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Old 5th June 2012, 02:57 PM   #1
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Default Help me pick el34b tubes

Hi guys, I know of you probably dont like this amp, but I bought a
Yaqin ms-20L.
It has el34b tubes in it now and I was looking at ordering some new ones.
I have a few questions. What tubes will fit without modding this amp?
I do want to get Genalex Gold Lion KT77, but I am unsure if they will be just an easy drop in.
I am also thinking about ordering these.
http://www.amazon.com/JJ-E34L-Glass-...907295&sr=1-44

But I don't really know enough about them yet. Can people give me some ideas on what tubes to get for this amp.
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Old 5th June 2012, 03:09 PM   #2
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The Svetlana Winged C EL34 is very good and works well in that amp, any EL34 will work without modding, but you need to lower the bias before fitting the new tubes and then set the bias for the new ones.
Not the SED type winged C.

Get these in the pic
Attached Images
File Type: jpg Winged C.JPG (25.2 KB, 207 views)

Last edited by data; 5th June 2012 at 03:13 PM.
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Old 5th June 2012, 03:14 PM   #3
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Why would have I have to lower the bias before inserting other tubes?
Also what should I lower it to?
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Old 5th June 2012, 03:52 PM   #4
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Because the new tubes might get too high a bias at the old setting.

This is standard practice when tube rolling.

With the amp off (give it 10 or 15min for the power caps to drain) back the bias off on each tube, you don't have to back it off all the way, what I do is turn each bias pot back fully and then take it up to about half the amount it was, that way you wont be feeding too much current when you put the new tubes in and power it up. But make sure you know what way is up and down with the pots in your amp, normally anti clockwise is down, but on occasion I have heard of amps with the pots wired *** about with it opposite.

Then after a few min' set each tubes bias, and re-check after about 2 hours of running.

If you haven't done this before, makes sure you are confident in what you are doing, as there are lethal voltages in the amp.

Edit:If you aren't too confident doing it (and it can be a little nervy to do at first) do you know anyone that is experienced that can help you with it for this first time?

Last edited by data; 5th June 2012 at 04:03 PM.
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Old 5th June 2012, 04:15 PM   #5
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In this vid Tube Rolling and bias adjust on MC-100B - YouTube the guy is doing it on a Yaqin 100B, and you will notice when he lowers the bias at first, he is turning the pots clockwise, and when bringing it up carefully he is turning anti clockwise.
This is opposite to the MC10L I had, where with my amp turning the pots clockwise increased the bias, and anti clockwise decreased it, so check how your amp works in this regard.

And be careful when setting them as some of these pots can be very touchy, so do it very slowly.

He uses a different tube of course, and a higher bias as a result, with the EL34's you want to set them at say 0.30v DC, make sure the meter is set to DC voltage.

Last edited by data; 5th June 2012 at 04:18 PM.
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Old 5th June 2012, 04:36 PM   #6
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Thanks for the help.
I have never had to bias a tube amp before. I have to bias this one and my friends H.H. Scott 222b.

I know this is asking alot but as far as tools I will need I keep seeing people using a bias meter. But then I also see people using a regular multimeter.
Is there any links to show how to do this correctly so I can bias all the tubes after they are done.

Also I can't find the tubes you posted the only ones I see say SED.
How are the jj ones I posted and the gold lion kt77?
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Old 5th June 2012, 05:25 PM   #7
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I get mine from this seller in the UK EL34 SVETLANA 'WINGED C' NOS MATCHED QUAD | eBay

A multimeter is all I use for doing the bias, as long as it can be set to read small DC voltage, It's fine, but the better ones are more accurate, and some use AA or AAA batteries, but the ones with a single 9v battery I find better as you don't have to change them as often.

I'll have a hunt round for links, but It's like that guy did in the youtube vid, but It's a pity it wasn't English speaking.
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Old 5th June 2012, 05:33 PM   #8
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BTW, if you are using the Chinese small signal tubes still, they are a good one to replace also, probably even a little more in the way of an improvement.

It's 3.30am here now so I'll have to look for links for you later today, need sleep
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Old 6th June 2012, 07:55 AM   #9
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i am using a Shuguang EL34 at 470volts plates, no issues.....
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the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
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Old 6th June 2012, 08:35 AM   #10
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Sorry Tony, but i'm not sure what you are getting at?

Shorty', I haven't found any worthwhile links to help, but the other guys here, and myself can walk you through it when you have the new tubes and a multimeter, you should have received a screwdriver (with a torx tip)for adjustment with that amp.....with an insulated shaft. It's pretty easy with that amp you have, but I don't know anything about the one your friend has.

The manual also would have a vague description on how to do it.
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