Bush EBS31 - valves and locations

[roberts54]

Hi, can anyone confirm the 5 valves needed for a 1952 Bush EBS31 AC export radio, and their respective chassis locations looking from the back?

What limited info I have found online suggests:

EL41
EZ40 or 41 - but which?
ECH42
EBC41
EF89 or EAF41 - but which?

Any source for the spec. sheet etc would be helpful too.

Many thanks.

[Nuvistor]

https://www.radiomuseum.org/r/bush_ebs31ebs_3.html

https://www.***********************/bush-export/

[Trifocaltrev]

PM Sent

[roberts54]

Thanks Frank for the superfast response, appreciated. Alas it was those two sources that contradict, and neither state valve chassis location.

I also cannot see the Radio Museum images clearly enough to know if they would help with the key valve question so don't want to spend $25 on a further gamble if I can help it.

[Station X]

Originally Posted by roberts54

I also cannot see the Radio Museum images clearly enough to know if they would help with the key valve question so don't want to spend $25 on a further gamble if I can help it.

Click on the image then click on the larger image to produce an even larger one. You can the then use the '+' button to zoom in.

As for alternative valves, go to this site to compare them:-

http://www.r-type.org/

http://www.r-type.org/exhib/abv0037.htm

[Nuvistor]

As a non member of radiomuseum you can download 3 images a day and a max of 10 within 30 days.
I just downloaded the circuit which quite legible.
The EF89 was introduced in 1955 so I don’t think it would be in the radio unless it is a modification done in service.

Have got the radio?

The valve locations should be easy enough to identify, each as a specific role and examination of the chassis should reveal their locations.

[roberts54]

Thanks for the tips Graham, noted!

Unfortunately, on the Radio Museum site when I click on the larger image, I just get a prompt to download and that download is too small to view properly. I think you need to pay to join at which point you might be able to actually see the images at full size thus readable.

[roberts54]

Hi Frank. OK, tried the download again and yes, appears at full size for me now. I reached my max. for today without answering the valve Q, so I will return to it tomorrow

Looks like the EF89 is ruled out then. Thanks.

[roberts54]

(cntd.) Yes I do have the radio but it is not picking up any stations so I thought I'd firstly check all the valves are the correct ones before replacing them if needed. Problem is on two the ink has smudged and I have no idea what they are.

And as a complete newbie I don't know which chassis location indicates which type of valve.

I appreciate all the help so far from everyone!

[ms660]

So far as I can make out from the available photo's....If it's an EAF41 the diodes anode is shorted to the cathode, that aside the EAF41 and the EF41 pentode wise appear to be more or less the same, they appear to be pin compatible. The Rmuseum schematic snippet shows pentode only for the IF amp, eg EF41, the valve given in radioworkshop is an EAF41, maybe that's what was fitted as found as it would be a sub for an EF41.

Lawrence.

[roberts54]

Thanks Lawrence, so EF41 the likely correct valve (with EAF41 a substitute that was as found and listed in the Rworkshop).

Looks like EF89 is a red herring. Meanwhile one site has EZ40 and the other EZ41, and presumably one is again a substitute. Logic would suggest Rworkshop, with EZ41, is the later substitute.

No one said it would be easy

[roberts54]

PM sent, thanks!

[Herald1360]

This may be a suck eggs and granny comment but...... do remember that valves are one of the least likely components to cause a set not to work unless they're obviously dead- no heater or lost vacuum.

As additional points- EF41 and EF89 are not physically interchangeable- they have different sockets, B8A vs B9A so a quick socket check will tell which should be there and EZ40 is unlikely as a candidate for rectifier in a basic 4+R set- it's heavier duty than the EZ41 and takes 50% more heater current.

[Nuvistor]

The circuit shows a reservoir cap of 50uf which would suggest an EZ40, a EZ41 Max is 32uf, but the transformer winding could be a value that could accommodate the 50uf so an EZ41 is still possible.

[roberts54]

Thanks Chris. As a newbie I'm new to vintage eggs.

I just want to establish what should be in there. I've been promised a copy of the service data by a forum member so hopefully this will make it all clear for simple me ie "these are the 5 valves you need and their respective locations".

[roberts54]

The plot thickens. Thanks Frank. Sounds like the two online refs match this ie suggesting EZ40 is correct but EZ41 a possible replacement. I'll wait and see what the promised spec / radio museum downloads say, if anything.

Thanks all to date!

[julie_m]

If you don't know which valve belongs in which position in the set, you can work it out just by seeing what is connected to it. In a radio receiver, each valve is associated with, and connected to, at least one other major part; so you just need to follow the wiring. The rectifier (EZ40 or EZ41) goes to the power transformer and main smoothing capacitor can. The audio output valve (EL41) goes to the speaker transformer. The Frequency Changer (ECH42) goes to the tuning capacitor. The I.F. amplifier (EAF41) goes to both I.F. transformers; that just leaves the detector / audio preamp (EBC41) to go in the last empty position.

Both EZ40 and EZ41 are full-wave rectifiers, and have the same electrical pinout. The EZ40 is rated for a higher anode current (90 mA as opposed to 60mA for the EZ41), but consumes more current in its heater (580mA aot 400mA). The EZ41 will be fine in this set, as it is only powering 4 other valves. A fancier set with a push-pull audio output stage, a "magic eye" tuning indicator and possibly an additional RF amplifier stage would need more HT current for the additional valves, and so would require an EZ40 (and a larger power transformer). (Note that the 9-pin rectifiers valves are numbered the other way round! EZ81 is the heavier-duty sister of the EZ80.)

While you are tracing the set's wiring, work backwards from pin 6 (the grid) of the EL41 until you come to a capacitor, probably between 10nF and 100nF. If you don't do anything else to the set, please replace this one capacitor with a modern polyester or polypropylene capacitor of the same value or as near as possible (22 for 20, 47 for 50). If it's faulty, it can ruin the speaker transformer and the EL41.

If in doubt, post pictures!

[roberts54]

Many thanks Julie for the detailed and informative response. Once I have figured it all out from your and others' feedback, I will post my conclusion for others' benefit.

Trifocaltrev helped me with what limited documentation is available but unfortunately no-one seems to have the part of the original Bush Service Instructions that specifies clearly the valves (assuming it did).

I appreciate everyone's help!

[Nanozeugma]

This is my understanding of what goes where...

[Herald1360]

The E*4* series of valves with B8A base has a fairly limited range of types- it was seen off quite quickly by the 9- pin B9A range which offered more pins and a simpler socket with inherent polarization similar to the earlier 7- pin B7G (the first popular all glass valve range).

So if it's the right sort of valve for its position in the radio, it's probably the right valve and will almost certainly work anyway.