C2 Radio Repair

[Rob M.]

I'm checking out an AM/FM radio of a fellow member and it looks like his X9 (DS-46) and X10 (DS-501) transistors are toast. I followed the signal path with a scope and checked the voltages and I'm losing the signal from the Collector of X8 (which is hooked to the Base of X9) onwards...

I found on the internet the NTE105 could be a replacement transistor for the DS-501 but are there also known replacements for the DS-46???

Furthermore the speaker isn't producing any sound when a battery is very briefly (100ms) tabbed against the unhooked speaker posts indicating it is dead as well (there was 12V on the speaker posts causing almost 2A running through the speaker due to the blown DS-501).

regards,
Rob.

[Jerry R.]

Re: C2 Radio Repair

The DS-501 rarely fails Rob although it will degrade and diminish audio quality. More than likely the .5 ohm fusible resistor has failed. Do an ohm meter continuity test on it (and the other transistors) before you spend a fortune on an NTE105.

X9 (DS-46) and X10 (DS-66) (from SAMS 31 manual) can be replaced with any medium duty silicon general purpose transistor such as a 2N2222. You can get a pack of substitutes at your RadioShack store in the parts drawers. Since the whole amplifier circuit is basically a simple current amplifier, the R2 bias control will compensate for variances among the devices and work just fine. The circuit is only dealing with low audio frequencies, not RF so it's not cricital.

It sounds like the wrong speaker was installed in the car. If it had the required 1.2 ohm load coil across the voice coil, it would not have failed. When you order a replacement speaker from the sources we all use, have them confirm that their load coil is 1.2 ohms and not .2 ohms as some of them ship. There's a big difference as the wrong speaker loads stress that DS-501 significantly (it's almost a short).

NTE105's are between $35 and $50. Loads of Delco radios used them. If it is defective, you could get an original part by buying a whole radio off of Ebay shipped for less than that.

A final suggestion, change the small electrolytic capacitors while you are in there. They tend to go leaky after all these years, especially the10 MF interstage coupling cap between the detectors and the pre-driver (X9 - DS-46).

_Jerry_

[Joel T.]

Re: C2 Radio Repair

The DS-501 rarely fails Rob although it will degrade and diminish audio quality. More than likely the .5 ohm fusible resistor has failed. Do an ohm meter continuity test on it (and the other transistors) before you spend a fortune on an NTE105.

X9 (DS-46) and X10 (DS-66) (from SAMS 31 manual) can be replaced with any medium duty silicon general purpose transistor such as a 2N2222. You can get a pack of substitutes at your RadioShack store in the parts drawers. Since the whole amplifier circuit is basically a simple current amplifier, the R2 bias control will compensate for variances among the devices and work just fine. The circuit is only dealing with low audio frequencies, not RF so it's not cricital.

It sounds like the wrong speaker was installed in the car. If it had the required 1.2 ohm load coil across the voice coil, it would not have failed. When you order a replacement speaker from the sources we all use, have them confirm that their load coil is 1.2 ohms and not .2 ohms as some of them ship. There's a big difference as the wrong speaker loads stress that DS-501 significantly (it's almost a short).

NTE105's are between $35 and $50. Loads of Delco radios used them. If it is defective, you could get an original part by buying a whole radio off of Ebay shipped for less than that.

A final suggestion, change the small electrolytic capacitors while you are in there. They tend to go leaky after all these years, especially the10 MF interstage coupling cap between the detectors and the pre-driver (X9 - DS-46).

_Jerry_

Hey Jerry;

Stop showing off!

Joel

[Jerry R.]

Re: C2 Radio Repair

Abuse me further and the souls of a thousand long dead radios will be dispatched to haunt you on this spooktacular weekend Joel.

I think it's excellent that Rob is willing to get in there and attempt a repair. If he succeeds, he can do C3 radios too. Same basic audio circuit for the mono models.

[Gerard F.]

Re: C2 Radio Repair

I'm checking out an AM/FM radio of a fellow member and it looks like his X9 (DS-46) and X10 (DS-501) transistors are toast. I followed the signal path with a scope and checked the voltages and I'm losing the signal from the Collector of X8 (which is hooked to the Base of X9) onwards...

I found on the internet the NTE105 could be a replacement transistor for the DS-501 but are there also known replacements for the DS-46???

Furthermore the speaker isn't producing any sound when a battery is very briefly (100ms) tabbed against the unhooked speaker posts indicating it is dead as well (there was 12V on the speaker posts causing almost 2A running through the speaker due to the blown DS-501).

regards,
Rob.

Rob,

I have used the NTE105 in place of the DS-501 and it works great. The DS-501's are still around but you have to dig to find them.

Don't know about the DS-46. On my 67 radio, I wound up changing the Volume-Tone switch, changed the DS-501, and cleaning up all the contacts within. It now sounds brand new with the correct speaker (with the little transformer).

I assume you have the service manual and wiring diagram for the radio (I think 65 -67 is the same). If not send me an email.

[Paul J.]

Re: C2 Radio Repair

I think it's excellent that Rob is willing to get in there and attempt a repair. If he succeeds, he can do C3 radios too. Same basic audio circuit for the mono models.

When I worked for Radio Shack people would bring thier radios and stuff in for repair, and we were supposed to send it to the repair center. The store manager said "If you want to try to fix it, have at it" as he could then cut out his repair center fees and make more profit for the store. I learned a lot, and the stuff that we could'nt fix was thrown in a box (not even reassembled) and shipped to the repair center.

I never shop at Radio Shack.

[Rob M.]

Re: C2 Radio Repair

The DS-501 rarely fails Rob although it will degrade and diminish audio quality. More than likely the .5 ohm fusible resistor has failed. Do an ohm meter continuity test on it (and the other transistors) before you spend a fortune on an NTE105.

Hi Jerry,

I've checked the fusible resistor but it is fine, still app. 0.6 ohm. The speaker is definitely toast (transformer is ok but speaker it self measures infinitive ohm). I have +11.6v on the speaker terminal so that's why I think the DS-501 is toast.

I doubt the X9 DS-46 because I measure signal up to it's base using a scope (I have some electronics background). It is a bear to get it replaced though since it is on an impossible place on the pcb to reach from the component side without completely remove the pcb from the chassis...

regards,
Rob.

[Rob M.]

Re: C2 Radio Repair

Rob,

I have used the NTE105 in place of the DS-501 and it works great. The DS-501's are still around but you have to dig to find them.

I assume you have the service manual and wiring diagram for the radio (I think 65 -67 is the same). If not send me an email.

Hi Gerard,

Thanks for the info on the NTE105 as replacement. I have a copy of the service manual providing me good info on measure points and positioning of the individual components...

regards,
Rob.