Bush SRG91

[jmedley]

Many years ago, about 1960 I worked in my fathers Bush dealership and Stereo LPs were now available for the first time, providing excellent domestic audio quality.
We had always loved the Bush brand having well constructed cabinets and finely engineered chassis.
The SRG91 stereo radiogram was a big favourite with LW MW & FM.
The record deck was a Garrard auto changer fitted with a Sonotone 8TAHC stereo cartridge.
The internal speakers were ( Celestion 10 inch round and Celestion eliptical 6x4 inch): for left and right channel.
It was a joy to listen to.

In my retirement I have restored many pre war radios, usually from the halcyon days between 1935 and 1940 however the SRG91 from 1960 was always on my wish list, often ignored when one was for sale, because of its size.
Recently I saw one advertised on eBay for £10, so I clicked on bid and surprisingly I won it! I collected it with help of a friend It looked extremely dirty having been stored in a garage or was it a hen house? There was no wood worm to be seen, but the top surface of the gram has 3 panels the centre one fixed and the others 2 lift up, one to reveal the record changer and the other the record storage compartment.
Oh what a mess, much of the "cellulose varnish" had peeled off and lots of sticky stuff was well spread all over. The front looked good and the speaker cloths were fine. Looking through the back panels was a sort of joy, all the components and valves were in place but under a carpet of dust spider webs and bits of straw. The previous owner said that it worked abit
Getting it home I wanted to check the cabinet veneer particularly of the grotty top panels.
A none volatile stripper was applied very liberally to the panels and was left overnight.
The next day all the residue was scraped off to reveal good veneer without any issues.
I had removed the chassis and mains transformer, this chassis is mounted on a board held with 2 bolts that only need loosening and then it all slides out very easily.
The mains transformer is mounted separately on the inside base of the cabinet all soundly secured with 2BA and 4BA nuts and bolts.
I started by checking the mains transformer and the attached side mounted rectifier valve.
The mains tapping was on the 250 volt setting and the rectifier was delivering over 300 volt D.C.which was present on one of the 3 tags of the 3 pack electrioytic
There was no bulging or anything that looked distressed however there were no voltages present on the other 2 tags of the electolytics.
All the valves were glowing OK but the heater volts were 6.9volts instead of the required 6.3 volts, anyway not too much to worry about at this early stage.

Well I had only the circuit diagram without a component layout so following where the wiring were connected to was needed. It turned out that the 550 wire wound resistor between the reservoir supply and the HT rails was open circuit. It had taken a few minutes to find its location since it was mounted on top of one of the audio output transformers!
Once replaced with 2 x parallel wire wounds the HT rails came up, but about 10% higher than the circuit diagram indicated, not to worry at this stage I pressed on
The many capacitors were either the wax paper type or those awful small black/ brown mouldseals. I replaced the lot, especially the coupling capacitors (that cap) I measured the removed capacitors and most were well out of specification.
The A.M aerial is a ferrite rod, but the F.M aerial is mounted on the cabinet!
Medium wave and long wave came up fine, with all the usual stations available in our area
When I tried FM, just with a short piece of wire clipped to the aerial input, I was a bit disappointed since I remembered from early days that it had been a very good performer on FM.
Wen I rigged up a sensible aerial for FM, it was worse, with lowish volume and distorted audio, particularly at the 100MHz end of the scale.
Much of the FM circuit of course, is common to all bands so I started looking around the FM tuner, which is mounted inside a cast aluminium enclosure .This enclosure has the ECC85 valve mounted onto it with its shielded valve holder.
When I moved the valve slightly the FM stations jumped into life which was encouraging. I pulled out the ECC85 valve to see that the pins were bent all over the place. I thought this to be a bit strange, but then thinking about it, a field service man trying to “fix” the FM fault, would try most things, before lugging a radiogram back to the workshop. Straightening the valve pins made no difference. With a bright light and a magnifier peering into the valve socket I could see that the forked socket connectors were badly deformed or missing, so a new valve base was needed.
This is where the good mechanical design of the Bush scored highly, the aluminium enclosure has a lid, nicely held in place with 6BA nut and bolts and access to the valve base connections very good. I fitted a standard valve base together with the old shield. When all re- assembled the original fault remained.
The slightest movement or vibration of the enclosure made the fault come and go, so after a bit of investigation the fault turned out to be the earthing connection from inside the enclosure to the main chassis. This connection was originally made with a very short piece of solid cored black sleeved wire. This wire had cracked at the enclosure end, it was difficult to see, until the wire was moved slightly. I replaced it with a slightly longer piece of stranded black wire and then the fault was cured and all was well with the FM.
The signal generator showed that the am Ifs were spot on and the FM Ifs were OK too.
The dial cord was fine but I freed and lightly oiled the small pulley wheels.
The station dial was refitted and all the station alignment were fine too.
Because the valve heaters were uncomfortably high and also the HT was high I decided to fit a dropper resistor near the mains transformers raw mains input. I think I ended up with about 70 ohms wire wound. All voltages spot on now
The next stage will be refinishing the cabinet and cleaning the speaker cloths.
Also the auto changer

[Nuvistor]

Nice write up, I remember the SRG91, sold a few and don’t remember fixing any, customers very happy with them.

[mark pirate]

My parents had an SRG91, It certainly impressed me as a child, I was most upset when they upgraded to a Dynatron system in the early 70's, and gave it to our neighbours!

Like you, it was on my list of wants. I got mine a few years ago for the grand sum of 99p, I was the only bidder, and it was only three miles away

I have yet to restore mine, although is does work.
Luckily mine has polished up a treat, it was dirty & unloved, but thankfully it lived inside all it's life.

Mark

[Edward Huggins]

Don't forget to test/replace the paper filter cap on the treble/mid-range speaker. Is that some kind of vent in the base of the speaker enclosure?

[jmedley]

Hi Edward, Yes that is a vent hole. The photograph shows the speakers that are beneath the record deck, which are sealed with a board, that fits onto the sloping battens, as can be seen in the photo.
The other pair of speakers are covered with two sloping shelves for record storage, however there is no vent hole in the base but there is about a 4 inch space under the shelves and the vent is through the usual slotted cardboard back panel.
Thanks
Jim

PS. Thanks for reminding me re the filter caps, I need to check them.

[jmedley]

i need some help with the magic eye EM84.

Pin 1 is fed with a varying negative voltage depending upon signal strength.
On MW and LW the eye responds well, at around 9 volts negative the eye is fully closed and no stations overload it
On FM I am getting up to 22 volts negative on most stations and the eye is swamped fully closed when tuned to a station
The wave change switch disconnects the LW,MW input to pin 1 and takes the output on FM from the EB91 ratio discriminator.
Any advice appreciated on how to adjust the eye for FM

Thanks
Jim

[jmedley]

Thanks Ed for the heads up re the capacitors feeding the smaller speakers

One side was OK at 5uf, the other was reading low and connection dry jointed.

Both of the original caps were none polarised electrolytics ?
The circuit diagram shows polarised electrolytics.
I have fitted 2 x 4uf polarised as shown in the circuit diagram. The output is great with the original speakers now set up correctly.
VE night was a joy, playing some of the war time favourites
Vera Lynn, Glen Miller etc. The neighbours were dancing on the front drive.
No personal contact of course within 10yards

[Phil G4SPZ]

Nice to read about your exploits with the Bush radiogram, Jim!

All I can suggest for the magic eye issue on VHF is to replace C40 in the discriminator circuit. Capacitors in this position have a habit of going 'low value' but that is usually accompanied by distortion.

Good luck and all the best!