How do I bias my Herbert.

  • Thread starter Thread starter robwalmsley
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robwalmsley

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My herbert is an older model with no external bias point. There used to be instructions on the Diezel web site but they are not there any more. Where can I get the instructions?
 
I would buy a bias rite or something - or are you familiar using a digital multimeter and work with 480V DC?
 
1. Take Herbie out of the headshell, place the transformers on two books (tubes !) with the pots facing you

2. upper right side: three fuses - from the left A, B, C

3. mid-left: three pots from the top: TrimA, TrimB, TrimC
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corresponding pairs:

A = 3 + 4 (inner pair)
B = 2 + 5 (inbetweens)
C = 1 + 6 (outer pair)


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4. gently push the first fuse out of its socket

5. install croco leads and hook them to your DMM, set to 200mA (!) DC (!)
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6. now (not earlier!) hook to mains + cab, vol = 0 and switch on (both, power and standby)

7. read DMM until value doesn't change anymore (1 minute, new tubes may take longer)
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8. adjust trimmer until you get the current given in the table bottom of post
clockwise: increasing current
counterclockwise: decreasing current


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9. switch Herbert off and unhook from mains

10. reinstall fuse you took out

11. repeat for the three pairs/fuses/trimmers


PS: set trimmer to read 60mA for a pair.
 
Thanks very much. Just what I was looking for. As always excellent support.
 
Is this similar to how it would be done on the VH4?

Can you please post those instructions as well?

I plan on retubing very shortly.

thanks!
 
How would you do this with a Weber Bias Rite? Do you still need to remove the fuses, or can you accomplish the Bias-ing with the fuses installed and the Bias Rite on the current pair of tubes being biased?

Also, can you swap between tubes without changing other components? Example: Swap a pair of EL34 for 6L6?

Thanks!
 
with the bias rite you dont need to remove fuses.

and you can go between pairs with no problem. If you need any help hit me up. I bias my boys with a Bias Rite. :thumbsup:
 
Scha-weet!! Is the recommend ~60mA on all of the pairs, regardless of tube type?

Thanks!
 
i would double check with Poppa on that one. I know a certain someone on here runs his 6550s a touch hotter...not pointing fingers
 
Thanks this info its awesome, i save some money in a technician.
 
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