Replace noisy germanium transistor in reel to reel tape recorder.

This is not a restoration. I'm attempting to get this to work without putting any money into it. I did the repair mainly just for recording this video.

[@muimasmacho]

I'ma fix. _"Hand me a NE5532, an LM3886, and that Makita drill motor from the junk drawer."_ _"Oh. And grab me a Mousetrap."_ *We be stylin' any minute now!* The early bird may get the worm, but it's the second mouse that gets the cheese. 😀

[@aurthorthing7403]

Sweet machine. The mechanical parts on these things are awesome. I have an old Panasonic that's in need of some TLC.

[@BogdanSerban]

I would completely rebuild the preamp, using a NE5532 op-amp, and just hook it up to an amplifier. I did that with an old Tesla turntable, works like a charm. EDIT: if the mechanical part wasn't that bad.

[@roberthorseman7432]

It sounds like the motor governor maybe slightly worn causing the wow and flutter.

[@martinprado5024]

Great! Beautiful Juliette 660 tape machine

[@stevenhoelderich9490]

You, need to put, some 3 in1 motor, oil plus some New, belts & new, caps too. Have on hand just in Case.

[@muimasmacho]

The lost Nixon tapes. And just like that... fortune slips right thru his fingies. *_Bad Munchies!!!_*

[@SophieFeet]

Steeleye! Good choice of test audio :)

[@JimRobb44]

I have a 1968 Panasonic that I just picked up for $1 US that is stereo and the left channel is doing the same thing. What is funny is that the transistors are potted into a plastic heatsink that is not attached to the board. I might give them a tap to try and break the tin whiskers!

[@larryshaver3568]

what stage was the bad transistor in?sometimes oiling the motor will get it turning more evenly . i've resurrected many fans by doing that

[@CoolDudeClem]

The old tin whiskers syndrome, giving that transistor a tap with a small screwdriver can be a temporary fix. Sounds like the tape to head contact is not very good, or the tape is worn out.

[@flatfrog69rr71]

Just an observion -why don't you build yourself a signal generator /tracker . Most workshops use 800hz this would give you a better idea of what you are dealing with

[@MarkoVlasicAudio]

Hi John. Do you have experiences with building germanium amps? With AD162 tranzistors?

[@kevinbeckenham3872]

Put a 10pF to 47pF Capacitor between base & collector that deal with some of instability with new transistor

[@larryshaver3568]

I have a Magnavox Astro-sonic receiver from 1965 that I suspect may have a few noisy transistors, are you familiar with Magnavox and the transistors they used then? I'd like to know how to findout which replacement transistors i'd need to get, so far finding a schematic hasn't been possible

[@golfman9290]

I'm not to bad on the basics of electronics, but as a hobbyist I would like to know how and why the bias would have been affected, and how the cap. prevents this. Having watched 100s of youtube vids, it's something I haven't heard of before. Have a early 60s Sound 555 and Truvox reel to reel that are awaiting my TLC. I've subbed. Cheers.

[@JohnAudioTech]

The base to emitter junction in a silicon transistor has a forward voltage of around .6 volts while Germanium is around .2v or less. Since the germanium transistor will turn on with a lower voltage, this can upset the bias designed for the circuit when a silicon transistor is replacing a germanium. Other transistor parameters can come into play as well. As for the capacitor I added to stop the oscillation, connecting a small value capacitor from collector to base will reduce the high frequency response of the transistor and can stabilize the circuit. Research the "Miller effect" for more information.

[@HillsWorkbench]

Or was he talking about the capacitor used while probing? In which case it is about not letting any DC current flow through the source, affecting DC bias.

[@golfman9290]

JohnAudioTech. Hill's workbench. Appreciate your replies, will read up on that, many thanks.

[@martinda7446]

Just to add a bit more detail. The silicon transistor most likely has higher gain, certainly a much wider frequency response and less inter electrode stray capacitance. Sticking it in willy nilly where the most sensitive amplification stage is was likely to cause oscillation due to those characteristics of lower capacitance and wide band operation - just as JohnAudioTech predicted. I was expecting it to distort too! The added capacitor allows high frequencies to be fed back and lowers high frequency gain - killing the oscillation. Miller effect is the effective multiplication of those stray capacitances by a factor of the gain and is a limiting factor to the frequency response of an amplifier. If JohnAT is reading this, using a fine (ish) grade of sandpaper- as last resort - and isopropyl alcohol on the idler rim can bring it back to life - be very careful if you use sandpaper on the pinch roller, but if this has hardened it's useless - often video recorders had a pinch roller just perfect for tape machine transplant. Diameter is very similar and of course not critical as capstan is speed governor.

[@HillsWorkbench]

Interesting... More capacitance base to collector (Miller loss) because of the early fabrication techniques or just because they are Ge? Wonder if modern ones have improved much in capacitance, gain, leakage, etc. Good mechanical tips, often there is just a slight glaze on the pinch roller, doesn't take a lot to get it off.

[@barneymiller844]

Had something like it long time ago

[@larryshaver3568]

can replacement germanium transistors still be found,if so where?

[@JohnAudioTech]

I see a bunch on eBay and they are a bit pricey.

[@jeffmassey4860]

Found a few GE 2N170 at a junque electronics shop in Huntsville,AL. Sadly,now closed. Mendelson's in Dayton OH. may be the next best thing if they are still around...EDIT:Mendelson's is off.

[@HillsWorkbench]

The replacement lines, like NTE still carry them, at a hefty price I'd imagine.

[@dhpbear2]

Replace them with silicons and adjust the gain and bias

[@jordanch68]

Go with the Russian / Soviet germainums found on Ebay.

[@MrBrymstond]

They don't make foam rubber like they used to

[@dhpbear2]

18:22 Henry Kissinger?

[@iceberg789]

why does a transistor become noisy ?

[@JohnAudioTech]

All electronic components have some noise associated with them and there are papers published on the subject. The large noise in these old germanium transistors is a type of failure mode and I didn't find any information on it. There is probably a study on it out there somewhere.

[@HillsWorkbench]

I'd bet that that transistor is probably quite leaky,

[@iceberg789]

i see, thanks.

[@JohnAudioTech]

It is leaking 85 uA. I don't know what is normal for that transistor (2SB75) but germaniums tend to be leaky.

[@andykirby9616]

@@JohnAudioTech I'll bet it is dendrite growth, sometimes known as 'tin whiskers' given the packaging style and age of this transistor. Sometimes you can 'fuse' the dendrites/whiskers by discharging a capacitor between the case and the lead(s), but you have to know what you're doing to avoid damaging the transistor. Some cool pics of dendrites here: nepp.nasa.gov/whisker/anecdote/af114-transistor/index.html (I am not affiliated with that site)

[@dineshbhatnagar2126]

I want to purchase a spool tape recorder. Some one can help me

[@kishorVittal]

Dinesh hope by now u must have got a recorder but still for your info there is mussiclovers in Pune www.mussiclovers.com/product-category/vintage-music-electronics/reel-recorder/

[@caulktel]

John, I have some Germanium transistors that I would be happy to send to you. Let me know if you want them. N6ALT