As someone else pointed out, the unbalanced splitter is actually an attempt to balance the unbalance due to a rather short tail in the 'long tail pair'. I'd give them a positive point for that since most miss this subtlety.
As for the rest, I'm afraid you are right, and it does get worse - look at the bias network. What happens if the pot wiper goes open, and the trimmers used are not of any great quality. Surprisingly this is a typical gross error - bias networks should be wired so that the bias voltage goes into maximum negative should the potentiometer fail.
There are a couple more issues with the mechanics and layout of the amp but all in all it's a great candidate for modifications, especially since the output transformers are sufficiently well made that it's worth the effort. However, there are versions for the EU/US market with 220/110V primaries on the mains transformer which seems to have been wound 'to the edge' and tends to work close to saturation on 230/115V nominal mains when it' on the high side, making the transformer run quite hot.
The input selector and pot could be of better quality, but the problem is they are located on the front which requires the signal wiring to pass around the mains transforemer - and it in turn actually sits on top of part of the driver circuit, which required some components to be bent out of place to accomodate the metalwork. The build is not a solid as it looks. In fact the transformer mounts are rather thin for the size of the transformers and can get bent in transport if the amp is handled a bit rough. The metal work in general is thinner than one would guess from the looks of it, there is a very thick layer of effect paint on the chasis which hider this.
I used to own a MC-10T - that I bought on a lark - it was a good amplifier, not great. For the price, however, it is a good introduction to tube newbies.
But...the PCB/wiring layout is a nightmare, making it the least favorite unit I've ever worked on. I had thought of improving the circuitry but gave up after replacing the coupling capacitors. I'm sure someone with a higher pain threshold than my own could put a standard Mullard type circuit in and be much happier with the results.
Of course the way the flimsy RCA jacks are done, the cheapo volume control, the oversized bias resistors, and the general layout - it may be better to just pull the transformers and use them on a different project.
But...the PCB/wiring layout is a nightmare, making it the least favorite unit I've ever worked on. I had thought of improving the circuitry but gave up after replacing the coupling capacitors. I'm sure someone with a higher pain threshold than my own could put a standard Mullard type circuit in and be much happier with the results.
Of course the way the flimsy RCA jacks are done, the cheapo volume control, the oversized bias resistors, and the general layout - it may be better to just pull the transformers and use them on a different project.
ClarityCap ESAs, not an ideal fit, but sonics rock. You can see me at it on a few pages back, page 21 I think
Yaqin MC 10T not a bad amp, but I recently tried to tube roll replacing the stock Chinese EL34s with some Russian Svetlanas. Bias was double checked and OK at 350mv before the swap. After the swap I left my voltmeter connected to the V1 bias points to monitor the bias immediately at turn on. The meter pegged and the 2.5A power fuse blew. (maybe a bad tube?) I replace the tubes back with the stock originals, replaced the fuse, and at turn on measured V1 bias to be a whopping 25 volts! I immediately cranked the bias pot down to min, but the best I could get was down to 8 volts. The other 3 tubes all were still stable at 350mv. Amazingly, both channels still sound fine, but I shut it down within 30 sec. fearing subsequent damage. Any thoughts before I pop the lid off? I'm hoping to find an obvious burned resistor in the bias measuring circuit, or something closely related.
Hi everyone
Yesterday I bought a Yaqin MC-10L, my first ever tube amp.
There is some hum in it though, at startup it stays for about a minute, later it goes away and it comes back after 30min-1hr of playing.
It's only on one side and the volume control doesn't affect it, it stays on the same level, even with volume turned down all the way. When I switch the powertubes to the other side, the hum also switches to the other speaker.
I still have to check bias, but if that doesn't help, sounds this like an almost certainty that one of the tubes is faulty and that I need to replace them?
Yesterday I bought a Yaqin MC-10L, my first ever tube amp.
There is some hum in it though, at startup it stays for about a minute, later it goes away and it comes back after 30min-1hr of playing.
It's only on one side and the volume control doesn't affect it, it stays on the same level, even with volume turned down all the way. When I switch the powertubes to the other side, the hum also switches to the other speaker.
I still have to check bias, but if that doesn't help, sounds this like an almost certainty that one of the tubes is faulty and that I need to replace them?
You should always check the bias on these amplifiers to make sure everything is operating correctly in the output stage. If set wrong, the current(s) through the affected tubes(s), if excessive, will give the hum symptom. A faulty tube is probably the reason here as the fault shifts over to the other channel when the output tubes are swapped. But when you swap tubes....PLEASE Check the Bias!
Which tubes do you switch? The small ones in the front? Or the big ones in the back? At any rate you will need to buy a new set (buy a whole new set, not just for one channel). I bought the Electroharmonix Russian 6N1Ps (maybe this isn't the right number, don't have the manual open right now) and the Electroharmonix EL34s and am very happy.
volume pot
Hello chaps, I replaced the vol pot with a stepped one from China off of ebay, made sure it was the required 20k. But I get little control at the quiet end with a sharp cut off. Makes late night listening rather tricky.
Is 20k actually correct ? The amp's tech sheet says so, but maybe an error ?
kE9s4,!!WIBQE8s+wwjw~~60_3.JPG)
Hello chaps, I replaced the vol pot with a stepped one from China off of ebay, made sure it was the required 20k. But I get little control at the quiet end with a sharp cut off. Makes late night listening rather tricky.
Is 20k actually correct ? The amp's tech sheet says so, but maybe an error ?
What you are showing is an attenuator without any resistors populated. So without knowing what resistors you soldered in, it is tough to know. Perhaps I am wrong on this, but usually a stepped attenuator is populated on the outside.
Can you provide a link to this item from where you bought it?
You need a logarithmic taper, not a linear and this will give you the control you need at the low end.
Can you provide a link to this item from where you bought it?
You need a logarithmic taper, not a linear and this will give you the control you need at the low end.
That's the 13s, some differences to the 10L. Some suppliers ofter the choice of EL34 or the 6CA7 for a little extra, those seem to be the 6CA7's.
which are well likes. Colour is just for show, no other change over standard Shuguang tubes.
The 13s is a nice amp, yaqin now make a number of EL34/6CA8 based amps, :- 10L mk3, 10T, 13s, 20L, 30L. Please note sometimes different numbers are used in some Country's for the same amp!
which are well likes. Colour is just for show, no other change over standard Shuguang tubes.
The 13s is a nice amp, yaqin now make a number of EL34/6CA8 based amps, :- 10L mk3, 10T, 13s, 20L, 30L. Please note sometimes different numbers are used in some Country's for the same amp!