Stevebr

Axle journal diameter not axle diameter

If I recall the B4 had an axle diameter of 4.5 inches and the B5 4 7/8”. Also in BRB speak they were the BT42 and BT45. Disk brake versions were BT21.

It’s because the power supply has not been upgraded in time. There are a maximum no of trains/hour that can run on the overhead and all the allocation is taken by the LNER. Upgrades are apparently “in progress”

I seem to recall that the BR5 bogies were fitted with 180A/200A alternators which provide output from 10mph or so

The Blood and Custard site has good info which should help https://www.bloodandcustard.com/SR-2BIL.html

I remember these controllers and performance was outstanding. Was a circuit diagram every published?

On my copy the 94xx is on page 98. Haven’t read the magazine but on a quick flick through it looks a good issue

This is looking pretty cool. Looks like a January project for me

This looks really interesting. Please continue

1N4001 diodes drop 0.6volts across each so 8 to 10 in series would drop the voltage

My grandfather, also GPO did exactly the same

After finding the last issue a bit average this is a really good issue which I read cover to cover (well the electronic equivalent)

That looks really good. Care to share the construction details. In term of spacing the lighting was generally much poorer than would be acceptable now. Based on my dim(!) memories no closer than 25 yards apart but happy if anyone has more knowledge

It looks like it could be a surface mount diode or perhaps a transient voltage diode (TVS)

I use RS components who have an extensive reasonably priced and easy to order selection. Try code 320-203 or similar. There is a detailed data sheet available. Delivery is excellent

Hi, Thank you everyone for the great insight. The issue around the 4th gear ratio appears to be 1:1 as it it shown as a direct drive with no reduction being shown (source railcar.co.uk/Technology/Gearboxes/Gears) and a document from the Western Region CMEE available at Silvermoon consulting. I did notice when looking at a picture of the DMU rev-counter that it was marked between 1100 rpm and 1800 rpm (as expected) but that it was calibrated to 1950 rpm which would give a theoretical speed of around 73mph on new wheels and 70 mph on worn which looks about right. I can definitely remember the needle being beyond this marked zone (1800) from observations behind the driver in the mid 1970's. I suspect that the power output drops rapidly after 1800 rpm but another doc indicates that fuel cut-off only occurs between 1900 and 2000 rpm. Happy if anyone can give any clarity on the above. Going forward I will update the info to include the higher powered (Class 123etc) units which had different final drives and a higher rpm (1900) but the same 70 mph top speed. I will then generate Tractive Effort vs Speed graphs for both which I will upload here and on my website.

Gravity plays a part definitely but the RPS archive shows many class117 units exceeding 70mph out of Paddington on the level. I do have a vague recollection that the rev counter was marked to change up at 1800rpm but was calibrated further (1850? or so)

Can anyone confirm the 1.1:1 ratio. In some publications it is shown as 1.1 and others 1.0

As I recall the 1st generation DMU's had a top speed of 70mph. If I use the maximum engine rpm of 1800 it equates to around 66-67 mph with new 36inch wheels. Did the engine operate beyond 1800rpm (my docs indicate it was governed to 1800) or are my assumptions wrong? I definitely remember them achieving 71-72 between Swindon and Kemble in the 1970's

I recall seeing them very occasionally at Gloucester. Didn’t usually stay that long before returning to Midlands

Try https://signalbox.org/~SBdiagram.php?id=%20270

Not a bad month but a pity the articles on locomotive performance seem to have died away

Sounds perfect

Is it critical to be Pitlochry. It’s a bit isolated for an MPD? How about a sub she’d of Motherwell maybe a bit like Carstairs in the 1970’s?