Eabc80

[regentone001]

I know that in the case of ECC85 used in FM tuners that it was bad for the valve to have the heaters running but no HT applied but does the same apply to an EABC80? The reason I ask is because in my Regentone NINE-3 I have noticed that AM while working well is muffled, I know that it will never be as clear as FM but this seems worse than normal, I mainly use it on FM or gram. Is it therefore that the valve is being damaged by not having a load on the diode, and in this case, the triode as that isn't used at all.
Steve

[vinrads]

Hi Steve It sounds like you have a fault on the AM side , the EABC80 will quite happy when using FM only .Mick.

[Sideband]

What a complete waste of a valve! Anyway to answer your question, as the triode is not used at all it's not going to have any effect on the radio either on AM or FM. At least the three diodes are used...two for the ratio detector and one as the AM detector. Where do you get the notion that the AM diode is not used? It's highly unlikely that a duff diode will cause a muffled sound but there is no reason why you can't try a replacement. More likely a general overhaul will get rid of the 'muffled' sound. Maybe its normal for this receiver. It has quite a sophisticated output stage with plenty of feedback and decent tone controls. Most AM radio stations these days use a lot of compression which tends to make them 'boomy'....not a problem when the radiogram was made.

[Boater Sam]

Is the triode used as an audio preamp for the gram?
If there is a tone correction cap across the output transformer primary it may be leaky. With today's compression of AM transmissions it is sometimes an advantage to reduce the value of this cap to lift the treble.

[Sideband]

Quite simply, the triode is not used for anything.....it's not connected at all. Only the three diodes of the valve are in use...two for FM and one for AM. Hence my comment 'what a waste of a valve'.

[Radio Wrangler]

It was probably the most convenient way of getting three diodes without using two bottles and two sockets.

Bad tone could also be a case of poor alignment of the IF.

David

[Boater Sam]

Never come across that wasting a whole triode. Odd diodes on EABC80s either strapped to each other or left off but not to use the triode does seem very wasteful.
I always thought the 6H6 was an odd arrangement, base and all the wiring for just 2 very ordinary diodes but I suppose it predates DD Triodes.
I seem to remember some amps that used the triode of a triode pentode ECL80 as phase splitter and ignored the pentode or vice versa rather than another ECC82.

I was surprised that even after semiconductor diodes were available, manufacturers continued to use the EABC80 rather than a triode and semi diodes, but then simple single triodes are not common except in B7G Americans EC91s maybe.

[Nuvistor]

Originally Posted by Boater Sam

I was surprised that even after semiconductor diodes were available, manufacturers continued to use the EABC80 rather than a triode and semi diodes, but then simple single triodes are not common except in B7G Americans EC91s maybe.

One possible reason for not using semiconductor diodes perhaps was the ones available had low inverse voltage specification. Example OA70 was 15v average 22.5 volts peak From a valve limiter last IF the voltage I can get across the AM rejection capacitor from a simple loft dipole aerial is 30-35 volts, inverse would be much higher.

This is from a standard radio, ECC85,ECH81,EF89 etc

The OA71 is much better but still on the borderline with 60v average and 90 volts peak.

It's conjecture on my part, it's possible the designers were more comfortable with valves.

Frank

[turretslug]

Wishful thinking under the bridge as it were, but the triode could at least have been used as a delayed AGC diode- but that would have involved a shilling's worth of extra components.... Perhaps you could try strapping the triode grid to the cathode and connect the anode to HT via 220k or 470k, just to see if a bit of emission work does improve things over a while!

DDTs seem to have been available from pretty early on, certainly from mid '30s as the superhet grew up- I assume that the 6H6 was for the widening field of electronics where clamps, gates, limiters etc. were starting to appear. Though compact, it still has a 0.3A heater, I wonder if it has higher emission capability than the diodes in the usual DDT packages.

[Boater Sam]

I suppose we could now use fast silicon diodes IN1448, I have used them in the past instead of the EABC80 diodes to prove the detector.
I have a liking for the 6H6(G,GT), its a pretty little button of a valve especially the can version, I have used them as rectifiers and the work quite well at low current.

[Herald1360]

1N1448 not IN1448

[Boater Sam]

I am a confused 1, oh, l!

Sorry, its late.

1, one junction
2, two junctions
3, three (used for dual gate mosfets, no junctions at all!)

I may be wrong!

[kalee20]

Yes, 1N4148... And OC71.

Reference the EABC80, yes what a waste! But, it does seem the only option with one valveholder. I did think, why not an 6AT6 double-diode triode, and strap the triode as the third diode? But of course that's no use for FM, where you want the diodes to have separate cathodes. The EB91 is a super pair of diodes, ideal for FM, but we want a third diode!

[regentone001]

I think they stuck with the EABC80 as the chassis is basically the A155 chassis but with twin output stages. In the ARG150 and NINE-16, both having push pull output, models the triode was used for amplification then the 2 halves of the ECC83 were used for tone control and phase splitter

[Synchrodyne]

That looks to be the most logical explanation, in which case production (and production cost) considerations evidently prevailed. Otherwise for example, why not use an EBF89 in place of the EF89 and an EB91 in place of the EABC80. Whilst both the EBF89 and EB91 were common valves on the domestic receiver scene, if they were not being used elsewhere in the Regentone range, then the overall costs (including complexity costs) of stocking them specially for this model could have been higher than using the EABC80 with a redundant triode section. Also, more chassis and wiring changes would have been required, incurring a further cost increments. Thus do choices that seem odd in isolation become reasonable when looked at in a broader context.

Cheers,