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Topic: Fox 5F8B Power tube replacement |
Bill Findlay
From:
Baytown, Texas, USA
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Posted 28 Jan 2014 1:17 pm |
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I need to replace the power tubes in my fox amp.
I will replace with four matched tubes but I know they will need to be rebiased. I have the equipment to rebias them but I have never did it . Does anyone have a step by step method to accomplish this .
If so could you sent me a private message with a procedure.
Thanks in advance.
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wrfindlay@yahoo.com
[quote:]Emmons D-10 LG, MSA SD10 Millennium, Mullen Discovery S10, Fender, Stringmaster D-8, Fender Steel King, Evans AH-200, Roland Cube 80XL, G&K Fusion & G&K MB200 Preamps,Boss DD-3, [/quote:] |
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Tim Marcus
From:
San Francisco, CA
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Posted 28 Jan 2014 1:20 pm
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if its possible to get the exact same tubes with the same plate current (or within 1-5mA) you can swap them with no bias adjustment.
I recall Ken using JJ tubes, which come in matched quads. On the boxes, you'll see a marking called IP or PC. Match that number and you're done
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Milkmansound.com |
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 28 Jan 2014 1:47 pm
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Here's one way:
Measure the bias current of what you have now... plug in the new set and set the bias current the same.
Here's another way:
Use one of those inexpensive laser-pointer IR thermometers ($30 at Harbor Freight) to measure the temperature of your final tubes' plates... bias the new set to the same dissipation temperature.
The IR thermometer is a great tool for all kinds of things... you can check if one tube's getting hotter, etc... I was able to trace a failing capacitor with it! It did help that the paper label on the capacitor was turning brown...
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New FB Page: Lap Steel Licks And Stuff: https://www.facebook.com/groups/195394851800329 |
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Ken Fox
From:
Nashville GA USA
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Posted 29 Jan 2014 6:51 am
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You can re-order those JJ tubes from Antique Electronics. Yours are rated 15/2.5. I kept records on all the power tube ratings in the amps I sold. Hope that helps.
Ken |
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Bill Findlay
From:
Baytown, Texas, USA
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Posted 29 Jan 2014 10:34 am
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Thanks everyone for the information.
_________________
wrfindlay@yahoo.com
[quote:]Emmons D-10 LG, MSA SD10 Millennium, Mullen Discovery S10, Fender, Stringmaster D-8, Fender Steel King, Evans AH-200, Roland Cube 80XL, G&K Fusion & G&K MB200 Preamps,Boss DD-3, [/quote:] |
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 30 Jan 2014 4:23 pm
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"Measure the bias current of what you have now... plug in the new set and set the bias current the same."
That might work if the tubes you are replacing were brand new. As they wear current draw changes. With old tubes I often find a pair with one tube hot or cold when compared on the bias meter. Rarely are they nearly equal as when installed as a matched pair of quad. I think temps are even more of a crap shoot.
Ken's numbers are the best way with out measuring plate voltage and doing the math or consulting an online bias calculator as on Weber's site IMO.
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On man....let the smoke out of another one. |
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