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 Post subject: Bias new tubes
PostPosted: Fri Nov 16, 2018 9:28 am 
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Location: Delta, BC, CA
Ok I am fairly new to this so I have a quad set of gold lion kt77 power tubes coming for my Will Vincent dynaco st70, need to know the bias voltage to set these at I have my voltmeter ready to go .There are two pots on the amp I assume one for the left channel and one for the right with the adjustment behind them using a screwdriver.Currently have el34 tubes is the bias the same? For the amp or do I adjust bias for the new tubes?


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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 9:47 am 
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Location: Moncton, New Brunswick, NB, CA
BE CAREFUL!

I once owned a pair of modified Dynaco ST 70's, and had an "interesting" experience.

I was setting the bias, screwdriver fully engaged....when the phone rang.
As I glanced at the phone, the screwdriver slipped.....touched something it shouldn't have, and resulted in a small fire.

Again, be careful.

Cheers, del Sol


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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 10:22 am 
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Location: Ottawa, ON, CA
Right now I have the top plate off of my rogue atlas --- so I can swap in/out KT88's and KT120's --- setting the bias makes me kinda nervous as I know there's very high voltage in there....

I have a Passion Audio PAK-i10 that is currently running a quad of the KT77 Gold Lions, what a sweet sound! Anyways, yes I bias them the same as the EL34's that the thing came with: 30mA, the same value used on the Rogue.

When swapping tubes, it's my practice to lower the bias down to around 15mA, power down, swap the tubes, power back up, wait a minute then check the bias. Doing this yesterday some of the initial values were ~50mA! So what would they have been if I hadn't turned the bias down???? Enough to burn the tube maybe?

~A


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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 1:06 pm 
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30mA might be a tad cool imo...

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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 1:25 pm 
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BinkyTheCat wrote:
30mA might be a tad cool imo...

I was thinking the same. I use a single ended amp but bias between 40 and 70.

Audiois1st

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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 1:29 pm 
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Assuming plate voltage etc....comparable to a stock st70.

OP shud know recommended bias...el34 / kt77 be the same.

And no, not all el34 etc idle the same. You will need to rebias!

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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 1:53 pm 
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Yeah, OK 30mA is a bit low, 35mA is the recommended. 40 will shorten the life, 30 will increase life but distortion may be increased.

https://www.audio-occasion.qc.ca/pdf/ma ... _i10_e.pdf


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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 3:13 pm 
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alzmtbr wrote:
Yeah, OK 30mA is a bit low, 35mA is the recommended. 40 will shorten the life, 30 will increase life but distortion may be increased.

https://www.audio-occasion.qc.ca/pdf/ma ... _i10_e.pdf


????

I had no idea all tube amps are created equal lol!!! op runnin a wv st70.

there's a bit more to it than picking a number out of a hat.

try a bias calculator - http://www.tedweber.com/webervst/tubes1/calcbias.htm

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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 5:37 pm 
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del Sol wrote:
BE CAREFUL!

I once owned a pair of modified Dynaco ST 70's, and had an "interesting" experience.

I was setting the bias, screwdriver fully engaged....when the phone rang.
As I glanced at the phone, the screwdriver slipped.....touched something it shouldn't have, and resulted in a small fire.

Again, be careful.

Cheers, del Sol


I use the old TV (RED) plastic adjustment tools to adjust bias on tube amps, now. No chance of shorting or sparks or electrocuting myself. My first experience was biasing a KT88 Push Pull amp. I also slipped with a mini steel screwdriver, but I was inside the amp. It went flying, I went into the wall and my elbow hurt like hell for a half an hour.

Here is a url to a set. "http://www.arcadeshop.com/i/1311/tv-monitor-adjustment-tool-set.htm"

Live and learn. If you live.... ;)


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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 5:53 pm 
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I dunno...

biasing an st70 couldn't get much easier.

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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 6:00 pm 
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Location: Moncton, New Brunswick, NB, CA
BinkyTheCat wrote:
I dunno...

biasing an st70 couldn't get much easier.


Just don't get momentarily distracted by the phone/doorbell/cat/dog/etc. .......that's all it took.

Cheers, del Sol


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 Post subject: Re: Bias new tubes
PostPosted: Fri Nov 16, 2018 6:14 pm 
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consider the st70 series 3, just released.

trimmers on front face with the asl style bias led's.... and an electricians screwdriver.

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 Post subject: Re: Bias new tubes
PostPosted: Sat Nov 17, 2018 1:15 am 
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Location: Delta, BC, CA
Ok, now I have seen bias set at 1.56 volts on a volmeter, what is ma? Sorry I don't know squat about the settings or electrical anything this the first tube amp I have ever owned and I don't want to blow up my tubes or amp.I need to know how to set my volmeter if it's volts I am ok ma don't know.Thanks for all the responses.


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 Post subject: Re: Bias new tubes
PostPosted: Sat Nov 17, 2018 1:55 am 
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You have never checked bias on this amp?
mA is milliamps.
The 1.5 volts is testpoint to chassis on stock st70. You have a modded one. What's been done we dont know...
Should have came with instructions? Perhaps ask previous owner or contact builder for correct procedure.

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 Post subject: Re: Bias new tubes
PostPosted: Sat Nov 17, 2018 2:37 am 
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Location: Delta, BC, CA
Ok, so I checked the bias running at approximately 1.40 volts each side a little down as I have not biased the tubes since new.Set the bias at 1.50 volts for both sides and will re check it tomorrow, these are the jj el34,s that came with the amp.I will bias again when the kt77,s arrive, thanks for all the feedback from my post, if anyone needs a speed box s for there project turntable I have one for sale on C.A.M. your turntable motor must be 16 volts or it will not work although the project website says it will work on mine it does not.I also have a kozmo passive pre amp with the vishay resistors inside if your intrested for $300, this thing sounds amazing for the price there is a review on 6 moons.Has three inputs two outputs if you have a sub like me. :D

-- 17 Nov 2018 03:49 --

Amp never came with instructions, I will try and contact Will Vincent about biasing for this amp, for now I am going with the stock dynaco settings.The amp is on you tube if you type Will Vincent Dynaco you will see Jim demoing the amp calls it the I pod dynaco.


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