Re: Rickenbacker guitar amp, need help with substitution

Hello all.
I have run into a - curiosity.
Since the supplier I found had the 2n5462 JFET in stock, I ordered one just in case, and today, when the parts arrived I put the new one on the TC1 Multi-function tester, to see if it tested the same. The old one tested as a 235.1 ohm resistor between legs 1 and 2, and ignored leg 3. The new one, marked 2n5462, (and also marked F(airchild) BK45), tests as a BJT-PNP, 1emitter, 2collector, 3base, hFE 512, Ube 802mV, Ic 5.8mA. (2/3 Greek).
Is this a fluke of the tester,...

Re: Rickenbacker guitar amp, need help with substitution

Thank you again Redwire. I removed the power amp transistors because they would not test; neither with my multimeter's diode setting, nor with the test leads on the TC1. Both methods tested one of them as faulty, and while I was removing one, I did the other because the testing felt iffy. Once removed, they both test fine both ways. Same reason I removed the JFET. I found a test procedure for an N channel, and the demonstrater said he had no P channel to demonstrate, but that it was done in the opposite way. I had hoped the...

Re: Rickenbacker guitar amp, need help with substitution

Thank you Redwire. The 470uf is hidden under the heat sink. What is there now is a 500uf 25V. It looks like a good solder job, but I suspect it is a replacement. I'll replace it again anyway, with a 470uf 35V or better. No telling how old it is.
I'll put the JFET back and test with 4 new caps.

I was going to get the new caps here- [url]https://talonelectronics.com/shop/item.aspx?itemid=5451[/url] because they have the specified JFET, although I'll have to stretch a radial 470uf cap because they have no...

Re: Rickenbacker guitar amp, need help with substitution

Thank you Jiroy. I shouldn't have needed a calculator for this, I guess 12 into 120 was just so much easier for my brain than 120 into 12. I hope I would have caught it when I pondered my large 500w/channel PA uses less than 10 amps.
When you say "the more I change capacitors, the better", are you thinking I need to change more than the 4 electrolytics that I see?
I'm thinking it would be a lot easier to follow R_J's advice and leave the power cord un-polarized and unfused. It has managed this long...

Re: Rickenbacker guitar amp, need help with substitution

Thank you R_J for your help. The output transistors wouldn't test in-line. they test fine, I'm waiting for some heat sink compound to put them back. Yes, I have the mica insulator that fell off. The jfet in the preamp did not test fine, so I removed it for testing. As best as I and my TC1 M-tester can tell, it tests as a 230.6 ohm resistor between the left and center leg, looking at the flat side, and nought on the 3rd leg.
Why I think it needs a polarized plug, is right now, either leg could be the hot leg, and the...

Re: Rickenbacker guitar amp, need help with substitution

Well, I just figured one thing, The back plate says 117v, 12 watts. Since we now have 120v in our mains, that would mean a 10 amp fuse minimum, so I'm guessing I should put in a 12 amp to give it a little room to fluctuate. Is that correct? Thank you for your help and patience.

Re: Rickenbacker guitar amp, need help with substitution

Thank you so much Jiroy. I'll order a couple just in case; I have found no fault in the preamp to explain it's demise. The amp has no fuse, and a non-polarized plug. I know how to replace the plug, but am unsure what amperage fuse to get. If anyone has any opinions, I would appreciate them. Now I get to choose capacitors- are there any good reasons not to choose these- [url]https://www.digikey.com/en/products/detail/nte-electronics-inc/NEH2200M35GF/11655527[/url] or any recommendations? Thank you.Re: Rickenbacker guitar amp,...

Hello- This is my first real project, a Rickenbacker TR7 guitar amp, first generation, (tremolo, no distortion) not working, 100 watt dim-bulb tester stays glowing, though not brightly. The 2n5462 (JFET?) the screwdriver would be pointing to in 2 of the pics tests as a resistor between center leg and one end according to TC1 M-tester. Part seems to be unavailable unless I get 20 shipped in from unknown expensive source. The 4 caps test low esr, but amp is 45+ years old, so I imagine I should replace at least the 2200u35v, and the 470u,35v electrolytics, and it seems I might as well replace the...

Re: New Members - please post your introductions here

Hello. My name is Peter, and I found this through the Learn Electronics Youtube channel. I have always tried to fix anything, but this is my first try at component level electronics. I have a few old guitar amps that need repair, so I'm giving it a try. Thank you.