VH4S Bias Clarification!

  • Thread starter Thread starter Ventura
  • Start date Start date
Ventura

Ventura

Well-known member
Helloooooooooooooo,

So, with the "S" version of the VH4, there are 2 OT's. Each OT responsible for 2 tubes, correct? If this is the case, each OT and its respective tube pair should be biased to 80-100mA for 6550's. And if this is the case, that means, roughly, each tube is running at about minimum 40mA to max 50mA PER TUBE, correct?

Thank you,
V.

PS - I always forget the simplest of things when it's been a while... I swear, if it's not going deaf, it's going dumb. Thank goodness for loud amps at least :lol: :LOL:
 
JUST an FYI....

According to a PM, several PM's actually, from Papa Diezel, he's recommending 35mA per tube, therefore, 70mA per pair. Contrary to the Tech Corner recommendation of 80mA to 100mA per pair.

I'm not sayin', I'm just sayin', you know what I'm sayin'...?? :confused:

V. :thumbsup:
 
are you sure thats not for EL34s??? that seems kinda cold for a 6550.
 
The website didn't change yet because

- I'm lazy, busy, a psycho, . . . you name it
- I have to change all manuals too - in three languages for three ampmodels
- I like to keep things straight, so I want to be everything online at the same time.

ok?

For 6550 use 40mA per tube or 80mA per pair.
Start from here and then let your ears and money decide if you want to go higher or even lower. The lower, the hollower they are sounding.

The safe range for 6550 can be seen here:
6550.gif

Your plate voltage is 480V, so the safe area per tube is from 40mA to 50mA. Diezel recommends to use the lower bias range because of the quality of modern tubes, so in case you should have really good 6550s (like NOS) then you can go as high as 50mA per pair. If you are using average, today's quality 6550, use 40mA.

ok?
 
My pleasure.

Peter and I "harmonized" the bias suggestions today on the phone, info can be found on the website as well . . .

40mA for 6550 / tube
30mA for EL34 / tube


EL34bias.gif
 
I believe a KT77 is the same bias range as an EL34...but if i am wrong...Olaf will chime in! :lol: :LOL:
 
duesentrieb":2qzl5x4j said:
The website didn't change yet because

- I'm lazy, busy, a psycho, . . . you name it
- I have to change all manuals too - in three languages for three ampmodels
- I like to keep things straight, so I want to be everything online at the same time.

ok?

For 6550 use 40mA per tube or 80mA per pair.
Start from here and then let your ears and money decide if you want to go higher or even lower. The lower, the hollower they are sounding.

The safe range for 6550 can be seen here:
6550.gif

Your plate voltage is 480V, so the safe area per tube is from 40mA to 50mA. Diezel recommends to use the lower bias range because of the quality of modern tubes, so in case you should have really good 6550s (like NOS) then you can go as high as 50mA per pair. If you are using average, today's quality 6550, use 40mA.

ok?
Click to expand...

I N T E R E S T I N G ! ! ! ! I got the amp back at 35mA per tube, and it sounds a bit weak... You say "hollow", that's kinda where it's at. Papa sent me a matched quad of Winged C 6550's. Maybe I oughta tweak up the bias a tad to 40mA or 42mA.

Will let you know - but regardsless - thanks!!
Mo
 
44mA or 88mA pair wise is 60% only of max plate dissipation. I swear these tubes get louder
and have more bottom end the higher you go. I have been happy at 44mA for at least the last six
months.
 
I flip my VH4 over on books, adjust the bias at the OT and let it run for half an hour.
I recheck it and then play test. The old, " Damn it sounded great before I put it back in the Head Shell" rule
applies...
 
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