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Topic: 1971 non-master volume Fender Twin Reverb |
Ken Fox
From:
Nashville GA USA
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Posted 12 Apr 2008 12:53 pm |
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Serial #A30530. Came with original cabinet cut down to a head cabinet. This is now in a 1983-1986 Era Twin Reverb II cabinet with some of the best (and biggest) Twin Reverb speakers I have heard.
New reverb bag, new 6L6GC power tubes, complete new filter caps, bypass caps and bias caps. Also a new cover and new pop-out casters. Bias tested with Bias King Pro and amp is ready to play!
Amp was factory drilled for casters, all I had to do was install them!
$850.00 plus the cost of shipping/insurance via FedEx. $65.00 Discount for local pickup.
PayPal OK.
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Chris LeDrew
From:
Canada
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Posted 13 Apr 2008 10:17 am
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I've just got my '70 SF Twin up and running, and it's incredible for steel. Looks just like this one except it has the tail on the logo. Absolutely delightful tone. And the weight isn't too far off a Session 400. Excellent double-duty amp as well. And if you buy an amp from Ken, you know it's working right.
Just the delicious smell of the tubes burning in these beauties is enough to warrant owning one.
_________________
Jackson Steel Guitars
Web: www.chrisledrew.com |
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Bob Hamilton
From:
California Central Coast
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Posted 13 Apr 2008 3:13 pm Current Measurement
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| Hi Ken, beautiful amp. What was the voltage measurement that corresponds to the current measurement shown in the pic. I have a '69 Twin that runs around 405V-410V, and I've got a JJ quad coming in the mail. Just curious how hot you bias these, Thanks, BH |
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Ken Fox
From:
Nashville GA USA
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Posted 13 Apr 2008 4:42 pm
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These amps do not have a bias adjust, as did the Blackface era amps. They have a bias balance. The amp was in a safe range, so I did not change the fixed bias resistor or worry about the plate voltage. After doing 100's of Fender amps I have a pretty good feel for the safe range of bias on the amps without doing a calculation of power dissipation using the plate voltage and current.
For an amp with adjustable bias I use a spreadsheet that auto calculates based on the type tube and plate voltage.
For you amp a range of 36 to 42 would be good, based on the conservative estimate on my spreadshhet. The Bias King formula shows a range of 36 to 54 ma for 410 volts.
Running an amp too hot does not seem practical for tube life. I had a Mesa Boogie power amp in this week with a fixed bias resistor. It was running too cold at 24 ma and showed crossover distortion on the scope. I put a pot in parallel with t 47K resistor in the bias circuit and adjusted the pot to get the amp out of crossover distortion. I then measured the resistance the pot had on it and use a fixed resistor near that value to parallel the 47K resistor. The tubes were running about 32 ma after that. |
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Bob Hamilton
From:
California Central Coast
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Posted 13 Apr 2008 5:15 pm Fender
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| Thanks Ken, the Fender schematic shows -37.5 V with the fixed resistor, but I have a pot in there to set the bias value. The fixed resitor always seemed a little hot for steel. Thanks again for the info, BH |
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Ken Fox
From:
Nashville GA USA
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Posted 17 Apr 2008 3:23 am
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| sale pending |
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