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Bedford MWR - radio bench


simon king

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i am currently recreating the radio bench for the MWR. It is the sort with the sliding pull-out extension under the top boards and a draw below that. All the pictures I can find on the web seem to show that this type of bench had a sloping draw front presumably to give more leg room. I intend to reproduce that type of draw

 

I inherited a newly made angle iron bench frame and slide out frame with the vehicle, as the originals were well pitted/terminally corroded, together with some rotted woodwork to act as patterns.

 

I have two different bench tops - each made of 3 1" planks. Both of these tops have witness marks showing that the bench tops came pre-installed with 5 metal strips each 131/4" x 13/4" in a precise pattern as can be seen in the different examples on the web (eg MLU Wireless Forum's 15cwt wireless truck furniture thread and pictures of the Garrison's MWR). Presumably these strips which seem to come undrilled were to take account of the different equipment which could be likely fitted on the bench.

 

I have some questions though

  • do you think it would have been necessary to use the Table Mounting Strips which came as a set with the Mountings, Carriers No 1 if the bench came pre - installed with those strips
  • I have been trying to match the holes in the shock absorber feet (both attached to the carrier) to holes in the tops. I cannot seem to match holes to the specified four 1/4" bolts per side - so would a bolt in just one of the two holes in each shock absorber suffice - two bolts per side can be matched
  • was the 19 set wireless and PSU somehow earthed via the No 23 carrier, and the carrier then earthed to the bench (possibly through the Mountings, Carriers) which in turn would have been earthed to the vehicle? Or was the wireless and PSU earthed directly to the bench - which seems at odds with the portability aspect of the installation.

 

Any advice gratefully received

 

Thanks

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i am currently recreating the radio bench for the MWR.

(... snip ...)

I have some questions though

  • do you think it would have been necessary to use the Table Mounting Strips which came as a set with the Mountings, Carriers No 1 if the bench came pre - installed with those strips
  • I have been trying to match the holes in the shock absorber feet (both attached to the carrier) to holes in the tops. I cannot seem to match holes to the specified four 1/4" bolts per side - so would a bolt in just one of the two holes in each shock absorber suffice - two bolts per side can be matched
  • was the 19 set wireless and PSU somehow earthed via the No 23 carrier, and the carrier then earthed to the bench (possibly through the Mountings, Carriers) which in turn would have been earthed to the vehicle? Or was the wireless and PSU earthed directly to the bench - which seems at odds with the portability aspect of the installation.

 

Er, which carrier (and also, which mountings) have you got for it?

 

Carrier No.1 (later renumbered 21) is all-metal construction and is for permanent installation in AFVs (mostly). It is fixed to a bench surface, shelf, or a pair of stand-off brackets by four shock mounts (the bridge type), and the set

and supply unit are earthed using braid straps bolted to the feet of the shock mounts. Metal strips may be fitted to

prevent the 'feet' of the shock mounts from spreading, which would cause the rubber mounting to fail.

 

Carrier No.3 (later renumbered 23) is a demountable wooden board carrier with metal fittings to take set, supply unit and a control unit of the No.3 series (3, 3A or 3B, usually). It has no shock mounts fitted as these are contained in the table clamps. The right-hand end of the carrier has an earth terminal fitted with a large spring clip that attaches to a length of earth braid in a vehicle or to an earth lead, counterpoise, or earth pin when used on the ground.

 

Carrier No.25 is of all steel construction and uses a single long strap to secure both set and supply unit to the carrier. The set and supply unit are earthed to the carrier by the braid straps and there is a spring terminal on the front face of the carrier to connect an earth lead to. A plate assembly on top of the set takes the variometer, control unit and an aerial base No.10 if required.

 

Mountings, Carrier, No.1 (two required) are metal clamps with built-in shock mounts. These bolt to the table top (via

suitable metal strips to stop the mount feet spreading), and the carrier slots into those at the rear and a tilting clip secures the carrier at the front. This will take the No.3, 23 or 25 carrier.

 

Mounting, Carrier is a later version using 'Barry mounts' as on more recent equipment instead of the fragile 'bridge' type. it has a fixed claw at the rear and a movable one at the front operated by a slotted screw. The Barry mounts secure to the table with four bolts each, and to the mounting with a single central bolt.

 

I'll see if I can dig out some illustrations.

 

Chris.

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Hi Chris,

 

it is the No 23 wooden board fitted in the MWR with the croc clip at right rear and an insulator on the right hand metalwork. The mounts are the correct carrier, mounting, no 1 used for the no 23 board. Two correct bridge type shock absorbers are fitted to each carrier, mounting, no 1.

 

i can easily make the strips that came in the kit with the carrier mounting no 1 , mounting bolts and the shock absorbers themselves, but I was just wondering if these were required if the radio bench already has those 5 strips factory fitted in the places where the shock absorbers would rest. My presumption was that the strips were intended just to prevent the shock absorber/bolts from digging too far into the wood surface through over-tightening.

 

Where is the bond strap from the front bottom RH corner of the 19 set attached to the metalwork of the carrier no23. It must somehow be in electrical contact with the croc clip.

 

thanks

Edited by simon king
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Hi Chris,

 

it is the No 23 wooden board fitted in the MWR with the croc clip at right rear and an insulator on the right hand metalwork. The mounts are the correct carrier, mounting, no 1 used for the no 23 board. Two correct bridge type shock absorbers are fitted to each carrier, mounting, no 1.

 

i can easily make the strips that came in the kit with the carrier mounting no 1 , mounting bolts and the shock absorbers themselves, but I was just wondering if these were required if the radio bench already has those 5 strips factory fitted in the places where the shock absorbers would rest. My presumption was that the strips were intended just to prevent the shock absorber/bolts from digging too far into the wood surface through over-tightening.

 

Where is the bond strap from the front bottom RH corner of the 19 set attached to the metalwork of the carrier no23. It must somehow be in electrical contact with the croc clip.

 

thanks

The strips with 4 holes are to make sure that the shock mount bolts don't spread under load (due to wear in the holes in the table top, etc), which would cause the mount rubber to separate from the steel part. There should be two strips per mount, one above the table, the other below, to guarantee a rigid fixing.

 

On the RHS of the carrier there's a piece of steel angle with round bars welded to it. The croc clip is fixed to the top surface of the angle at the rear of the carrier, and according to the EMER, there's a spring terminal fixed to the side of the angle, about 1/3rd of the way from the front (facing inwards, towards the set). The earth lead is supposed to fix to this...

 

...but on my carrier someone has dismantled the spring terminal and fitted a large lug (and cable) to the terminal before reassembling it, and the cable connects to the croc clip! This will make it very difficult to fit an earth lead or the counterpoise to that terminal, and I suspect it's wrong. The most likely attachment for the set earth cable is to either assemble it under the spring terminal (which would make it impossible to install/remove the set), or more likely to cut a slot in the lug on the braid so that it fits onto the terminal in the usual way and can be unclipped when you need to remove the set from its case.I may have some 'cut' lugs like that somewhere, I can't remember offhand.

 

Anyway, the croc clip is for earthing the set to the braid inside a vehicle, and the spring terminal is for attaching Leads, Earth, No.2 (as an extension cable) and/or Leads, Counterpoise when the set is used outside the vehicle as a ground station.

 

I hope that makes some sort of sense. :-D

 

Chris.

 

Just re-read your post: the "insulator on the right hand metalwork" is the spring-loaded earth terminal. :-D

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this is the refurbed No 23 carrier, and associated carriers, mounting no 1 although there is no springiness in the spring loaded earth terminal - so that will need looking at again

 

IMG_2834.jpg

 

There was an earth strap attached to the front right bolt which passes through all plates and the wood when obtained.

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this is the refurbed No 23 carrier, and associated carriers, mounting no 1 although there is no springiness in the spring loaded earth terminal - so that will need looking at again

 

 

There was an earth strap attached to the front right bolt which passes through all plates and the wood when obtained.

 

You will find that the spring loaded terminals have a VERY strong spring.:-D

 

Having given this some thought since yesterday, I reckon that the lug on the earthing strap from the WS19 goes between the spring-loaded terminal and the steel plate, and the terminal is fitted after the set is installed. This does mean you have to remove the terminal to release the earth connection before you can withdraw the set from its case in order to change a valve, but that is true of all the other carriers where it's firmly bolted to either the carrier or the metal shelf the carrier is fixed to. (Carrier No.1 has the set braid bolted to the carrier and a second braid on the same bolt going from the carrier to the underside of the shock mount 'foot' where it's bolted to the vehicle shelf. I think there are instructions to scrape the paint off in the contact area in order to get a good connection.)

 

I need to put a set on my rather scruffy carrier and see how it all fits together.

 

Chris.

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You will find that the spring loaded terminals have a VERY strong spring.:-D

 

Having given this some thought since yesterday, I reckon that the lug on the earthing strap from the WS19 goes between the spring-loaded terminal and the steel plate, and the terminal is fitted after the set is installed.

 

...and I'm wrong! :(

 

Installation instructions for Truck & Ground station:

 

(20) Connect the Sender-Receiver ground strap located on the lower right hand side to the terminal on the right hand side of Carriers No. 3.

 

(21) Fasten one end of Leads Earth No.2 to the ground post located on the vehicle wall and the other end to the spring clip on the right hand side of the Carriers No. 3.

 

So it looks as though they either just slip it into the terminal (which is 'iffy') or cut a slot in the lug so that it can be slid all the way home in the terminal for a good connection. I'm sure I've seen ground straps that have been slotted in this fashion. Must have a rummage through the 'bits' pile.

 

(It also means that my carrier has been 'bodged' because the parts list does not show any cable from the spring clip to the terminal - it relies on the clip and terminal being screwed to the same piece of steel angle. I shall correct this.)

 

Chris.

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...and I'm wrong! :(

 

Installation instructions for Truck & Ground station:

 

(20) Connect the Sender-Receiver ground strap located on the lower right hand side to the terminal on the right hand side of Carriers No. 3.

 

(21) Fasten one end of Leads Earth No.2 to the ground post located on the vehicle wall and the other end to the spring clip on the right hand side of the Carriers No. 3.

 

So it looks as though they either just slip it into the terminal (which is 'iffy') or cut a slot in the lug so that it can be slid all the way home in the terminal for a good connection. I'm sure I've seen ground straps that have been slotted in this fashion. Must have a rummage through the 'bits' pile.

 

(It also means that my carrier has been 'bodged' because the parts list does not show any cable from the spring clip to the terminal - it relies on the clip and terminal being screwed to the same piece of steel angle. I shall correct this.)

 

Chris.

 

l wonder if the "iffy" nature of the designed earth contact point for the tx/rx earth strap on the carrier was the reason for some operators to attach the earth strap directly to the front fixing bolt which meant that there was a good and direct electrical contact to the croc clip.

 

ps the spring IS strong isn't it.......

Edited by simon king
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