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Old 11th November 2010, 06:43 PM   #1
laki101 is offline laki101  Serbia
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Default can something be made using these tubes

I found these tubes in a 50 year old radio so I was wondering could I make some tube amp (never done it before) with them
the tubes are:
ECH81
EF89
EABC80
EL84
EZ80
EM80

the tubes do work and the radio works but it isn't on fm so its useles

any schematic would be good
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Old 11th November 2010, 06:56 PM   #2
Arnulf is offline Arnulf  Europe
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It would be a shame to tear apart a functional old radio. Tube layout (3 signal diodes) suggests your radio might have FM functionality. Why not have somebody with suitable gear (for IF tuning) have a look at it and fix it for you instead ?

You can't build much (ecept for other radios, obviously) by tearing it apart as there is only a single power tube in it (EL84).
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Old 11th November 2010, 06:58 PM   #3
laki101 is offline laki101  Serbia
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so you think it can be made to work with fm signals?
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Old 11th November 2010, 07:56 PM   #4
Arnulf is offline Arnulf  Europe
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Can you give us the maker and model of your radio ? This way we wouldn't have to speculate as to whether it does in fact have FM or not. Tube complement suggests that but a schematic would be far more helpful.

If your radio did have FM capability before, it can be made functional again. It could be something trivial (like a dead tube) or a more challenging problem (like out of tune IF, which can't be fixed without certain equipment and knowledge) but it should definitely be fixable.
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Old 11th November 2010, 08:45 PM   #5
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That's an AM tube complement. I'll take a guess that it's SW capable.

The ECH81 looks like it could serve as a TRF front end, along with being a combined local oscillator/mixer. The EF89 is the IF amp. The EABC80 serves as 2nd detector, AGC rectifier, and audio voltage amplifier. The EL84 is the audio "final". The EM80 is tuning indicator. Last, but certainly not least, the EZ80 is the B+ rectifier, without which all the other bottles are useless.

A FM capable set would have more than 1 IF gain stage.
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Old 11th November 2010, 10:07 PM   #6
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Well, --the term TRF means no mixer, predates superhetrodyne. None the less, model number please.
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Old 11th November 2010, 11:42 PM   #7
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Quote:
Originally Posted by firechief View Post
Well, --the term TRF means no mixer, predates superhetrodyne. None the less, model number please.

A radio receiver can have a TRF (tuned radio freq.) stage at the antenna I/P and still be SUPERHET. All good FM tuners employ the arrangement, not so much for weak signal strengthening (the IF strip takes care of that), as for "image" freq. rejection. Remember, 2 signals (1 10.7 MHz. below the local oscillator freq. and 1 10.7 MHz. above the local oscillator freq.) heterodyne at the IF strip's tuning. Only 1 of those signals is desirable. The additional tuned circuitry at the antenna I/P disposes of the unwanted "image" signal.
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Last edited by Eli Duttman; 11th November 2010 at 11:45 PM. Reason: clarification
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Old 12th November 2010, 01:10 AM   #8
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OK, Possibiltiy for thread jacking, and I started it.
I get what you are saying, and this may either be off topic, or a case semantics. But a TRF radio is a specific kind of design that commands a place in the annals of radio development history. Virtually all front ends are "tuned" to some degree or other. I submit that the specific term TRF radio is reserved to a non superhet radio. I hope the schematic is readable. I depicts a design that is a TRF radio, and not a superhet.
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Old 12th November 2010, 02:41 AM   #9
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That, indeed, is a 100% TRF design. An AA5 SUPERHET AM receiver has as its 1st stage a combined local oscillator/mixer. Pick any respectable FM tuner, say a McIntosh MR71, and you will find SUPERHET circuitry, with a TRF stage in front of the mixer. The tuning cap. has 3 sections, while an AA5 has a 2 section part.

BTW, untuned, grounded grid, RF stages are common enough at the antenna I/Ps of superregenerative setups. In this case too, "extra" gain is not the primary object. Keeping spurious radiation out of the antenna system is key. Look here for a "cute" circuit that reflexes the detected audio back through the untuned GG stage.
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Old 12th November 2010, 10:32 AM   #10
DF96 is offline DF96  England
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TRF is a type of receiver, not a stage in a receiver. That is certainly the usage in UK, and everywhere else as far as I know. I have never before heard anyone use TRF to describe the input stage of a superhet. It is true that some superhets start with a tuned radio frequency amplifier, but this is always abbreviated to 'RF amp', not 'TRF amp'. Tuned RF amps are so common that 'RF amp' is taken to mean tuned RF amp; an untuned one is called 'untuned RF amp' or 'aperiodic RF amp'.

The valve lineup described is clearly an AM/FM superhet, as an AM set would not use an EABC80. Somewhere in there is an ECC85 VHF front-end, possibly in a separate screened box. On FM the ECH81 acts as an IF amplifier, so there are two IF stages for FM. On AM the ECH81 is mixer/oscillator - the same functions as the 6BE6 does in an AA5. It is very rare for an AM broadcast receiver to have an RF amp, although I have one (Bush VHF80) which has an extra UF89 to do this.
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