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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 10th Aug 2019, 10:32 am   #1
dazzlevision
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Default Ferguson 3214 (3 speed 4 track mono) - "ingenious" modification to record level meter

Hello,

I recently acquired an early production Ferguson 3214 tape recorder and, upon opening it up to establish its internal condition, I noticed that someone had made a modification in order to overcome a faulty record level indicator meter (the "SMITHS" type, which will have invariably failed by this time).

The internal meter movement seems to have been removed and a neon placed where the display should be, with a black card underneath it. A screened lead emerges from the meter and is soldered to a preset pot on the copper side of the PCB.

I'll investigate further, to find out where this is connected into the circuit........and report back.
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Old 10th Aug 2019, 10:46 am   #2
paulsherwin
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Default Re: Ferguson 3214 (3 speed 4 track mono) - "ingenious" modification to record level m

Interesting bodge. It probably does give enough information to set the record level reasonably well. You could presumably do something similar with an LED nowadays.
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Old 12th Aug 2019, 2:09 am   #3
Maarten
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Default Re: Ferguson 3214 (3 speed 4 track mono) - "ingenious" modification to record level m

Except the neon can be used to indicate a certain threshold, while with a LED the brightness will increase gradually.
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Old 12th Aug 2019, 7:48 am   #4
dazzlevision
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Default Re: Ferguson 3214 (3 speed 4 track mono) - "ingenious" modification to record level m

I have now traced out the circuit.

The audio signal from the anode of the third preamp stage (triode of ECL86) is connected to the neon, via a 500kOhm variable preset series resistor, which is adjusted to give the desired neon striking level. The other end of the neon goes to chassis.

I have seen this type of record level indication method used in a GEC (and Sobell) branded tape recorder from the 1960s, fitted with the BSR TD2 tape deck.

I have a working meter from a later production recorder, which uses the same Thorn deck and electronics, but the meter is a German made “Bertram” type, which has proven to be much more reliable over time, so I’ll fit that and set up as per the service manual procedure.

Apart from the meter, the recorder is basically working, but will need a mechanical service, a new counter belt, plus a few electronic component changes (as there are a lot of Erie PCB type carbon composition resistors, plus a few suspect electrolytics). Thorn have at least used a carbon film type for the anode load of the first preamp stage (ECC83).

The date of manufacture is around September 1965 (printed on the Plessey multi-section HT smoothing “can” electrolytic).
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Old 12th Aug 2019, 10:39 am   #5
paulsherwin
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Default Re: Ferguson 3214 (3 speed 4 track mono) - "ingenious" modification to record level m

Quote:
Originally Posted by Maarten View Post
Except the neon can be used to indicate a certain threshold, while with a LED the brightness will increase gradually.
You would need a Schmidt trigger using a couple of transistors or an op-amp to get the same effect, so the neon is certainly simpler.
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Old 12th Aug 2019, 12:55 pm   #6
Boulevardier
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Default Re: Ferguson 3214 (3 speed 4 track mono) - "ingenious" modification to record level m

My first tape recorder (1963; TD2 + ECC83, ECL82, EZ80) had this form of neon indicator - the poor man's (or scrimping manufacturer's) Magic Eye. It seemed fairly effective at what it did, but of course was just a "go/no-go" indicator, with no indication of level below the strike voltage.

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Old 12th Aug 2019, 5:58 pm   #7
TonyDuell
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Default Re: Ferguson 3214 (3 speed 4 track mono) - "ingenious" modification to record level m

My Agaphone wire recorder uses the same neon (on the panel) both as a recording level indicator (as described here) and, when you press one of the keys, as part of a relaxation oscillator to put a 'beep' on the recording.
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