Line Voltage with Yaqin MC-100B amp - diyAudio
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Old 29th January 2010, 10:03 AM   #1
xmas111 is offline xmas111  United States
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Default Line Voltage with Yaqin MC-100B amp

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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Old 31st January 2010, 09:15 PM   #2
xmas111 is offline xmas111  United States
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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.

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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Old 1st February 2010, 12:28 PM   #3
kesa32 is offline kesa32  Australia
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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
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Old 1st February 2010, 11:03 PM   #4
xmas111 is offline xmas111  United States
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Quote:
Originally Posted by kesa32 View Post
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
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
Attached Images
File Type: jpg yaq1.jpg (76.8 KB, 256 views)
File Type: jpg yaq2.jpg (70.8 KB, 249 views)
File Type: jpg yaq.jpg (67.8 KB, 245 views)
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Old 5th February 2010, 11:32 PM   #5
kesa32 is offline kesa32  Australia
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Hi John, heres a couple of old links on voltage issues on our amps ..Yaqin MC 100B Chinese Tube Amp Mods

also Yaqin MC-100b schematic diagram

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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Old 7th February 2010, 10:57 PM   #6
xmas111 is offline xmas111  United States
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Quote:
Originally Posted by kesa32 View Post
Hi John, heres a couple of old links on voltage issues on our amps ..Yaqin MC 100B Chinese Tube Amp Mods

also Yaqin MC-100b schematic diagram

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
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
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Old 8th February 2010, 10:46 PM   #7
xmas111 is offline xmas111  United States
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Quote:
Originally Posted by kesa32 View Post
Next will be the 6sn7's when l can afford it .....

Just out of curiosity what 6SN7's are you thinking about?

Would something like these be worth checking out? 6SN7

Thanks,
John
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Old 9th February 2010, 01:43 AM   #8
kesa32 is offline kesa32  Australia
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Quote:
Originally Posted by xmas111 View Post
Just out of curiosity what 6SN7's are you thinking about?

Would something like these be worth checking out? 6SN7

Thanks,
John

Yeah those tubes are cheap enough , and l'd imagine they'd be pretty good quality
..........l'll research some more soon........gotta ease up on the c/c for a bit


cheers ken
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Old 9th February 2010, 05:11 PM   #9
kevinkr is offline kevinkr  United States
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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.
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Old 9th February 2010, 08:25 PM   #10
kesa32 is offline kesa32  Australia
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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
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