Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bub on November 16, 2010, 01:44:05 pm
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Hi Gent's
I pull my Ampeg B15nf out of storage, turn it on, rectifier sparks, replace with new one, turn it on and check voltages.
Pin 3, both 6l6s 480v
Pin 4, both 6l6s 480v
Pin 5, both 6l6s -51v
V1 Pin 5, 2 180v, pin 6, 2.7v, pin 3, 2.4v
V2 Pin 5, 2 180v, pin 6, 2.8v, pin 3, 2.4v
V3 Pin 5, 2 250v, pin 6, 2.8v, pin 3, 3v
I pulled the 6l6s and checked resistance between the OT blue and brown leads, 270 ohms, between the yellow and green speaker jack leads I get .7 ohms with leads disconnected.
Before I disconnected the OT leads I plugged my guitar in, absolutly nothing coming out of speaker and then one of the 6l6s sparked.
Is my OT toast?
Thanks for any help
Rob
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Measure from the OT center tap to each leg on pin 3 with the power tubes out.If it's drastically different then you have a problem.
Get another pair of 6L6's and try again.Don't assume the preamp tubes are good.
Measure from the common on the OT secondary to each leg.Is it multiple impedance?If so readings like .5, .7 ohms are in the ballpark,the highest being the highest impedance tap.
What are the heater voltages?
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Thanks for the reply phsyconoodler,
I did all the checks you suggested and everything checked out and then I found the problem. Somebody had installed an additional speaker jack and had wired it incorrectly. When I was in the stock jack I was on a the yellow and green OT output wires and when I was on the installed jack I was on yellow and black, yellow being centre tap. The stock jack is insulated from the chassis where the installed jack was not. I have no idea how it worked before. I guess it didn't like my new 4/10 plugged into it. Anyways, my panic is over, it sounds sweet like a B15 should and now it's back on the market for sale.
Thanks again
Rob