Transistors for 690-A Hybrid Amp

Hey folks. I'm looking at a plastic baggie full of shorted output transistors from my 690-A chassis, and wondering what the best strategy for replacing them might be. From everything I've read online, the RCA part number, "TR35144" is cross-referenced to NTE-121. Of course, the NTE option is expensive ($22 each x 8), not highly regarded among the online communiity for some reason, and might not even be the optimal replacement, purely from a specification standpoint. What I'd like to try to do is find some NOS or even used stock transistors that would have close enough specs to the original parts. Problem is, despite an online search, and also a search through a 300-page RCA semiconductor databook from 1966 at the local library, I can find no reference at all to the "TR35144" number. I'm sure they're an RCA type 2N something or another, but I can find nothing to tell me which type that actually is.

So, I guess my questions to the group are:

1) Does anyone know which RCA type the TR35144 part number actually corresponds to?
2) Has anyone ever replaced the transistors in the 690-A with anything else besides NTE-121? If so, what did you use, and are you pretty satisfied with the results?
3) Are NTE output transistors really that bad, or is that mob-speak?

Thanks!!

Hi
I have the same amp in my 1965 Ambassador console. You can use an ECG121 for replacement which was made by Salvania. If you do a search on Ebay under germanium transistors ECG121 you may find RCA transistors with the same output ...I think there are coded something like SK3009...but not sure.
If your transistors have shorted then you best find out the reason why before replacing them with new ones. These germaniun transistors are very hard to find. I have a spare amp as back up that I have completed recapped. There are four output alienment pots on the amp....DONT FOOL WITH THEM!!! I have the service manual on the amp. If you would like I could send you a photo copy.
Good luck
George

retrokid 52 said:

Hi
I have the same amp in my 1965 Ambassador console. You can use an ECG121 for replacement which was made by Salvania. If you do a search on Ebay under germanium transistors ECG121 you may find RCA transistors with the same output ...I think there are coded something like SK3009...but not sure.
If your transistors have shorted then you best find out the reason why before replacing them with new ones. These germaniun transistors are very hard to find. I have a spare amp as back up that I have completed recapped. There are four output alienment pots on the amp....DONT FOOL WITH THEM!!! I have the service manual on the amp. If you would like I could send you a photo copy.
Good luck
George

Click to expand...

Thanks George. I have very little experience with transistors or their specifications in general but, based on my intuition, it does seem like the '121' series (ECG or NTE) may be the safest option here. I say that because it's looking very unlikely that I'll be able to lay my hands on the datasheet for the original transistors, and the 121's probably exceed the parameters of all transistors to which they are cross-referenced.

And yeah, I hear you about figuring out why they shorted. Problem is they were already shorted when I bought the console ($15 as-is sale), so I don't really know the history. All I do know is that three of the four 2-amp fuses in the output stage were blown. I am in the process of re-capping the chassis right now, and my thinking was to go ahead and finish that job, replace a few resistors that were open or out of tolerance, and then start checking some voltages. Thing is, I'm not sure if I can do that without the transistors being in the circuit, but I'll figure that out before powering up with the variac, etc.

Hi Jkanclark
If this helps...I replaced two transistor in my amp with ECG121 and it worked fine.
I am not at all an expert but I gave it a shot and it worked.
I wish I know a month ago that you needed the amp. I just sold a fully restored 59A
on Ebay. It was one of my two back ups that I had. By the way, the 59A and the 690A are interchangeable. The only difference are the two large ceramic resistors near the transistors. In the 690A they are surface mounts and in the 59A they are under the chassis. If I remember correctly all the values of the caps were the same.
Good luck with your project.
George
Good luck
George

I think I saw your amp on eBay, and nearly placed a bid on it. I thought that it would be nice to have a backup or something for spare parts etc. One way or another, I'm going to get this poor thing up and running again. I was considering trashing it, but it won't let me. You know how those Avery-era Fishers can be...