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RJF
New member
87ma would blow 6L6's to pieces. 35ma would sound about right to me. As far as KT88's, I love them and run 3 pairs in my Herbert and don't plan to ever change. I have mine biased to 55ma.
My tech and I couldn't understand how to bias the amp with the fuses out, so we just biased the amp with them in and just adjusted each pair slowly until all 3 read 55ma with the amp running. I also asked a similar question to yours, and never could get a strait answer on it. When you bias it, with the fuses in, and your multi meter shows you what ma it's reading, then that should be the m/a that the tubes are running at.
My tech and I couldn't understand how to bias the amp with the fuses out, so we just biased the amp with them in and just adjusted each pair slowly until all 3 read 55ma with the amp running. I also asked a similar question to yours, and never could get a strait answer on it. When you bias it, with the fuses in, and your multi meter shows you what ma it's reading, then that should be the m/a that the tubes are running at.
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evilsaint
New member
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shadow070
Active member
The Herbert has 3 bias points.
Pair a: tubes 1 and 6
Pair b: tubes 2 and 5
Pair c: tubes 3 and 4
When biasing pair A, just remove the fuse for pair A and afterwords put the fuse back.
When biasing pair B, just remove the fuse for pair B and afterwords put the fuse back.
When biasing pair C, just remove the fuse for pair C and afterwords put the fuse back.
This is how P. Stapfer learned me to do it.
Pair a: tubes 1 and 6
Pair b: tubes 2 and 5
Pair c: tubes 3 and 4
When biasing pair A, just remove the fuse for pair A and afterwords put the fuse back.
When biasing pair B, just remove the fuse for pair B and afterwords put the fuse back.
When biasing pair C, just remove the fuse for pair C and afterwords put the fuse back.
This is how P. Stapfer learned me to do it.
MARK2C
Member
A. Run your presence higher before you change tubes.
B. See what preamp tube you have in the V1
Everyone runs straight to the power tube swap on Herbert's before anything else.
You can pull all three fuses and bias them all at once.Don't forget that Herbert needs to have each pair balanced. When you bias one pair of tubes
the bias set on the other may go up or down. You have to slowly balance them all out to your target MPD. Adjust, check, adjust, check, adjust and keep checking all three duets
until they are at your calculated MPD.
The 6L6 is a 30W tube, so 70% of max plate dissipation is 44mA or 88mA per pair in the Herbert.
So, 88mA a pair is fine. Diezel's recommendation of 70mA per pair is also good as well around 60% MPD.
B. See what preamp tube you have in the V1
Everyone runs straight to the power tube swap on Herbert's before anything else.
You can pull all three fuses and bias them all at once.Don't forget that Herbert needs to have each pair balanced. When you bias one pair of tubes
the bias set on the other may go up or down. You have to slowly balance them all out to your target MPD. Adjust, check, adjust, check, adjust and keep checking all three duets
until they are at your calculated MPD.
The 6L6 is a 30W tube, so 70% of max plate dissipation is 44mA or 88mA per pair in the Herbert.
So, 88mA a pair is fine. Diezel's recommendation of 70mA per pair is also good as well around 60% MPD.
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