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natey wrote:Greetings, all!
I recently became the proud new owner of a 1974 (I think) B410. It's definitely a good news / bad news situation. The good news is, I got it cheap! The bad news is, it's missing a few things...like output tubes. And the reverb tank. And the cabinet. And I'm pretty sure the output transformer is blown.
Of course, this was expected, since I bought it as a project, and I'm pretty confident in my ability to electrically restore this amp. I've got the schematic, but there are a few pieces of information that I need to really get the amp working to original spec again, and the googler has been unhelpful on these points:
1. What are the specs of the output transformer? I know it's a 4 Ohm output, what about the input? It looks to me like the B410 output section is identical to a fender twin reverb - can I just use a modern replacement designed for the twin, or are there other factors to consider?
2. What are the specs for the original reverb tank? I don't know what model tank came in the amp originally, and so I don't know which Accutronics replacement to order. (Sadly, the Accutronics replacement will probably not be made by beautiful girls in Milton Wisconsin...)
Thanks for any help you can offer...
natey wrote:OK, not much response, I see...I will continue to post updates anyway, in an effort to help out the next person that tries this....
natey wrote:Greg - If you have any way to directly measure the input and output impedance of the original reverb tank, that would be great. If not, then can you read the model number stamped on the side of the tank? If I knew that, then maybe I could find a data sheet for the tank with the original specs...
JPS - Not sure what influenced the design of the b410's reverb circuit, but it uses both triodes of a 12AT7 in parallel to directly drive the tank, so the Gibson design is going to have a different driver impedance.
I calculated the driver impedance of the b410, and got something in the neighborhood of 3k Ohms. The highest impedance Accutronics-style tank I found was 2k. I ordered one, figuring it couldn't hurt to try it. I'll post results when I've had a chance to try it out.
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