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Old 20th Jul 2017, 11:35 am   #1
The-Triode
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Default EF805S and EF85 Vs EF89 as IF tube for a HF receiver

Hello, I'm about to start a new project, that's to make an HF general coverage receiver with tubes. I've heard on the EF89 as a preferential tube for such application in IF section. But, I have some EF85 and many EF805S. Giving a quick look to the respective datasheets, I seem to observe the EF805S pretty close to the EF89.

I have also plenty of EF183 and I noticed they have been used in HF receivers IF too. Though, I haven't made any decisions for this last option.

I would be glad to hear your opinions or, better, comparative experiences.

Thanks

Cris/The-Triode
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Old 20th Jul 2017, 9:35 pm   #2
ionburn
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

I haven't done any extensive work but do use the EF183 at times. According to the National Valve Museum the EF183 superseded the EF85 and were for use in TV receivers. I cannot really comment on your other valves without a details look as I have not got any of them, but would say the EF183 is worth looking at.
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Old 21st Jul 2017, 2:36 am   #3
Maarten
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

The EF183 is a frame grid tube, technically probably the most modern, advanced design of the bunch.
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Old 21st Jul 2017, 3:36 pm   #4
G8HQP Dave
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

EF85 and EF183 are high transconductance valves for use with wideband low impedance circuits. EF89 has mid-level transconductance (and very low feedback capacitance) for use with narrower band high impedance circuits; in the right circuit it can give more gain than EF85. You need to choose the valves in conjunction with choosing your IFTs.
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Old 21st Jul 2017, 3:59 pm   #5
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

I have just made a receiver using a built front end and scrap gram chassis. The EF89 followed by EABC80 had insufficient gain so I rewired the ECH81 socket as an extra IF amp using EF183. I utilised the existing AGC circuit. It is always better to use separate RF amp, Oscillator, and Mixer for best performance.
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Old 1st Aug 2017, 9:02 am   #6
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

A lot of very good points to think upon. But in my 'depot' I still have many EF805S tubes ... unused. The German Rohde & Schwarz preferred this tube in his excellent EK07 receiver, that I have. R&S generously disseminated this tube throughout the EK07. It's schematic is worth to pay a look ... I will scan it and post it here. So I also started to ask myself why R&S used that tube extensively. The 'S' means 'Long Life - High Quality' component. But my gut feeling is that this tube has other features my ignorance is not allowing me to identify ...

Cheers
Cris
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Old 2nd Aug 2017, 11:19 am   #7
G8HQP Dave
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

The EF805S is similar to the EF85, not EF89. As I said, it depends on your IFTs.

Putting an EF89 and EF183 on the same AGC line will cause problems, as on mid-strength signals the EF183 will be near cutoff with the EF89 still having lots of gain.
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Old 2nd Aug 2017, 3:16 pm   #8
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

The EF183 and 184 - can have a tendency to oscillate if used with high-Q tuned grid and anode-loads. They were designed really for things like colour-TV IF stages where the tuned circuits were deliberately made low-Q to get uniform response over a several-megahertz bandwidth.

Using them in a MF/HF receiver IF with sharply-tuned IFTs could be somewhat problematic.

I built a HF Preselector some decades back to 'liven up' the performance of an old WWII-surplus HF receiver and provide it with some additional image-rejection on 14/28MHz. With both the grid and anode circuits tuned it would oscillate at max-gain; I solved this by replacing the anode tuned-circuit with a 1mH choke.
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Old 2nd Aug 2017, 6:44 pm   #9
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Arrow Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

Quote:
The EF183 and 184 - can have a tendency to oscillate if used with high-Q tuned grid and anode-loads. They were designed really for things like colour-TV IF stages where the tuned circuits were deliberately made low-Q to get uniform response over a several-megahertz bandwidth.

Using them in a MF/HF receiver IF with sharply-tuned IFTs could be somewhat problematic.
My experience exactly. The EF183 / 184 are intended for high-gain, wide bandwidth ccts. Dramatically reduce the B/W (to an I.F. of 465 kHz, say), and the stage gain goes up - 'up' enough to make the whole stage unstable. No amount of external screening will fix that: I suspect that it's due to minute circulating earth currents and coupling inside the valve.
Personally, I would choose the ubiquitous EF39.

Al.
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Old 2nd Aug 2017, 6:47 pm   #10
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

I seem to remember some of the EF183/184 were prone to inter electrode shorts, blue sparks comes to mind.

Lawrence.
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Old 2nd Aug 2017, 11:14 pm   #11
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

For a receiver with multiple IF stages at relatively low frequency, the EF92 was quite popular, also for RF applications where it was desired to interface between tuned circuits with sensible, rather than headline-grabbing, gain. It's a relatively low-gm variable-mu pentode that seems to have been intended as a miniature updated replacement for octal favourites like the EF39 mentioned, the 6K7G and so on.

Not sure how common B7g valves/tubes like this and others are in Italy- as with so many other things, the UK liked to pick-and-mix the most popular tubes from both the USA and mainland Europe.
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Old 3rd Aug 2017, 1:04 am   #12
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

Perhaps the most widely used miniature HF remote cutoff pentode was the American 6BA6 (EF93). It was part of the immediate post-WWII series and had a slope of around 4 mA/V, a step-up from the previously common number of 2 mA/V or so. There was a 2 mA/V valve in the series, namely the 6BD6, but this was overshadowed by the 6BA6. The 6BA6 was never directly superseded in the valve era, whereas American “VHF” valve development for TV IF applications, etc., starting with the 6AG5, went through quite a few gymnastics, in part to address AGC problems. Some of these TV valves, such as the 6BZ6, were taken up by HF receiver makers, but possibly not without problems and in some cases for “show” purposes.

There was also the 6BJ6, with a 6.3 V, 150 mA heater, that was primarily a low consumption version of the 6BA6 (but also useful in receivers with 150 mA series-string valves), and which was somewhat better at VHF. (The 6BJ6 did not acquire a Pro-Electron designation, although there was a European SQ version, namely the E90F.)

The UK and European valve makers preferred to stay with the established 2 mA/V slope for their early HF remote cutoff miniatures, hence valve such as the W77 (EF92), 6F15 and EF41. Philips’ early “FM/AM” radio receiver valve range included the EF85 to serve as AM IF amplifier and FM 2nd IF amplifier. The EF85 was a TV valve, more-or-less the remote cutoff version of the EF80. But evidently this was not entirely satisfactory in the radio application, and within a couple of years or so the EF89 was released. This was 4 mA/V slope HF valve, so broadly like the 6BA6, but I think with slightly lower Cag and a smoother AGC curve. One of its claimed features was that it could be used without neutralization in many applications. (Although in some cases it was neutralized, perhaps more to avoid passband tilt than actual oscillation.)

Thus, one might say that the EF89 was tailored to the HF task, and better at it than the EF85, despite its lower slope. It was very widely used in domestic receivers through to the end of the valve era. I don’t think that it made major inroads into the communications market, but it would have been difficult to break the hold that the 6BA6 had established, and the latter was a valve that had assured worldwide availability.

The EF183 was the frame-grid successor to the EF85, so developed along the TV IF strip requirement vector. Vert broadly, one might say that if the EF85 had proved to be “too much” valve for AM and FM IF applications, then the EF183 would be “way too much”.

Hence, the arrows seem to point to the EF89 and the 6BA6 as the logical candidates for HF receiver IF amplifiers. There does seem to have been more diversity in respect of RF amplifiers, particularly 1st RF amplifiers. With wider bandwidths and usually relatively low gains, these seem to have been more amenable to the use of is of TV-type valves. For example, the ECC189 frame-grid cascode seemed to find a place as 1st RF amplifier in late valved HF receivers, an example being the Eddystone 940, (which used the 6BA6 in the 2nd RF and both IF positions.)


Cheers,
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Old 3rd Aug 2017, 11:32 am   #13
G8HQP Dave
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

There was also the EF89F/6DG7; something like a 6BA6/EF93 on a B9A base. Similar to an EF89/6DA6 but different pinout. It seemed to be rarely used.

I think the EF92 is often overlooked, perhaps because of its 'low' gain. It ought to make a good RF stage before an ECH81 precisely because it has low gain. The ECH81 is quiet (for a multi-grid mixer) so does not need much gain in front of it.
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Old 3rd Aug 2017, 2:25 pm   #14
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

Must admit, for HF receivers with only a single RF-amp I always liked the EF95/6AK5.

Low noise, so you can use it very loosely-coupled to the tuned-circuits - I've used it with a capacitive divider across the tuned-circuit so the grid only gets about 1/3 of the peak voltage across the tuning-capacitor - this way the tuned-circuits are not loaded/damped so much by the valve's input-resistance and so have higher 'Q' and hence improve the adjacent-channel rejection - and more-importantly the image [you really need more than 2 signal-frequency tuned circuits in a superhet if you want decent image-rejection on 28MHz]

Must admit, in the past I've pondered using really-gainy high-slope valves in a multi-valve IF stage, but tapping the grid and anode-connections down the tuned-circuits in the same way as base/collector taps are used in transistor circuitry. This would both reduce the overall stage-gain (so producing stability) and also the damping-effect of the valves on the tuned-circuits themselves. 3 or 4 IF-stages coupled this way (10 tuned-circuits!) could be seriously selective.
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Old 3rd Aug 2017, 4:52 pm   #15
G8HQP Dave
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

The EF95 would be good at the higher end of HF as it has low grid noise. At lower frequencies it might suffer from poor AGC performance.
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Old 4th Aug 2017, 8:03 am   #16
The-Triode
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

Here the data of interest for our comparisons, for EF85, 89, 183 and 805S. At first glance 805S looks pretty similar to EF89. While, EF183 clearly shows the features that some of us have experimented. EF85 looks slightly less similar to EF805S than what appears commonly believed.

Had not time to make a point-to-point curves comparison, but a quick glance seems to be summarized as above.

Cheers,
Cris
Attached Files
File Type: pdf EF85-curves.pdf (58.8 KB, 174 views)
File Type: pdf EF89-curves.pdf (62.5 KB, 181 views)
File Type: pdf EF183-curves.pdf (72.3 KB, 120 views)
File Type: pdf EF805S-curves.pdf (52.5 KB, 393 views)
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Old 4th Aug 2017, 11:01 am   #17
G8HQP Dave
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

Those graphs show that the EF89 has the smoothest curves, EF85 the kinkiest, and EF805S and EF183 somewhere in between. As you have EF805S you can use them, but EF89 is better.
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Old 4th Aug 2017, 1:31 pm   #18
The-Triode
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

Yes ... you're right. I have so many EF805S that would be a waste of money to buy some EF89 and perhaps also unnecessary. I have appreciated your valuable comment, Dave.

By they way, '89s' are becoming expensive: I guess because '89' is close to '86' only as number, as that of EF86, thanks to the 'Audio-phools' ... ....
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Old 5th Aug 2017, 12:30 am   #19
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

To add another perspective, here is a comment made by Mullard in its early literature about the EF89:

“An indication of the maximum amplification obtainable from an r.f. and i.f. pentode is given by a quality factor defined as the ratio of slope to anode-to-grid capacitance. When designing the EF89, the small anode-to-grid capacitance of the EF41 (Ca-g1 <0.002pF) was used as a starting point, and the design of the EF41 modified to produce the highest practicable slope without increasing the capacitance.”

The slope to anode-to-grid capacitance ratios of the valves at interest are:

EF89: 4 ma/V / <0.002 pF
EF85: 6 mA.V / <0.007 pF
EF805S: 6.5 mA/V / <0.007 pF

On this basis, the EF805S comes out a bit better than the EF85, but not as good as the EF89, which aligns with the expectations derived above.


Cheers,
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Old 5th Aug 2017, 10:37 am   #20
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Default Re: EF805S and EF85 Vs EF89 as IF tube for a HF receiver

True. But in a fixed-frequency application, would it not be possible to neutralise the capacitance? It's an extra complication, though not a massive one. A couple of extra capacitors, maybe an overwind on one of the IFT's, an extra adjustment, job done. Then you can use the EF85, EF183, etc and get the maximum gain it is capable of.
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