supply. Any adjustment that is provided is to set the valves operation in their normal range. The maximum cathode current is always specified on the data sheets, plus the maximum plate (anode) power dissipation. This is important so that you don't cook the valves, a sure way to shorten their life.

I assume most respectable valve amp suppliers will specify the bias setting, usually a voltage rating that is derived from the cathode or a sense resistor somewhere in circuit. Usually a good idea to follow the manufacturers advice.

:cool: Alan

[Figlet108]

Hi Alan,

thanks for such an extensive and informative reply.

Is there no cheaper DIY alternative to the valve tester?
As for measuring the output power, I would love to but haven't got an oscope yet (keep swinging between looking at CRO antiques on ebay and fancy new modern ones)
Any easyish ways to measure output power without an oscope?

The 509s don't auto bias but I have the service manual.

Does it stress valve amps to have their load removed while up and running? I've been comparing different pres today and done a fair bit of cable swapping (pretty tedious actually)

[anthonyTD]

No worries, the only way [as Firebottle has suggested] to get a fair indication of the condition of the valves is to test them, i use AVO 163 testers, however,they wont tell you exactly how much life is left in them, but you can usually make a rough guess by the physical condition, and by the test results themselves,when the time comes i would be happy to test them for you.
Thanks Anthony. Preventative maintenance rather than reactive does make sense.
But at what intervals and at what costs? I think the last time these 509s had a service was in 2003, and I'm not sure the valves have ever been replaced...

Is there a way to measure how much 'juice' is left in a valve?

[anthonyTD]

You shouldn't really remove the speakers from a valve amp when its on.
Hi Alan,

thanks for such an extensive and informative reply.

Is there no cheaper DIY alternative to the valve tester?
As for measuring the output power, I would love to but haven't got an oscope yet (keep swinging between looking at CRO antiques on ebay and fancy new modern ones)
Any easyish ways to measure output power without an oscope?

The 509s don't auto bias but I have the service manual.

Does it stress valve amps to have their load removed while up and running? I've been comparing different pres today and done a fair bit of cable swapping (pretty tedious actually)

[Figlet108]

...i use AVO 163 testers, however,they wont tell you exactly how much life is left in them...

Wow, that looks like a serious bit of kit...
http://tubes.tubeampdesign.com/instruments/AVO/HR/ValveTesters/photos/VCM-163-1.jpg

Thanks for the offer Anthony.

[anthonyTD]

No Worries,
These were amongst the last valve testers produced, and compared to the AVO MK2, 3, and 4, [which i had before them] they were a god send as unlike the others, you are able to see current draw, and MA/V at the same time,without having to reset anything...
Let me know.
A...

[anthonyTD]

Here is an interesting, article on the 509, that goes into a brief description of the circuit design,[without getting too complicated] and also describes the bias system, and how to adjust it etc.

http://www.izzy-wizzy.com/audio/powamp.html

[Figlet108]

By the way, if the tubes are going to get replaced preemptively as part of a service is it advisable to replace them all? In the case of the 509s there's 5 per amp, 3x small 9-pin twin triodes that don't seem to glow much or get very hot, and 2x PL509 which do get very hot. Is it just the PL509s that would get pre-emptively replaced, or all of them?

[Figlet108]

Here is an interesting, article on the 509, that goes into a brief description of the circuit design,[without getting too complicated] and also describes the bias system, and how to adjust it etc.

http://www.izzy-wizzy.com/audio/powamp.html

Thanks - interesting read.
I found this quite comforting: "Nothing has ever failed circuit wise and only one ECC85 went wrong once. An absolutely incredible design that proves valves can be as reliable as solid state. I never have to worry about these amps and they also prove that tube amps need not be more troublesome to own - OK, you have to re-bias now and then - big deal!"

[anthonyTD]

Hi Jason,
Small signal valves tend to outlast output valves by on average around 4 to 1, so, unless their micro phonic, or have any other noise issues, and as long as they test ok, i would re-fit them.
By the way, if the tubes are going to get replaced preemptively as part of a service is it advisable to replace them all? In the case of the 509s there's 5 per amp, 3x small 9-pin twin triodes that don't seem to glow much or get very hot, and 2x PL509 which do get very hot. Is it just the PL509s that would get pre-emptively replaced, or all of them?

[Figlet108]

Thanks Anthony - good to know.

[DSJR]

When Tim de P brought the 509's to us, he made a big point about the durability of the 509 output valves, which were normally thrashed at 1540kHz or so in TV line output drives. Used for audio, they apparently have a very easy life and can last decades. Naim had too much sway (especially the once lovely 250 in bolt-up form) and we let a great opportunity go sadly.

The 509's tend to last and last on original valves, so PLEASE don't try to 'mod' them or do anything un-necessary while they're running so nicely :)