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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Line Voltage with Yaqin MC-100B amp

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xmas111

Member
Joined 2009
Quick question for you guys.

My line voltage seems to run between 123 and 127 volts. I've used three different meters and tested various outlets around the house to verify it.

Could this create a problem with the Yaqin MC-100B?
Spec for this amp is 115 VAC.

If so, what would be a better solution to get the voltage down a little. Bucking transformer, VARIAC??

Here's the specs for the amp:
Specifications
· Tubes: KT88-98 × 4 (Output Tubes)
6N8P × 4 (Drivers and Cathode followers)
12AX7B × 2 (Voltage amplifiers)
· Maximum Output:
30W per channel (8Ω and Triode Mode)
60W per channel (8Ω and Ultra linear Mode)
· Output Jacks: Two channels with two groups gold plated jacks
· Output Impedance: 4Ω and 8Ω
· Input Jacks: Gold plated Isolated RCA jacks, 4 groups (CD, DVD, Tape, and Tuner) on rear, and 1 group on front as the input of post-stage mode
· Input Sensitivity:
0.25V in integrated mode (CD, DVD, and Tuner)
0.6V in pure post-stage mode (Front input connectors)
· Distortion of Harmonic Wave: ≤1.5%
· Frequency Response: 5Hz ~ 80KHz (-2dB)
· Signal-to-Noise Ratio: 90dB (A weight)
· Supply Voltage: AC 115V, 60Hz
· Power Consumption: 280W
· Net Weight: 23kg
· Shipping Weight: 30kg
· Shipping Dimension: 60cm x 52cm x 36cm


Thanks,
John
 
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xmas111

Member
Joined 2009
I'm hoping I answered my own question...

I measured the bias voltage on each of the KT88, (very easy to do on this unit with access points on top of the chassis behind each tube) and all measured 0.555v. So I'm guessing the line voltage being a little high shouldn't be of concern.:xfingers:

The only change I made so far is exchanging the 12ax7's with 5751's.

I'm using my old AR-LST2's that I rebuilt last year with this amp and overall I think this amp sounds wonderful.

John
 
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xmas111

Member
Joined 2009
kesa32 said:
Hi john, how do you find these 5751's sounding compared to the stock 12ax7's?
l have the same amp though it's been modded a bit.....here's a link to the mod JLTi EL34 & KT88 Amps

l'm going to try the 5751's myself soon

cheers ken
Click to expand...

That's some nice mods!

I feel the 5751's took just a little of the brightness away and pumped up the bass a tad. I really like the sound now.

Don't have a many hours on it yet so hoping it keeps getting better!

I'm using the Yaqin as a secondary setup in my kitchen with my old AR LST2's that I rebuilt last year. Nice to have some tunes playing while at the table eating. It's hooked up to the preamp in my main system(which is in the room beside the kitchen) so I can listen to either setup or both at the same time.

Included a few pictures of it.

John
 

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K

kesa32

Member
Joined 2006
Hi John, heres a couple of old links on voltage issues on our amps ..Yaqin MC 100B Chinese Tube Amp Mods

also http://www.diyaudio.com/forums/tubes-valves/109958-yaqin-mc-100b-schematic-diagram-13.html

Easy enough to get fixed, if you are handy with a soldering iron even better :)

l just ordered 2 GE 5751 Blackplates 3 mica's etc , looking forward to giving them a whirl in this amp...l .. l already replaced the stock kt88's as one was faulty , l went with the kt88z's ( Black treasures ) shugaungs .....very nice tubes :)

Next will be the 6sn7's when l can afford it .....oh btw , the guy that modded my amp said to set the bias's at .45 otherwise the tubes won't last as long.

cheers ken
 
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xmas111

Member
Joined 2009
kesa32 said:
Hi John, heres a couple of old links on voltage issues on our amps ..Yaqin MC 100B Chinese Tube Amp Mods

also http://www.diyaudio.com/forums/tubes-valves/109958-yaqin-mc-100b-schematic-diagram-13.html

Easy enough to get fixed, if you are handy with a soldering iron even better :)

l just ordered 2 GE 5751 Blackplates 3 mica's etc , looking forward to giving them a whirl in this amp...l .. l already replaced the stock kt88's as one was faulty , l went with the kt88z's ( Black treasures ) shugaungs .....very nice tubes :)

Next will be the 6sn7's when l can afford it .....oh btw , the guy that modded my amp said to set the bias's at .45 otherwise the tubes won't last as long.

cheers ken
Click to expand...

Ken,

Thanks for the links.

There's a lot of reading there and from what I got from it was a few resistor changes and adjust the bias's to .45, as you said. Those mods shouldn't be a big deal at all. And of course some more tube rolling.

One thing for sure I want to do is quite down the blue LED power light! That thing will practically light the whole house.

Just picked up John Coltrane, "A Love supreme" cd. I'm not a big jazz fan but this cd sounds fantastic!

Thanks,
John
 
kevinkr

kevinkr

Administrator
Joined 2004
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Paid Member
I've got a lot of different 6SN7 in my stash and have found NOS or good used Sylvanias are pretty hard to beat in most applications. Worth a shot although YMMV.. I would avoid the last few years of production in the late 1980s, but other than that all are good. They're readily available on eBay often at relatively reasonable prices if you shop carefully.
 
K

kesa32

Member
Joined 2006
Hi Kevin, any specfic 6sn7's that you prefer mate?......l've read a lot good reports on sylvanias 5751's when l was researching to replace my 12ax7's , so hopefully their 6sn7's are rated just as good too.
Is there any new stuff worth considering , or was it just the late 80's stuff you did'nt like ?


cheers ken
 
X

xmas111

Member
Joined 2009
kesa32 said:
Hi Kevin, any specfic 6sn7's that you prefer mate?......l've read a lot good reports on sylvanias 5751's when l was researching to replace my 12ax7's , so hopefully their 6sn7's are rated just as good too.
Is there any new stuff worth considering , or was it just the late 80's stuff you did'nt like ?


cheers ken
Click to expand...

I'm curious about those too.

I'm also looking at these 6550 TUNG SOL TUNGSOL REISSUE NEW RETAIL MATCHED QUAD to replace the stock KT88's.
And are the 6550's an exact replacement for the KT88's? Or would some adjustments be required other than the bias?

Thanks,
John
 
K

kesa32

Member
Joined 2006
l reckon they were a good buy mate....it'll be interesting to see how all your tube changes affect the sound , if the seller has the tested specs with each tube mix them with one of the stronger tested and one of the slightly weaker tested together each channel, keep them mirrored , say with the strongest on the oustside and the other2 opposite each other in the middle :)


good luck,


ken
 
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xmas111

Member
Joined 2009
Got the 6SN7's the other day...and finally had a chance to put them in.

Talk about a night and day difference! WOW!

The whole sound field has opened up with excellent clarity.

These tubes have made the most dramatic change of all the tube changes I've made on this baby. $100.00 well spent!

So anyone interested in getting the Yaqin MC-100B, think about getting some good 6SN7's and enjoy some wonderful sounds. I think you'll be surprised how good this little gem is.

John
 
kevinkr

kevinkr

Administrator
Joined 2004
kta-hifi.net
Paid Member
Hi John,
I think you lucked out on finding some of the best sounding versions of the Sylvania 6SN7. Glad they are working out for you.

Glad to see you here on diy.. Enjoyed reading your turntable exploits when I discovered your site sometime ago.

IIRC we live not too far apart if you are ever want to meet a few more local tub-o-philes. (Quincy)

Kevin
 
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