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Post subject: Re: Blues Deville, with blue speakers, "fender" tag on the f
Posted: Thu Jan 13, 2011 2:16 pm
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Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
foossh wrote:
Wow this is great, so It lools like the adjust pot is R82 which I noticed when I took off the back cover, and the Test point is TP26. Its not as simple as my Twin with the portols on the back of the amp, but I assume I use my volt meter and put the positive on TP26 and the Negative where? somewhere on the chassis? and set it to 60mva, Then where do I test to make sure the reading is balanced? "00".

I can look it up if you don't know off hand, this will make it much easier! Thank youi.


Correct on R82 and TP26. TP26 reads off a 1 ohm resistor that combines the cathode current of both power tubes. There is no way to balance the plate current. The best you can do is use a bias probe (which I highly recommend) and measure the cathode current of each power tube individually. I have a Blues Deluxe Reissue and I use this:

http://www.amp-head.com/product_info.ph ... 037973adf5

It lets you safely measure cathode current and plate voltage. With those measurements, I then use the Weber bias tables to calculate plate current and plate dissipation:

http://www.webervst.com/tubes1/calcbias.htm

I currently bias my BDRI (with JJ 6L6GCs) at 36 mA plate current/406 VDC plate voltage (83 mV at TP26) which is right at 50% plate dissipation. They are balanced within 1.5 - 2 mA. You might want to look at this:

http://www.eurotubes.com/euro-Fender-HRDV.htm

Note that if you are using the stock power tubes, you should not bias them this hot.

If you are looking to retube, check this out:

https://ssl.eurotubes.com/cart/index.ph ... ory_id=122

Have fun. :D

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Post subject: Re: Blues Deville, with blue speakers, "fender" tag on the f
Posted: Thu Jan 13, 2011 2:23 pm
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Hobbyist
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Joined: Tue Jun 09, 2009 11:43 am
Posts: 20
Location: Phoenix
I will most likely put in NOS 5881's, but I may hit up my tech friend that works at Fender and buy him a 12 pack to walk me through making these adjustments the first time and use his scope. For now I will push these stock tubes as far as I can. Too bad it's not real simple like the Twin but no biggie, it works fine now. Thanks for all this info, I will come in handy.

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Scott Johnson
09 Fender Telecaster JA-90 Ebony
97 Gibson 1960 Les Paul Classic Gold Top
95 Fender 62 reissue Jaguar (Antiquity humbuckers/LesPaul Bridge Mod)
94 Fender Strat Mexico-(Mini Humbucker Mod)
2000's Fender Twin Amp
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