Rickenbacker TR35B issues

[DPM309]

Working on a Rickenbacker TR35B that is shorting out somewhere. Put an new volume pot in and it worked for awhile and then experienced low, distorted volume. Put the old one back in and it worked while the chassis was removed from the speaker cabinet. Installed it the cabinet, and then it blew a fuse. Replaced the fuse and powered it up using a lamp limiter which showed there was a short somewhere. The 2 power transistors (Q9 -TIP42B and Q11- TIP41B) where bad. Replaced them with new a TIP42C and aTIP41C.Powered it up with the light limiter and it did not even light up. Powered it up without the limiter and heard a loud hum and then a pop and Q9 blew up! Don't know where to go from hear. I don't think using a TIP42C instead of a TIP42B was the issue since these are very similar transistors. Luckily I purchased a batch of TIP42C and TIP41C so I have spares. I attached the schematic for reference. I usually work on tube amps and was trying to help out a friend on this SS amp.

[Jon Snell]

Firstly the TIP41B is an 80volt version of the TIP41C no other differences.
Output transistors blow eithe due to an excessive load or excessive current demand.
Are your TIP***s from a reputable dealer; OnSemi, Farnell, RS, Mouser etc or fromthe amuzun or fleabay.
If the latter, suspect the poor quality TIPs.
If propper transistors, the most likely cause is over current. Check the bias adjust pot has not been damaged and set to about 1.4v between the bases of Q8 & Q12.
These power amplifiers, (designed originally by RCA back when transistors were in their infancy as a quasi symetrical amplifier), are quite simple and reliable.

[DPM309]

Thanks for responding Jon. I usually work on tube amps and avoid SS amps for these type of issues. I did buy these on Amazon and the supplier seemed reliable and had good reviews. I tested both of these before installing. I did notice that the 100uF, 40V e-cap was leaking green ooze and did not get any reading on it. I have a replacement cap I can install and hope this solves the issue. Will re-post after I get a chance to change it out.

[g1]

Also, were you careful with the insulators for the output transistors? They can get lost in the shuffle. If they are missing or damaged, the collectors (metal case) of output transistors get shorted to the chassis.

[DPM309]

g1, are these the insulators you are talking about? I need to be careful when reinstalling the transistors.

[g1]

Yes, that is the insulator. There should also be a plastic shoulder washer which prevents that screw or nut from contacting the metal tab (case) of the transistor.

[DPM309]

The plastic shoulder washer is in place. I will be careful in reinstalling new transistors to make sure the case is not grounded out. I also noticed the 100uF/40V e-cap was leaking green ooze from the positive side and will replace.

[g1]

If Q9 went, Q7 may also be bad. Check Q7 and Q11 as well. And all associated resistors if you have not already checked them.
Continue with limiter lamp, do not connect any speaker or load until amp is stable with no DC volts at the output.

[DPM309]

Installed new power transistors, Q9 and Q13 and checked Q7, Q11, and Q8 and they all passed the diode test. Replaced the 100uF/40V cap that was leaking. All of the associated resistors checked out. Plugged the amp into the light limiter and it did not light up at all.
Also wondering what this component in the attached picture. Looks like a red coil of some sort

[g1]

Yes, it's a coil. Probably in series with the output. Is the white wire the output wire? Is there any DC voltage at the output?

[g1]

I don't think using a TIP42C instead of a TIP42B was the issue since these are very similar transistors.

Did you check the pinout? I just double-checked and the datasheet I found says the original transistors were EBC where the TIP's are BCE, so they will not work. (edit: unless board was revised)

[DPM309]

The original power transistors where TIP41c and TIP42c. According to the datasheets I referenced, the pinouts on TIP41c and TIP42C were the same as TIP41B and TIP42B. I will double check though. The white wire is the output and I will try to measure the voltage on it when I run it with the light limiter. What I don't understand is before I fried the power transistor, the light limiter lit up brightly indicating a short. Now I am not getting any light whatsoever. Tried the light limiter on my working GKRB400 and it lit up dimly indicating no short.

[DPM309]

The amp was working fine with both TIP41B and T42B before I started. This might have been a change later models of the TR35B which switched the power transistors from the 2N****s to the TIPs. You are correct that the pinouts are different.

[g1]

Yes, they must have changed it. The coil does not show on the schematic either, so I assume what you have is a later version than the schematic shows.
When the bulb was lighting up before, did you have a load or speaker connected?

[DPM309]

I believe the speaker or a dummy load was connected and the light lit up brightly indicating a short. When I tried it recently, there was no load connected but the light did not even light up at all.