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Old 10th October 2007, 09:09 PM   #1
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Default Help. Bogen m60a

I just bought a Bogen m60a converted for guitar use, but my problem is this....(I know of nothing about biasing and stuff)


Since they no longer produce 8417's what are some cheaper power tubes that won't **** the amp up?

The preamp uses 6EU7's I also have no idea on the cheaper alternatives for these either?

Phase splitter/invertor? uses a 7247 which I searched and found that its the same or equal to 12DW7.....?


Any help would be awesome.
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Old 11th October 2007, 12:15 PM   #2
KaDe is offline KaDe  Germany
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An almost direct replacement for 8417 is the Toshiba 6GB8.
I have changed to these in one of my hi-fi amps with good results.
But most amps that use the 8417 have been modified for 6550.
The 6550 mod. requires a bias supply adaptation.
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Old 20th October 2007, 12:51 AM   #3
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How much would it cost to get this done on average? Its 60 watts, but I dont want the wattage to drop. Also I would like it to be replaced with tubes that'd be around for along time, and that is cheap in cost. Is 6550 the only replacement?
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Old 20th October 2007, 01:50 PM   #4
KaDe is offline KaDe  Germany
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As there is no other reply on the forum yet I presume nobody did this 6550 mod. on a Bogen m60a before.
Im not familiar with the Bogen m60a but would guess that two resistors in the bias-supply need to be changed.
If you have a service man nearby the most cost would be labour charge and the calculation for the new resistor values needed.
If he knows his job well it should be fixed within one or two hours.
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Old 18th January 2008, 11:26 AM   #5
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Default 6GB8 schematics

KaDe wrote:

"An almost direct replacement for 8417 is the Toshiba 6GB8.
I have changed to these in one of my hi-fi amps with good results."

I have some 6GB8s which I would like to put in an SE circuit. Can anyone who has built an amp around this valve provide a/some circuits.

Thanks.
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Old 18th January 2008, 03:59 PM   #6
KaDe is offline KaDe  Germany
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Default 6GB8

I use the Toshibas in a PP amp, no SE build yet.
Here is a SE schematic I found somewhere in the japanease net:
Attached Images
File Type: gif 6g-b8s.haisenzu.gif (24.5 KB, 115 views)
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