Another Bush A640

[linescan87]

Good evening everyone,

I picked up this set other day complete with stand. It has a regunned tube in it dated Nov '80. Date stamped in cabnet september '71.

Thinking it may have been subjected to damp conditions I replaced the lopt with the one from thread a couple of months ago, it's own lopt placed in the airing cuboard to dry out.

With the borrowed lopt in place I switched on. The results were quite amazing, no other work was carried out.

In the previous thread I stated that these duals standard sets were getting thin on the ground, maybe not!

Cheers,
John Joe.

[Hybrid tellies]

That looks really good. I think it might be the later more compact version of the A640 especially if it's a 1971 model. You can confirm this by looking at the main smoothing block. If it's the later Z146 it will just have one multi section can instead of two.
There seems to be quite a few of these RBM dual standards around and they are all worth saving.

[FERNSEH]

That set was still available to special order in 1972. The 20" set I used to use was made in Eire, is that so with yours?

DFWB.

[linescan87]

Hi Ferseh,

Yes this is an irish set. I believe that they were made here, not just assembled. A friend of mine said he remembers seeing them making the lopts up in Shanowen Road. They wound them then dipped them in pitch, then placed them in a vacuum to drive the picth in between the windings.

Hi Hybrid,

It does indeed have the single large smoothing block.

[Hybrid tellies]

So it is the later version. Buts it's electrically identical to the A640 chassis. As Ireland used 405 and 625 on VHF this chassis would have been ideal for Ireland as it was easy to make the set run on either 405 or 625 by simply changing the tuner keys on the tuner.
I only heard that RBM had their factories in Cornwall and Plymouth so would be very interested to know more about their Irish operation.

[Nuvistor]

Does the set have th RBM integrated VHF/UHF tuner? I can see BBC2 on the front but this could have been translated down to VHF in a wired aerial system.
Frank

[linescan87]

Hi Frank,

This set has the VHF only tuner fitted. Cable TV was popular in Dublin in the eighties so that could explain it.

John Joe.

[dazzlevision]

Originally Posted by Hybrid tellies

So it is the later version. Buts it's electrically identical to the A640 chassis.

If my memory is correct, the Z146 chassis didn't use a LOPT desaturation choke (fitted on the main chassis, immediately above the LOPT, but still inside the LOP stage screening).

I've also come across (in the mainland UK), a 20" Bush branded set fitted with the UHF/625 hybrid mono A774 chassis. However, it was actually styled identically to a UK made Murphy branded model with the same chassis.

Inn addition, I once had a 22" Rank Arena branded CTV, using the UHF/VHF (with 6MHz intercarrier sound) version of the Rank Z170 110 degree delta gun solid state chassis. Possibly also made in Dublin...?

With the demise of Rank Radio International in 1982, an Irish firm were offering genuine RRI spec LOPTs - possibly using the equipment in the former RRI Dublin factory? They were advertised in the rear section of "Television" magazine.

[Tazman1966]

A top notch performer as well. In my opinion, the best dual standard mono's around.
Now if only I hadn't got rid of my little 19" Murphy Acoustic Deluxe....

[michamoo]

I once had an identicle looking 24" Bush set but was fitted with the disliked (here) A774 chassis. Id quite like another actually

[Welsh Anorak]

Hi
Oddly it looks as though the IF panel doesn't have any wording on it unlike the timebase panel. Never seen one like that in such a late set. Is it a different PCB?
Glyn

[linescan87]

Hi Glyn,

Your quite right, there is no print at all on the board. Perhaps there was a fault with the silk screen printer.

The set is indeed a very good preformer, with a rock solid black level.

Cheers,
John Joe.

[Welsh Anorak]

Hi
The excellent black level clamp was a major feature of this series of TVs. They were an example of how chassis evolve. They started off with the first dual-standards (TV125 series), then the circuit was updated and put onto two PCBs (TV141 series). The IF strip was then transistorised and an integrated tuner was made (TV161 series). The whole chassis was then refined to get to your run-out set which had minor differences to the PSU and flywheel circuitry. The good thing was Bush engineers always could feel at home with ten years of model changes.
Then came the hybrid A774 and solid state A816 - both totally different in design and construction. The former had LOPT and earthing problems and wasn't as good a performer as the A640 and the A816, despite having excellent performance, had a baffling power/EHT generation circuit plus another unreliable LOPT.
The A640 was one of the best dual-standard receivers in my opinion - so much so that the single-standard A794 version of the chassis would run rings around the purpose-made singles. Confusingly the TV183D was the dual 640, the 183S was the single A794 version of the 640 and the 183SS was the A774.
Glyn

[dazzlevision]

I'd agree that the RBM A640 chassis was a very good all round performer, including a complete lack of vision/intercarrier buzz on UHF/625 working.

The black level correction circuit (it wasn't really a clamp as such) was very simple - a few passive components, but it did make a remarkable difference to dark scenes.

The reset accuracy of the six pushbutton integrated VHF/UHF mechanical tuner was also the best of any contemporary chassis from other makers (Bush Band1/3 tuners were always very well made).

The there's the phenomenal sensitivity of the tuner/IF strip (just unplug the aerial to see the screen flood with snow/noise).

However, the chassis did suffer from a somewhat unreliable line output transformer (be it the RBM or Plessey made version) and carbonisation of the printed panels around the "hot" valves (e.g. PCL85 and PCL82). In the days when these sets were in everyday use and I repaired them, I would fit a stand-off valveholder for the two PCLxx valves.

The nadir of RBM dual standard mono TVs was the TV135R and TV138R (R = intended for rental), with mediocre sensitivity, IF and video performance (especially on UHF/625) and a small, square timebase PCB that carbonised fairly quickly. The TV135R was a substantially downgraded/cheapened TV125 chassis. The same basic TV135R electrical design continued with the TV141 and TV148 (which had the same two vertical PCBs layout as the later A640).

I agree the A774 was pretty awful, but the A816 all solid state chassis performed very well (with a customer switchable 4.43MHz colour subcarrier trap and tone control). I was always surprised that the Bush models used that artificial veneer, whereas the Murphy "Acoustic De Luxe" A816 sets used real wood veneer.

[Nuvistor]

Agree with the comments on the TV135R (valve IF), but the TV135 ( transistor IF) was an excellent reliable set with good picture. The U Suffix added the UHF tuner.
Frank

[dazzlevision]

Yes, the TV135/TV138 was a TV125 chassis but with transistorised tuners and IF stages (the A430 receiver unit was a PCB). It also used the PFL200's sync separator section pentode in a black level correction circuit (a Mullard design).

Then there was the TV135L/TV138L, which was a "quick release" version of the TV125 chassis, with a more modern looking cabinet and a direct vision CRT.

[linescan87]

Hi Everyone,

I was in the shed earlier on and looked into the back of the other set, the IF panel in it also has no print on it. So maybe it is a different panel.

This set is giving sterling service in the living room at the moment.

Cheers,
John Joe.

[unitaudio]

I think we had a 183S (silver fascia, 625 only) from Granada rentals when Dad decided £18 a year for the colour license was highway robbery! The Philips colour set was sold and the Bush rented in it's place. I was 5 or 6 then and I don't remember anyone in the household being particularly bothered strangely enough.

I remember the repair man being a fairly regular visitor. "Hello, Granada rentals? Yes, I've got a problem again with the telly I'm renting from you. Yeah, it's doing that wobbly picture thing again..."

We had the Bush from about 1975 until 1981 when colour returned to our hovel courtesy of Granada rentals again and a 24" ultrasonic remote controlled Finlandia set. Posh! Or so we thought at the time...

Regards,
Paul