xlr8or Posted April 8, 2021 Posted April 8, 2021 (edited) It's a problem related to the dual meter. Initially, I thought the problem was related to the tubes but youve confirmed that isn't the case.. The rest of the swaps won't change anything as they're unrelated. You've confirmed bias can be set correctly. I would feel more comfortable purchasing a cheap bias meter on eBay to confirm the plate current values. If the VU meter is playing up then all that is needed is a new meter to be fitted in its place. Whether it's the left or right VU meter playing up is going to be challenging to call. Sorry to hear you've experienced such a problem. You would've hoped that QA/QC would've picked this up. Edit: The VU meter is just an aesthetics thing. If the tubes are properly biased to 40mA you can ignore the VU meters and sit back and enjoy the sound. That's what really counts. Edited April 8, 2021 by xlr8or 1
al2813 Posted April 8, 2021 Posted April 8, 2021 1 minute ago, xlr8or said: It's a problem related to the meter. Initially, I thought it was related to the tubes but youve confirmed that isn't the case.. The rest of the sways won't change anything as they're not related. You've confirmed bias can be set correctly. I would feel more comfortable purchasing a cheap bias meter on eBay to confirm the plate current values. If the VU meter is playing up then all that is needed is a new meter to be fitted in its place. Sorry to hear you've experienced this problem. You would've hoped that QA/QC would've picked this up. I guess they are mass produced, boxed and shipped out with this important step skipped. I probably forgot to mention the fact that the speaker matching the “higher” meter is playing louder. And I swapped the wiring to make sure I am not imagining. I will test with a second amp I have tomorrow.
xlr8or Posted April 8, 2021 Posted April 8, 2021 (edited) 50 minutes ago, al2813 said: I probably forgot to mention the fact that the speaker matching the “higher” meter is playing louder. And I swapped the wiring to make sure I am not imagining. I will test with a second amp I have tomorrow. Cool. I think the bias is not also reading correctly on the left channel. The spring in the dual meter appears to have lost some of its full scale deflection capability or the zero point hasn't been adjusted accordingly on the meter and is offset. The tubes are probably under biased and sounding lower in volume output. One of these would help to dial in 40mA for all 4 tubes. https://www.ebay.com.au/itm/Dual-Bias-Current-Probe-Tester-VU-Meter-for-EL34-KT88-6550-Vacuum-Tube-Amplifier-/392702491739 Edited April 8, 2021 by xlr8or 1
Major_Dundee Posted April 9, 2021 Posted April 9, 2021 My own personal opinion is to send it back for another unit. I just had an issue with one of the KT-88 tubes popping. I switched the tubes around until I isolated the culprit. After talking to the manufacturer, I had to make a video showing what the issue is. Now they want me to mail the tube back to them. I haven't done it yet, because I'm not convinced it is worth the postage and time from the USA to China for a lousy stock tube. I think I'm going to slowly replace them. 1
al2813 Posted April 9, 2021 Posted April 9, 2021 Let’s see when the store comes back to me. I am inclined to return it if possible. I still have my previous amp.
al2813 Posted April 9, 2021 Posted April 9, 2021 8 hours ago, xlr8or said: Cool. I think the bias is not also reading correctly on the left channel. The spring in the dual meter appears to have lost some of its full scale deflection capability or the zero point hasn't been adjusted accordingly on the meter and is offset. The tubes are probably under biased and sounding lower in volume output. One of these would help to dial in 40mA for all 4 tubes. https://www.ebay.com.au/itm/Dual-Bias-Current-Probe-Tester-VU-Meter-for-EL34-KT88-6550-Vacuum-Tube-Amplifier-/392702491739 Again I am not an expert so going for this kind of fix is a bit annoying. The seller needs to swap the amp with no questions unless he can find a way to have the issue fixed without doing this. I prefer to spend the extra cash on rolling tubes rather than fixing a bias issue
xlr8or Posted April 9, 2021 Posted April 9, 2021 I wouldn't have the confidence in a replacement unit not exhibiting the same phenomenon in the near future. What I proposed above as a precautionary measure was suggested to avoid frying your power tubes if the tubes on the right were in fact over biased. If the tubes red plate they can take out the OPT amongst other critical circuitry components, which would then be a costly repair job. The bias meter would give you peace of mind that the tubes were in fact biased correctly. Everything else is secondary.
al2813 Posted April 9, 2021 Posted April 9, 2021 In the meantime I have been in touch with the seller shop. At his request I swapped now the 12AU7 tubes and indeed it is now the right-hand side meter and speaker that show the same issue. Below two pictures while the same song plays (Chasing Pavements of Adele - one of my favourite "test tracks" )
al2813 Posted April 9, 2021 Posted April 9, 2021 (edited) Based on that the seller tells me it is the 12AU7 tube that is faulty, and he is sending me a new one. Isn't it better to replace both 12AU7 tubes? And one more question - I have a passive LDR pre amp in the house. I connected it and used the pre-in mode of the X7 - still the same issue... Edited April 9, 2021 by al2813
xlr8or Posted April 9, 2021 Posted April 9, 2021 Yes - it's best to replace the pair. Does the 12AU7 control the VU meter and output?
al2813 Posted April 9, 2021 Posted April 9, 2021 Just now, xlr8or said: Yes - it's best to replace the pair. Does the 12AU7 control the VU meter and output? I don't know in all honesty. This is all new to me. The seller told me not to use the amp until he sends me the replacement tube. He says that I can only replace the faulty one. I am looking right now to see if I can get my hands on a pair of 12AU7 tubes. 1
xlr8or Posted April 9, 2021 Posted April 9, 2021 (edited) 6 minutes ago, al2813 said: I am looking right now to see if I can get my hands on a pair of 12AU7 tubes. This is exactly what I would be doing as well. It sounds like one triode in the suspect 12AU7 is not working properly. There is one thing for sure - the 12AU7 is super critical to the output circuitry going to the power tubes. Edited April 9, 2021 by xlr8or 2
al2813 Posted April 9, 2021 Posted April 9, 2021 Managed to get the tubes. Bought Slovak ones for cheap as prefer to hunt for the real replacement online. I replaced both 12AU7 and the 12AX7. The issue is solved and the amp sounds now properly as well the meters. Really happy. Now will let the system burn in - this will take a few weeks. 3
Timster Posted April 15, 2021 Posted April 15, 2021 On 08/12/2020 at 11:50 AM, Relaxasaurus said: Using the Iotavx sa3 as a pre. Better remote, tone controls, and better phono stage. Plus I can power my speakers sans-tube amp with just the sa3 for tv watching with the use of a speaker switcher. When using the X7 as a power amp, and an external Pre, do you know if the pre-inputs completely bypass all pre-amp circuity in the X7?
clappy Posted April 16, 2021 Posted April 16, 2021 Just snagged a used x7 in NZ. Early days but really like this amp - came with NOS Mullard 12au7s and 12ax7 and a couple of NOS gz34 rectifiers (azdam Mullard and phillips miniwatt). Have got the stock tubes in so I get the upgrade experience (thanks to some good advice from Paul at Vintage audio tubes in Akld) so looking forward to some tube rolling. Enjoying this thread! Cheers, Geoff 4
xlr8or Posted April 16, 2021 Posted April 16, 2021 (edited) On 15/04/2021 at 2:41 PM, Timster said: When using the X7 as a power amp, and an external Pre, do you know if the pre-inputs completely bypass all pre-amp circuity in the X7? According to the circuit diagram below it looks like the volume control circuit is the only thing that is bypassed when using the pre in option. Edited April 16, 2021 by xlr8or 1
al2813 Posted April 28, 2021 Posted April 28, 2021 So my first set of tubes is on its way from the Netherlands. I hope I get them tomorrow. I got a matching pair of Philips Miniwatt 12AU7 produced in Heerlen and a single Amperex Bugle Boy 12AX7. This is my first experience with tube rolling but from what I read this looks nice. I am hesitating now with the rectifier GZ34. These are much more expensive. Any feedback on the benefit of replacing it? For now I keep the stock Muzishare KT88. 1
clappy Posted April 29, 2021 Posted April 29, 2021 13 hours ago, al2813 said: So my first set of tubes is on its way from the Netherlands. I hope I get them tomorrow. I got a matching pair of Philips Miniwatt 12AU7 produced in Heerlen and a single Amperex Bugle Boy 12AX7. This is my first experience with tube rolling but from what I read this looks nice. I am hesitating now with the rectifier GZ34. These are much more expensive. Any feedback on the benefit of replacing it? For now I keep the stock Muzishare KT88. I rolled some NOS Mullard into mine (being a bit lazy I rolled the rectifier, 12au7s and 12ax7 all at once) and it made a big difference - I will try putting the muzishare rectifier back in and see what difference, if any, it makes - have read very good things about the bugle boy! 1
al2813 Posted April 30, 2021 Posted April 30, 2021 On 29/04/2021 at 10:15 AM, clappy said: I rolled some NOS Mullard into mine (being a bit lazy I rolled the rectifier, 12au7s and 12ax7 all at once) and it made a big difference - I will try putting the muzishare rectifier back in and see what difference, if any, it makes - have read very good things about the bugle boy! Thanks curious to get your feedback. Mine will be very skewed because I got yesterday my MHDT Orchid DAC which is just incredible. I will plugin the new tubes later to see the differences. 2
clappy Posted May 1, 2021 Posted May 1, 2021 14 hours ago, al2813 said: Thanks curious to get your feedback. Mine will be very skewed because I got yesterday my MHDT Orchid DAC which is just incredible. I will plugin the new tubes later to see the differences. Hi, Just did a reasonably quick and unscientific test by adding back the muzishare 5ar4 back into my x7. I listened to "love and misery" by Leon Majcen (streamed via YT music and my sonos port - not hi res) 3 times and then switched my NOS Azdam Mullard 5ar4 back in and listened to the same track 3 times again. I was really surprised what an improvement the nos 5ar4 made. I do not possess a golden ear (i can not reliably tell the difference between 320kbs files and hi res!) but the improvement was quite marked. With the muzishare 5ar4 the vocals were quite veiled compared to the nos 5ar4 and it all just sounded less precise with the muzishare - it clearly sounded "better" with the nos 5ar4 (terrible description!) and I wasn't expecting it. All the 12au7s and 12ax7 tubes are 60's nos mullards (which came with the amp when I bought it) with the kt88s being Ruby's and 1 muzishare (i possibly need to do some research on using non matched kt88s and what impact this has but they are all biased at the same level). Based on my experience adding a nos 5ar4 made a big improvement but ymmv. worth borrowing one if you possibly can to try it? Would probably recommend making your changes with 12au7s and 12ax7 first and then do the 5ar4 as i am unsure if i had swapped out the 5ar4 while using the muzishare 12au7s and 12ax7 if i would have been able to tell the difference so easily... Hope this helps. Cheers, Geoff 4
xlr8or Posted May 1, 2021 Posted May 1, 2021 (edited) @clappy Can you please share a few close up photos of the Adzam 5AR4? I suspect it's a Sittard 'X' or Brussels 'L' f3* GZ34 rectifier. Edited May 1, 2021 by xlr8or
clappy Posted May 1, 2021 Posted May 1, 2021 30 minutes ago, xlr8or said: @clappy Can you please,share a few close up photos of the Adzam 5AR4? I suspect it's a Sittard 'X' or Brussels 'L' f3* GZ34 rectifier. Hi, I was going by what the seller told me but it appears that you are correct and it is a GZ34 -no.5. Paul from Vintage Audio Tubes in Auckland tested all the valves and left some clues about it on the tube! I also have a Phillips miniwatt rectifier - will have to check to see what is... 1
clappy Posted May 1, 2021 Posted May 1, 2021 With the benefit of hindsight the no5 is probably NOS... Cheers, Geoff
xlr8or Posted May 1, 2021 Posted May 1, 2021 (edited) Very nice rectifier. Can you see any 2 lined etched codes on it on the glass envelope near the tube base or underneath the tube base around the pins? f3-number Letter-number-letter or f3-number Letter-number-letter-number Edited May 1, 2021 by xlr8or
clappy Posted May 1, 2021 Posted May 1, 2021 16 minutes ago, xlr8or said: Very nice rectifier. Can you see any 2 lined etched codes on it on the glass envelope near the tube base or underneath the tube base around the pins? f3-number Letter-number-letter or f3-number Letter-number-letter-number Sorry couldn't see much more but have taken a photo of both rectifiers...
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