Post by Graham on May 13, 2017 11:10:24 GMT 12
A sad day indeed. I regret to inform anyone who is slightly interested that one of my Gold Lion KT88 valves passed away this morning. It will be sadly missed.  Considering I bought the Yarland amp from Ben back in 2013 I guess I have had a pretty good run, as like light bulbs I knew that one day one or all would croak. I have installed the original set of 4 Shuguang KT88-98s and after biasing them correctly I have to admit they sound very very nice. To my ears just as good as the Gold Lions. Who said the Chinese cant make good valves. At some stage I need to get another set of 4 matched valves to future proof my amp. Does anyone have any suggestions locally, or am I best to source from overseas ? Cheers Graham
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Post by Owen Y on May 13, 2017 11:47:57 GMT 12
Hi Graham - did the valve just fail to light up? or did it expire in more dramatic fashion? And how many hours would you estimate the valve had done, ballpark? Chinese manufacture can be pretty good now I believe, but maybe service life of modern valves is still not as good as old days - but a lot depends on how hot they are run in the amp design. Local sources are thin, service technicians import for their own work, music shops possibly, but yes overseas.... There are many overseas suppliers, but probably best advised to start with one of the bigger, well established audio suppliers such as Parts Connexion (Canada). They have quite a few options I see.
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Post by Graham on May 13, 2017 12:22:37 GMT 12
It died rather quietly and peacefully.
I noticed it wasn't glowing like the other 3 and there was a hum from the RH speaker.
I swapped the 2 RH valves just to make sure it wasn't a connection issue, and the same valve failed to light up.
Hard to say how many hours but I guess 1-2 hours most nights for 4 years equates to 1500-2000 hours.
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Post by Owen Y on May 13, 2017 13:44:33 GMT 12
Ohh....sounds like heater failure. You'll see that the centre of a KT88 has a rectangular cathode tube into which the white-coated heater disappears inside - the 2 centre wires. If the coated heater element is not lighting up, the tube won't function. Gold Lions these days I believe, are Russian production replicas of the orig British KT88.
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Pundit
Post by Gryffles on May 13, 2017 23:07:20 GMT 12
They had done approx 300 hours when you got them GrahamPretty good life span considering you can get a quad for $350ish
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Post by Owen Y on May 14, 2017 17:56:23 GMT 12
4 years is not too bad. You might expect some sonic degradation, but ideally not sudden failure. How is the bias set on this amp?
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Post by Graham on May 14, 2017 19:44:58 GMT 12
Hi Ben and Owen.
No complaints about the life of these valves ( well one anyway, the other 3 were still going strong )they have performed well.
Bias is set manually to 0.4v with 2 valves each side sharing the trim pot.
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Post by cooksferry on May 16, 2017 14:39:25 GMT 12
That's not what I like to hear. My quad have been ticking over since 2009 or there abouts, definitely have to put a replacement set on the to buy list.
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Post by guitardude on May 16, 2017 15:57:42 GMT 12
Hi Cooks, I see Simon had some valves on his website that he is selling out of. Might be worth a call when he gets back. You definitely need at least one spare set IME.
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Post by cooksferry on May 16, 2017 17:00:12 GMT 12
Hi Cooks, I see Simon had some valves on his website that he is selling out of. Might be worth a call when he gets back. You definitely need at least one spare set IME. I have a virgin quad that came with the amp, branded Melody as amp but would bet 100% they're Shuguang. Now saving for some Psvane if all goes well.
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Post by Owen Y on May 24, 2017 10:49:15 GMT 12
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Post by Graham on Jun 9, 2017 20:17:58 GMT 12
Very tempting Owen , however I have just been offered a matched quad of new Gold Lion KT88s locally.
You may be able to answer a question regarding the test data that comes with them. It means nothing to me 
Valve 1 gn = 7.7 Ia = 83 Valve 2 gn = 8.5 Ia = 75 Valve 3 gn = 8.3 Ia = 87 Valve 4 gn = 7.4 Ia = 84
What on earth do these figures mean ? 
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Post by Owen Y on Jun 9, 2017 22:42:35 GMT 12
Ia = Anode Current, mA - is a emission current reading of the valve, under 'static' conditions. Gm = Transconductance (change in plate current/change in grid voltage, ie. mA/V). This gives an indication of the 'dynamic' behaviour of the valve. ideally, you'd want pairs matched in both Ia & Gm. On your amplifier, not sure, but it appears that you can adjust/match the static current (Ia) of ea PP pair in-amp. So, you'd then choose to place a Gm-matched pair on ea channel. Do you know on what valve tester these readings were taken? Or at least what % of 'new' values these readings are, on that particular tester?
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Post by Graham on Jun 10, 2017 9:22:18 GMT 12
Sorry, I have no more info. This data was hand written on tabs on the individual boxes. These were bought from a US vender as a matched quad but have never been used.
I haven't fitted them yet.
The only external adjustment I can make is to the paired ma draw so do I presume I am best to pair up 1 & 2 and 3 & 4 ? They are not a particularly close match but then neither are the current Shuguangs or the previous Gold Lions.
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Post by Owen Y on Jun 10, 2017 10:29:51 GMT 12
Hi Graham - such 'non-matching' will usually have non-noticeable sonic consequences, is my guess. However, it is good to 'match' to suit your amp - which in this case is a P-P stage, with some manual 'bias' adjustment. Usual thinking is that it is better to match the 'dynamic' characteristic, ie Gm in pairs - 1-4, 2-3. But, as you can see in this case, that means that one ch is ~10% lower Gm than the other ch. One thing I've been meaning to ask.... How exactly is 'bias' adjusted on ea ch?
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Post by Graham on Jun 10, 2017 11:43:32 GMT 12
Bias adjustment is only provided for the paired valves per channel.
One externally trim pot is used for each pair so in the past I have had settle on a slight mismatch either side of the recommended 0.4v setting.
There appears to be an internal trim pot to balance bias between the 2 valves but I presume this is a factory setting and I don't want to start poking around underneath when it is live.
I'll try the valves maybe tomorrow and see how they match up and possibly swap them around for best readings.
I spent a lot of time agonising over this when I first set the amp up with the original Gold Lions, but came to the conclusion that a perfect match is near impossible and bound to change with time anyway.
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Post by Owen Y on Jun 10, 2017 12:49:52 GMT 12
I meant, what do the instructions actually say, when doing this adjustment? And what do they call it? To find out more, you really need the schematic - or trace the circuit at least for the output stage.
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Post by Graham on Jun 10, 2017 12:56:55 GMT 12
Exact instructions are laughably brief !!
" Adjust the adjustable resistance to maximum ( DC voltage is 0 V ), and put in the power valves.
Adjust adjustable resistance.
The DC voltage as follows
Power tube KT88-98 = 0.40V
Power tube KT90 = 0.45V "
That's it !!!!!
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Post by Owen Y on Jun 10, 2017 13:05:27 GMT 12
What are the 3 probe holes? Are they labelled? The 4th hole is for a single trim pot I presume?
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Post by Graham on Jun 10, 2017 13:12:53 GMT 12
Not labelled on the amp.
But the centre of the 3 is common and the other 2 relate to each valve.
Yes the 4th hole separate to the others is for accessing the trim pot.
There is a very vague diagram in the handbook that identifies these probe holes.
The only real criticism I have for this amp is the pathetic Owners Instructions.
There was quite a lengthy conversation on Audioenz when I first got it trying to fathom out what the 'instructions' actually meant.
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Post by Owen Y on Jun 10, 2017 13:32:45 GMT 12
So... You can measure volts for ea of the 2 valves per ch.... But there is only one pot, no switch. Am I correct in thinking then, that the one pot affects both valves & so you are adjusting to 'balance' them until both valves read the same voltage? (Usually voltage readings are just a convenient way of measuring the valve current, eg. by measuring volts across say a 10 ohm R, a 0.45V reading would indicate 0.045A (45mA)). V = I*R - Ohm's Law.
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Post by Graham on Jun 10, 2017 17:39:01 GMT 12
No unfortunately the adjustment is not being used to balance the valves.
The pot is shared by both valves so if the value is increased for say valve #1 it also will increase for valve #2.
Ideally the valves with this set up should be identical but that has not been the case with all the valves I have used.
For example if valve #1 has a low reading of say 0.38v but #2 has 0.4, if I increase the reading using the pot for #1 to 0.4v valve #2 will go up to 0.42v.
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Post by Owen Y on Jun 10, 2017 18:20:07 GMT 12
OK then.... I would pair up valves 1-3, 2-4. This way, a stronger Gm valve can 'assist' a weaker Gm valve, in P-P action. And the 2 channels will approx match in this way. Unfortunately, valve 2 is weaker in Ia, so when you do the static biasing, valve 4 will be limited to 0.40v. However, you may find that the test data given may not match what you see when biasing in-amp! (The reason I asked about the tester used for the readings, is that different testers set different voltages for testing a particular valve & the Ia reading for example will be different for the same valve on 2 different testers - so, the test data should state '%' compared to a new valve, eg. 80%, 100%, etc)
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Post by Graham on Jun 11, 2017 11:32:15 GMT 12
Well Owen, the in amp readings bear little relationship to the test data as you suspected, so I question their accuracy.
I simply plonked the valves in the amp in numerical order left to right and after about 1/2 an hour warm up adjusted to the following readings.
LH position 1 valve # 1 = 0.420v
LH position 2 valve # 2 = 0.399v
RH position 3 valve # 3 = 0.416v
RH position 4 valve # 4 = 0.399v
Close enough for me !!!
Thanks for you advise.
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Post by Owen Y on Jun 11, 2017 16:37:31 GMT 12
Looks pretty good to me. Don't forget to try the spkr connections reversed phase/polarity (if you haven't already).
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Post by Graham on Jun 12, 2017 8:44:32 GMT 12
Looks pretty good to me. Don't forget to try the spkr connections reversed phase/polarity (if you haven't already). Yep, tried the speakers with the polarity reversed with several pieces of music but must confess I couldn't hear any difference.
So I guess this means
a) My choice of music didn't demonstrate this. b) My ears are stuffed. c) It's an urban myth.  d) All of the above !!!!
Cheers 
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Post by Owen Y on Jun 12, 2017 9:40:53 GMT 12
Or, this aspect is simply not high on your list of sonic priorities Coincidentally (& maybe only slightly relevant), a pal overseas last night sent me a link to this short opinion piece on Listening vs Hearing. www.gcaudio.com/tips-tricks/listening-vs.-hearing/
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Post by Graham on Jun 12, 2017 13:11:03 GMT 12
Ha ha ! I thought that would get you going.
Interesting article though.
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