Vox Repeater 2N2646 replacement? (kinda lost)

[Rob Strand]

_I_ had assumed telephone receivers (earpieces). That's what the drawing suggests. The 100-200 Ohm impedance is a fair fit for a 3V system. Internally they are a fixed magnet and coil with moving iron diaphragm. Reversible.

That's a good call.     Those things were fairly available in the day.

We need some frequency shaping to get the thin sitar sound, which must come from the ear pieces.   The telephone receiver (the "speakers") aren't where the telephone sound comes from, it's the microphone part.   Using one of those ear pieces performs as a microphone might just do it.  Butting the two ear pieces together with no damping will add to the effect.

[iainpunk]

or we find a way to make our won telephone style microphone, based on a sheet wit tension on it, and basically a guitar pickup. we could use a PET sheet and use the mountain banjo method of tensioning it to be drum-like, just add a piece of (ferro)magnetic material, like an iron washer, or simple magnets.

cheers, Iain

EDIT: forgot the apology for derailing the thread and the video link:https://www.youtube.com/watch?v=M5XBbv_A27c

[PRR]

While trying to find info on old receivers (info which has vanished from the web ), I was reminded that the improved Bell 500 came out before the investment in the Bell 302 was fully sunk. There was a back-room industry putting used 302 parts in 500-style housings. The 500 was better on very long lines, but the 302 was fine in town, but the 500 shape was so good people demanded "new phones" and accepted a 302 in 500 clothes.

Worn/abused 302 parts got dumped on the surplus market. Both 302 and 500 receivers (ear-parts) have strictly controlled resonant responses (which would be clear if the internet were not barren). The 302 more peaked than the 500. Damped so the response did not "ring", but put two in series and the Q soars, "ringy/singy".

In this hunt I discovered that the guy who has run Play Things Of Past since before the internet has passed away. He had some very nice telephone bits.

[Rob Strand]

In this hunt I discovered that the guy who has run Play Things Of Past since before the internet has passed away. He had some very nice telephone bits.

I found this UK version, which is from GE/GEC, but it would be nice to compare it against the Bell version.   We had STC parts here in au but I don't trust my memory.  I know I got some ear pieces from AWA equipment but I can't remember if AWA made there own.  I had a feeling AWA started to outsource stuff in their later days.

http://www.samhallas.co.uk/repository/documents/gec_subscribers_telephones.pdf

[PRR]

Interesting. Balanced armature is about unknown in US Bell equipment (common pre-1922 'loud'speakers, hearing aids, and now musician in-ear monitors). The response curve in that paper is exactly typical for a BA.

The Bell 500 receiver is not built like the image above. The stationary signal coil is near the rim of the cartridge. The diaphragm rocks on the rim, edge-driven. It is a real bang-up design job and and a truly good transducer within its communication goals. Low distortion, damped intelligible resonances, and incidentally it can induce signal in an external coil (phone-tap, hearing aid).

Instead we have the image below.

[Rob Strand]

You might be able to make more sense out of the construction from this,
http://www.samhallas.co.uk/repository/documents/poeej_rocking_armature.pdf

As a kid I pulled a few earpieces apart and a few microphones.   I honestly can't remember the fine details but I thought the speaker side had a fixed coil.   In the back of my mind I remember two different (but similar) constructions for the speaker and two completely different constructions for the mic.    The microphones where very different to the speaker.  The earlier mics looked different to the ear-piece, they were bigger and I think they might have been carbon.   The later ones looked a lot more like the earpiece except they had more holes.  I'm pretty sure those were dynamic.

The later ones were something along these lines,
https://www.royalsignals.org.uk/inserts/rocking_armature_inserts_en.pdf

Note the peak in the mic response around 1.5kHz, like the GEC paper.

When I look at the UK stuff it seems to follow what we had here.