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Dyantron T99A Tuner  

 
turretslug
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That is a very impressive tuner and, as you say, well put together- it must be pretty much at the top of the domestic tuner tree before getting into communications receiver territory. Certainly a step above the Chapman S6BS electronically and mechanically, itself a well-specified device. Interested to hear that it goes to 30MHz- rather than stopping just above 26MHz for the 11m band- but I suppose most amateurs still used AM then, relaxing stability and bandwidth considerations. Things like this deserve to be preserved as an example of just how good valve kit can be!

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Posted : 27/11/2014 12:39 am
Synchrodyne
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That is certainly a very nice unit. I have not seen the schematic for the T99A, but I suspect that it is similar to the slightly later T139. The latter differed in having six bandspread SW bands and a slide rule-type dial. It was essentially of the 3-gang, one RF and two IF stages layout, but with the addition of a broadband grounded-grid RF preamplifier (a triode-strapped Z77) that was used on the bandpsread and upper SW ranges. I am not sure if the T99A had this. Another feature was a separate oscillator valve.

Perhaps indicative of performance and construction quality, Marconi Marine used both the T99 and T139 as the basis for shipboard PA system central broadcast receivers. That Marconi did this, rather than using one of its range of HF communications receivers for the application, supports the notion that a receiver optimized for shortwave broadcast reception with program listening rather than DX’ing as its main mission is on a somewhat different design “vector” to communications receivers in general. Three gangs were probably enough for the broadcast receiver, on the basis that although at the higher HF frequencies, say above 20 MHz, images would be apparent, in practice it would be most unlikely that a strong image from another station would be right on top of a wanted broadcast. On the other hand, a four gang front end was de rigueur for self-respecting single-conversion communications receivers.

Basis just an “on-paper” assessment, I’d agree that the Dynatron T99A and T139 would have ranked above the Chapman S6BS, which in turn might have been a bit above the Armstrong BS125. The Lowther DT/4 and DT/5 might also fit in this group, but the available information on these is insufficient to know. Possibly for the best reception – in the groundwave area - of wideband MW transmissions, the Quad AMII and AM3 would come into the picture. Back in the day I think that the AMII was ranked above the S6BS for that purpose.

The 30 MHz upper tuning limit is an interesting item. I wonder if that number was chosen simply because it was the upper end of the HF band. The Bush EU24 receiver was the same; it went to 30 MHz. (In fact it had continuous coverage from 524 kHz through 30 MHz in six bands.)

Cheers,

Steve

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Posted : 27/11/2014 4:19 am
mark pirate
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I had the same tuner fitted to my Dynatron radiogram, I remember just how good it was.
Unfortunately that was many years ago, so it probably got scrapped for the amp after I sold it on :ccb
These were a very high end instrument at the time, and very expensive too.

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Posted : 27/11/2014 11:08 am
turretslug
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I rather like the idea of a Perspex case- the standard of construction is that good that it seems a shame to hide it away. I've heard them described as almost military quality build and the tuning capacitor cover, coil-pack shrouds and detail metal-work are reminiscent of Eddystone products- some of which were also sold under the Marconi badge. To me (and I could be in trouble here...), Eddystone stuff wasn't always the most innovative and sophisticated electronically but it was neatly, precisely and sturdily made with good mechanical detailing. I'm sure I recall that Eddystone afficionado Gerry O'Hara clothed an casing-less set (forget model number) in Perspex as part of a restoration,

Colin.

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Posted : 29/11/2014 8:21 pm