Rickenbacker guitar amp, need help with substitution

[Plind]

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 2- 22u25v while I'm at it. Any opinions?
So, what I'm hoping for is a direct replacement for the 2n5462, and the directions as to which leg goes where in comparison to the 5462, and I would appreciate any advice as to which caps to use, Mouser, Digikey or ?
Right Model No. but wrong schematic I think- Wrong, decade newer model, but right amp schematic I think- Closest preamp I could find- Pictures attached. Thank you for any help or advice you can give, I'm an old dog trying to learn new tricks. -Peter.

[jiroy]

Re: Rickenbacker guitar amp, need help with substitution

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 2- 22u25v while I'm at it. Any opinions?
So, what I'm hoping for is a direct replacement for the 2n5462, and the directions as to which leg goes where in comparison to the 5462, and I would appreciate any advice as to which caps to use, Mouser, Digikey or ?
Right Model No. but wrong schematic I think- Wrong, decade newer model, but right amp schematic I think- Closest preamp I could find- Pictures attached. Thank you for any help or advice you can give, I'm an old dog trying to learn new tricks. -Peter.

This nte326 jfet is identical to 2n5462 , and have the same pins/legs .

https://vetco.net/products/p-channel...0v-10ma-nte326

[Plind]

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- https://www.digikey.com/en/products/...M35GF/11655527 or any recommendations? Thank you.

[Plind]

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.

[R_J]

Re: Rickenbacker guitar amp, need help with substitution

12 watts at 120vac is approx. 0.1 amps (100ma)
There is no need for a polarized plug as this has a ac line transformer

I doubt the jfet is your problem, What was wrong with the two output transistors? I see they are removed.

[Plind]

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 switched leg has a .01M .4kV disk capacitor after the switch, to chassis ground. I was going to force the switched (and soon to be fused?) leg to be the hot leg, but now I'm wondering if I should wait until it is back together, and see if either leg grounds to chassis. It should be the unswitched leg shouldn't it? The schematic does not help, since it does not match the board; there are two versions of this amp, this is the earlier one.
Yes, I did my math backwards. I can claim brain damage, or a senior moment, but that is no excuse. That is why I do everything twice. This is a 7 watt amp with a "Bounce back transformer", whatever that means, that is claimed to be as strong as a 15 watt. It belongs to the 101 year old leader emeritus of our senior center's ukulele group. It seems to me that a fuse is never a bad idea (250w?). If I can get this working, I have his original "Cry Baby" pedal that also needs work. It would be fun to see him use this again. Thank you for your help. I plan to keep learning until I die. And then some.

[jiroy]

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- https://www.digikey.com/en/products/...M35GF/11655527 or any recommendations? Thank you.

Welcome Plind .. R_J is following , and i'll be around to help .
Capacitors Nte series are good , and being a 45 years old Amp. , the more you change capacitors ,the better .

About fuses , I always use online calculators , for many reasons ,hope it will be useful to you :

https://www.rapidtables.com/calc/ele...alculator.html

[Plind]

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 as is. Thank you all.

[redwire]

Re: Rickenbacker guitar amp, need help with substitution

I think you need to first know what section is malfunctioning. Pre-amp? Power amp? Narrow it down instead of bouncing around.

It's normal for a JFET to read low ohms D-S, they are a normally-on device. I would suspect the TC1 M-tester because a P-ch JFET is an oddball and 2N5462 has a VGSoff of up to 6V and your tester puts out less than 5V or not enough to switch off the device, and possible to give a false report. As I recall the tester can't do P-ch testing properly, firmware bungles the test. The JFET might be fine although they do get static electricity zapped at the guitar jacks.

I would first focus on the power amp. The blue Philips electrolytic capacitors don't last, I would replace them. C3, C5 22uF 25V. Your power amp pics don't show the output capacitor C6 470uF, where is it? It's on-board in the Rickenbacker schematics.

[Plind]

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- https://talonelectronics.com/shop/item.aspx?itemid=5451 because they have the specified JFET, although I'll have to stretch a radial 470uf cap because they have no axials in that range- https://talonelectronics.com/shop/item.aspx?itemid=7239
22uf- https://talonelectronics.com/shop/it...x?itemid=12758

-unless someone warns me off of this establishment.

For the $2 I might as well get the JFET just in case.

Does the TC1 tester work well with N channel JFETs? I'm trying to file away knowledge for the future. Thank you all. You are most appreciated.

[redwire]

Re: Rickenbacker guitar amp, need help with substitution

I find the testers are limited to the ~5V they can put out. I also think they don't test P-ch JFET's properly. It's common to see some N-ch JFET's need up to 8V to turn off. P-ch is very rarely used and I have a drawerful J174, J176, J177, J270, 2N5460.
I think the meter firmware guys have never actually tried a P-ch part to test, nobody really has any lying around nowadays.
I have not tried Talon but they look OK. I think the blue Philips caps are for sure toast but the bigger ones I find do last though.
Basic in-circuit diode test can tell if the power amp transistors are OK.

[Plind]

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 tester would be smarter than I.
I just removed the 2200uf, which I knew seemed faulty, and off the board, it tests zero ohms both ways with a capacitance of 0.L so we know it's Out of Luck. It was glued on with the same hot glue(?) that is holding the 500uf 25V hidden under the heat sink, which seems to test good, in circuit, and the solder joints look the same, so I guess it might be original, though of a different make, and marked W-Germany, Which probably makes it old enough to replace. The blue 22uf caps also test good, but I will bow to the wisdom and replace all 4 electrolytic caps. Thank you again.

[jiroy]

Re: Rickenbacker guitar amp, need help with substitution

Hi Plind .. You're dealing with a fairly old device , and moreover , an Audio system . Any tiny leaks in capacitors , you will hear it from the speaker .

[Plind]

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, since it was suggested that the TC1 can't handle N channel JFETs, or might it be a mis-labeled component? I hope one of you will enlighten me.
Thank you all so much for your help.

[petehall347]

Re: Rickenbacker guitar amp, need help with substitution

2n5462 are obsolete . not saying you wont find a genuine one but tread carefully .