What's a safe bias range for 6550's in my VH-4?

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Mizati20

Mizati20

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On the tech corner section of Diezel's Website it says 80-100 mA per pair, but in light of the recent opinions from Papa not recommending them I've heard 60 mA? I have them sitting at 60 mA right now and there is virtually no heat that was mentioned to be a potential problem, the EL-34's I had in it before we literally 3x hotter... let me know fellas, the tubes are burning in now!

Oh also, I'm doing a comparison video since there has been so much talk of EL-34 vs. 6550 recently... so I recorded a vid before I pulled the EL-34's, and will make another one once I get the 6550's running so you can compare the two, I don't have any professional recording equipment at my house so it's just a digital camera, not sure if you will notice a difference, but I figured it was worth a shot, vids will be up within an hour or so!
 
I've got a herbert and have been thinking of putting some or all 6550 in it. There are currently el34's in it.
I can't wait to hear the comparison..
:rock:
 
i run KT-88's in mine and i bias them at 90mA it gets really hot and sounds awesome :rock:
 
6550's were recommended to be 35 a piece, 70-75 per pair.

This came direct from Papa when he was on the 6550 bandwagon.

V.
 
Guess i had better rebias this weekend. I think i am still running @ Peters original 45-50ma per tube. Thats why it sounds so damn good!! ;)
 
I have mine biased at 60 mA and it sounds fucking incredible and there is very little heat, maybe I'll raise it to 70 or 75 just for kicks.... (for the pair obviously)
 
...my pair is biased @ 90-100.....hot hot hot!!!!! Good thing i have 2 external fans! :loco:
 
PaulyPanacea":1m0ptofq said:
...my pair is biased @ 90-100.....hot hot hot!!!!! Good thing i have 2 external fans! :loco:
Click to expand...

Wow that thing must sound absolutely incredible!
 
Great Vid's Kit !!!!

I recommend 60mA per pair because of the heat. You can try 70mA, but anything over that and the amp really gets hot.
On the Herbert, six 6550's at 80mA will start getting the power transformer VERY hot after 20 minutes. I have swapped the
6550's in the Herbert for all EL34's and it does not get hot with all duets at 70mA after hours of playing.

You can adjust the settings below to your taste and the plate voltage. The higher the current draw, the lower the plate voltage.

For example, at 40% MPD/60mA per pair the plate voltage would be 470V due to the increase in bias current.
It still calls for around 60mA at 470V. At 60% MPD/88mA the plate voltage may be 460 and the math would call
for 91ma. Not too much of a difference, but for those who chase the tone dragon and need thing dead ass nuts,
it's the way to make sure your hearing and seeing the bias settings recalculated for the drop in plate voltage.
For anyone else, 477V is close enough.

35W @ 477V- VH4 or Herbert

40% MPD= 60mA
45% MPD= 66mA
50% MPD= 72mA
55% MPD= 80mA
60% MPD= 88mA
65% MPD= 94mA
70% MPD= 102mA
75% MPD= 110mA

40%-50% may look like the tube is not being used to it's full potential, but I assure you it sounds excellent.
Used your ears and you will hear a loud, clean amp with great dynamics in the bottom end and much less sizzle
in the treble.
 
MARK2C":s1zoq1xh said:
40%-50% may look like the tube is not being used to it's full potential, but I assure you it sounds excellent.
Used your ears and you will hear a loud, clean amp with great dynamics in the bottom end and much less sizzle
in the treble.
Click to expand...

Mark, maybe this is a newbie-question, but biasing a tube below to its recommendation does not affect to its sound? only to the output level?
 
RaulTx":1syonw83 said:
MARK2C":1syonw83 said:
40%-50% may look like the tube is not being used to it's full potential, but I assure you it sounds excellent.
Used your ears and you will hear a loud, clean amp with great dynamics in the bottom end and much less sizzle
in the treble.
Click to expand...

Mark, maybe this is a newbie-question, but biasing a tube below to its recommendation does not affect to its sound? only to the output level?
Click to expand...

No, it's a good question. Papa says that the 6550's get too hot over 35mA each/70mA per pair and he is 1000% right.
Looking at the bias settings it's up to you to decide what sounds good and where you can safely run the tube. You can run it
anywhere between 40% MPD to 75% MPD because there is no real recommended setting. To listen to Papa and satisfy my ears,
I use 60mA, but I have heard the VH4 with 6550's at 75% and the amp compresses a bit, has more power but it also gets the
power transformer very hot. Try what settings you want and listen to the difference. I am just trying to keep the amp running cooler
and the tubes to last a bit longer. I ran six 6550's in my Herbert for a year with no problem at 80mA a pair. The VH4 has been running
6550's for 18 Months. I have tried everything from 40%-75% and I honestly could not be happier at 60-70mA. Good tone, cool running
and longer tube life. Again, if your tone is the best at 80mA then do it, but I don't honestly hear enough difference between 45-55% to
warrant the hotter setting.
 
Just to chime in, I first biased them at 60 mA, then raised them to 70, and noticed hardly any sonic difference what-so-ever, but there was a noticeable heat increase... I think 60 mA is perfect, YMMV, but like Mark said, it's a happy medium between sounding incredible and following Peter's advice as far as the heat warning goes...
 
I've got mine (VH4S) at the 70mA per pair (give or take) as per Poppa's recommendations and it's a gorgeous sounding head. Secondly, keeping things efficient and not to the point of boiling makes me feel as though I might be getting some life outta my tubes... They ain't cheap.

V.
 
So Peter is recommending 60 or 70mA per pair now with the 6550s?
This means 30 or 35mV with a bias probe (per tube), right?
 
Vigier Arpege":3viqwdvq said:
So Peter is recommending 60 or 70mA per pair now with the 6550s?
This means 30 or 35mV with a bias probe (per tube), right?
Click to expand...

Correct.
 
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