Dynatron TV32

[FERNSEH]

Originally Posted by Mikey405

Alas I do not have the remote control for this set.

Hi Mike,
We could make one. I've got the circuit here.

Regards,
David.

[FERNSEH]

The circuit of the cable remote control. Two rotary controls, volume and a channel selector switch.

DFWB.

[Synchrodyne]

Originally Posted by FERNSEH

The circuit diagram of the three stage vision IF amplifier of the Dynatron TV32.

The two interstage and the demodulator IFTs have what appear to be tertiary windings, normally associated with overcoupling, which in turn provides a broader IF bandwidth, albeit with a dip in the centre of the bandpass (usually cancelled out by a peaked response somewhere else in the IF chain). In this case the tertiaries are in series with the primaries, whereas in radio applications I think that in having the tertiaries in series with secondaries was the norm. Anyway, the apparently overcoupled IFTs do speak to the notion that Dynatron was looking for maximum video bandwidth.

It looks as if the EF80 2nd IF stage is agc’d, as well as the 1st EF85 stage. That I think was something advocated by Mullard, with typically 0 to -15 agc volts on the EF85 and 0 to -5 V on the EF80, so that the EF80 did not get to the sharp curve on its characteristic before the EF85 was biased right back.

Originally Posted by FERNSEH

This Ekco designed set does it properly in having the standard 38.15Mhz TV sound IF and 10.7Mhz for the FM radio.
An interesting refinement is the automatic frequency control of the tuner which is active on both TV and FM.
On TV a 6D2/EB91 double-diode (V7) acts as the AFC discriminator and on FM the control voltage is derived from the FM ratio detector.
The AFC control vari-cap diode is CD1 and is a type XD901.

The FM demodulator might actually be of the Foster-Seeley type, which I think would have been unusual in a TV-FM receiver. The use of a valve discriminator for the TV AFC discriminator but semiconductors for FM is curious; maybe at 38.15 MHz the 6D2 was better than the germanium diodes of the time. V6 (6F23) looks as if it is an amplifier/limiter, with grid-derived agc fed back to an earlier sound IF stage.

It would appear that varicap diodes were used for TV receiver AFC quite early on, at a time when FM receiver AFC was still typically done with reactance valves. I guess that there was no room for an additional valve in the typical VHF TV tuner, whereas a varicap diode could be added quite easily.

Originally Posted by Nuvistor

One advert for Westinghouse TV's was " New Westinghouse BROAD BAND TV gives 22% MORE DETAIL"
It then goes on to explain how the it works, well sort of, this was 1957.
Seems like others were narrowing the IF passband to keep the gain up and valve count down.

One can imagine the bean counters (those who knew the cost of everything but the value of nothing) leaning on the engineers to cut corners, and the engineers doing so rather reluctantly in order to keep their jobs. (One could paraphrase a line from the theme song from a 1960s TV show as “he was a poor engineer but he kept his family fed.)

Westinghouse developed an interesting TV AFC (AFT) system in the late 1950s, that used a combination of vision bandpass flank slope and intercarrier bandpass peak rather than say a vision carrier centre zero in order to derive the AFC DC signal. At that time I think that AFC was returning to American TV receivers. It had been used in the early post-WWII years with split sound receivers, derived from the sound channel, but disappeared when intercarrier sound became the norm.

Cheers,

[FERNSEH]

Originally Posted by Synchrodyne

The FM demodulator might actually be of the Foster-Seeley type, which I think would have been unusual in a TV-FM receiver. The use of a valve discriminator for the TV AFC discriminator but semiconductors for FM is curious; maybe at 38.15 MHz the 6D2 was better than the germanium diodes of the time. V6 (6F23) looks as if it is an amplifier/limiter, with grid-derived agc fed back to an earlier sound IF stage.

The FM demodulator is a Foster-Seeley type.
http://www.radio-electronics.com/info/rf-technology-design/f...eeley-fm-detector-discriminator.php

The Dynatron TV50 chassis is a development of the Ekco 21" TV/FM models T345 and T346. In these receivers the FM ratio demodulator is a 6D2/EB91 double-diode. The AM demodulator a CG13E crystal diode. The series AM noise limiter is a Westinghouse WX6 metal oxide rectifier.
The chassis metalwork is the same in the TV50 and the Ekco T345 receivers.

DFWB.

[Mikey405]

Originally Posted by FERNSEH

The circuit of the cable remote control. Two rotary controls, volume and a channel selector switch.

That's quite an advanced selection system and remote control really David. You can actually choose the channel you want directly (like the buttons on the front of the set) without the usual "next - next - next - next etc." button pressing to jump to the right channel.

[FERNSEH]

Hi Mike,
We'll have to make a remote control handset for the set. Actually the only critical components to find are the connector that plugs into the set and the multi-way cable.
I'm sure we'll find those parts.

DFWB.

[FERNSEH]

Circuit of the motor tuning system in the TV50.
Transformer T5 is for mains isolation of the circuits. The volume control on the wired handset is in the secondary circuit of the sound output transformer.

DFWB.

[Mikey405]

Sounds like an excellent idea David. I do like the fact that it doesn't just "clonk" round and round in one direction - It always seems to take the quickest path to get to the station you want.

[Ed_Dinning]

Hi David, how many cores needed in the multicore, I may have some here.

Ed

[FERNSEH]

Hi Ed,
I reckon after looking at the circuit diagram it is a ten core cable.
Also, we have to determine what kind of plug is used. I'm sure it'll be an industry standard one.
Certainly would be fun to have a cable remote control connected to the set.

DFWB.

[Ed_Dinning]

Hi David, should have both of those then.

Ed

[FERNSEH]

Hi Ed,
We just need to determine the value of RV11, the remote volume control. Probably 10 ohms will do.
I might have a suitable switch for the channel selector.

DFWB.

[Synchrodyne]

A closer look at the TV50 sound circuits shows some interesting features. V6 (6F23), the final sound IF stage, has a switchable HT voltage via a resistor that is switched out for TV, but in circuit for FM. Thus it probably acts as a limiter only on FM. This is consistent with the fact that the TV AFC discriminator (V7, 6D2) also acts as the AM demodulator, where limiting would be unwanted. The AFC voltage is not zero-centred, as was usually the case with valve FM equipment, but had a positive standing voltage applied to the “lower” diodes of each discriminator by a potential divider with a VDR in parallel with the lower leg. I guess that the use of a varicap diode for oscillator control dictated that the AFC voltage be offset. It looks as if V9 (½6D2) provides delayed agc to V4 (6F23) sound If amplifier in the TV mode, but that V4 operated as full gain in the FM mode. Thus the agc derived from V6 grid when it is acting as a limiter in FM mode is likely used for tuner RF agc, given that the “usual” vision-derived agc source is not available when switched to FM. A somewhat incidental feature of this (and probably quite a few other TV-FM receivers) is that when considered as an FM receiver, it has a rather more elaborate front end than – cascode RF amplifier and effectively four gangs – than was customary for valve FM receivers and tuners. Cascode RF amplifiers were not common in British FM receiver and tuner practice, and two gangs was the norm, with three gangs seen in a minority of models.

Cheers,

[nicam49]

There is one of these beasts for sale on Facebook Marketplace, and here are pics of it.

[high_vacuum_house]

That looks particularly interesting, do you have a link for it or its location?

Many thanks,
Christopher Capener

[Cobaltblue]

Originally Posted by high_vacuum_house

That looks particularly interesting, do you have a link for it or its location?

Many thanks,
Christopher Capener

Its near Nottingham, Heanor

Not that far from Belper

Dropped you a PM

Cheers

Mike T

[nicam49]

Of extra interest to anyone local, is the label on the back, Pearson Bros, Long Row, Nottingham. A VERY exclusive department store,.. sadly no longer with us..

[high_vacuum_house]

Well, I am now an owner of the Dynatron TV32.

The first thing it is extremely heavy and the only sane way to move it without damaging the cabinet was to remove the chassis in situ. Luckily the speaker and record player can be unplugged, and the whole chassis complete with front knobs and CRT all come out on an angle iron frame after the record player was removed. This assembly was particularly heavy on its own!

I was surprised that the speaker was quite a small oval one. I was expecting something much bigger for the size of the set.

Other than someone in the past has linked out the 3 pin Bulgin mains socket for an IEC on a dangly bit of wire and a Pinnacle branded valve, and the cover missing off of the EHT cage the chassis looks untouched.

Christopher Capener

[simpsons]

Christopher

The restoration of your Dynatron TV32 would make a superb article for the BVWS Bulletin.

The posts on the set's Ekco original design and Dynatron's philosophy to improve the engineering to the n'th degree just captures the essence of British engineering at its best and how 405 line television, with the necessary bells and whistles, was not bad at all!

Chris

[high_vacuum_house]

Good evening,
It certainly would make a good article for the bulletin. (reminds me to get the demolished Tefifon article written up soon!)

I will need to sort out the workbench first and finish putting a Bush TV62 back together.

The chassis is absolutely huge! Check out its size compared to a 9" Pye behind it!

That AW53-80 CRT certainly is a beast of a tube 21" and 90° scan angle means a very big bulb! and a fair amount of glass in it judging by the weight of it.

The LOPT is defiantly an EKCO design. The Perspex cover with the EY51 in a cradle in the centre. This looks in good condition and not crumbling.

The only fault I can see at the moment is the concentric on/off volume and brightness pot. The on off volume part rotates all of the way round 360° and no linkage to the mains switch on its back. Hopefully I can dismantle and repair it unless some oaf in the past has forced it all of the way round!

The record deck looks ok, though the speed selector is jammed in the 33rpm position. The idler tyre looks ok and supple and the various spindles and switch trip linkages all work freely. The brown knob on the turnover cartridge has snapped off in the past.

The cabinet looks ok from a distance, but could do with a good clean and polish and touching up various nicks it has sustained over the years. Some white spots on the top of the set.

p.s. the green panel with little white labels under the table is part of the Spondon 132KV substation control panel which I managed to salvage along with the synchroniser panel from Spondon H coal power station. All the switches were full of rainwater and had to be cleaned up! Another little project.

Christopher Capener